Duke University Trinity College of Arts and Sciences

Wave Power: Harnessing Energy from Our Seas

JJ Liao

Math 89s: Mathematics of the Universe

Professor Hubert Bray

4/25/2016

The major forms of energy we know of are broken down into five categories: wind

power, solar power, biomass, geothermal energy, and hydroelectric power (Danielson, 2013).

However, there’s a sixth, lesser-known, less talked-about form of renewable energy found in our

ocean’s waves. In fact, “wave energy is an uninterrupted and continuous source of energy that

has the potential to be among the most enduring suppliers of the world’s future needs” (Think

Global Green). Collecting energy from the world’s waves can generate as much as 40% of the

world’s energy needs (Maehlum, 2013). This paper will explore the merits of wave energy: how

it works, advantages and disadvantages, why it currently lags behinds it competitor forms of

renewable energy, and its future potential.

How It Works

There are currently many different design proposals for the best way of harnessing

energy from waves. Since 2011, wave companies have patented over 1000 methods for utilizing

wave energy (Maehlum, 2013). According to Green World Investor, a good wave energy device

must be able to face a wide range of wave sizes, have the ability to withstand severe storms, and

guard against problems like algae, barnacles, and corrosion (Shah, 2011). Three methods have

emerged as the most promising forms to be used with capturing wave power: The Oscillating

Water Column (OWC), the Surface-following Attenuator (also known as a Line Absorber), and

the Buoyance Unit (also known as a Point Absorber).

Figure 1 shows the Oscillating Water Column and how it works. This is a shoreline

device that uses an inclined concrete cylinder as a capture chamber. This capture chamber sits

partially in the water, with an opening beneath the surface of the water that allows water to flow

into and out of the chamber as a wave passes (theAneja, 2009). In the upper part of the chamber,

Figure 1: Oscillating Water Column (Source: House, 2013)

there is a hollow section filled with air. When water is pushed into the chamber by a wave

crashing into the shore, the air inside compresses and is forced through a set of turbines

(Maehlum, 2013). Typically, a Wells Turbine is used, which has the unique ability to rotate in

the same direction despite the direction of air flow, as air will be moving both ways in the

turbine (House, 2009). It is this rotation of the turbines that ultimately produces energy.

Figure 2, 3, and 4 shows the Surface-following Attenuator, or the Line Absorber. In this

energy-collection method, a series of long units are connected and float on water parallel to the

direction of the waves. They follow the motion of the waves and effectively “rides the waves”

(Shah, 2011). As a wave passes, the units that make up this device are at different heights. The

flexing where the segments connect are connected to hydraulic pumps or converters, as seen in

figure 4, where the energy is connected (Houghton, 2009). The relative motion of the two arms

as a wave passes generates energy (EMEC). An underwater cable then transports this electricity

Figure 2: Pelamis Wave Energy Converter Figure 3: Inside View of Converter

(Source: Houghton, 2009) (Source: Ocean Power Delivery Ltd, 2005)

Figure 4: Inside Look into a Line-Absorber Joint (Source: Construindoo ponto com, 2016)

to shore. The Pelamis design as shown below might be the most promising design to harness

waves thus far.

The third option is the Buoyancy Unit/Point Absorber. These float on waves or beneath

the water surface and are fixed to the sea floor. They follow the vertical movements of the

waves, which drive a pump (Maehlum, 2013). It is the motion of the buoyant top relative to the

base that generates electricity (EMEC). Currently, this power generation of a typical ocean wave

energy unit is about 1 MW, but its expected this will increase as the technology increases.

Figure 5: Point Absorber Figure 6: Diagram of Point Absorber (Source: Beachapedia, 2016) (Source: Marsh, 2014)

Advantages

The main motivation for developing wave power as an energy source for the future is that

it is green, renewable, and environmentally friendly (Maehlum, 2013). Because waves are

created through the contact of wind on the surface of oceans, “harnessing wave energy comes

without the emissions of harmful greenhouse gases” and will never run out. Unlike fossil fuels,

which lose their usefulness as soon as they are consumed, waves will “flow back from the shore,

but they always return” (Rinkesh). Improving upon renewable energy sources allows countries to

be less dependent on foreign oil production, helping to curb air pollution as well as reduces

damages to land that occurs in the extraction of fossil fuels.

Not only that, wave energy has an enormous energy potential and is also area efficient.

Wave energy can supply the world with as much as 40% of its energy needs, equivalent to 800

nuclear power plants, and occupy a smaller space while doing so. An area that is less than a half-

square mile in area can generate more than 30 MW of energy, able to power 20,000 homes

(Maehlum, 2013). With offshore power capabilities, negative environmental effects can be

reduced, since power farms often hamper tourism and disrupt local sceneries while also

generating ever more power. Offshore power is also incentivized as the power generation

potential is higher further into the ocean. Along shores, the typical energy density for a meter of

wave is around 30-40 kW, which goes up to 100 kW further from shore.

There are a wide range of places where wave power can be utilized. Many big cities and

harbors near oceans can harness wave energy, and since coastal cities are often well-populated,

many people can use wave energy plants (Maehlum, 2013). Many areas of the world also have

consistent-enough wind forces that allow for continuous waves. Waves are rarely interrupted and

almost constantly in motion, making them more reliable compared with solar and wind energies.

Utilizing wave power in areas of the world that don’t receive enough sunlight for solar power to

be feasible could bring greater access to renewable energy to these parts of the world. Wave-

power-rich areas include the western coasts of Scotland, northern Canada, southern Africa,

Australia, and the northwestern coast of the United States (Houghton, 2009).

Drawbacks

There are, however, several drawbacks to wave energy on the basis that is a renewable

energy form that is in the very early stages of development. The long-term effects to sea life and

marine ecosystems are mostly unknown. As large machines need to be put into water in order to

gather the energy, especially with buoys needing to be connected to the ocean floor, this

inevitably changes the habitat of near-shore and sea-floor creatures, like crabs and starfish. Noise

from the collectors could disturb sea life, and there remains the risk that toxic chemical used on

the wave energy platforms could spill and pollute the water (Conserve Energy Future). The

amount of energy transported by waves is also variable, especially dependent on seasons, and

wave energy typically has a larger potential during the winters (Maehlum, 2013). There is

research to show that performance drops significantly in rough weather, which creates an

additional challenge in creating devices that withstand rougher weather.

Power collection devices may also pose a problem for private and commercial vessels.

These energy plants create the greatest benefits when constructed near populated coastal cities,

but cargo ships, cruise ships, recreational vehicles, and beach goers are also likely to utilize these

key areas and may be disturbed by the presence of a wave collection device (Conserve Energy

Future). Ultimately, with so many unknowns, it’s also hard to speculate what the eventual costs

may be, but regardless, implementation required government funding (Maehlum, 2013).

Why It Lags Behind

With the threat of climate change ever increasing and making the need to transition away

from fossil fuels and towards renewable energy more and more necessary by the day, wind and

solar energy have distinguished themselves as the clear choices for renewables, despite

numerous studies showing that wave energy “could contribute massive amounts to the overall

energy picture” (Levitan, 2014). “Experts agree that [wave energy] remains decades behind the

other forms of renewables” and that large amounts of money and research are required for wave

energy to catch up.

One challenge to wave energy is simply the collection device. Although the OWC, line-

collector, and point-collector are all available and promising options, Robert Thresher, research

fellow at the National Renewable Energy Laboratory asserts that “we may not have even

invented the best device yet” (Levitan, 2014). George Hagerman, a research associate at Virginia

Tech’s Advanced Research Institute and contributor to the U.S. Department of Energy in its

assessment of the potential of wave energy, states that “no one seems to have settled on a design

that is robust, reliable, and efficient…. In wave energy, you’ve not only got the height of the

wave, but you’ve got the period of the wave, so it becomes a more complicated problem.”

The largest roadblock to to wave energy is also the cost, and without an agreed-upon

technology to tackle this dilemma, small companies are “picking off small amounts of

government funding where they can” (Levitan) and will need participation from larger

companies like GE or Siemens before wave power can really take off.

Future Potential

In 2007, a commercial offshore wave energy facility began operating off Portugal’s

Atlantic coast by the Scottish company Pelamis Wave Ltd (Ocean Power Delivery at the time).

They started with three, 140-meter long Pelamis P-750 wave energy conversion devices (the

Surface-following Attenutor design), each which generate up to 750 kW of electricity. Upon

installation, these devices brought back a generation capacity of 2.25 MW, which is enough to

power 1,500 homes, but an additional 25 converters can add 21 MW, enough to power 15,000

homes (The Renewable Energy Website, 2014).

Portugal is aiming to generate 60% of its electricity, 30% of all their power usage, with

renewable energy sources by 2020. Since wave energy is predictable and sustainable, this is a

key choice from them to invest in. The first phase of this program cost about 9 million euros to

execute, and Portugal currently pays about 0.25 euros per kWh unit for electricity generate by

renewable sources.

There is a lot of unexplored potential in wave power. According to the Renewable

Northwest, the United States receives 2,100 terawatt-hours of incident wave energy along its

coastlines each year (2007). Tapping into just one-fourth of this potential would be equivalent to

the amount of energy already produced by the entire U.S. hydropower system. Wave power is

typically best harnessed at latitudes between 30 and 60, and waves tend to be the strongest on

western coasts, making Oregon and Washington the states with the greatest wave energy

potential in the lower 48. Eventually, several thousand megawatts of electricity could be

harnessed in this form.

The Electric Power Research Institute (EPRI) estimates the total wave energy resource

along the outer continental shelf is 2,640 TWh/yr, with just 1 TWh/yr being enough to provide

93,850 average U.S. homes with enough power for one year (Boem). Because the ocean is not

fully utilizable because of alternative uses of the ocean (such as shipping, commercial fishing,

naval operations, and environmental concerns), the total recoverable resource in the United

States is 1,170 TWh/yr, still nearly a third of the amount of electricity used in the U.S. every year

(Boem).

Because of this high potential, several projects were undertaken to harness energy in the

U.S. pacific northwest, beginning in 2007. Permits were given to several companies looking at

developing wave energy, including AquaEnergy Group, Ltd for a wave power plant at Makah

Bay, Washington, and to Ocean Power Technologies to explore a utility-scale wave energy

facility off the coast of Reedsport, Oregon (Renewable Northwest, 2007). The vast majority of

the projects planned in the United States will use offshore floats, buoys, or pitching devices.

However, despite numerous permits handed out to research building wave energy

harnessing plants in 2007, the difficulties in developing wave energy persist. By 2014, still no

commercial-scale wave power operations exist in the world. Even so, wave energy research is

expanding. Portugal’s small-scale installation proved successful though, and in February 2014,

Lockheed Martin announced plans to “create the world’s biggest wave energy project, a 62.5-

megawatt installation slated for the coast of Australia that would produce enough power for

10,000 homes” (Levitan, 2014). Since, another Australia company, Carnegie Wave,

commissioned a commercial-scale installation near Perth that has seen success in its testing

(Carnegie, 2016).

Scotland, surrounded by rough Atlantic and North Sea waters, too has become a popular

area for wave-energy research and development. 10% of Europe’s total wave resource comes

from the seas surrounding the Islands of Scotland (Hi-Energy), and the Scottish government has

started tapping into this potential, approving a 40-megawatt wave energy installation in the

Shetlands Islands as well as setting targets for wave and tidal energy to constitute 100% of its

renewable sources by 2020.

There are also signs of big-company buy ins beginning, which is promising for the future

of wave energy development.

Conclusion

Overall, wave energy plays a key role in developing a more sustainable future for the

globe. The environmental benefits wave energy would bring make it an important strategy in

preventing further climate change and curbing emissions, and provides a good alternative energy

source as we slowly move from our dependence on fossil fuels. However, wave power is

definitely still decades behind its competitors, solar and wind power, and it will take many more

years and many more millions of dollars in order for it to catch up. Research now needs to go

towards developing the best possible and most efficient energy collection device before wave

energy will be able to be utilized at a commercial-scale to provide energy for the world.

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