Deltares Renewable Energy From Water and Subsurface 2010

Renewable Energy from Water & SubsurfaceDiscovering the Potential & Considerations for Application

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from W

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cePO Box 1772600 MH DelftThe NetherlandsT+31 (0)88 335 [email protected]

Renewable Energy from Water & SubsurfaceDiscovering the Potential & Considerations for Application

2 Renewable Energy from Water & Subsurface

To achieve that goal various developments and innovations are being implemented to improve energy efficiency, to develop renewable energy technologies and to reduce CO2 emissions. Many solutions appear to be both energy and water issues.

One example of an underexploited renewable source is water. Of course, hydro-power is generated at large dams, such as the Hoover Dam in the U.S.A. However, energy can be produced from water in many other ways, such as: low head hydro power in rivers, tidal and wave energy, thermal energy from surface and ground-water and salinity gradient power in coastal areas. Some of these technologies are ready to be implemented whilst some are still under development but will become technically feasible within the next few years. Besides the technical challenges, it is of the utmost importance to create solutions that are friendly to the environment, acceptable to society and economically feasible.

Energy is vital for man and society. However, fossil fuels are becoming scarcer and more expensive to extract and remain a burden on climate. Therefore, the policy of the Dutch government – and of many other coun-tries – is to seek a reduction in energy use and in emissions into the environment. The Dutch government has set a target to reduce the CO2 emissions by 30% by the year 2020 compared to 1990 and to ensure that 20% of the energy produced is from renewable sources by 2020.

Preface

Renewable Energy from Water & Subsurface 3

This overview document is an attempt to assess the different technologies that produce energy from water, from an international perspective and – where possible – with a focus on The Netherlands to create a more detailed understanding. It comprises a first order approximation of the energy potential, in a manner similar to the method the oil and gas industry uses for estimating its reserves.

I hope this booklet will create an insight into the different possibilities and consid-erations for the application of water-based, renewable energy sources, and will contribute to a faster exploitation. This booklet only covers the most promising methods and innovations for renewable energy from water. This means that very early innovations, and small-scale plans or initiatives were not considered, although it is recognized that the implementation of those may have major local influence.

Enjoy reading this introduction to water as a source of renewable energy and the related considerations and I hope that governments make their policy and regula-tions more suitable for exploitation of this resource and that businesses will be inspired to keep on developing water-based energy solutions.

Marcel BruggersDeltares Renewable Energy TeamDeltares, June 2010


Preface 2

1 Deltares 7 Our Expertise 8 Coast and Sea 9 Policy and Planning 10 Rivers, Lakes and Groundwater 10 Soil and Subsurface 10 Software 11 Research Facilities 11

2 Energy-related Research at Deltares 13 Water 14 Subsurface 15 Focus on the North Sea 16

3 Fired up by Water 17 Sources 18 Definitions of Energy Resources 21 Estimating the Potential 22

Table of Contents


4 Discovering the potential 25 Tidal Energy 26 Wave Energy 32 River Energy 37 Blue Energy 45 Thermal Energy from Urban Surface Water 46 Thermal Energy Storage 49

5 Considerations for Application 53 Renewable energy and the environment 54 Environmental Aspects 57 Life Cycle Analysis 63 Environmental Flows – the Tool to Mitigate Hydropower Impacts 67 Bottlenecks When Innovating 71 Pilot Installations – Crucial Proof of Practice 75 Lessons Learned from a Pilot Tidal Energy Plant 78

6 Acknowledgements 83

1 Deltares


At the same time, we continuously develop our own innovative products and services, integrate them with the advances achieved by other bodies and make the results publicly available around the world. We advise both the public and private sector, often as early as the initial phase of a project, using our state-of-the-art expertise to make sound independent assessments of the physical condi-tion of delta areas, coastal zones and river basins.

Our ExpertiseAll over the world, habitable space in deltas and river basins is under increasing pressure from economic expansion, growing populations, subsidence and the impacts of climate change. Deltares has the knowledge and resources to tackle

Deltares is a leading, independent, Dutch-based research institute and specialist consultancy in matters relating to water, soil and the sub surface. We apply our advanced expertise worldwide to help people live safely and sustainably in delta areas, coastal zones and river basins. To achieve this, we constantly extend our knowledge base via government research programmes and contract research, forming consortia with universities and other research institutes, encouraging innovation, and accelerating the practical implementation of new theo-retical advances.

Deltares


water and subsurface issues worldwide in a new, integrated way we call ‘delta technology’. This means we never focus exclusively on technological issues. Our approach invariably takes account of ecological factors and administra-tive constraints like spatial planning, with all the associated policy agendas, competing interests, and legal and economic processes. The integrated applica-tion of our various areas of sophisticated know-how produces solutions that are more sustainable, better for local people and, often, more economical. We aim towards the sustainable enhancement of the living environment, with high-grade technological solutions that have the support of society as a whole, putting into practice our strategic principle: ‘Enabling Delta Life’.

Coast and SeaToday’s coastlines are under threat from climate change, rising sea levels and coastal erosion. To secure them and avert the threat of coastal flooding, it is vital to understand how coasts and seas function as systems. Deltares has this understanding of natural processes and applies it to the engineering and management of coasts. We work hand in hand with nature, pursuing a philos-ophy of sustainable coastal engineering that involves encouraging the develop-ment of natural features and using natural dynamics to maintain coastlines and improve flood protection. Climate change causes more extreme weather conditions. Deltares studies how this affects the environment, water defences,


coastal engineering projects, energy supplies and transport. Based on inte-grated coastal management, Deltares supports policies and management for the coastal zone, targeting the impact of climate change, but also examining the effects of interventions on water and soil quality. We have integrated what we know about ecosystems into models and monitoring systems that can be used to implement European initiatives such as the Water and Marine Strategy Framework Directives. We help government authorities to tackle pollution and disaster management more effectively. We develop early warning systems for the timely identification of threats. We search for solutions that draw on the potential of the coastal system, that enhance safety in densely-populated coastal zones and that minimise the ecological impact. Deltares acts as a specialist consultant during the realisation of projects for coastal engineering, coastal safety, recreation, energy supply and transport.

Policy and PlanningAround the world, spatial planning now takes increasing account of water and the subsurface. Deltares supplies the requisite specialist know-how to enable public authorities to prepare their area development, innovation management and flood safety policies and plans with these factors in mind. We analyse existing policy and conduct strategic reviews, scenario studies and integrated studies for the development of new plans and the elaboration of innovations.

Deltares looks far ahead to recognize the challenges we will face as a society and to identify the expertise needed to respond to them. Our knowledge and experi-ence are invaluable in the initial phase of studies and projects, when problems are being defined and potential solutions examined. Together with our clients and other research institutes, we work today to confront the major challenges of tomorrow: the design and management of sustainable and climate-robust deltas, coastal areas and river basins.

Rivers, Lakes and GroundwaterDeltares’ consultancy work and simulation models are rooted in a clear under-standing of how water systems work. Our models help public authorities make vital predictions concerning matters like river levels or the flow patterns and quality of groundwater and surface water. Since the quality and quantity of groundwater and surface water are inextricably linked, we produce linked models in this area and use integrated water management techniques to support policy-making and management in the area of freshwater reserves. We also apply our understanding of the interaction between groundwater and surface water to areas that may seem at first glance completely unrelated, such as energy from seasonal thermal storage in the subsurface. Local populations need to be protected from river flooding but river water is also essential to their economic and social well-


Deltares

being. Deltares advises on flood safety measures, water transport, and the use of groundwater and surface water for drinking, irrigation and cooling, as well as for nature conservation. Our consultancy services are founded on an advanced knowl-edge of hydrology, geology, morphology, riverine hydraulic engineering, ecology and economics. We work hand in hand with public authorities and water boards to ensure that river valleys are safe, pleasant places in which to live and work.

Soil and SubsurfaceThe ground beneath our feet is valuable in many different ways. It contains commodities like sand, gravel and clay. It serves as a firm foundation for infra-structure and provides extra space for additional functions. And it contains groundwater, which interacts with the surface water in lakes, rivers, ditches and streams. Deltares brings together expertise in all these areas to arrive at inno-vative solutions. For example, we apply our knowledge of geological structures to expertise in dredging and sand production, or we apply our understanding of urban groundwater on the one hand and of soil on the other to the creation of infrastructure. After all, an expert knowledge of geotechnology and foundations is essential to reduce the risks inherent in construction on and in soft subsurfaces (like those in The Netherlands). Furthermore, we also map soil quality risks and advise on remediation in many places around the world where past industrial activity has resulted in pollution of the subsurface.

SoftwareDeltares software gives users rapid access to the latest advances in the area of water and the subsurface. Out in the field, it generates new research issues and produces new insights. Together with users and knowledge partners, we engage in a constant cycle of application and development that results in ever-wider use of our knowledge through the medium of our software. The integration of data, software and expert knowledge enhances the range of applications available to users. For example, Deltares supports decision-making during flood alerts by producing software that helps authorities predict high water levels, patterns of flooding following dike failures, and the consequences of measures like evacu-ations. Likewise, we produce linked models for groundwater and surface water and, in a major new move, we are working with public authorities and research institutes to develop a set of National Models for The Netherlands. Our aim is to provide open architecture software fully compatible with third-party programs. Under the name Deltares Systems, our software is currently used in more than 60 countries worldwide. It covers our whole sphere of expertise including coastal waters and estuaries (Delft3D), rivers and urban water management (SOBEK), the design of diaphragm wall structures (MSheet) and the stability of flood defences (MStab), as well as an operational forecasting system (FEWS).


Research FacilitiesDeltares has its own in-house physical laboratory facilities (including an environ-mental laboratory, a Delta flume and a GeoCentrifuge). These are used not only to conduct water and subsurface research for the validation of new models and software, but also to test designs and scale models for hydraulic and geo-engi-neering structures or for the biochemical strengthening of the subsurface. They are also made available to external researchers from around Europe. The wide range of in-house facilities allows us to study all the facets of ground and water behaviour. We conduct research not only on the water quality and morphology of rivers, lakes and coasts, but also on ground and subsurface strength, the effects of wave loads and currents on structures, and the stability of these structures. Experiments are often designed to examine multiple physical processes simulta-neously (for example, both the wave load on a dike and the strength of the dike in terms of soil mechanics). The extent of our facilities allows us to progress in a carefully considered way, via a combination of small and large-scale experiments, towards the practical implementation of our knowledge – building flood defences, constructing foundations or using bacteria to modify the properties of soils.

2 Energy-related Research at Deltares


Alternative renewable energy sources are increasingly being explored and the development of solar and wind energy is at the forefront of this advance. The market and the capacity for solar heat has grown exponentially in Europe in the last 20 years and, in terms of capacity, recently installed wind energy repre-sents over 30% of all installed electricity capacity in the EU over the last five years.

In the fields in which Deltares is specialised, there is still a great deal to do. In some cases, the technologies for generating energy from water and the subsur-face need further development or still have a low efficiency or are very expen-sive. These technologies are nevertheless promising, and with further develop-ment and elaboration, they have – especially in delta areas – great potential for energy production. Deltares can play a significant role in developing knowledge, improving technologies, and in estimating the impact of these developments on the environment.

Energy-related Research at Deltares

Renewable energy will undoubtedly play a major role in the next 20 to 40 years, which creates a great opportunity for science and industry to get involved in the fast-growing market of research and consulting. Responding to energy and climate change is a vital social task and one in which Deltares must be involved.


Water Hydroelectric power is generally accepted as an effective form of renewable energy. In Scandinavian countries a large proportion of energy originates from hydroelectric power (around 98.8 %!) Techniques to extract energy from saline gradients (i.e. Blue Energy), tidal energy (e.g. the C-Energy project in Borsele), wave energy (e.g. the Aguçadoura Wave Park, Portugal), and to extract heat from water (e.g. the Maas Tower in Rotterdam) are less developed, and not yet frequently used. These technologies offer good opportunities for continuous research and application. The technology of extracting heat from water using heat pumps has only recently begun to advance, and has been found to be very successful in Scheve-ningen (The Netherlands) where a whole new urban area is heated by seawater. The large amount of surface water near buildings in The Netherlands facilitates further development in thermal energy storage and there is therefore a significant increase in the market for thermal energy pumps.

Subsurface For some time geothermal energy from land (and geysers) has been produced in the form of heat and electricity, but the capacity growth in recent years has been very small. Especially in Southern Europe, where the soil has a high


enthalpy, potential exists for further developments in extracting geothermal energy. A development which has had strong growth over the past years is ATES, Aquifer Thermal Energy Storage. ATES systems temporarily store energy in the form of hot or cold water in an aquifer, for respectively heating or cooling a building. In The Netherlands ATES is relatively widely used compared to other European countries. With the knowledge on this subject in The Netherlands and its widespread application, the possibilities for further development remain important and necessary.

In The Netherlands 30% of the energy consumption is spent on the heating and cooling of buildings. With the usage of ATES systems it is possible to reduce locally the energy demand by 50 to 70%, which can lead to a total overall saving of 15 to 20% for The Netherlands. To promote this form of renewable energy the Dutch Ministry of Housing has created an ATES taskforce.

Focus on the North Sea The government is working on the Spatial Perspective North Sea to provide clarity on the space for development of the various uses of the North Sea, including features such as wind energy, oil and gas extraction and storage of gas and CO2. A major expansion of offshore wind farms and stimulating the production of oil and gas from small fields are the first steps towards using the North Sea as a renewable energy source. Other options such as tidal and wave energy, saline gradient energy and algae for bio-fuels are being considered. The government will, together with (commercial) market parties and knowledge institutes, develop and explore different options and provide a clear perspective. This also includes a multifunctional energy island with large-scale electricity storage in the North Sea.

The above shows that huge potential exists in delta areas for renewable energy. What is the role of Deltares in this area? This booklet identifies some of the areas in which Deltares’ expertise can be deployed.

3 Fired up by Water


Sources All the earth’s energy is derived from three natural, primary energy sources. These are the sun, where solar fusion delivers solar energy; the moon, where the gravitational force that it causes delivers lunar energy; and the earth, where heat has been stored in the nucleus since the creation of the planet. Surface water and subsurface water both directly and indirectly catch a lot of energy and therefore contain enormous amounts of energy.

The SunThe largest natural primary source is – of course – the sun. The energy reaches the earth’s surface by solar radiation, caused by nuclear fusion in the sun. A part of this energy is converted by plants through photosynthesis into (aquatic)

Fired up by WaterThe resource of energy

The first part of this booklet will provide insight into water as a primary source or carrier of energy. It concerns water directly extracted from or stored in the environment. It does not cover water used in industrial processes or secondary sources such as cooling water from industry. The solutions presented can significantly contribute to the renewable energy sector in the world.


biomass. The energy content in biomass depends on the amount of carbon or oil it contains. These substances can be converted in different processes into thermal, mechanical or electrical energy that we can use. Biomass is not within the scope of this document.

Solar radiation also heats the surface of the earth. Due to the rotation of the earth, the surface is not homogeneously heated. Differences in the absorp-tion capacities lead to an unequal temperature rise of the earth’s surface. The surface, be it water or land, heats the air above it. Differences in air temper-ature cause differences in air densities that manifest itself as high and low pressure areas. This creates the phenomenon of wind and, with the friction of the wind over water, waves are created. The kinetic energy in waves can be extracted through a variety of different methods and converted into electrical energy.

The heating of the surface also includes lakes, seas, and oceans where water evap-orates. The clouds that contain this water cause precipitation in the higher parts of the earth’s surface, where they constitute the source of rivers. With free flow turbines in rivers, or with turbines in hydraulic structures in the rivers, electricity can be generated. Water also gets desalinated through the process of evapora-tion. This offers the possibility of generating electricity via ‘Blue Energy’ tech-


niques, such as Reversed Electro Dialysis (RED) and Pressure Retarded Osmosis (PRO), in or near the mouths of rivers.

The differences between land and water concerning heat capacity and absorption and emission speed lead to temperature differences between these substances. Generally, in summer this leads to a water temperature which is lower than the temperature on land and which in winter is warmer than on land. The temperature difference represents a thermal energy (difference), which can be extracted using heat exchangers.

The primary sources of energy

and their conversion to ‘usable’

energy.


Fired up by Water

The radiation of heat on the earth’s surface also leads to vertical differences in water temperature, thermal stratification. The application of systems, such as OTEC (Ocean Thermal Energy Conversion), can convert this difference in tempera-ture – actually, thermal energy – into mechanical energy. Large differences in temperature, from about 20°C, are sufficient to yield electricity. This situation hardly ever occurs in The Netherlands, which is why this sort of energy is not included in the remainder of this report.

The MoonThe second primary source is the moon. Although not an active source of energy, such as the sun, the presence of the moon creates a gravitational force. This gravitational force, the rotation of the moon around the earth and the rotation of the earth on its axis, gives an uneven pull of the moon on the elements of the earth. Because the ocean covers such a large part of the earth’s surface, gravita-tional forces within this body continually differ in magnitude and direction. This creates tidal movement, i.e. tidal currents and fluctuating water levels, which is best noticeable in the coastal areas. This tidal energy can be converted into elec-trical energy through the use of (non) free flow turbines.

The Earth’s CoreThe earth, the third natural resource, also produces and contains energy. The earth’s core contains heat that originates from processes during the formation of the earth and from radioactive decay. By radiation, conduction and flow, a portion of the heat is transported to and into the crust. In the earth’s crust, at different loca-tions and depths, aquifers are present that contain hot water. Through deep drilling in the crust, in the order of several kilometres, this thermal energy is extractable. At these depths, the thermal energy is so huge that it is feasible to generate electricity using steam turbines. At places where aquifers are not present, closed systems with circulating fluid may provide a solution to extract the thermal energy.

Conversion of energyThe presence of energy manifests itself in various forms, such as kinetic energy (water current/movement), potential energy (water level differences), electro-chemical energy (saline gradient in the water) and thermal energy (heat or cold) and they inherently require different methods through which this energy can be extracted from water. The concentration of energy per unit of water volume, the method(s) capable of obtaining this energy and the degree of presence in the particular waters or aquifers being considered roughly determine the potential.


Definitions of Energy ResourcesThere are several ways to define and to quantify the energy supply. The natural base supply, or more clearly, the total amount of energy present in the natural system that – in theory – can be extracted, is the potential energy resource. Despite all current and future innovations and developments it is not possible to extract this whole potential. Practical limitations are set by the geometry of the plant or system, the necessary space for performing maintenance and maintaining safety and – of course – conversion and frictional losses. The technically extract-able energy resource is therefore lower than the potential energy resource. The exploitable supply, however, is even smaller, due to social and economical aspects. The part of the technical extractable resource that is acceptable from an envi-ronmental, social and societal point of view, is defined as the socially extractable energy resource. The other limiting factor is the economic feasibility. Locations are only exploitable if the investment and operational costs are lower than the revenues from energy sales. We then speak of the economically extractable energy resource. The figure below illustrates the relationship between these supplies. The estimations made for these resources in this report are based on a first order approach. They do not represent proven resources or reserves. Thorough quantitative studies with a location-specific approach are necessary to provide more certainty with the estimates. Since most of the technologies require further development or are very dependent on location-specific conditions, it is not (yet) possible to calculate the economically extractable energy resource.

Apart from producing energy, water can also be used as an energy storage medium. This is especially interesting if economic supply and demand do not match. This report, however, does not cover this aspect; it is limited to the identi-fication of opportunities for energy generation from water.

Estimating the PotentialMaking quantitative estimates of the extractable supply is a difficult task. The total extractable potential is huge. However, it is undisputed that it is not feasible to extract the whole potential energy resource. Especially with innovative solu-tions, with technologies that are not common or are location-specific, assump-tions have to be made and criteria have to be set. These are based on ‘engineering judgment’, i.e. experience and existing knowledge. It is recognised that these criteria and assumptions determine the outcome of the estimation and with that the insight into the chance of (commercial) success of the technology.


Fired up by Water

Defenitions of energy resources.

4 Discovering the potential


In general with tidal energy, large-scale constructions are required, to extract the energy from the water. Large constructions, however, can also be expected to have severe environmental consequences. When exploring the steps and considerations required to extract energy from this source, it is necessary to go beyond technical matters. Economic and societal issues and existing or required legislation are critical in determining the chances for successful realisation and exploitation of tidal energy.

Methods of extracting tidal energyWater contains two forms of energy caused by the tides: the potential energy related to the continuous change of the water level during the tidal cycle (tidal

Water contains huge amounts of energy in many different forms, sometimes highly concentrated, but mostly diffused. It can be present in the form of kinetic energy, thermal energy or chemical energy and the water, containing the energy, flows through several distinctive cycles. In this chapter six different water/energy sources are considered, that comprise most of the potential energy present in the earth’s water.

Tidal Energy

Discovering the potential


range energy), and the kinetic energy in the currents caused by the tides (tidal current energy).

With tidal range energy, constructions are needed to convert the potential energy into kinetic energy. This is always done by creating a water level difference, the head, by restricting the water flow in or out of a storage basin (often an estuary). Dams or (natural) barriers usually form the boundary of these storage basins. The turbines that extract the potential energy are placed in the barrier that encloses the lagoon. The head over the basin boundary or dam creates a current through the installed turbines, which generates electricity. The storage basin can be a natural part of the water system, such as an estuary or an inland sea arm, or can be a man-made lagoon. In the first case ‘simply’ a barrier has to be constructed, while in the second case a lagoon must be created. These lagoons can be connected to the coast or detached at sea, depending on local conditions.

Energy can be extracted whenever there is a head over the basin boundary, either when the outside water level is higher than inside, or vice versa. However, the flow characteristics of the basin determine if it is possible to generate electricity by filling or emptying the basin, or in both situations. Two-directional generation requires special turbines, which are more expensive than one-way turbines, but generate more energy.


The higher the head that is created, the higher the potential for electricity produc-tion. In addition, closing constructions are required to minimize water flowing in or out, in order to optimize the head over the tidal cycle. The timing of the opening and closing of the closing constructions in relation to the conditions of tides and wind is crucial to achieve a high production efficiency. Extra financial benefit can be obtained when the turbines are also used for pumping the water up at night when the energy tariff is low, and extracting the energy again when prices are high. This is done at several hydropower facilities in mountainous areas to create a larger head at low costs. However, the utilization of the daily tariff fluctuation is, generally speaking, not efficient in tidal basins or lagoons since the water surface is often too large, and the water level increase by pumping is negligible. Tidal energy generally depends on large surface areas with a relatively small head, whereas mountainous hydropower depends on relatively small surface areas with large heads.

The other way of extracting energy from tides is to use the tidal current energy directly. Energy in currents can be harvested by free-flow driven turbines. Tidal currents are variable, both in velocity and direction. The energy production depends on the water velocity, direction and the type of turbine that is used. When turbines are used that rotate in a plane perpendicular to the flow direction, like windmills in the wind, a construction is needed to adjust their orientation to the

Artist’s impression of a power

plant for Tidal range energy.


Discovering the potentialTidal Energy

direction of flow. Generally, this type of turbine will be placed in barriers, under bridges or in tidal flow channels where flow directions are more or less constant. A two-directional-flow turbine can then generate electricity during ebb and flood tides. Turbines with a vertical axis (the Darrieus type) are not dependent on the direction of the flow.

Potential energy resourceIn most parts of the world the tidal cycle describes a semidiurnal pattern with a period of 12 hours and 25 minutes, exactly half a tidal lunar day. Thus twice a day there is a high tide and a low tide. The potential energy resource is deter-mined by the volume of water that is moved during this tidal cycle. For tidal range energy and for tidal current energy this is the same base supply. The esti-mation of the potential energy resource is based on the following approximations and assumptions:- the vertical cross section of the sea or ocean, parallel to the coast- the average flow velocity through the cross section, twice a dayFor The Netherlands, the cross section measures about 250 kilometers in length, 22 meters in depth and the average flow velocity is about 1 m/s. With this it is estimated that the total potential energy resource along the Dutch coast is about 85 PJ (24 TWh), independent of the presence of lagoons or estuaries.

Artist’s impression of devices for

Tidal current energy.


Technically extractable resourceNo more than a fraction of this potential can be extracted. Tidal energy extrac-tion systems, based on tidal ranges, can only be considered at a few locations, depending on local conditions such as tidal ranges, current velocities, the presence of ‘natural’ basins or the possibilities to create storage basins. To determine the technically extractable resource, only estuaries and sea arms are considered to be potential sites. The water level difference between high and low water – together with the basin surface area determine how much potential energy is available. Some estuaries in the United Kingdom have tidal ranges up to 14 meters, but unfortunately along the Dutch coast the tidal range is limited from approximately 1 m at the Northwest to about 4 m at the Southwest.

The Dutch water surface that can be put under the influence of the tides is esti-mated at about 1900 km2. Taking into account the estimations on effective-ness, location specific tidal ranges, friction and conversion losses the technically extractable tidal range energy resource is calculated at 11 PJ per year.

The exploitation of tidal current energy is less bound by the presence of reser-voirs; however, most of the interesting tidal currents, i.e. flow velocities exceeding 1 m/s, are located within estuaries. Other interesting locations lie between islands near the coast. Free-flow turbines convert maximally 30 – 40% of the potential energy into electricity. A rough estimation of the technically extractable tidal free flow energy along the Dutch coast amounts to 5 PJ.

Social feasibilityThe acceptance of large constructions by the public may be a difficult issue. Although the generation of electricity from tides will be received positively by the public, the interference with other functions in the estuary or sea may become problematic. Closing off parts of an estuary may have enormous consequences for fishing, ecology, the environment, navigation, recreation etc. In addition, these projects require large investments and complicated connections to existing infrastructure. The best opportunities are found where tidal energy extraction can be integrated in existing infrastructural constructions such as dams, barriers and bridges. Another opportunity is to create underwater installations; an additional advantage of this is that the best locations from an efficiency point of view, i.e. high current velocities, can be found in deeper gullies and in openings of dams. If the water depth is sufficient to avoid interference with navigation and sediment transport, good opportunities can be found here. One of the ever-present require-ments is that turbines are designed such that fish mortality is avoided.

Viewed from an environmental perspective, the creation of tidal lagoons may cause many ecological concerns. Estuaries play an important role in the ecology


Discovering the potentialTidal Energy

and health of the connected coastal sea. They serve as nurseries for fish and they feed, with their high productivity, the coastal sea. Therefore, building a dam or otherwise changing the water circulation pattern may affect many aspects of the local ecosystem. Thus, it is necessary to prevent the algal population from expanding and to prevent deterioration of soil populations and shellfish produc-tion grounds due to changes in sedimentation patterns and to prevent interfer-ence with migration routes for fish and mammals and feeding grounds for bird populations.

In particular, the closure of an estuary may affect the morphological processes in the area. These processes take many years to reach equilibrium, if ever. In the short term, navigation channels may be affected leading to increased dredging volumes. In the longer term, morphological changes may result in the (dis)appearance of tidal flats, possibly affecting the stability of dikes and thereby affecting the safety of the land behind them. Morphological changes may also affect salinity gradients in the estuary, which in turn may have a serious impact on the ecology.

Finally, the closure of an estuary has an impact on the landscape and seascape. This is difficult to avoid unless underwater installations are used. Since empti-ness and unobstructed views are two of the major qualities of the coast for the public, large-scale constructions will not be accepted easily. Large-scale interfer-ence with estuaries requires very careful study into the many and widespread consequences.

Technical challengesA proper selection of both location and technology, in line with other functions, is a first step, and determines the issues that need to be solved. Turbine technology for tidal range energy is well developed, although designs avoiding fish mortality remain a challenge. Free-flow turbines are still under development; however, some are in a (pre-)commercial phase. The main challenges that are faced now are to combine these technologies with structures that also serve other purposes and to reduce the environmental impact. Besides this, the technologies have to be optimized in order to extend the range of flows where high conversion efficiencies can be achieved. In addition, maintenance is an important issue. In the first place, turbines must be protected against debris, rubbish, and larger animals (the latter must also be protected against the turbines) to ensure an uninterrupted operation. In addition, the salty marine climate is particularly harsh, reducing the lifetime of the machines and necessitating high-quality housing and installation. If cleaning is frequently required, downtime will accumulate and the production will be lower. The less regular maintenance and repair are required, the better. Downtime may accumulate substantially over the lifetime of the machines (20 – 40 years).


Costs and yield Recovery of tidal range energy requires large investments, which is uneconomic for smaller heads. Consequently, the designed lifetimes of constructions need to be long (~100 years). Economic calculations are rather arbitrary since large-scale structures such as dams or barriers will not be built for the single purpose of energy extraction, but will provide other functions such as protection against floods, traffic connection etc as well. Nevertheless, there are some estimates of the unit production price of barrage systems in the UK and The Netherlands, which amount to 0.075 and 0.15 €/KWh, compared to 0.04 €/KWh for fossil fuels. Since tidal current energy is still in a pre-commercial phase, cost price estimation cannot generally be done.

Spatial planning issuesAs previously stated, with the exception of tidal currents, extracting tidal energy comes down to large-scale projects and its realisation is therefore a national matter, with regards to investments and acceptance, as well as with regards to spatial planning issues. Careful designs, evaluations, impact assessments, cost calculations and acceptance trajectories are part of these developments, as is complying with spatial planning legislation.

Wave EnergyThe seas and oceans are used in several ways. Besides the natural inhab-itants of the aquatic ecosystems, the seas and oceans are used for naviga-tion, defence, oil and gas recovery and – of course – fishing. The nearshore locations are also perfect for recreation and tourism. In addition, the sea wind delivers a cool breeze on the beach – especially welcome during warm weather. We already extract (wind) energy from this cool breeze. In the Dutch part of the North Sea the first wind park was installed just off the coast at Castricum. The wind waves on the North Sea are not yet used for energy generation. This is because with the current state of the art, commercial exploitation has not yet been proven.

On the North Sea, the waves are relatively small compared to the waves on the ocean. This is caused by the small fetch on the North Sea, the length over which wave generation can take place. The average energy content in the North Sea supply is around 10 kW per meter of wave at thirty kilometres off the coast. That may be five to eight times less than elsewhere, but each 10 meters of wave still offer as much power as a car engine of 140 hp. The advantage that comes with this is that the wear and tear on wave energy facilities in the North Sea is supposedly much lower than in the oceans. The North Sea seems to be an inter-


Discovering the potentialWave Energy

esting testing ground for developing new techniques. Depending on the cost of energy of these systems and the development of (fossil fuel) energy prices, it will become clear whether commercial exploitation is possible in the near future. Some pilot installations are already installed in several places in the world, such as in Scotland (Pelamis, WaveGen, Oyster1), Ireland (WaveBob) and Australia (Oceanlinx). Some systems are designed specifically for nearshore application, such as Oyster1, Oceanlinx and Wavegen. Generally these are located in areas just before the waves break. The driving principle is an oscillating movement in or of a chamber, caused by the fluctuating water level of the wave. An advantage of the nearshore installations could be the reduction of wave loading on the coast. In the Mutriku project in Spain wave energy convertors are integrated in the break-water system.

Methods of extracting wave energy Hundreds of concepts are currently under development. Roughly they can be divided into the following four principles of operation:

1. Point absorbers and surface attenuators. As a result of a passing wave a buoyant body at, or below the surface, makes an up-and-down, a back-and-forth or a rotary motion. One or more of these movements can be converted into electricity.

Artist’s impression of floating

devices for Wave energy.


2. Overtopping. The upper part of a wave is channelled to an elevated reservoir. The kinetic energy of the upper part of the wave is converted into potential energy. This water flows through a turbine back to the seawater level and generates energy.

3. Oscillating water columns. Waves enter an enclosed structure pushing or sucking the air in an air chamber, which in turn drives an air turbine. The prin-ciple is similar to a blow hole.

4. Hydrodynamic lift. Especially in the upper layers of the water, the water parti-cles in a wave move in an orbital motion. Through a combination of vertical and/or horizontal blades the wave energy can be converted into a rotary or oscillating motion, which can be converted to electrical energy via conven-tional transmissions.

Potential energy resourceJust like we build offshore wind farms, we can also build offshore wave power farms, possibly near to wind farms developed in the future. These combinations would offer great synergetic benefits. The waves on seas and oceans are caused by friction with the wind. The longer the fetch, the more energy is transferred into the waves, resulting in higher waves and longer wave periods. Depending on the height and the period waves contain energy that is to some extent exploitable. Analysis of the waves in the Dutch North Sea leads to the conclusion that the

Artist’s impression of air

chamber devices for

Wave energy.


Discovering the potentialWave Energy

annual average significant wave height (H1/3) is 1 to 1,5 meters. The significant wave height is defined as the average height of the highest one-third of all wave heights in a wave field (sea state). The corresponding average wave period TH1/3 gives the average wave periods of the highest third of the waves and appears to be 5.8 s. Based on these data, the average supply of wave energy per meter corre-sponds to a wave power 10 kW/m, at about 30 km from the coast. The potential energy supply is determined by integrating the energy flux to the coast over the whole coastline, and over all occurring wave heights, wave periods and wave direc-tions. This integration gives a potential energy resource of approximately 54 PJ (15 TWh). This means an average instantaneous power of 1700 MW, which is enough for about 900,000 households per year.

Technically extractable resourceThe advantage of wave energy over other forms of renewable energy is that the energy is constantly present and that it is more predictable and constant than wind or solar energy. The disadvantage is the extreme loading conditions it has to withstand and environmental conditions such as corrosion and fouling. Although this type of energy has much attention and many wave energy systems are developed, there is still a lack of pre-commercial plants, of knowledge about the effects or yields and of evidence about the most appropriate wave concept in rela-tion to efficiency and survivability. Research on the application of wave energy facilities in parks, such as is the case with wind turbines, is also still necessary. Because of the diffuse nature of this energy, it is indeed necessary to build parks so that several installations benefit from the infrastructure built and make use of the reserved space. The technically extractable energy supply is, considering the above, an extremely difficult matter. The aspects which – in any case – should be addressed to make a quantitative estimate on this resource are:– conversion efficiency of kinetic energy from the wave into mechanical energy

in the plant– the efficiency of conversion from mechanical to electrical energy– the installation density and the yield of the park (group effect)Given a multitude of comments and a hypothetical application of wave energy plants on a large scale, the technically extractable resource of 3 TWh (10 PJ) per year seems realistic.

Socially acceptable extractable resource The North Sea is not available exclusively to extract energy. As already mentioned, a large number of functions lay spatial claims on specific parts of the seas and oceans. Especially the locations near the shore are full of activity (navigation, fishing, etc) and combining multiple functions is not only desirable, but often necessary. Using the existing areas already assigned to wind turbines for wave energy will provide both economic and social benefits. In the light of these claims


on space, the possibilities of combining functions and other limitations, it is esti-mated that roughly 50% of the locations along the Dutch coast assigned to wind power can be made suitable for the exploitation of wave energy. Given the current understanding of expected returns, the socially acceptable extractable resource for wave energy is approximately 5.5 PJ (1 to 1.5 TWh) per year.

Whether this supply will be extracted depends on political choices and extensive collaboration and is therefore not easy to determine. However, as sites for wind energy can simultaneously be used for wave energy, the economic feasibility will increase greatly, because a great deal of infrastructure for maintenance and elec-tricity networks has already been built.

Technical challengesExtracting wave energy is not easy. Besides the above aspects, there are tech-nical limitations. The movement of the water particles must be converted by a system into electrical energy. The problem is that every moving object in the water creates its own waves. The yield will therefore usually be relatively low. It is estimated that the maximum proportion of energy from waves that can be captured is approximately 40-50%. In addition, there is the conversion efficiency of mechanical energy into electrical energy, which is between 80% and 90%.

A construction for extracting wave energy will be most effective for a limited range of wave periods. The plant also has to be well adjusted to the most common range of periods of waves. Preferably, a location must be chosen with a large supply of wave energy, which would typically be at sites with high swells and swell waves. If techniques require a dominant wave direction, it is also important that they are placed in locations with a relatively constant main wave direction.

In addition, the construction must be built very robustly, so that the heaviest storms cannot cause any damage. Because these situations do not match the optimal range, energy production under such circumstances is not possible. More-over, the generated energy has to be transported to the mainland. This requires additional installations such as transformer stations and grid connection points. This makes this type of energy extraction relatively costly compared with the amounts of energy that can be gained.

In conclusion, it may be said that in the short term, energy from waves can only be extracted in an economically feasible way at coastlines by open oceans. At these locations a relatively constant supply of long swell waves is present.



River EnergyWater currents have always been used as a source of energy. Tradition-ally, energy was extracted in the form of mechanical energy by water mills, and in modern times, energy is extracted in the form of electricity. The ubiquity of this source is appealing. Flowing rivers transport massive amounts of water and thereby offer a great potential energy resource. In this chapter, the focus is on small-scale techniques, such as low head hydropower and free flow energy, suitable for various locations. In most rivers, flowing water has to provide different services simultaneously, such as for navigation, irrigation, recreation, drinking water and as an industrial commodity. Energy extraction must comply with these other services. This chapter explore the steps and considerations required to extract energy from rivers. This goes well beyond technical matters since economic and societal issues as well as existing or required legislation also determine the opportunity for successful exploitation.

Methods to extract river energyThe presence of energy in rivers is in essence diffuse, though at hydraulic struc-tures in rivers or at rapids it is concentrated and the energy is extractable using existing techniques. Mainly two types of energy extraction are applicable in rivers; first the installations that extract the potential energy (head difference) and second, the types that extract the kinetic energy (water currents). Both work best when the maximum volume of water is channelled through the construction. The constructions needed, however, may not interfere with the other functions. Therefore, most promising opportunities are located where electricity generation can be combined with some other function(s).

Potential energy extracting methods enforce the water flow though a turbine, where the potential energy changes into kinetic energy, which is converted by a turbine into electricity. Turbines used are of various types such as the Kaplan, Cross flow, Archimedes (screw), Bulb and the water wheel. The prevailing flows and heads at the location are important selection parameters for the turbine type to be used. Especially in cases of variable flow – the head is relatively constant in most cases and has therefore few consequences – careful design is required to create high efficiency over an extended range of flows. In order to obtain the highest amount of energy, (hydraulic) losses must be avoided as much as possible. Much care must given to the optimal design of inflow and outflow struc-tures, though construction costs may rise considerably.


Kinetic energy extraction methods, also known as free flow turbines, do not require a head difference, but do require a minimum velocity to generate electricity. The various types of turbines can be categorized as follows:– turbines rotating on a plane perpendicular to the flow direction, like a wind-

mill;– turbines rotating on a plane in the direction of the flow, like traditional water

wheels;– turbines with a vertical axis (the Darrieus type).Sometimes the flow velocity is increased by a venturi construction, located in front of the turbine. Behind the turbine a construction is needed to mix the flow smoothly with the surrounding flow to avoid turbulence losses. Many variations exist in turbine and construction to turn the water flow into a rotation that drives the electricity generator. Some rotate in one direction only, while others support two directions of rotation. Depending on the type of turbine energy extraction is possible with uni-directional flows (rivers), bi-directional flows (tidal rivers) or varying flow directions (broad rivers with non-consistent flow patterns).

Potential energy resourceBetween the location where rivers enter (e.g. geographical border) and where they leave (e.g. the ocean) the river bed level difference causes the water to discharge. When the bed level difference is larger than strictly necessary for discharging the


plant for River energy.


Discovering the potentialRiver Energy

water, this surplus height difference can be utilized to extract potential energy. The total potential energy resource, so the energy included for discharging the water, is calculated for the rivers in The Netherlands. As a rule of thumb, a river discharging an average 500 m³/s over a level difference of 50 m represents a potential power of ca 250 MW, i.e. an energy content of ca 2150 GWh per year. For comparison, an average annual discharge of 500 m³/s represents a river some-what larger than the Meuse (250 – 400 m³/s), but much smaller than the Rhine, which has an average annual discharge of 2200 m³/s. The bed level difference for the Rhine is only about 10 m and for the Meuse approximately 45 m. The combined annual flow of rivers in The Netherlands amounts to almost 3000 m³/s. This provides the potential energy resource of 3 TWh (11 PJ) per year. It must be noted that a part of this energy is still needed to discharge the water from the location of entry to the location of exit.

Technically extractable potentialOnly a small part of this potential at a limited number of locations can be extracted. This is due to the requirements of the turbines in terms of head, velocity, requirements by other functions and – as mentioned – to discharge the water to the ocean. It is also due to the fact that river discharges vary over time. When discharge is low, energy generation is very limited. However, with high river discharges no obstructions, including turbines, can be allowed in the river flows to prevent risks of flooding.

When a river is used for navigation or irrigation, hydraulic structures are often already in place to maintain safe water depths and to provide a substantial irri-gation resource. At these hydraulic structures potential energy is extractable under regular conditions. In practice, substantial energy generation is limited to situations with a head of at least 1 m and a minimum average flow of 25 m³/s. Currently, electricity production in Dutch rivers is about 100 GWh, and given the possibilities for expansion of hydropower the technically extractable potential is estimated to be 300GWh.

Social feasibilityEnergy can only be produced when not interfering with the other functions of a river. A number of other potential obstacles must also be considered. An important envi-ronmental issue is fish passage. Most turbines are not fish friendly and any selec-tion of a technology should take this into account. Improvements on this point may very well decrease the efficiency of electricity generation or require complicated, expensive constructions. Connecting the generators to the grid is another issue, both from a landscape point of view as well as economically. The public resistance to overhead power lines in an open and unspoilt landscape might be severe, while underground connections might be very expensive and less economically feasible.


Technical challengesA careful selection of both location and technology, in line with other river functions, is a first step, and determines other issues that need to be solved. Hindrance to other river services and environmental issues such as fish passage can be solved in many ways, and are highly determined by local circumstances. Turbine technology is well developed. The challenges are mainly how to combine this technology into structures used for other purposes, such as sluices, weirs and bridges and how to reduce any environmental impact, and with that increasing economic feasibility. An existing turbine challenge is extending the range of flows where high conversion efficiencies are realised. Maintenance is also an important issue. In the first place, turbines must be protected against debris and rubbish to ensure uninterrupted activity as much as possible. If cleaning is required frequently, downtime will accumulate, lowering the production. The lesser regular maintenance and repair that is required, the better. Downtime may accumulate substantially over the lifetime of the machines (20 – 40 years).

Costs and yield Cost calculations for economic feasibility should include investment costs including construction costs and maintenance costs. Both are difficult to estimate due to the combination with other constructions and location specific conditions. Investment costs for turbines range from ca. 1000 – 5000 €/kW installed power, not including construction costs. Maintenance costs might be substantial if the turbine is sensitive to debris or substantial growth of mussels, or other biofouling. Then the choice has to be made between regular cleaning or accepting lowered efficiencies. For each location and set of (environmental) conditions the downtime has to be assessed. This factor determines to a large extent the cost price of the energy delivered. An estimation of the cost price for energy production in the Dutch rivers amounts to ca 0.09 €/kWh, compared to 0.04 €/kWh for fossil fuels.

Spatial planning issuesThe fact that installations to extract energy from rivers always interact with other river functions may complicate spatial planning. In addition, connecting to the grid may require an enhancement of the capacity of power lines, and of control technology. Governments at various levels will probably be involved. In addition, political decisions must be taken with respect to the importance of ‘river energy’ compared to other functions. A careful design project, involving stakeholders and government, is required, but public acceptance will support the process due to sympathy for fossil-free energy generation.



Blue EnergyBlue Energy is the name for energy generated from saline gradients (i.e. the difference in salinity concentration between two solutions). Energy from saline gradients in water is one of the most promising concepts of renewable energy. The global potential is enormous and will prove especially valuable in densely populated delta areas where rivers flow into a sea or ocean.

Suitable locations for Blue Energy power plants are those marked by big saline gradients. Interesting saline gradients occur at sites where freshwater and salt-water meet. The most striking example of one such location is the mouth of a river into a sea or ocean. At these sites large quantities of fresh and saltwater are usually guaranteed and provide the necessary flows for a reliable operation of a Blue Energy power plant. Unfortunately, due to e.g. tidal movements and currents and fluctuating river flows, the river water and sea or ocean water mix, thereby reducing the potential. Therefore, sites with a physical separation of the salt and freshwater, as in the case of a lock, dike or dam near the mouth of a river, that prevent this mixing and maintain the concentration difference are even more interesting for the realization of a Blue Energy power plant.

Methods of extracting saline gradient energyTwo main techniques are known to generate electricity from fresh and saltwater: Pressure Retarded Osmosis (PRO) and Reverse Electro Dialysis (RED). Both tech-niques require membranes that initially separate the fresh and saltwater and let the water from the two water sources ‘mix’ under controlled conditions, producing vast amounts of electricity.

The PRO technique is based on the principle of osmosis. The PRO technique uses a semi-permeable membrane between the two liquids that can only be passed by water molecules and therefore prevents the salt ions from migrating. The principle of PRO through which energy is gained from water is named osmosis. Osmotic phenomena occur when fluids with different concentrations of dissolved substances are brought into contact with each other. In the same way as diffusion, they strive for equality in concentrations, but the semi-permeable membrane allows only the water molecules to migrate. The osmotic pressure drives water molecules through the membrane from the freshwater to the saltwater side, thereby diluting the saltwater and balancing the concentrations. If freshwater is available in abundance, this process can lead to a water level rise on the saltwater side of up to approximately 250 m, depending on local conditions. By limiting the water to rise up to the maximum, the water pressure builds, which can then be used to set a turbine in motion. In practice, about half of the 25 bar pressure built


up is used for driving a turbine since at this point the pressure-flow optimum is reached and with that an optimum for energy generation is achieved.

The RED technique is based on reversed electro-dialysis. In the RED method-ology, there are again two compartments, this time separated by ion-selective membranes, which can only be passed by salt ions. The chemical potential differ-ence creates a transport of ions through the membrane from the saltwater side to the freshwater side. Here the salt ions (parts of salt molecules) migrate instead of the water molecules through a membrane. The migration of ions, that all have an electrical charge, create a potential which can be transferred to an electrical current when linked to a cathode and anode. An energy cell consists of a cathode and anode permeable membrane, providing a migration route for the positive and negative ions. The cells can be stacked as regular batteries, and the energy output equals the product of the number of cells and the output per cell. The total energy yield per cubic meter from fresh and saltwater is comparable to that of the PRO method.

The power output – and therefore the annual average energy production – depends on the installation and the present resistance, such as required for treatment, and losses on the membrane pumps and possibly turbines. Pressure Retarded Osmosis (PRO) as well as Reverse Electro Dialysis (RED) state that a realistic production is around 0.7 MW per m³/s.


plant for Blue Energy.


Discovering the potentialBlue Energy

Both methods have already been known about for decades, but so far high costs and low technological and energy yields have prevented these techniques from becoming a realistic substitute for fossil fuels. However, technological improve-ments, anticipated economies of scale and rising awareness of the energy problem, together with the increasing costs of fossil fuels, mean that Blue Energy is slowly becoming an interesting and viable alternative.

Potential energy resourceThe total potential for Blue Energy in The Netherlands is very large. The combined average annual flows of the rivers in The Netherlands deliver almost 90,000 billion litres of freshwater into the North Sea. That means that every second approxi-mately 3,000 m³ of freshwater flows into the sea unused. The osmotic pressure difference between freshwater and saltwater is about 25 bars. This means that every cubic meter of freshwater – enough for the presence of saltwater – represents 2.52 MJ of energy. This corresponds to 0.7 kWh. The total potential energy resource is thus 220 PJ per year (60 TWh). Converted into instantaneous power this is 7000 MW. As an indication, the approximately 7.2 million Dutch households consume a total of between 400 and 500 PJ annually. If a full utilization of this potential was possible, this source would provide half of the required energy supply.

Technically extractable potentialDespite all the technological possibilities and innovations – now and in the near future – it is not possible to extract the whole potential. The causes lie in the efficiency of conversion processes, the practical limitations of the geometry of the plant, the necessary space for performing maintenance and safety, and – of course – the friction losses within the plant. The technically extractable supply is therefore lower than the potential energy supply.

In the remainder of this section it is assumed that the PRO method has similar losses to the RED method. The losses are partly due to the efficiency of the stack, which is about 40%. In addition, a further reduction of the estimated poten-tial has to be applied, because of differences between actual and average river discharge. It is very likely that a PRO or RED system cannot adapt to all discharge fluctuations that occur in reality. Where there is an actual discharge at a produc-tion location which is below the average discharge, it is clear that the production is lower than the production based on average discharge. If the actual discharge exceeds the average discharge, the production then depends on the installation for whether it can adapt sufficiently. It is obvious that this is not always the case and that both situations lead to an additional reduction in production.

The estimated annual number of hours that a RED or PRO system actually oper-ates for is 6,500 hours, due to variability in freshwater discharge. Furthermore, it


is assumed that the PRO method has similar losses to the RED method. For RED, these losses are partly due to the efficiency of the stack, which is about 40%. This means that the annual technically extractable resource in The Netherlands is estimated at 65 PJ (20 TWh). Converted to instantaneous power this would be equal to 2000 MW.

One cubic meter of river water and one cubic meter of seawater provide a theoret-ical capacity of about 1.7 megawatts, and when there is endless saltwater avail-able, as much as 2.5 megawatts per cubic meter of freshwater can be generated. In practice, approximately one megawatt maximum is achievable. This value is still dependent on local conditions, such as salt concentrations in different rivers, seas and oceans, temperature and environmental factors. The Rhine is the most ‘energetic’ river of Europe. The technically extractable potential of the Rhine and Meuse is estimated at 2.4 gigawatts and the economic potential at 1.5 gigawatts – enough to power four million households.

Socially acceptable energy resource In reality, the extractable supply is even less since environmental arguments and social interests have a limiting influence on the number and size of exploitation locations. In particular, navigation (to maintain the required water depth), agricul-ture (irrigation), the production of drinking water and providing cattle with fresh-water, all reduce the socially acceptable extractable resource. Therefore, what is available is difficult to quantify. Based on engineering insight, only one third of the river flow seems available for power generation. The available cumulative flow is thereby determined at 900 to 1,000 m³/s. The socially acceptable extractable resource lies at just over 22 PJ per year; this is equivalent to 6 TWh annually. Converted into instantaneous power this is about 700 MW, which is still about 5% of the total annual electricity demand in The Netherlands. The last limiting factor is economic feasibility. Locations are only exploitable if the investment and operational costs are lower than the – possibly subsidized – revenues from energy sales. It is expected that within five or ten years Blue Energy power plants will be in operation and working commercially. The magnitude of the energy production depends on the chosen location.

Technical challengesA membrane costs about five dollars and generates about five watts per square meter. It is expected that if a large commercial market for Blue Energy membranes forms, the price will go down significantly. With regard to yields, current findings show a large negative impact on the energy yield of the membranes when the saline gradient drops slightly. Robustness remains a critical aspect when trying to commercialize Blue Energy. The thickness of membranes has recently been reduced from 0.6 to 0.2 mm. However, when installing a Blue Energy plant of 300


Discovering the potentialBlue Energy

MW about 60 million membranes are needed, creating a volume of approximately 1,200 shipping containers.

The source water may contain many impurities. These range from floating mate-rials such as algae and sediment to dissolved substances at the molecular level, such as salts and nutrients. The impurities reduce the efficiency of the membranes which therefore need to be cleaned regularly, which is quite costly. Something that certainly requires further study is ‘biofouling’ – the encrustation and attach-ment of organic material, which can result from being clogged.

For both RED and PRO, laboratory-scale experiments have demonstrated that the technology works (proof of concept). Both techniques have now reached the stage of scaling up to small-scale pilot plants under realistic field conditions: for example, there is a pilot plant with PRO in Norway and in The Netherlands with RED. A major pilot demonstration would be the necessary next step, and after that an operational plant, both of which still lie in the future.

Research indicates that RED is best suited for The Netherlands because of the slightly turbid rivers. PRO works well in highly concentrated salt streams (such as brine in the salt industry), and with relatively clear water. The reason for this is that with PRO huge amounts of (polluted) water need to pass through the PRO membrane, while only with RED the ions have to pass the membranes. Whether this also means that the PRO method has less future depends also on other factors, such as the complexity of the installation and developments in the PRO and RED or membranes.

Spatial planning issuesNot all challenges are physically related to the actual power plant. The integration and positioning of a plant in the water system lead to interesting questions. Blue Energy requires the supply of fresh and saltwater and the discharge of brackish water. The inlets for fresh and saltwater should be positioned in such a way that short circuit currents between the inlet and outlet will not occur. In addi-tion, the positioning of the inlets must be positioned at those locations where the maximum saline gradient is achieved.

In addition, the water intake and outlet points change the flow pattern of the river locally, which can lead to the deposition and erosion of sediment. To maintain the current functionalities of the river, such as shipping, dredging might become necessary, or a well-proportioned design should be used. The use of freshwater in the power plant will limit the quantity remaining available for other functions and uses. How much water can be used is a political choice: how much water should be reserved for navigation, agriculture, environment or energy? Possibly already existing hydraulic structures can play a role in dealing with this potential problem.


Thermal Energy from Urban Surface WaterThe focus on using renewable energy sources is an important effort in reducing the ongoing environmental impact of conventional energy generation. One renewable option for heating and cooling of buildings is the use of surface water coupled with underground thermal energy storage (TES), instead of traditional heating systems that often rely on gas combustion. Urban surface waters have a large potential for heating and cooling buildings located in the same neighbourhood, regardless whether it is occupied by households or industries. In The Netherlands, the surface water bodies coupled to TES are usually lakes with a water depth of 20-40 m. However in Dutch urban areas these depths are not met. Urban water is subject to special micrometeorological charac-teristics such as low wind speeds and relative high air temperatures. The effect is known as the heat island effect. TES is under development in many countries e.g. The Netherlands, USA, Germany, and China. Although the technical feasibility of TES has been proved, a detailed study of the different components, the combination with the usage of urban water and the assessment of the effects on ecology are still neces-sary. A feasibility study has been carried out for a new urban develop-ment ‘De Draai’ in Heerhugowaard, The Netherlands.

Method of extracting energy from urban surface waterThere are four important stages when deploying this system, which are: the extraction from the source (the urban water), the extraction and the storage of the thermal energy and the distribution to the final users. In order to extract the thermal energy from the water an exchange system must be established. A heat exchanger is usually installed to do this. For thermal energy storage the reader is referred to Section 4.6. The figure below schematizes the four stages as a chain, but in reality, loops can be created. For instance, after distribution of thermal energy to the user, the heat or cold might be recaptured and returned to the source. Another option could be that the heat or cold is directly distributed, often using water as a medium, for heating or cooling spaces without the usage of a heat exchanger.

The locations of the extraction, storage and the users are critical to the efficiency of the system. When distributing thermal energy over longer distances large losses can occur, as is generally the case with thermal energy systems. There-fore the source, i.e. the water body, must be relatively close to the final users.


Discovering the potentialThermal Energy from Urban Surface Water

Luckily, within larger cities it is common to find ponds, canals, natural existing urban waters and sometimes lakes within close range. It is obvious that the size of the surface water area and the depth of the water bodies determine the thermal energy exchange with the atmosphere and the total storage capacity. It is worth mentioning that the stored thermal energy usually needs to go to boilers before going to the user. This applies especially for the provision of hot water. Depending on the user’s demand and the state of the thermal energy system, storage can be skipped and a direct connection between the heat exchanger and user can be established.

Potential energy resourceUrban waters are readily available and are considered a renewable source of energy. As an example of the potential of urban water as an energy source it has been computed that the pond located in the ‘Paleiskwartier’ in Den Bosch, The Netherlands, which is 1,000 m², could provide 4,355 [GJ] of heat per year. This amount of energy is sufficient to provide thermal energy (heat) to 132 house-holds. Another example is ‘De Draai’ in The Netherlands, where 207,000 m² of water area could provide sufficient heat for 2,816 households.

Social feasibilityAs long as the urban water bodies preserve their ecological and visual value,

Artist’s impression of a system

for using Thermal energy from

surface water.


this method of generating thermal energy will be socially accepted. Since heat extraction leads to lower water temperatures in the water bodies, the chances are reduced for the development of bad smelling algal biomass. Another aspect that may contribute to social acceptance of the technology is the energy price. Users will benefit directly from the reduced costs, even though it is known that the cost savings are currently usually kept by the energy distributors.

Technical challengesEach component defined in the above figure is and has been subject to thorough research. Special attention is given to the water source geometry, to the natural flow conditions and to the influence of the heat exchange with the atmosphere. Furthermore, once the water body attains a temperature different to its equilib-rium temperature – due to thermal energy extraction – it will extract according to its particular characteristics. These characteristics are very dependent on the geometry of each water body. In conclusion, temperature prediction can be diffi-cult if proper analysis has not been performed. Therefore one of the major chal-lenges is the optimization of the combined system.

Heat pumps and exchangers have already been studied thoroughly by industry. However, TES technology is relatively new and the effects on ecology at microbial level still need to be studied. Thermal energy dispersion in the subsurface has not yet been properly investigated. Feasible technologies for such research include the use of fibre optics for real monitoring of heat movement.



Thermal Energy StorageDuring the seasons the temperature of the air and the surface layer of the soil (with water) fluctuate, but the temperature of the lower layers of the soil remains stable. It is precisely this phenomenon that is used in Thermal Energy Storage. A heat and cold surplus can be added to the soil to create a temperature difference between the top and base of the lower soil layers. The segment ‘filled’ with the cold surplus can be used in summer to provide a source for cooling and the segment filled with the heat surplus can be used in winter as a source for heating. The application of this concept on a small or large scale is old, but nowadays this concept is being applied to the energy management of offices, homes and other buildings.

Methods of storing thermal energyThe two main types of thermal energy storage (TES) are Aquifer Thermal Energy Storage (ATES) and Borehole Thermal Energy Storage (BTES). With ATES the groundwater is pumped up, cooled or heated and then re-injected. With BTES a piping system is fitted in the subsoil in which a coolant circulates and – depending on the temperature difference – the soil warms up or cools down. Because the heating and cooling alternate depending on the season, excess heat in summer can reduce primary energy usage for heating needs in winter and vice versa for cooling in summer. The relatively small temperature differences between the soil or groundwater and the circuit of a building often require the use of a heat pump.

Both techniques can be applied when the possibility exists for drilling boreholes or wells. In areas with thick aquifers ATES will have the advantage but where the soil has less potential for attracting and injection of groundwater, BTES will have the advantage. Both systems have advantages and disadvantages and the choice between one of these systems is not only dominated by the subsurface properties. The availability of knowledge on the two techniques means that each country may differ in a striking preference for one or the other.

In The Netherlands the preference now lies with ATES; over 1,000 systems are in use, of which hundreds have been deployed in the last few years. Nevertheless, there are also already 20,000 boreholes made for BTES. In The Netherlands, the attention is focused on open systems because the power generation per system often exceeds the BTES systems. Also, BTES systems do not require a registration, meaning that the number is an estimate. Elsewhere in Western Europe energy storage systems are also widely used. In Sweden and Germany particularly BTES systems are deployed. Moreover, the design of these systems differs greatly from the Dutch designs.


Potential extractable resourceThe determination of the potential extractable resource of ATES is a little ambig-uous, firstly since ATES is an energy storage system and secondly, since there are several thousand billion cubic meters of groundwater in The Netherlands. If this groundwater is only heated or cooled over a few degrees, it creates a heat and cold source that goes far beyond the current demand. At a temperature difference of approximately 4 degrees we are talking about an order of magnitude of 15,000 PJ per year.

A very large part of The Netherlands offers good potential for TES, because there are many highly permeable layers in the subsurface due to our location in a river delta. Moreover, permeability is a basic requirement, but not the only criterion that determines the possibilities. The depth of the water layers also makes a difference and the presence of various redox conditions within an aquifer may restrict the possibilities. The criteria for BTES systems are different, since these systems do not fully rely on the permeability and are often installed nearer to the surface than ATES systems.

Technically extractable resource The two main factors when estimating the technically extractable resource are the number of systems that can be placed and the average capacity per system.

Artist’s impression of an Aquifer

Termal Energy Storage system.


Discovering the potentialThermal Energy Storage

It is inherent to the TES systems that they should be placed near the customers because of the energy loss over larger distances. It also needs to be taken into account that a water and/or heat pump require electrical power, so that the savings on heating and cooling can never be 100%. The current systems will save around 50%. Assuming that it proves possible to provide every building with a TES system, there could be a potential saving of 50% of the current consump-tion: 50% x 960 PJ, thus 500 PJ, with regard to The Netherlands. Regarding the required or available space very little can be said, since this also depends on the method of allocation of the soil and the average size of future systems. In any case, to get to the 500 PJ a total capacity of around 300,000 MW needs to be deployed. This requires a permit to be issued for 100 billion m³ of groundwater movement.

The number of systems that are needed to achieve this is difficult to estimate. First, a trend exists toward more neighbourhood-oriented systems instead of building-oriented systems. Second, the applied techniques can also be made available for small-scale applications, by which the ‘small’ market will grow. The energetic efficiency of the systems does not directly correlate to the size of the systems.

Social feasibility The stated technically extractable resource puts a major claim on groundwater. Groundwater supports many uses, so conflicts with other interests will arise. Some of the current uses or functions of groundwater are:– Draining excess water– Storing water (peak season) – Water supply – Holding, transporting and/or breaking down contaminants – Support of a terrestrial nature – Storage of thermal energy (hot and cold) – Maintaining anaerobic conditions in the subsurface – Reducing weight (rms tension) – Reduction and oxidation of settling – Water for fire fightingIn addition, structures with foundations are present on or below the soil surface, and these can be affected negatively by a change in groundwater flow direction. Besides the issue of the allocation of groundwater, the water quality change caused by TES systems remains unclear. The temperature changes of the soil can bring about chemical reactions; changing the flow direction may cause the mixing of different water qualities leading to a change in redox equilibriums and changing fresh/saltwater boundaries in the soil, with corresponding changes in the microbiological composition. In some areas TES systems may not be allowed


to operate, due to regulations concerning drinking water supply or concerning general water quality aspects.

The economic feasibility equals the social feasible potential, as the systems have fairly limited payback times. Whether these payback periods increase in the future is not known, and therefore the economic profitability of these plants remains unproven. The size of the systems will affect the economic viability, but as mentioned above, this can result in either larger or smaller systems. An obstacle with larger systems is the way the reduction in energy demand, and thus the reduction in energy costs, is passed on to the individual user.

Technical challenges The technique itself is well developed and the application is carried out routinely. The challenges will be to standardize further to reach a larger market or scaling towards larger collective systems. TES can also be seen as a part of water and energy management in urban areas, so there may be links established with other water and energy flows (surface water, process water, sanitation, public space cooling requirements, etc).

Expanding our knowledge on both negative and positive effects on the soil due to TES systems may also contribute to reducing the effects or to eliminating unnec-essary legal barriers.

TES systems are primarily installed in urban areas, where contaminants may be present. In principal TES is not desirable in areas with contaminated soil because of the unwanted spread of the contamination or the potential for reduced func-tioning of the system. However, there are some new ideas under consideration for realizing one or more concepts combining TES with decontamination of the soil, so that both objectives can be achieved.

Spatial planning issues As indicated above, the spatial use of TES systems produces a possible problem with the widespread realization of these systems. The interaction with other underground features must be properly balanced. At the moment there is no formal instrument to decide on spatial interests and allocation. This may lead to an obstacle in the realization of TES systems in densely populated areas.

5 Considerations for Application


Considerations for Application

The previous chapter shows different possibilities for extracting energy from water. Despite the fact that water is a renewable source of energy, it remains necessary to consider several aspects, before realizing a power plant that extracts energy from the water. Renewable energy is only renew-able and sustainable when the source is renewable, the energy extraction is in harmony with environment and society and the energy extracted makes the initial energy costs and the emissions insignificant. This chapter contains some of the important aspects to be considered.

For renewable energy installations, just as for traditional oil or gas installations, placing a structure in an environment will lead to changes in the surrounding param-eters, if only locally. Offshore renewable energy installations can cause changes in small and large-scale hydrodynamics around the structures, sea bed morphology, sediment transport and ecosystem functioning. By adding a structure the original habitat is changed, which can lead to changes in the ecotope, changes in species richness and bio-productivity. In addition, the operation of installations may have specific impacts on the surroundings. Osmotic power installations (Blue Energy) change the composition of water by extensive filtering and/or reverse osmosis,

Renewable energy and the environment


and can thus have an effect on water quality and ecosystem productivity (as also nutrients are removed by the filters). However, adding a structure to an environ-ment does not necessarily have negative impacts on the surroundings; some effects may also be beneficial. Offshore wind farms are generally prohibited areas for commercial fisheries and navigation, which can result in the development of relatively bio-productive and bio-diverse refuges. Nevertheless, for every installa-tion it is necessary to assess the type and extent of the immediate and long-term impacts on the environment. It should also be noted that large networks of instal-lations, such as large-scale offshore wind farms, could have cumulative effects, for instance on wind or ocean currents. With extensive knowledge of large-scale and local hydrodynamics, morpho-dynamics, ecosystem functioning and spatial planning, site selection for installations can be optimized to result in maximum energetic yield, as well as in minimal negative effects on the surroundings. Taking environmental knowledge into account in the earliest stage of renewable energy development will lead to ecologically and environmentally optimized installa-tions, and can avoid delays and costs in later stages due to required mitigating measures or nature compensation measures.

Environmental legislationIn order to ensure that environmental impacts are taken into account in the design, development, site selection, construction, operation, maintenance and


decommissioning of structures, environmental legislation has been developed in Europe. Several national and European laws and directives have been put in place to protect specific species, habitats or regions, and to minimize negative impacts of plans or projects on the environment.European Community and/or European Union countries work under the EU regu-latory demands such as the Habitats Directive, the Environmental Impact Assess-ment Directive (on the assessment of the effects of certain public and private projects on the environment), the Strategic Environmental Assessment Directive, the Wild Birds Directive and the OSPAR Convention (which is the current legal instrument guiding international cooperation on the protection of the marine environment of the North-East Atlantic). For this reason, Environmental Baseline Surveys and Habitat Assessments are carried out in advance of any significant marine development. Most research or consultations relate to detailed sediment and water quality analysis within a designated area, looking at physio-chemical and biological factors as stated in the OSPAR guidelines.

Environmental assessmentsThe EU Habitats and Species Directive (Directive 92/43/EEC) requires that any plan or project not directly necessary to the management of a designated habitats site, but likely to have a significant effect thereon, is to be subject to an Appropriate Assess-ment (AA) of its implications for the site in view of the site’s conservation objectives. Where significant negative effects are identified, alternative options should be exam-ined to avoid any potential damaging effects. A Strategic Environmental Assessment (European SEA Directive 2001/42/EC) is a system of incorporating environmental considerations into policies, plans and programs. Generally, a SEA is conducted before a corresponding Environmental Impact Assessment is undertaken. This way, information on the environmental impacts of a particular plan is involved early in the decision making process, ideally reducing the amount of work that needs to be undertaken in later EIA stages. An Environmental Impact Assessment (European EIA Directive 85/337/EEC) is a technique used for identifying the environmental effects of development projects. An EIA is now a legislative procedure to be applied to the assessment of the environmental effects of certain public and private projects, which are likely to have significant effects on the environment. In many countries, an EIA is a statutory requirement for projects that involves offshore and coastal construction. The purpose of the EIA is to interpret both long-term impacts of proposed works and operation, and possible short-term impacts during the construction and decommis-sioning phases in a manner consistent with formal EIA procedures, and is recom-mend appropriate measures that can be taken to reduce any adverse impact.

Eco-engineeringEco-engineering is the use of engineering solutions that improve the ecological benefits of traditional structures. Renewable energy installations serve as possible


Considerations for ApplicationRenewable energy and the environment

habitat for flora and fauna that depend on hard substrates for attachment, shelter and food. The eco-engineering concept aims at enriching these hard substrates, by effective eco-dynamic design of engineering projects. These integrated designs use ecosystem services to fulfil or complement engineering functions. Thereby, ecological and societal functions are taken into account as well. Often this can be realized in a cost-effective manner, ideally even reducing (maintenance) cost in the long term, while substantially increasing benefits for both nature and human well-being. The basis of these designs is the preservation of the original structural func-tion. The result is a larger biomass and diversity per surface unit, a more appealing marine landscape and a positive influence on the neighbouring waters.

Environmental AspectsThis paragraph indicates the effects on the environment and surround-ings of energy from water devices and focuses on the five most relevant options. These options are wave energy, tidal energy (both current and range), blue energy, thermal energy storage (without and with regenera-tion) and river energy. The potential contribution as well as the effects of these options on the surroundings are given.

Effects on the surroundingsIn the inventory of the effects on the surroundings, a standard approach was employed which uses two lines of approach to ensure complete coverage. The lines of approach are ‘People-Planet-Profit’ and ‘Sender-Message-Receiver’; the latter could be typified as ‘Causer-Effect-Affected’.

The People-Planet-Profit approach is used in order to give an insight into which effects on the surroundings are influencing which elements. To this end not only the negative effects on, for example, nature are shown but also the beneficial effects such as the use of renewable energy. The following table gives an overview of the elements that make up the triple P approach.

The Sender-Message-Receiver approach is also adapted in order to be used in the analysis into the effects on the surroundings:Sender: The three primary parts of the lifecycle of a technology (preparation/

construction, operation/maintenance, decommissioning) and inci-dental events.

Message: The message is the event or the effect that can occur with the sender. Examples could be the production of noise during the construction phase, the changing of the ground’s physical properties, a shipping ban or temperature differences.


Table 2 Framework analysis of

the effects on the surroundings –

Sender, Message, Receiver.

Category Subject

Sender Preparation/constructionOperation/maintenanceDecommissioningIncidents

Message SoundChange in physical propertiesVibrationTurbulenceChemical emissionsElectromagnetic radiation (Working) partsVisual aspectsFishing and shipping banEnergy (only regarding renewable energy production)Shutting of waterwaysChange in fresh/salt concentrationsChange in nutrient management Released/residual damaging materialsPumping groundwater roundTemperature variationsOther emissions

Receiver The receivers of the message are in the categories within the People-Planet-Profit line of approach. For example: the Sender of hydropower is the installation, which is in operation. One of the Messages is then the ‘shutting of a waterway’. Receivers therefore are ship-ping (Profit) and fishing (Planet).

Table Framework analysis of the

effects on the surroundings –

People, Planet and Profit.

Category Subject

People Health PolicyLandscape RecreationSafety

Planet (Sea)mammals GroundFish WaterBirds Climate (CO2)Benthos

Profit Fishing Energy potentialTourism Synergy


Considerations for ApplicationEnvironmental Aspects

Figure Schematic view of

framework.

Receiver: The receiver of the message or the effect is the same as the category Profit from People-Planet-Profit. Therefore, the fish are the receivers of the Message sound from the Sender operation/maintenance.

The table below gives an overview of all parts of the Sender-Message-Receiver classification.

Because all the energy technologies under consideration are analysed based on this uniform framework, a consistent picture is formed concerning the effects on the surroundings of the various options. The figure below illustrates the layout of this framework schematically.

ProfitPeople Planet

Sen

der

Mes

sag

e

Receiver

The effects on the surroundings can be positive as well as negative. Not all the effects are relevant for all the options and sometimes the effects are simply still unknown, because it involves new technology. With regard to negative effects the research looked into whether mitigation or adaptation is possible and what the consequences of this would be. With regard to positive effects the research exam-ined whether these could be strengthened.

The analyses show that the various options have a wide range of effects on the surroundings. The full overview of this can be found in the background reports. The paragraphs below give the most typical effects on the surroundings, including the positive as well as the negative.

Tidal energyHigh water and low water occur at coastal locations twice a day. The difference can be from ca. 0.5 meters up to 15 meters. The tidal current that is caused can be as much as 5 m/s in coastal zones with a high water level difference; in The Netherlands the rate of flow is approximately 2 m/s. The research considered two options; one for getting energy from the current and one for using the tidal range.


Most of the effects in the construction phase are temporary and can be minimised with careful planning and implementation. The location and design must be care-fully chosen (effect on water transport; migration route or location of fishing). However, the biggest negative effect is expected on the benthic flora and fauna. In general it is mainly species that move the slowest that, given the constructions and cabling that must be anchored in the ground, will encounter negative effects.

In the operational phase tidal height, speed and time will be affected. By large-scale application in, for example, the coastal and mudflat area, this can lead to a reduction in the available food particularly for birds (smaller area of shoreline and shallows) and changes in sediment formation and depositing due to the reduction in tidal speed. With small-scale application these effects are not expected. There is still uncertainty over the effects of the moving parts for fish and sea mammals. A number of the negative effects can be easily prevented by applying suitable measures, such as placing the installations under the water’s surface. This will also minimize the hindrance for shipping. Possible incidents are leakages in the lubricants, paint or coatings, which could lead to water pollution.

When use is made of the difference in height between ebb and flood, then the effects on the surroundings will be different. The study looked at the effects of building a tidal power station in the Brouwers Dam (Brouwersdam) at Lake Grev-elingen (Grevelingenmeer) in The Netherlands. Because this construction already exists, the effects of the development phase (sound, vibration, and turbulence) are expected to be of a temporary nature. The effects of the operational phase are bigger and more permanent. A few negative effects such as sound, vibration, effects on the landscape and possible incidents are in contrast with the positive effect of a noticeably improved water quality in Lake Grevelingen due to the reintroduction of tides. The decline in water quality over the last few decades is one of the most important reasons for this research into the possibilities for a tidal power station at the Brouwers Dam.

Wave energyMost of the effects of the construction phase are temporary and concern sound, vibration and turbulence. These effects have a negative effect on receivers from the Plant category: sea mammals, fish, birds, benthos, and the ground. Careful planning and execution can minimize these effects.

Also in the operational phase it is mainly sound and vibration that have a negative effect on the Planet category. Other negative effects can be the electromagnetic radi-ation (the effects of which have not yet been clearly investigated) and the changes in the wave or sea currents. Positive effects are the creation of a fishing-free zone, where sea mammals, fish, birds and benthos benefit and the parts of the installa-



tion that can serve as artificial reefs or resting places for them. Then again these positive effects have a downside in the risk that fishing-free zones will have negative effects on the fishing industry or that sea mammals will injure themselves on the (moving) parts of the installation. Just like the construction activity, the effects of the decommissioning also have a temporarily effect. In addition, it is legally laid down for offshore windmills that the location must be returned to its original state. The most important effect of incidents (such as a cable break or collision with a ship) is oil emissions that come from ships, which are involved with the incident.

River energyIn The Netherlands the height differences in the rivers are very limited. The exploi-tation of hydropower is therefore only possible on a relatively small scale. The hydropower station under consideration is a combined installation of a dam, which provides the necessary drop, and an installation with turbines that gener-ates the electricity.

Most of the effects in the construction phase are temporary. These are mainly the effects of the activity, such as vibration, sound, and damaging of the sedi-ment in the river. In addition more infrastructural adaptations are being made, which can affect the landscape and the recreational value of the landscape. The most important effects in the operational phase are the production of renewable electricity (positive), and sound, moving parts and shutting off waterways (nega-tive). The sound can create problems for life in the water (fish and benthos) as well as for those living close by and recreation. The large turbines in the installation are insurmountable obstacles for fish and therefore it is necessary that suitable measures are taken here. In addition, the whole installation shuts the waterway, which can have consequences for shipping.

With the decommissioning of the hydropower station the situation can be returned to its original state. If done correctly then the effects of the decommis-sioning are only temporary. Two types of incidents are considered possible. These are either incidents whereby the hydropower station causes polluting emissions due to, for example, a disaster (a fire, leak, etc) or incidents in which external influ-ences on the power station occur (for example, a collision with a ship).

Blue energyThis technology makes use of the saline gradient between freshwater and salt-water. With this variation ions, respectively water molecules, flow through a membrane that is located in a Blue Energy power plant. The building of a Blue Energy power plant will have a considerable effect on the surroundings. In partic-ular, the constructions that are placed under water will (probably temporarily) damage the ground, benthos and fish.


The most important negative effects are expected in the area of water pollution. In order to keep the membranes clean the water that flows through needs to be very clean. Various methods are available for this, using large quantities of chemicals. In addition, there can be a disturbance in the nutrient balance; unnecessary algae growth on the freshwater side is seen as just one of the hazards. Furthermore, shut-ting the waterway could cause a problem for shipping as well as fishing if it has not already done so. The above ground part can have an impact on the landscape.

Thermal Energy Storage (TES)With thermal energy, storage makes use of subsoil layers, which is where the thermal energy is stored. In the Winter heat is withdrawn from the subsoil and cold is injected into the subsoil and in Summer vice versa. A heat pump is also often used to bring the water to the required temperature. Because in built-up areas the demand for heat is much higher than the demand for cold, additional measures must be taken in order to keep the temperature of the subsoil in balance. This can be done through regenerating the ground by using of surface water.

Planning permission must be requested for an aquifer and the system must comply with a series of guidelines. As a consequence of displacing the ground-water, possible contamination within the aquifer can be spread and the natural water flow in the aquifer can be disturbed. The system can also affect the ground-water temperature but this difference is so small that it has no effect on the biology and/or chemicals in the subsurface.

ConclusionsBy using the two lines of approach, ‘People-Planet-Profit’ and ‘Sender-Message-Receiver’, an complete analysis has been carried out into the effects on the surroundings of the various options for energy technologies based on water. This approach leads to an indication of the opportunities and bottlenecks and to the extent to which these can be improved or limited, respectively.

It can be concluded that the Thermal Energy Storage option shows the most favourable overall picture; there are hardly any (or none) negative effects, which cannot be mitigated or adapted. The options for Blue Energy and river energy also have a reasonably good overall picture. However, for both options there is sound nuisance; the Blue Energy power plant also has a localised influence on the fresh and saltwater concentrations and river energy causes a nuisance for fishing and shipping. The application of tidal energy in closed off basins or estuaries has many positive effects on water quality, fish, plants, birds, benthos and limited negative effects.With wave energy there are more relevant negative effects, such as sound, vibra-tion, the influence of moving parts and the influence on wave and seawater flows.



However, the option also has potential advantages concerning safety and protec-tion of birds and fish. The same bottlenecks and advantages for tidal energy from currents also largely apply to wave energy.

Life Cycle AnalysisA frequently asked question is whether the application of renewable energy is profitable. Usually this means whether a necessary finan-cial investment pays back within the near future. This chapter does not consider the financial profitability, but the energy profitability. Therefore it reveals whether the energy investment that is made pays back during the lifetime of the device. The key question here is how long the renew-able energy application is necessary ‘to earn back’ the construction, user and decommissioning phases.

Energy payback periodA renewable energy technology is only really renewable when it saves more fossil energy during its lifespan than it cost to build, use and decommission. In order to give insight into whether the various techniques really justify themselves research has been carried out into what the Energy Payback Period (EPP) for the technologies is when these are applied to The Netherlands.

To calculate the EPP the total energy that is needed during the whole cycle of a technology (obtaining raw materials, production, transport, installation, mainte-nance, decommissioning and recycling) divided by the number of years of renew-able energy that is created:

EPP =Total energy required

Annual amount of energy created

Life cycle analysisThe two elements that are necessary to calculate the EPP are obtained in two ways. The total energy demand (energy input) is obtained using a chain anal-ysis based on the life cycle analysis (LCA) method; the annually created energy (energy output) is obtained by making a calculation of the expected product of the technology, when this is applied in The Netherlands.

With LCA, a chain analysis for a particular technique or product is carried out, in which various environmental aspects of the complete lifecycle are examined according to an established procedure. The results of these analyses are however


not absolute but relative. Therefore, this method is excellent for the comparison of various techniques or products that have a similar function (in this case elec-tricity production). It is important for the results of an LCA, and therefore for the comparison, to realise that variations in approach can lead to significantly different results. Therefore, a consistent approach to the system boundaries, the allocation and the choice of impact categories is important. For the definition of the system boundaries, the research employed four parts or phases in the technology:– Production of raw materials and components– Assembly and installation– Operation and maintenance– Decommission and waste processingFor the allocation of impacts over the various user phases, the input method was chosen. For the impact categories – the subjects that were examined in the analysis – only the primary energy use and the CO2 emission equivalents were regarded.

Extensive chain analysis is carried out, almost completely based on the methods used to carry out LCA. These chain analyses are mainly carried out for the produc-tion and decommissioning phases. The energy use during assembly, installation and operation is estimated based on rule of thumb and expert opinions. Due to this consistent approach of the various technologies the comparability is high. The results of the EPP are very dependent on the energy device regarded. The calculations of the EPP are carried out for one technology per option. An overview is given below.

Tidal energyProduction of electricity from tidal currents can be carried out in various ways. Here the Wave Rotor is used for the calculation of EPP for tidal energy. Because this technology is commercially available, the information from a pilot installa-tion in the Western Scheldt (Westerschelde) is used.

The Wave Rotor is a single rotor installation with a capacity of 30 kW. The energy input is dominated through the production of the raw materials and components, which have a share of more than 80% of the total energy input. The energy output of the Wave Rotor is very dependent on the current speed of the water. For The Nether-lands, this is approximately 2 m/s on average, which is below the optimal speed for a suitable energy technology. Nevertheless, the Wave Rotor has an EPP of 3.4 years compared to a considered lifespan of at least 20 years. In ideal circumstances where the tidal current is stronger such as in Ireland, the EPP can easily reach 1.5 years.

A second method of producing electricity from the tide is by using the tidal range. In The Netherlands this is possible at the Brouwers Dam. The tidal range at


Considerations for ApplicationLife Cycle Analysis

this location is relatively small, approximately 0.7 meter. As a consequence the energy output is less than ideal. However, because the installation can be adapted to existing infrastructure and new techniques are available, the energy input is also relatively low. This means that this technology achieves a designed EPP in The Netherlands of 6.3 years.

Wave energyFrom the swelling of the waves, energy can be obtained by the height and pres-sure difference (potential energy) as well as the movement (kinetic energy). Also with the Pelamis the production of the raw materials and components has a great deal of influence on the energy input. A large part of this can however be compensated for because at the end of the lifespan an environmental advantage occurs through the recycling of the materials. However, when this recycling is not included in the calculation, then the EPP for The Netherlands is approximately 15 years. Although this is still within the desired lifespan of 20 years, there is a big difference between this and the EPP in an optimal study (for the coast of Portugal) where an EPP of 2.8 years can be achieved.

River energyRivers have been used for centuries as a source of energy. Originally, this was for normal water mills, but in the last few decades also as a source of electricity by hydropower. By placing of a dam in the river and leading water via turbines, it is possible to generate electricity. In The Netherlands electricity has been produced in this way in several places for a number of years. The research looked at the EPP of the already existing hydropower station in the Meuse (Maas) at Linne (with a capacity of 11.5 MW).The calculations of the energy input and output show that these differ very little from each other. Therefore, the EPP is 0.9 years. With a desired lifespan of 40 years, it has a favourable energy production ratio (lifespan divided by the EPP) of at least 44.

Blue energyThe creation of electricity with the help of osmosis is a form of renewable energy that is based on the differences in salt concentration of (salty) seawater and (fresh) river water. The difference in concentration between the fresh and salt-water can be used in two ways: through PRO (Pressure Retarded Osmosis) and through RED (Reverse Electro Dialysis). The latter was chosen to determine the EPP. A Blue Energy power plant consists of an installation with stacks of membranes and sieves (lifespan of five years) and supporting infrastructure (lifespan of 30 years). This means that during the whole lifespan of the power station the membranes and sieves will have to be replaced several times. These parts put a lot of pressure on the energy input of the power station. The energy


output of the 10 MW power station in the research was just sufficient to have an EPP that is lower than the lifespan, namely 29.5 years. This EPP is for a hypo-thetical power station, based on details of non-commercially produced parts. By scaling up to mass production of the stacks (almost three quarters of the energy input) the expectation is that this could be improved dramatically. Therefore, the EPP would reduce considerably.

Thermal Energy Storage (TES)The use of the subsurface to store warmth and cold is already being applied in The Netherlands. This application differs from the previous options, in the sense that it is an energy saving technology and not an energy extraction technology. When calculating an EPP the avoided energy use in comparison with a reference situation is also considered. For The Netherlands this is traditional heating using natural gas. The amount of saved primary energy is very dependent on the performance of the system. The research looked at a system with a collective heat pump with a coef-ficient of performance (COP) of 4.5; the system in The Netherlands has an EPP of 2.8 years. A higher or lower COP rapidly leads to a different EPP, varying between 2.3 and 4.4 years.

Thermal Energy from surface waterA particular variation of TES is a thermal storage system whereby a link is also made with the surface water. The surface water is thereby used as a source of heat or cold and as regeneration for the aquifer in the subsurface. This is an extra energy source and means that other techniques for regeneration (such as cooling towers) can be discarded. In The Netherlands the first initiatives are being set up in various places to adapt to this form of renewable energy. In order to calcu-late the EPP an initiative in Groningen, the Tasman Tower, has been examined. Because there is no energy creation with this application either, the EPP cannot be calculated in the usual manner. Therefore the EPP is calculated for this tech-nique using the saved electricity and material use in comparison with a reference situation whereby cooling towers are used for the regeneration of the aquifer of the cold/warm system. The research has shown that the EPP for this option is negative, which means that this option costs less energy during its entire lifespan than its alternative. Therefore no energy has to be earned back with this option. It is important here that the surface water is near the Thermal Energy System, because the longer the pipes to and from the system, the more likely that there will be a tipping point where an EPP will occur.

ConclusionThe following overview gives a picture of the spread of the EPP and the EPR for the various options. The EPR show the relationship between the lifespan and the EPP.


Considerations for ApplicationLife Cycle Analysis

The higher the ratio, the more favourable the relationship. This means that the application will be earned back many times. As can be clearly seen, a number of options have a very favourable EPP of between 0 and 5 years. This, combined with the options’ EPR, leads to the conclusion that the options of tidal energy, river energy and TES are options that use water very favourably as a source of renew-able energy, if only the energy use during the whole lifespan is taken into account.

Option EPP in The Netherlands EPR

Tidal energy (current) 3.4 years 5,9

Tidal energy (drop) 6.3 years n/k

Wave energy 15.0 years 1,3

River energy 0.9 years 44,0

Blue energy 29.5 years 1,0

TES in the ground 2.8 years 10,7

TES of surface water <2.8 years >10,7

Accuracy of resultsThe above figures are the results of the analyses carried out based on the best available information sources. However, in a number of cases the application is just starting to be developed or is not yet implemented. Therefore, some data had to be estimated.


Environmental Flows – the Tool to Mitigate Hydropower Impacts The generation of hydropower can provide a renewable source of energy. However, large reservoir construction to generate hydropower also has many environmental and social consequences. The construction will have impacts upstream of the dam, in the valley that is inundated to create the reservoir, but also downstream as a result of regulation of the natural river flow regime. Although hydropower generation does not by itself consume water, associated large reservoirs do looze a lot of water through evaporation and change the natural variation of the flow regime. Generally, large peaks in river discharge are stored, while low discharges are augmented.

Ecosystems of rivers, levees, wetlands and estuaries are to a large extent the result of the natural variations in low and high flows. For example in Africa, flood plain inundation provides a suitable environment for young fish to mature and moisturizes the soil to support vegetation growth. Fishermen fish these waters, while recession farmers grow their crops when the floods recede and pastoral-ists herd their cattle on the grasslands, fertilizing the soil with cattle manure. In this cycle different groups of people interact with the ecosystem and are highly dependent on the natural variation in discharges over the year. Changing the flow regime will therefore without doubt lead to a change in the ecosystems down-stream of the dams. This may not only harm flora and fauna, but also the liveli-hoods of many people who make use of these ecosystems.

The fact that reservoirs can have such profound influences on ecosystems and the services they provide for people does not imply that hydropower generation is not a renewable solution. It does mean that attention needs to be paid to how the ecosystem and the well-being of people is affected by the operation of a reservoir. Then, solutions can be sought, that minimize the impacts or that compensate for the damage done. To evaluate hydropower as a renewable source of energy all positive and negative impacts during (and after) the lifetime of the dam are to be taken into account. Environmental flows offer a tool to mitigate downstream consequences of dam operation.

Environmental flows The concept of environmental flows has been developed to mitigate downstream impacts of river regulation and can be defined as the quantity, timing and quality of water flows required to sustain freshwater and estuarine ecosystems and the

Group discussion with bird

hunters to duscuss the impor-

tance of hte Hamoun wetland

in Iran.


Considerations for ApplicationEnvironmental Flows

livelihoods and well-being that depend on these ecosystems. Assessment of these requirements is essential to balance interests in river basin and integrated water management. It is important to note that this requirement is more than just a ‘minimum flow’ and should include all components of the flow regime, such as low flows, small seasonal floods and large floods, as well as their timing.

How can environmental flows be determined? In the past few decades a large number of methods have been developed to determine environmental flows. One of the oldest is the Instream Flow Incre-mental Methodology (IFIM), which has long enjoyed legal status in the United States of America. Other methods include the Flow Duration Curve Analysis (FDCA), Indicators of Hydrologic Alteration (IHA), Texas Method, Annual Minima Method, the Building Block Methodology (BBM) and the Downstream Response to Intended Flow Transformations Methodology (DRIFT). Generally speaking, the methods can be divided into two broad categories: those that address only part of the ecosystem (e.g. a single species or group of species) and those that are of a holistic nature, which try to assess requirements for the entire downstream ecosystems and human uses.

Basically, the assessment of environmental flows requires answering three ques-tions:– How the construction and operation of water resources infrastructure, such as

dams and diversions, affect the existing river flow;


– How these changes in flow regime affect downstream ecosystems and services; and

– How the societal benefits as well as impacts from alternative water manage-ment strategies are distributed among the various stakeholders.

For the first question, knowledge is required on the hydrology and hydraulic condi-tions of the river system vis-à-vis the modifications that are envisaged through the proposed water development project. Besides the most obvious consequences for the annual river flow regime, attention should also be paid to changes in the annual variability. Often, downstream impacts are felt greatest during years of exceptional drought or higher than average rainfall. Furthermore, the impact assessment should include potential changes in the water quality and sediment discharge of the river. A well-known effect of large dams is the entrapment of sediment in the reservoir, which can lead to a significant increase in downstream river and coastal erosion.

Once the changes in the downstream flow regime have been assessed, their ecological consequences need to be estimated. This requires flow alteration – ecological response relationships, which are mostly river and site-specific. Often local ecological expertise is needed to prepare such response relations, using on-site knowledge of the aquatic and riparian vegetation and fauna combined with historical information.

Based on the expected changes in ecosystem structure and functioning, a trans-lation into the eventual loss of ecosystem services is needed. These services are often crucial for the livelihood of people living alongside rivers, e.g. for drinking, washing and bathing, but also for fishing and other food, construction materials or navigation.

Successful environmental flow assessments are characterised by utilising the most appropriate models and tools, which are tuned to the local conditions. Hydrological, ecological and socioeconomic models and knowledge need to be integrated, which requires cooperation of scientists from various disciplines as well as interaction with the various stakeholders.

Environmental flows as a tool to mitigate hydropower impactsHydropower projects should preferably be considered as part of basin-wide water resources planning. Knowledge of environmental flows is essential for an ecosystem-based approach to integrated water resources manage-ment (IWRM). Water development projects are no doubt capable of boosting economic development but there are always costs involved as such projects


Considerations for ApplicationEnvironmental Flows

may result in a loss of downstream ecosystem services. Which ecosystem services are given the highest priority or whether a certain level of ecosystem change can be accepted is ultimately a societal choice. Understanding the rela-tionships between flow conditions and downstream ecosystem processes and functions is needed for assessing these trade-offs between upstream water use and downstream consequences. Therefore, the assessment of environmental flow requirements should be regarded as a logical, essential and obligatory part of any integrated water resources management study or hydropower feasi-bility or design project.

Understanding flow-ecosystem relationships and required flows to maintain a certain ecosystem condition is the basis for finding alternative operation strate-gies for reservoirs. Advanced modelling tools and inflow forecasts can contribute to finding solutions that provide the largest benefits for all users of the reservoir, including downstream ecosystems and its beneficiaries.

Incorporating this knowledge in the early phases of the design process may help to identify other solutions such as ‘run-of-river’ power plants or a cascade of small reservoirs. Both options have less storage and consequently fewer river regulations and environmental impacts as a result. When large reservoirs are chosen, it is important that gates are designed in such a way that both small and large releases are possible and that temperature, sediment content and other water quality parameters of reservoir releases can be controlled.

Understanding the flow-ecosystem-society relationships is crucial to find solu-tions that best match all interests and make sure that hydropower installations generate renewable energy in a sustainable way.


Bottlenecks When InnovatingGiven the need to achieve a more renewable society and with that a more renewable energy sector, it is important that renewable energy projects are realized. This also applies to energy from water projects. Many of the technologies that provide energy from water are still innovative, still under development or only implemented in some places. This is due to the current state of the art and the fact that these technologies are not yet fully developed to commercially exploitable levels, or certain obsta-cles are still to be overcome. The obstacles in the implementation process that can be encountered are of a different nature and have inherently a different impact on the process. To control the realization process and to monitor and anticipate any obstacles, it is important to conduct a bottle-neck analysis. For the Blue Energy technology (see page 45), a bottleneck analysis is carried out and barriers are identified. This case study for Blue Energy technology is of indicative value for other types of energy from water technologies.

Case study for Blue Energy The bottlenecks that may play a role are categorized based on the relationship with the power plant. The categories are defined by the following boundaries: – the components of the plant itself – the physical environment of the power plant – the institutional environment of the power plant – external factors (no influence)

It should be clearly noted that the focus here is exclusively on the bottlenecks and not on the possibilities, opportunities or the favourable effects compared to conventional energy production. This may appear in this chapter as a negative experience, while Blue Energy is seen by many, and by the authors of this piece, as a promising technology.

Assumptions This chapter focuses on the current state of the art, the necessary innovations and the overall feasibility of a Blue Energy installation in The Netherlands (as known in mid 2010). To achieve this, research into the technical aspects and the influence of and on the environment has been carried out. The result is a set of generic points and contains no site-specific analysis. Such analysis may lead to deviations from the barriers identified in this chapter.

Both the RED and PRO Blue Energy power plants share the vast majority of many


Considerations for ApplicationBottlenecks When Innovating

similar components. Both methods are still in the development stage and it is expected that several components will be adapted for specific application in one of two types of plants. Nevertheless, it is assumed that at the present stage, the presently known characteristics and bottlenecks of equal components in both methods are valid.

Bottleneck analysis The figure on the next page, called a mind map, lists the key challenges and bottlenecks in the realization of Blue Energy installations. What we believe are the most crucial factors are shown in red.

Main bottlenecks identifiedThe mind map shows around 70 bottlenecks which are not all equal in weight and many of which are in interaction. Without further discussion, it is ambiguous to say which bottlenecks deserve priority. From the authors’ perspective, the following are the key factors in the innovation process of Blue Energy:

– The prevention of short circuit currents between the water inlet and outlet. Based on a suitable location short circuit currents are the greatest threat, because two water supply/discharge flows and three flows are necessary for exploitation.

– The cost of energy and the purification These costs amount to between a third and a half of the total costs incurred to purchase and maintain the components. This is remarkable, because the goal is electricity-generating energy and not the purification of water. Additionally, the absolute cost of treatment is very high and forms a barrier to commercializa-tion.

– Water quality requirements of the membranes The water quality of the membrane determines the appropriate intensity (number of purification steps) for the treatment and thus a large part of the cost.

– The power density of the membranes The efficiency of the membranes (amounting to Watt/m²), the costs of the membranes and the durability are not a combination that is commercially exploitable.

– The use of detergents Chemical cleaning substances cannot be discharged into surface waters. Environ-mentally-friendly alternatives must be developed.

– The impact of the installation on the environment Current interests could be harmed when a Blue Energy power plant is operational.


Mindmap of bottleneck for Blue

Energy.

The conflict of interests inevitably leads to confrontations, which generally does not accelerate the realization. Three categories can be distinguished: impact on (i) nature and (ii) functions and (iii) impact on the perception of the environment.

– The suitability of the location The suitability of the site is defined by the saline gradient and the composition of the streams (sediment and water quality).Water claims (fresh/salt) by other functions, applicable laws and regulations, and the volume of freshwater supplies are examples of this category.



– Design subsidy The energy issue is a societal issue with societal interests and therefore requires an economically-viable political and economic incentive in the form of, for example, subsidies.

– The adequacy of laws and regulations Various components have yet to evolve which still require years of research. The feasibility of Blue Energy can be achieved earlier when processes are followed in parallel. Changes in laws and regulations may take years before all the procedures


are completed. If this is already prepared, the critical timeframe will be consider-ably shortened. It is often the case that with innovations a certain drive, flow or power in society or between certain parties has to be made use of. When pilot realization or pilot testing is delayed by years because of obstacles in legislation, there is a chance that the innovative power between the parties will disappear. From the perspective of promotion by the government, it is worthwhile putting effort into the preparations. When players see that the government is serious, traders will certainly want to get involved.

– Publication of results Sharing knowledge and experience increases the knowledge of research institu-tions and universities. The larger the group is that focuses on this issue and the higher the level of knowledge in this group, the more likely that the necessary breakthroughs will take place in the shorter term.

– Resistance due to environmental impact or to competition between players Due to the environmental impact standpoint or to competition between various parties, resistance is to be expected.

– Lack of competition Lack of competition, both nationally and internationally, results in companies feeling little pressure to operationalize the developed knowledge and thereby staying too long in the funded research phase. Lack of competition may also be interpreted as a lack of developing parties.

– Lack of investors The creation of a Blue Energy power plant has a financial risk for investors, espe-cially if it is not clear what the price will be for electricity in the future.

Preliminary advice– Organise a workshop with experts to determine bottlenecks on the critical

path and prioritize on that basis the actions and further research (see below);

– Explore during the workshop with the stakeholders if it is possible to accel-erate the innovation process, by executing various studies and development projects in parallel;

– Even if it takes several years before a commercial Blue Energy installation can be realized, it is advisable to reserve space now in places where a Blue Energy installation could be built in the future;

– Besides the technical challenges (e.g. membrane development, purification), it is also important to look at the actual availability of fresh and saltwater, environmental impact and feasibility in the area.



Recommendations for further research Components of a Blue Energy power station: – Investigate opportunities for cost-effective water treatment – Research into high-performance membrane modules – Research into lower pollution sensitivity of the membranes – Research into environmentally-friendly cleaning products

Physical surroundings of the station: – Research into effects on the (natural) environment – Research into effects on water-related functions – Research into effects on stakeholders – Investigate the suitability of sites, including the availability of sufficient fresh

and saltwater

Institutional environment of the plant: – Research into methods of providing financial incentives by the government – Research into methods of providing non-financial incentives by the govern-

ment – Research into the possibility of better knowledge and experience sharing – Research into the prevention of public resistance

Pilot Installations – Crucial Proof of PracticePilot installations provide answers to questions and give insight into the feasibility of objectives, formulated in advance, which cannot be obtained by other methods. They generally concern a new product, a new tech-nique or a new application.

A pilot is conducted when the question or objective cannot be answered more reliably by studying or consulting existing knowledge, which is expected to be much less costly and faster than realising a pilot installation. It determines if a concept is feasible, whether it has the assumed potential or – more generally – to provide the proof of practice. Topics that can be evaluated are: technical aspects, economics, environmental aspects, safety issues, risks, durability, sustainability, and acceptance by governmental bodies and general public. A pilot therefore has the character of a general acceptance test of a working prototype under field conditions and is consequently more than an investigation of the processes and/or techniques. At the successful conclusion


of a pilot, the feasibility of large-scale application can be assessed with more confidence.

Necessary competencesDeltares specializes in assessing, testing and improving concepts and technolo-gies. The essence of all the conversion techniques to extract energy from water is understood. Examples are the conversion to energy from the head of water mass in elevated reservoirs, kinetic free-flow energy, wave energy, rotor-based devices, flotation-based devices, continuous uni- and bi-directional flow devices and saline gradient devices. Relevant issues that might be influenced by the technique are identified, e.g. the disturbance/erosion of the stream bed, the influence on the functioning of hydraulic utilities and their structural integrity, water discharge, and the influence on water quality, turbidity, ecology, fish and water life.

Especially with non-tangible issues such as safety and ecology, it is important to convert them to a set of parameters or indicators to monitor, and to know how to interpret the measurement data. Typical parameters are, amongst others: flow velocity and velocity profiles, water levels, mechanical forces (load cells) and the operational conditions of the device. Before measuring it is crucial to set up a measuring strategy with a plan containing what, when, where and why to measure and to calibrate the measuring devices, if necessary.

The data is interpreted to make the results transferable to different locations, to apply to calculations for large-scale application and for the water managers to establish permit criteria and to safeguard sustainability from all perspectives.

Deltares also assesses spatial integration aspects, which – in a water body – are mostly determined by morphology, ecology, hydrodynamic and safety issues and fish-friendliness. However, to fully advise on spatial integration, it is impor-tant to look further and zoom out to check on interference with the existing envi-ronment and infrastructure. This integral approach has proven to be a valuable asset within Deltares’ projects.

Case pilot installation in an estuaryIn estuaries hydraulic energy is predominantly harnessed from the flow velocity (=kinetic energy) already available in tidal currents. In river deltas, hydraulic energy is best harnessed at hydraulic structures where water level differences are a source for potential energy. In the coastal zones, hydraulic energy is present in waves and ocean currents. Contrary to wind, river discharges, waves, tidal currents and water level differences are very predictable, providing a reliable resource.


Considerations for ApplicationPilot Installations

The most efficient way to harness this energy is by using turbines that are specif-ically designed for local flow conditions. Nevertheless, if the kinetic energy of the flow is to be harnessed the theoretical maximum efficiency of any device is 59 % (Betz 1920). The reason is that upon extraction of kinetic energy, the device becomes an obstacle to the flow, and the flow partly diverges around the device. However, Betz’s theoretical maximum is never reached in practice because of deviations from the ideal flow. For extraction of kinetic energy, existing concepts such as horizontal axis and vertical axis turbines are used. By virtue of the specific hydrodynamic shape of the rotor blades, lift forces are produced that drive the generator. Turbines are capable of extracting energy in a very efficient way.

The energy is preferably harnessed in confined flows such as in hydraulic struc-tures or narrow passages in rivers and estuaries. Here the flow speeds up, signifi-cantly enhancing the possibility of extracting its kinetic energy, by virtue of a significant drop in water level across the utility or passage, since the energy generation is relative to the water velocity to the power 3. However when a turbine is situated in a confined area, it becomes noticeable that the turbine is acting as an obstacle to the flow. By installing turbines in sluices or barrier openings their discharge capacity may reduce to some extent, which is an aspect of concern to water managers.

In harnessing any significant quantity of kinetic energy from free flow, it will be necessary to install arrays of water turbines. If the turbines are closely spaced, the array itself will also act as an obstacle, diverging part of the flow around the array. The theoretical maximum efficiency of this array will consequently drop below the Betz maximum for a single turbine. A computational fluid model will be necessary to calculate the production of clusters of closely spaced turbines, of which the characteristics of a single turbine have been determined beforehand (in a pilot test for instance).

Within the framework of the national Water and Energy Innovation Program, Deltares facilitates monitoring and evaluation. In this evaluation it looks into: robustness of the turbine, reliable production of electrical energy, efficiency of the turbine, drag of the turbine, fish-friendliness and the influence on the river bed.

Considering the above, it is necessary for entrepreneurs to determine the effi-ciency of a turbine and turbine drag beforehand. The efficiency is needed for the calculation of production capacity and for the economics of the operation. The establishment of drag properties is necessary for the calculation of the economics of clusters and the influence on the discharge capacity of hydraulic utilities. Deltares can facilitate this, but the strength of Deltares focuses more on integra-tion capabilities and sustainability issues, as mentioned in the text above.


Lessons Learned from a Pilot Tidal Energy PlantBetween 2008-2010 Ecofys realized a unique tidal stream pilot project in the Southwest of The Netherlands. The project, dubbed C-Energy, was the result of collaboration between 10 organizations including contractors, NGOs, public authorities and research institutes such as Deltares. Below the project manager for the C-Energy project, Peter Scheijgrond, shares his ‘lessons learned’.

Project plan and visionThe project plan must start with a clear vision of why you are taking the next step in scaling up your technology and at what cost. There has to be a balance between the learning objectives and the investment required for the project. In our case, we wanted to focus on the performance of the core technology: the rotor and drive train. All other parts were secondary and had to be designed to maximize the learning potential from the core technology. That also meant we would not yet focus on the mounting and foundation of the system for a commercial applica-tion. Too often in the past, developers have taken too big steps in order to demon-strate their technology at say ¼ scale, going to extreme locations and eventually learning more about offshore installation than about the actual performance of their core technology.

Choice of consortium Open Innovation versus confidentialityOpen Innovation is the key word here. When you want to learn from each other with a limited budget and uncertain outcome, you need other organizations to bring in the best available expertise for the tasks at hand. However, make sure that critical components and the core technology stay fully within your own control. Involve others for the more generic solutions and make sure you are involved in all agreements and expectations between partners in the project. If there are any parts that need IP (intellectual property) protection and you have not yet done this, make sure you start the IP process before you start talking to partners, because in Open Innovation you need to feel free to talk about all the details of your technology from an early stage in the project. Confidentiality hinders progress in getting the consortium together.

Small or large-scale companies?During the consortium-forming process, we learnt that it was easier to make progress with smaller (SME) companies rather than the larger corporations.


Considerations for ApplicationLessons Learned

Although the latter may be more interesting from a strategic and investment point of view, they were also more difficult to approach and to agree with on the terms of participation. At this stage the main objective was to demonstrate the technology, so we needed to move with flexible organizations, short communica-tion lines and balanced interests.

Local or (inter)national?From an EU funding point of view and from a market potential point of view, it would appear that an international consortium is the way to go. However, it slows down team communication despite all modern ICT tools available and it adds to the project management cost. A strong local consortium has a powerful network in the region of the project, which will come in useful during the various stages of the project. A local consortium creates goodwill and a sense of involvement of the community, at local governmental level and with the regulators. The strong local content was also key to successfully securing funding from the European Fund for Region Development (EFRO).

Utility involvementIdeally, a large utility would have been part of the consortium, because it would have added prestige to the project. For various reasons, mostly related to conflicts of interest, we did not succeed in convincing a large utility to participate in the project. Towards the commissioning phase of the project, we received efficient support from a large Dutch utility in connecting the system to the grid and in making purchasing agreements and kWh registration. Going through the complete process of grid connection and power purchasing agreements was a good learning process.

Agreements & expectationsSince ocean energy is such a new and fascinating area of development, many companies and NGOs new to the business are willing to participate in the project without claiming ownership of IP or results, and even to invest partly in the project. They will participate because they will learn in the project; it is good for their project portfolio and it has tangible marketing and PR value. The bottom line is that the companies involved expect to enter a new market or be involved in spin-offs that will repay their investment. When drawing up the agreements, it is wise to clearly state each organization’s reasons for participation and to define who is entitled to what part of the IP, know-how and results. The involvement of a legal person used to drafting collaboration agreements is paramount in this process.

FinanceIt is very difficult to make an accurate budget in the early phases of the project, when the scope is not yet fully defined. Make a reasonable estimate and double it – you may come closer to the actual cost of the project.


Look at subsidies and how you can combine public funding (e.g. local innovation grants with EU funding, with special grants for local SMEs or provincial support, awards or sponsorship from utilities or other public bodies). Co-financing comes from the parties involved in the project. The party which claims most results from the project should make the largest investment. In our case we received 25% from an innovation grant and 40% from an EU programme. We invested 20% ourselves, and 10% came from industrial parties and 5% from public organizations.

Site selectionWe drew up a list of criteria for the ideal testing site for our next phase in real waters:

– Minimum operational currents of 1.5 m/s, maximum 2.5 m/s– Minimum 10m depth to avoid seabed turbulence effects– Within 2-3 hrs drive of the development team’s main office – Not easily accessible for 3rd parties / public

Pilot installation of the Wave

Rotor in the Western Scheldt.


Considerations for ApplicationLessons Learned

– Easily accessible with cranes to avoid offshore installation costs– Grid connection nearby– Possibility to have high speed internet connection for fast data transfer– No conflict of water use (e.g. nature reserve, shipping, or recreation etc)

We found most of these criteria at a location in Zeeland, which was already under consideration as a tidal test site by the local municipality. It was a pier owned by a refinery.

PermitsGetting permits is a slow process with many stakeholders, mainly authorities. For our trial we needed to submit five permit applications. In this project the local municipality offered to prepare and submit all permits, since they had an interest in the successful implementation of the project. This proved to be a very good solution, which saved a lot of time for the development team. The local munici-pality had the right network with the issuing bodies, which greatly helped to accelerate the process.

Design & engineeringThe most important lesson here was: start as soon as possible with a detailed loading analysis of the system. It will determine all other engineering tasks and is the main driver for the overall cost of the support construction.Keep a logbook for each design decision, to avoid reiteration in the development team.

RealizationSome important lessons in the realization phase were:

– Make sure you have an adequate car insurance for all activities– Prepare a detailed Health & Safety document, stating working protocols and

what to do in case of an emergency– Plan sufficient meetings with both the consortium and with other stake-

holders to inform everybody about the realization. Include relevant manage-ment, communication, and Health & Safety staff.

– Keep a detailed record of all changes in the scope of supply with contractors. This will help during the final negotiations

– Simulate (changes in) the installation process, preferably in a virtual 3D environment. Does everything still fit together when you change the order of installation?

– Test fit all critical fittings before final assembly on site– Calibrate all sensors before site installation and carry out a signal test imme-

diately after installation


– Record everything with a video camera for promotional purposes– In case of any defects, do not delay in asking the supplier to solve the problem.

Some warranties on installed product lapse after 6 months.

Monitoring and scaling upThe project has been running now for over 12 months, and is delivering energy to the grid. We are collecting a lot of performance data. The system performs according to our model predictions and is a valuable stepping stone for our next project. The design tools we have developed have been validated by the data from the prototype, which allows us to confidently design systems for even higher flow velocities. Also in terms of publicity the project has gained a lot of attention both nationally and internationally, giving us a more solid base for attracting future investments.

Finally, lobbying should not be forgotten – lobbying for better support mecha-nisms to fund these projects now and in the future. A demonstrably working project helps you to lobby convincingly for adequate financing.

6 Acknowledgements


Deltares:Marcel Bruggers (project leader)Arno TalmonCilia Swinkels Evelyn Aparicio Medrano Frances Kelly Hans Goossens Helena Hulsman Karen Meijer Lily Derksen Marcel Marchand Margriet Roukema

Mattijs SchaapNiels van Oostrom Rens van den BerghRob de Jong Rutger van de Brugge

Acknowledgements

This booklet has been written for the Singapore International Water Week 2010 to provide a glance at the energy-related subjects Deltares can contribute to. However it was not possible to cover several inter-esting subjects due to the limited time available. The content has been put together with utmost care and has been reviewed both internally and externally.

Many thanks are due to the contributors.


External:Benno Schepers – CE Delft Jos Benner – CE Delft Peter Scheijgrond – EcofysRutger de Graaf – Deltasync

TranslationClaire Taylor

For more information on renewable energy projects within Deltares, please go to: www.deltares.nl/renewable_energy, or send an e-mail to: [email protected]

Deltares © june, 2010

Deltares Renewable Energy From Water and Subsurface 2010

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