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Support to Scale Up Renewable Energy:

Capacity Building in Assessing Renewable Technologies and Enhancement of Renewable Energy Network – Case Studies

A Workshop sponsored by

The Energy Sector Management Assistance Programme (ESMAP)

and managed jointly with

The World Bank (East and Pacific Region) for workshops in Indonesia, Vietnam and the Philippines, and

China’s Energy Research Institute (ERI) for the workshop in China

Presented by

Dr. Roland R. Clarke Clarke Energy Associates

Barbados www.clarkeenergyassociates.com

clarkeenergy@aol.com  

Source of presentation materials – www.retscreen.net   

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Power - Wind turbine - 20,700 kW / Jamaica

Purpose of this Case Study To demonstrate the general functionality of RETScreen to workshop participants. Case study assignment A developer has proposed the construction of a 20 MW wind farm in the southwestern part of Jamaica. The output of this wind farm - the first major wind project on the island - would be sold to the local utility. The developer has proposed the use of twenty-three 900 kW Vestas wind turbines. You have been hired by a funding agency to prepare a preliminary feasibility study of the project, as a quick first verification that the proposal is reasonable. Site information The project site is located on a ridge, 900 to 1,000 meters above sea level, near the community of Wigton, Manchester, about 60 km west of Kingston. Meteorological towers have been installed on the site for the past several years, and measurements at 50 m indicate average wind speeds of 8.3 m/s. The wind farm is to be constructed on land that is owned by a bauxite mining company and that will be leased to the developer for a 20-year period. A minor road accesses the site and the area is in close proximity to a small port. There are no transmission lines nearby and therefore a line will have to be constructed to an interconnection point approximately 11 km away. The costs of travel to and accommodations near to the site are modest. Financial information The project developer, a government-owned entity, has negotiated the sale of wind-generated electricity to the local utility at a price of US$0.056/kWh for the first five years of operation, and US$0.05051/kWh for the next 15 years. The twenty-year contract between the two parties is for energy only. The developer plans to sell the GHG emissions reductions for US$10/tonne of CO2 equivalent under the Clean Development Mechanism; the vast majority of the Jamaican electricity supply is generated from oil-combusting power plants. The developer has already arranged much of the financing for the project. A commercial loan for US$16 million has been negotiated, the developer can put up US$3.2 million in equity, and a grant of US$7 million has been provided by an international donor. Additional financial figures are provided by the developer: the debt interest rate is 14%, the debt term is 15 years, their discount rate is 15%, they expect an inflation rate of 10%, and they foresee the US dollar, currently worth 65 Jamaican dollars, appreciating by around 7.5% per year against the Jamaican dollar. Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis. Additional notes

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There is no annual land lease costs foreseen for the twenty-year duration of the project. Since the contract for energy sales is in US dollars, the fuel cost escalation rate is, in

Jamaican dollars, 7.5% per year, the expected rate at which the Jamaican dollar will depreciate against the US dollar. It is assumed that the GHG credit will be priced in US dollars at a fixed rate, and therefore 7.5% is used as the GHG credit escalation rate.

The sale of GHG reduction credits enhances the financial feasibility of the project but is associated with some uncertainty regarding the transaction fees to be paid for administration costs of projects operating under the Clean Development Mechanism.

High downtime losses are foreseen due to the frequent occurrence of hurricanes within the Caribbean. Indeed, it could be argued that the annual contingencies for O&M in the Cost Analysis page should be at the high end of the range suggested by RETScreen (i.e. 20%) due to tropical storms, although you should use 10%.

The average atmospheric pressure and annual average temperature were estimated by adjusting the data from the Kingston/Norman Manley meteorological station for the 1,000 m difference in altitude between the weather station and the site. A 1,000 m increase in altitude will normally be associated with a roughly 6 ºC decrease in temperature. At 1,000 m, the average air pressure will be around 90 kPa.

System description The wind farm consists of 23 NEG Micon NM 52/900 wind turbines, each with a rated power of 900 kW. The hub height is 49 m. Each turbine has its own low/medium voltage transformer situated inside the tower base. The turbines are sited on a ridge, approximately 100 m apart, in two rows separated by 300 to 350 m. Each turbine is connected to a project-site substation. Interconnection to the utility grid substation is via a 69 kV transmission line.

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Power - Photovoltaic - School - 0.4 kW - Off-grid / Argentina

Purpose of this Case Study To demonstrate the use of the RETScreen’s Load and Network spreadsheet to calculate facility loads prior to sizing a PV system for off-grid applications Case study assignment A local public utility has undertaken an electrification program for rural schools in the province of Neuquén in the remote mountainous region of Patagonia, Argentina. The schools are generally far away from the electrical grid and the two main power supply options being considered are diesel gensets and stand-alone photovoltaic (PV) systems. You are an engineer at the utility in the provincial capital and you have been asked to evaluate the financial viability of using PV to supply electricity to a school in one particular village. Site information The school is located in the foothills of the Andes (39°S, 71°W), on the Aucapan reservation of the Mapuche people, one of the region's indigenous populations. The nearest major town is the provincial capital Neuquén, some 430 km to the northeast. The school consists of classrooms and an apartment for a visiting teacher (who generally comes from an urban centre). The climate is harsh: hot and dry in the summer and cold, with high snowfalls, in the winter. Since the snow makes access particularly difficult, the school holidays take place in the winter (June through August) and the building is unoccupied at that time. When the school is open, its electric loads are estimated as follows (the lights and radio telephone use DC power while all other loads are AC): Based on your previous experience with similar projects, you decide to use imported polycrystalline PV modules from BP Solar rated at 50 Wp. Due to the occasional long periods of cloud cover in the mountains, you design the system for 6 days of autonomy.

Financial information

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For the project's 25-year analysis period, assume 5% fuel cost escalation rate, 2.5% inflation and 9% discount rate. The PV modules are imported to Neuquén city at a cost of US$ 8,000 per kWp plus 10.5% value added tax (IVA). This IVA is a reduced rate for renewable energy equipment. The general IVA rate is 21%. The pre-2002 exchange rate is 1 ARS = US$ 1. Local experience has shown that PV system batteries last about 3 years in these applications. The smallest commonly available diesel genset (2.5-3 kW) and appropriate shelter are estimated to cost about ARS 3,200 (including 21% IVA). Even such a small genset however would be oversized for the school's small load and would likely run at a 10-20% load factor. Genset maintenance costs are high due to harsh operating conditions and inexperienced users. Based on the utility's study of genset operation in schools, maintenance costs are estimated to average ARS 500 per year (including periodic overhauls and travel expenses). Diesel fuel costs around ARS 0.5/L in the cities, but is estimated to be 50% more expensive in remote villages. Prepare a RETScreen study, documenting any assumptions that you are required to make. Additional notes

The coincident electrical load for the school is not expected to exceed 0.25-0.5 kW. Diesel gensets however are commonly only available starting at 2.5 or 3 kW. A genset therefore would be expected to run at 10-20% capacity, resulting in poor fuel consumption of around 1.5 L/kWh.

The Argentinean peso (ARS) is taken to be on par with the US dollar for the purpose of this case study, since cost information is only available for the period prior to the currency devaluation of January 2002. Before devaluation, the Argentinean peso was pegged to the US dollar at a rate of 1:1.

For either scenario (PV or genset), the same number of technicians will likely be brought in from the provincial capital to install the power supply and the inside wiring, light fixtures, etc., all on the same trip. Transportation costs are thus assumed to be equal for both scenarios. The only difference in labour is due to the longer time needed to install the PV system components. This incremental cost is conservatively estimated at ARS 800. A transportation and labour charge of ARS 250 is added to each tri-annual battery replacement.

A 2.5 or 3 kW diesel genset, of acceptable quality, is estimated to cost about ARS 2,700 in Neuquén (including 21% IVA). It would require a secure, weather-protected shelter outside the building. The price of such a shelter (materials, labour and taxes) is estimated at ARS 500.

System description The PV system's main components include eight polycrystalline PV modules totaling 408 W, 7 lead-acid batteries (each 12 V and 110 Ah) and one 250 W modified square-wave inverter. The

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PV array and controllers were imported while all other components and the installation labour were provided by EPEN. Electrical loads in the school consist of lights, TV, VCR, radio-cassette player and a radio telephone.

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Power - Photovoltaic - 1,000 kW / Germany (Extra Assignment)

Purpose of this Case Study To demonstrate how RETScreen can be used for grid-tie wind energy applications in a high rise office building. Case study assignment Your engineering firm has been hired to advise the municipality of Herne in Germany on the financial feasibility of installing a large Building Integrated Photovoltaic (BIPV) system in a proposed new educational centre. The design for this facility has been selected via an international competition and incorporates many innovative architectural and environmental concepts. Site information The town of Herne is in the state of Nordrhein-Westfalen in western Germany, some 60 km northeast of Düsseldorf and about 170 km west of Kassel. The new training centre will pioneer a "micro-climatic envelope" design: an exterior shell of glass and semi-transparent PV modules will enclose some 12,000 m² of floor area. The enclosed volume will hold the buildings and structures that comprise the centre's lecture halls, meeting rooms, civic hall, library, gymnasium and other facilities. The objective of the glass envelope is to simulate a mild Mediterranean climate in northern Germany. It will shelter, but not completely seal off, the interior space from the outside. Natural airflow and breezes will be maintained via numerous motorized openings in the shell. A sophisticated shading system based on the strategic placement of PV cells in rooftop panels will help keep the interior from overheating. The glass envelope will thus moderate interior temperatures to reduce both the heating and cooling loads of the enclosed buildings while still allowing for the sensation of being in an outdoor environment. Most of the roof surface will be made up of 925 kWp semi-transparent PV modules. The rooftop modules will be tilted 5º from the horizontal and oriented to the south. Another 75 kWp of PV modules will be installed vertically on the west-facing façade of the structure. A large number of small inverters will feed the solar generated electricity to the loads within the structure and any excess to the grid. For the greenhouse gas analysis, you can assume that the conventional electricity generation fuel mix that the project will displace is approximately as follows: 31% coal, 7% natural gas, 28% #6 oil, 30% nuclear, and 4% wind and other renewables. Financial information Some initial cost estimates have been obtained for the project and show that on average, the selected polycrystalline PV modules will cost about €5,670 per kWp while the total cost of inverters will be approximately €600,000. Installation of all BIPV system components will cost

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about €860,000. Planning and engineering tasks, including the feasibility analysis and all project development costs, are expected to cost about €560,000. Overall annualized maintenance costs are estimated at about €15,300 per year. The use of PV modules as roofing material will replace the need for conventional glazing and shading systems that would have otherwise been required for such a design. These avoided costs amount to approximately €2.5 million. To promote PV installations, the German government guarantees a premium purchase price for PV-generated electricity. The training centre BIPV system will thus receive €0.457/kWh for at least 20 years. Also, since it is a prominent demonstration project, about 50% of the total initial cost of the BIPV system will be subsidized by the state and federal governments. The municipality will provide the balance of the capital and will own and operate the project. It will also receive all income from electricity sales. You may assume typical financial figures for the analysis: fuel cost escalation of 3%, inflation rate of 2% and a discount rate of 8%. The project life is estimated at 30 years. Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis. Additional notes

As a simplifying assumption, the PV system was modeled as if all PV modules were installed 5º from horizontal.

Use the RETScreen default value for the efficiency of poly-Si PV modules. The published projection for the energy output of the actual project (700,000

kWh/yr). Transportation costs for the PV modules are assumed to be roughly equal to the

transportation costs for conventional roof glazing that would have been incurred if the modules had not been used. These costs cancel each other and are therefore not included in the analysis.

All periodic costs are assumed to be annualized and expressed as part of the annual O&M costs. While inverter repair or replacement are often the major periodic cost in a PV system, in this case many small inverters are used and it is thus possible to budget for a certain annual failure rate (about 4 to 6 units per year).

The incentive, or grant, amount is calculated as 50% of total real initial costs (i.e. not including the €2.5 million in materials credits).

System description Nearly 10,000 m² of the roof's surface is made up of 925 kWp semi-transparent PV modules. Each module is tilted slightly (5º) south. Another 75 kWp of PV is installed vertically on the west-facing façade of the structure. Several different types of multi-crystalline PV cells are used,

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all of them manufactured by Solarex and ASE. Some 569 individual Sunny Boy 1500 inverters (1,500 W each) are installed in multiple series strings to deliver the solar electricity to the Mont-Cenis buildings and to the grid.

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Power - Hydro turbine - 220 kW / Canada

Purpose of this Case Study To demonstrate how RETScreen can be used for policy analysis using the Excel function, Goal Seek. Case study assignment You own a farm near Ottawa, Ontario, Canada. A creek flows through your property that appears to have the potential to generate electricity. The government of Ontario is offering $0.11 per kWh for energy generated by new renewable energy projects connected to the provincial electricity distribution grid. You believe that there is possibility of developing a qualifying mini-hydro project on your property and you wish to determine if it makes sense to seriously investigate the project. Site information The creek on your property drops approximately 13 m over a distance of about a kilometre. The creek is fed by a lake upstream that is controlled by a small dam with manually operated stop logs. Regulation of the lake provides some dampening of high and low flows. No hydrology data is available; however you have been told by local authorities that the drainage area upstream of the dam is 182 square kilometres. Some water will have to be left in the creek for environmental reasons (residual flow). You have been advised to assume a value approximately equal to the flow in the creek that is equaled or exceeded 95% of the time. Determining the residual flow will be a key aspect of the environmental assessment. A local small hydro turbine manufacturer offers standardised water-to-wire packages (turbine, generator and controls). One model is available that may be suitable for your site, a 220 kW unit assuming an available net head of 12 m (i.e., allowing about 1 m for hydraulic losses). Financial information The 220 kW package would cost $380,000, exclusive of civil works. The budget price includes delivery to your site, installation and commissioning. The price provided can be considered accurate to within plus or minus 15%. Discussions with the Ministry of Natural Resources have informed you about the steps required to get approval for development of a waterpower project on privately owned property. You have been advised that the process could take several years to complete and will involve some level of environmental assessment. A local consultant specializing in small waterpower projects has advised you that the cost of a feasibility study would be approximately $20,000 and the cost of project development, including the environmental assessment and approvals, could vary between $20,000 and $100,000 depending on the issues identified and field work required. If the project is approved, engineering costs (final design and construction supervision) would cost between 5% and 10% of the total project cost.

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To develop the project you will need to divert water from the creek into a canal (or pipeline). A penstock (likely steel) and a building to house generating equipment will also be required. The consultant also mentioned that the overall cost for a mini-hydro project of the size being considered could be up to $4,000 per kW to build and install. You have available equipment and manpower on the farm to undertake the civil works for the project and, therefore, you are confident that you will be able to build the project and realise considerably savings. You own all the land required for the project including the river bed and associated water rights and, as such, there will be no annual water rental charges. Annual costs will be limited to insurance and spare parts. For initial budgetary purposes you have been advised to estimate annual costs as 1% of the total initial costs. Your accountant has advised you that a benefit-cost ratio of 1.0 or higher, using a discount rate of at least 15% over a 25 year project life, is a good financial threshold on which to evaluate the project. The annual inflation rate is assumed to be 2%. Financing is available to you at 7% with repayment terms up to 15 years on 80% of the total project costs. The contract offered by the Ontario government includes Consumer Price Index escalation on 20% of the $0.11 paid per kWh. Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis. Additional notes

The analysis of the project involves determining the maximum allowable total project cost based on the owner's established financial thresholds agreed to with the consultant.

Hydrology for the site is determined using the specific run-off method. The site is near Ottawa, which lies within the green coloured specific run-off zone (see Canadian Specific Run-Off Map) but close to the yellow zone. A specific run-off value in the middle of the two ranges (0.016) can be used to get an approximate flow-duration curve.

Goal seek can be used to determine the approximate design flow for the proposed project assuming reasonable values for losses. Run a goal seek of 220 kW on the value of the cell "Power capacity" of the Energy Model worksheet by changing the value of the cell "Design flow".

Initial costs for the Feasibility study, Development, and Engineering can be estimated based on the available information. For engineering costs estimate, the total project cost can be assumed to be $4,000 per kW. Note the formula in this cell for cost per kW on the Cost Analysis worksheet.

Goal seek can then be used to determine the maximum allowable cost of all other components by setting a single "User-defined" cell in the Cost Analysis worksheet to represent all other project costs. In Goal seek the value of the cell "Benefit-Cost ratio" of the Financial Analysis worksheet is set to 1.0 by changing the user-defined unit cost

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value of the cell "Initial cost - Other" of the Cost Analysis worksheet. Note that the quantity value for the user-defined cost "Initial cost - Other" must be set to 1.

The financial viability of the project is extremely sensitive to variation in annual costs, which would indicate that more study into annual costs would be an important aspect of a feasibility study. Similarly, changes in residual flow have a significant effect on energy production and project viability.

System description The Misty Rapids Power mini-hydro project comprises the following components:

Timber crib dam to divert water to an open channel; Open channel 800 m long; Penstock intake with trash rack; 42 inch diameter steel penstock (used), 68 m long; Powerhouse with single 630 mm Kaplan turbine directly coupled to an induction

generator; Tailrace returning the water to Waba Creek; and Connection to the provincial grid involving 1,200 m of 12.48 kV 3-phase

transmission line.

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Power - Hydro turbine - 6,500 kW / China

(Extra Assignment)

Purpose of this Case Study To demonstrate how RETScreen may be used to adjust a natural flow duration curve for hydro, to model a storage dam. Case study assignment A Chinese electric utility has hired you to prepare a pre-feasibility study for implementing a small hydro project in the Hunan Province of China. Based on the utility's load projections, 4 MW of firm capacity will be required in the near future to supply base load power to the local electricity grid. In order to insure reliability, it is utility policy to install a second identical back-up turbine and generator. Site information The proposed project is located in the Ruchen County in the Hunan Province of China on the Jiujiedai River. The site location is easily accessible by road. Based on the results of a preliminary site investigation, a project developing 150-m gross head would be technically feasible. A suitable site exists for the construction of a concrete dam with a crest length of 70 m that would provide some seasonal water storage without extensive upstream flooding. This is considered a "run-of-river" project. The site is located downstream of an existing hydroelectric project with additional storage capacity. A preliminary assessment has indicated that the combined available storage will be approximately 15.5 million m³. The following flow-duration curve for the natural flow at the site (i.e., before effects of storage) is available from previous studies.

An environmental analysis has concluded that natural inflow to the river downstream of the proposed dam would be sufficient to allow diversion of all but 0.1 m³/s of the available flow during low-flow periods. The topography between the dam and proposed powerhouse location is steep and unsuitable for aboveground water conveyance structures. As such, a 3.4-km tunnel will be required, which can be hand-built using local, experienced labour. Based on a preliminary geological assessment it is anticipated that the rock will be ideal for tunnel construction and that only 20% of the tunnel will have to be lined. Approximately 45 km of temporary access road will be required for the construction of the tunnel to allow the removal of excavated material.

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The powerhouse can be located on a stretch of the river where the river level will rise a maximum of 2 m during high flows. A 50-m long tailrace canal will have to be excavated in rock that has a side slope of approximately 30 degrees. A 485-m penstock will also be required. In order to connect the project with the central-grid, approximately 6 km of 110 kV transmission line will have to be constructed through relatively flat, open terrain. For the greenhouse gas analysis, assume that natural gas is the fuel that will be displaced. Financial information The utility considering the project will invest in a detailed evaluation of the project if the pre-feasibility study indicates a positive net present value given a discount rate of 9%. The utility will consider financing 75% of the project costs at 9% over a period of 15 years. The current electricity tariff is yuan 0.40/kWh (US$0.048/kWh), which is expected to increase 5% annually. General inflation is anticipated to be 2% over the 25-year evaluation term. All amounts are to be expressed in US dollars. An exchange rate of 0.63 US$/CDN$ can be assumed. Costs in China relative to Canada can be assumed to be 80% for construction equipment, 50% for labour and 85% for equipment manufacture. Fuel costs in China can be assumed to be approximately equal to fuel costs in Canada. Annual operation & maintenance (O&M) costs would include property taxes (0.2% of total project cost) insurance (0.5% of total project cost), transmission line maintenance (5% of transmission line and substation cost), spare parts (0.25% of total project cost) and labour cost of US$80,000. An additional 10% (of the annual operation and maintenance budget) should be allowed for administration and 10% for contingencies. It is anticipated that approximately US$100,000 will be required every 10 years for major maintenance. Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from the analysis. Additional notes

A Francis turbine is well suited for the site (150 m head and 4 MW firm power). Assuming a standard efficiency curve for a Francis turbine, efficiency is at least 90% between approximately 60% to 100% of the turbine's design (maximum) flow.

To generate 4 MW assuming 150 m gross head, 90% turbine efficiency, 5% hydraulic losses, 95% generator efficiency, 1% transformer losses and 1% parasitic electricity losses, a flow of approximately 3.4 m³/s will be required. Adding residual flow requirements of 0.1 m³/s, the firm flow becomes 3.5 m³/s.

Based on 3.4 m³/s corresponding to 60% of design flow, a design flow of 5.7 m³/s can be selected.

In order to assess the storage needed to maintain a firm flow of 3.4 m³/s, manipulation of the flow-duration curve is required such that the total area under the modified curve is

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equal to the area under the curve representing the natural flow conditions. An example of a possible solution is presented below.

The rest of the RETScreen analysis can be completed using the available data and the formula costing method and applying a factor of 2 to the cost of the renewable energy equipment to account for the cost of the backup turbine and generator.

System description The Jiujiedai Hydro Project is located in Ruchen County, Hunan Province, China, on the Jiujiedai River. The project was completed within 3 years and is expected to achieve good economic benefits. The installed capacity of Jiujiedai station is 6.3 MW (with an auxiliary back-up 6.3 MW turbine and generator) and the annual energy output is anticipated at 51.37 million kWh. The simple dam and resulting storage reservoir resulted in minor flooding and resettlement. This project consists of a 3,377 m long low-pressure tunnel with a diameter of 3 m and a steel penstock of 486 m with an inner diameter of 2 m. The water diversion system consists of an intake gate of the tower type, located 30 m away from the dam. A surge tank with an inner diameter of 6 m is located 53 m away from the outlet of the tunnel. The dam is a single-curve masonry arch dam with a maximum height of 26 m and crest length of 69.5 m. The crest width is 4 m and the bottom width is 7.9 m. The dam is divided into a spilling section and a non-spilling section.

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There are two powerhouses; a main powerhouse and an auxiliary powerhouse. The electrical switchgear is located in the auxiliary powerhouse. The 5.7-km long 110 kV power line connects the project with the Wenmin substation. From this switch station, the electricity is sent to Chenzhou grid through Denman 110 kV transmission line.

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Combined heating & power - Reciprocating engine - 50 kW - Biogas / Canada

Purpose of this Case Study To demonstrate the use of the Tools spreadsheet to calculate the characteristics if a special user define fuel, in this case biogas from dairy cows. Case study assignment As a supplier of farm biogas cogeneration technology, you need to quickly produce system performance and cost estimates for a farm with a herd of 140 dairy cows. Your technology consists of an anaerobic digester, with cow manure as the feedstock, which produces biogas that is fed to a reciprocating engine-powered generator. Site information The farm is located in the Ottawa valley near Pembroke, Ontario, Canada. The nearest weather station is Ottawa Airport. The biogas will be combusted in a spark-ignition compression engine and used to produce heat and power. The heat will be used for regulating the digester temperature to 40°C, with excess heat used for farmhouse space heating and hot water. Assume a typical farmhouse with 300 m2 floor area, currently heated with propane and moderately well insulated. The average farm electrical load is 30 kW (all months). Electricity can be used to offset the farm's electrical load or traded with the utility according to a net metering agreement. The figure shows the energy flows involved. For this study, select a 50 kW engine to allow for system expansion and set the heat recovery efficiency of the engine to 50% to cover digester heating.

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Financial information Assume that electricity rate is $0.11/kWh and that propane fuel cost is $0.50/L. Initially assume no credits from GHG emission reductions or green power. Development costs are $10K for a feasibility study, $20K for engineering, $150K installed for the digester and associated works, and $1,500/kW for the reciprocating engine and generator. O&M costs about $5K/year (mainly for engine maintenance and refurbishments), and construction will take 6 months. Assume financial conditions of 0% inflation and fuel cost escalation; 20-year project life with 6% discount rate; 100% agricultural loan available for 15 years at 6% interest. The income tax rate is 36% with 15% depreciation in year 1, with 30% per year thereafter. Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis. Additional notes

For the heating load, typical values would be 70 W/m² with a base case heating system seasonal efficiency of 65% and an additional 10% for hot water.

The engine availability depends on the volume of biogas available - 155 m3 per day or 56,400 m3 per year. The Energy Model worksheet calculates how much biogas is consumed by the engine. For a 50 kW engine with a typical electrical energy efficiency of 30%, this will provide an availability of 2,853 hours for the year.

The "Biogas Tool" user-defined facility can be used with the following data to give an annual biogas production: 140 dairy cattle; 545 kg average weight.

Since electricity is net metered, the minimum engine-generator size has no effect on the overall economics except for the initial and maintenance costs. When choosing the size of the engine-generator, selecting an availability of around 50% allows for future increased biogas yields and for taking advantage of time-of-day electricity pricing. Short-term stopping of the engine for a few hours is possible without excessive build-up of methane pressure or cooling of the digester.

GHG emission reduction is achieved for two reasons. First from the combustion of naturally occurring methane to carbon dioxide. Methane is 21 times more active than carbon dioxide and is produced naturally from the decomposition of the manure. Second, from the displacement of other fuels used for heating and electricity production.

In Canada, the Tax Class 43.1 rule allows for 15% depreciation in year 1, with 30% thereafter. The user needs to toggle "Yes" on the line "Half year rule - year 1" of the Financial Analysis worksheet.

System description The current feedstock to the digester is manure from the farm's herd of 140 dairy cows. From this, the digester produces some 400 m3 of biogas per day with an average methane content of 55%.

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The types of engine most commonly considered for biogas cogeneration are spark ignition reciprocating engines (biogas only) and compression ignition reciprocating engines (using a mix of biogas and 10% diesel fuel for combustion stability). Micro-turbines can also be used. This facility uses a dual-fuel compression ignition engine, which drives an alternator that produces some 700 kWh of electricity per day. This can either service farm electrical loads or be exported to the grid where it is traded in accordance with a Net Metering agreement (which means that the farmer is not paid for any net export of power over the year). An incentives scheme for selling of electricity is also available, but would require the farmer to lock into a 20-year rate with only partial index-linking. The heat from the combustion process is used for heating of the digester and the farmhouse. The digester temperature is regulated to 40 °C, which is the optimum temperature for biogas production. During winter, the heat produced is just sufficient to meet these loads. Significant excess heat is available in summer, and ways to best utilize this heat, such as crop drying, are currently under investigation.

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Medium Scale Wind Energy – 390 kW Isolated Grid - Canada Purpose of this Case Study To test participants on their newly acquired skills in RETScreen. Case study assignment You are a developer investigating the possibility of building a wind farm to provide electricity to an off-grid, island community. The community currently runs one or more of three installed 925 kW diesel generators, with an average fuel efficiency of around 4 kWh/litre, to meet its electricity requirements. You would like to approach the utility that operates this system, and offer to reduce their fuel consumption, when the wind is blowing, by feeding onto the community grid the output of six reconditioned 65 kW stall-regulated turbines. You are aware that the diesel generators' operation at light load is not recommended because of reliability concerns, risk of failure, and premature generator ageing; and expect that the utility will be reluctant to operate their generators at a power level below 30% of their rated capacity. To accommodate this, your system will incorporate a dump load and automatic controller that will dissipate surplus wind farm output as heat whenever the output of the turbines is greater than the portion of the community load that is in excess of the minimum generator loading level. Site information The island, located about 10 km off the south coast of Newfoundland, Canada, has 700 inhabitants; it was formerly a remote fishing community. Winds are generally strong along this coast, and a weather station located around 23 km from the island indicates a long term average wind speed of 6.5 m/s at a 10 m measurement height. However, the Ramea Island seems to get similar average wind speed at 25 m (turbine's hub height). Winds tend to be significantly higher in winter than summer. The annual electricity demand for the island is around 4,300 MWh; the peak load is 1,200 kW and the minimum load is around 200 kW. The estimated annual load duration curve for the grid is shown in the figure. Average monthly loads during the winter are nearly double those of the summer. Financial information You will ask the utility to compensate you on the basis of the fuel savings they achieve. The current delivered price of diesel fuel is around $0.775 per litre, and you expect this to rise at a rate slightly higher than the inflation rate. The utility will retain the greenhouse gas emissions reductions achieved by the project over its 20-year lifetime. You anticipate financing around 32% of the project initial costs with debt. You expect to obtain a 15-year loan at a rate of 7.5%. Your company's income tax rate is 35%. You will depreciate the capital costs of the project according to a declining balance method at a rate of 30%. Due to the risks involved in this project, you will not embark on it unless it offers a high rate of return, i.e., exceeding 15%.

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Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis.

Additional notes

Average temperature and atmospheric pressure data from Burgeo, Newfoundland, is to be used.

The power curve for a Windmatic wind turbine is to be used. This turbine is not in the RETScreen database, but results will be essentially unchanged if another 65 kW stall regulated turbine power curve (such as the Entegrity Wind Systems AOC 15/50) is used in its stead. Twenty-five metre lattice towers are typical for these relatively small machines.

The wind energy absorption rate is included in Miscellaneous losses and is rather difficult to estimate based on the information provided. The job is simplified if it is initially assumed that the wind farm power output and the community load are completely uncorrelated. Since it is known that there is a positive correlation between load and wind speed, this assumption should cause underestimation of the absorption rate.

A simple approach to calculating the wind energy absorption rate is outlined below. It should be noted that while this method happens to yield reasonable results in this case, it is not rigorous and could be seriously in error in other situations.

- Set the wind energy absorption rate to 100% and calculate the average wind farm output based on the capacity factor provided by RETScreen (i.e., 31% capacity factor with 100% absorption x 390 kW rated capacity yields an average output of 121 kW). This means that the energy absorption portion of the miscellaneous losses are 0%, miscellaneous losses are 2-6%.

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- Find the "typical" power output of the combination of the wind farm and the generator operating at its minimum loading level (i.e., 121 kW plus 280 kW totals approximately 400 kW).

- Assume that at community loads above 400 kW all the turbine output is used by the load, and below 400 kW it is all dumped. The load duration curve indicates that the load is below 400 kW around 35% of the time, implying an absorption rate of around 65 %.

The wind energy absorption rate has been adjusted to 70% (i.e. miscellaneous losses of 30%) based on the observation that positive correlation in the wind farm output and the community load will cause the above two methods to underestimate the absorption rate. More accurate results could be obtained if seasonal average wind speeds and load duration curves were known.

Operation and maintenance costs have been estimated by multiplying the renewable energy collected (803 MWh) by a lumped maintenance cost of $0.025/kWh.

The electricity export rate is found by dividing the price of fuel, per litre, by the energy generated per litre of fuel, i.e. $0.19/kWh.

The cost of $1,200/kW for refurbished wind turbines was used. This is considerably lower than new turbines of the same rating, which are around $2,200/kW.

System description The wind farm consists of six 65 kW wind turbines, a dump load, and an advanced automated control system. The turbines are reconditioned Windmatic WM15S stall regulated machines mounted on lattice towers; the hub height is 25 m. Used turbines were employed in order to keep initial costs down. The WDICS controller is responsible for, among other functions, adjusting the power dissipated in a variable dump load. The load is adjustable in 1 kW increments between 0 kW and approximately 200 kW. The control system dumps wind farm output in order to keep the diesel generator operating at no lower than 30% of its rated capacity; below this loading, the generator operation is hazardous and unreliable, also the generator may wear prematurely. A sophisticated monitoring system monitors and logs the operation of the wind farm. The WDICS controller, supplied by Frontier Power Systems, is based on the technology developed by the Atlantic Wind Test Site, a Canadian government facility on Prince Edward Island.