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Wavepower Energy Information

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All About Wavepower Energy

 

Waves are a free and sustainable energy resource created as wind blows over the ocean surface. The greater the distances involved, the higher and longer the waves will be. Energy is stored in this way until it reaches the shallows and beaches of our coasts where it is released, sometimes with destructive effects.

Key Facts

  • Oceans cover three quarters of the earth's surface and represent a vast natural energy resource in the form of waves.
  • The World Energy Council estimates that 2TW of energy could be harvested from the world's oceans, the equivalent of twice the world's electricity production.
  • In the UK alone it has been estimated that the recoverable wave energy resource exceeds total UK electricity demand
  • As a general rule coastlines with an ocean fetch of greater than 400km are suitable, but even greater resources are available between latitudes 300 and 600 in the Northern and Southern hemispheres.
  • If less than 0.1% of the renewable energy within the oceans could be converted into electricity it would satisfy the present world demand for energy more than five times over.

The technology involves two basic elements; a collector to capture the wave energy and a turbo generator to transform the wave power into electricity.

 

A tremendous amount of energy can be tapped from our oceans. Wave and tidal power are increasingly joining the mix of promising offshore renewable energy resources.

 

Wave energy refers to the harnessing of the Herculean power of water waves. Waves hold a gargantuan amount of untapped energy, some of which we can use to power at least a portion of the world's everyday electricity. Though estimates vary about how much power waves could contribute to the world's energy consumption, some say it could realistically contribute about 10 percent [source: OEC].

Theoretically, however, this is not even close to the amount of energy ocean waves could provide. Indeed, only about 0.2 percent of the energy in ocean waves could power the entire planet [source: Drollette]. Given this knowledge, one might wonder why people aren't paying more attention to and investing in the development of wave energy.

The tough part is coming up with ways to turn this power into usable energy. In this article, we'll investigate the different methods engineers have developed for gathering wave energy. But first, it's important to know just how waves get this energy in the first place.

 

Wave Energy Fundamentals: How Waves Form

Wave energy, in one sense, is just another form of solar energy. This might sound odd, but just consider that waves start from wind, which forms as a result of the sun's heating of the ­Earth.

The sun doesn't ever heat the Earth evenly. Depending on the Earth's natural formations as well as its orientation to the sun, some spots get heated more than others. As some air gets heated, it becomes less dense, and thus lighter, and naturally floats upward. This leaves an open space for denser, colder air to rush in and take its place. This air rush is the refreshing cool breeze you feel on a sunny day.

Wind is also responsible for our very powerful waves. As wind rushes up along the water, the friction causes ripples. Wind continues to push against these ripples in a snowball effect that eventually creates a large wave. Essentially, this action is a transfer of energy from the sun to the wind to the waves.

A few factors determine how strong an individual wave will be. These include:

  • Speed of wind: The faster the wind is traveling, the bigger a wave will be.
  • Time of wind: The wave will get larger the longer the length of time the wind is hitting it.
  • Distance of wind: The farther the wind travels against the wave (known as fetch), the bigger it will be.

Interestingly, waves move energy, not water, far distances. Water works as the medium through which kinetic energy, or energy in motion, passes. The water is moving, of course, but only in a circular motion. In other words, water particles work as rollers in a conveyor belt do -- they rotate in order to move the belt on top forward, but they themselves don't go forward in the process. This is why buoys will rise and fall in a vertical motion with the water.

But if we already have wind turbines to harness wind energy, why use ocean waves? Though they may seem like an unnecessary middleman, waves have a few advantages over wind when it comes to gleaning usable energy. For one thing, ocean waves are dense with energy. In other words, whereas wind might take up a lot of space to contain some energy, waves can collect a great amount of energy and pack it into a small space.

Another advantage is that ocean waves are reliable -- we can more easily predict which way the waves will be moving than which way the wind will be blowing. Also, wind can start a wave and then on its own, the wave can travel a great distance. Large waves that travel far from their origin are called swell waves. This means that the entire surface of an ocean can collect energy, and without us doing any work, the waves come to us, even from very far away.

 

 

Methods for Harnessing Wave Energy

The idea of harnessing energy from the ocean's waves was tossed around for a couple hundred years. But it wasn't until the oil crisis of the 1970s that it started to gain some significant attention [source: CRES]. The concept resurfaces whenever oil prices rise.

So far, engineers have developed and implemented several methods for collecting wave energy. These methods can be implemented on the shoreline, near the shore or offshore. Most devices that are near or offshore are anchored to the sea floor. Here's a list of the major kinds of wave energy converters (WECs), or devices that transfer wave energy to usable electricity.

Terminator: Wave energy devices oriented perpendicular to the direction of the wave, are known as terminators. These terminators include a stationary component and a component that moves in response to the wave. The "stationary" part could be fixed to the sea floor or shore. It must remain still, in contrast to the movable part. The moving part works kind of like a piston in car -- moving up and down. This motion pressurizes air or oil to drive a turbine.

An oscillating water column (OWC), shown in the image above, is a terminator. OWCs have two openings -- one on the bottom that allows water to enter the column and one narrow passage above to let air in and out. As waves come and fill the column with water, this pressurizes the air inside, which forces the air through the opening above. The air encounters and drives a turbine. Then, as waves pull away, water rushes out, which sucks more air back down through the top, driving the turbine again.

 

 

Another terminator, an overtopping device, includes a wall that collects the water from rising waves in a reservoir. The water can escape through an opening, but while passing through, drives a turbine. The most famous kind of terminator, however, is truly the Schwarzenegger of WECs. Salter's Duck includes a bobbing, cam-shaped (tear-shaped) head that drives a turbine. Though not fully realized, theoretically, this device would be the most efficient WEC.

 

 

Point absorber: These devices aren't oriented a particular way toward the waves, but rather can "absorb" the energy from waves that come from every which way. One such device is called the Aquabuoy, developed by Finavera. In a vertical tube below the water, waves rush in and drive a piston, a buoyant disk connected to hose pumps, up and down to pressurize seawater inside. The pressurized water then drives a built-in turbine connected to an electrical generator . Many Aquabuoys can send electricity to a central point. From that point, electricity is sent down to the seafloor and then to shore via a cable.

 

Several WECs grouped together, such as Pelamis or Aquabuoy structures strung together, make up a wave farm.

 

 

Obstacles to Wave Energy

Whenever oil prices rise, the world thirsts for renewable energy alternatives. Despite this welcoming attitude, several problems prevent wave energy from really quenching the world's appetite.

As we mentioned earlier, some estimates say today's wave energy technology could possibly fuel 10 percent of the planet's energy consumption. In theory, however, if wave energy technology advances considerably, it might someday do a lot more. As we saw on the previous page, engineers are trying several different methods, and still no single method achieves high-efficiency energy conversion. One of the design dilemmas with wave energy is that wave frequency is too low to run turbines very effectively .

Not only that, but these devices must be cheap enough to make it worth our while to develop and use them. If wave energy is never as cheap as fossil fuels like coal and oil (even as costs rise) or nuclear energy, it will have a hard time becoming a significant contender in the energy battle. Indeed, in Europe during the oil crisis of the 1970s, proponents for wave energy competed with nuclear energy proponents for grants, and lost, which is why some wave energy research programs ended. The investment in nuclear energy seemed more promising than wave energy.

However, even this 10 percent is a large amount if we consider that only certain areas of the world are naturally fit for capturing wave energy. Because we need consistent and energetic waves to power the WECs, the best zones for setting up wave power are those that lie between 30- and 60-degree latitudes [source: EUOEA]. For the U.S. , the shores of Oregon prove to be the most practical places. Scotland , which is hit with strong waves, is a hotbed for testing and implementing wave energy methods. And, Portugal has been working on the world's first wave farm, utilizing Pelamis devices.

Even though waves are in some ways more reliable than wind, we can't always depend on lots of wave action, meaning we need effective energy storing methods. On the other hand, sometimes waves and weather are far too harsh for wave energy devices to withstand. So, not only do we need more efficient WECs, but they need to be incredibly durable, which can drive up the price.

 

Wave & Tidal Energy Technology

 

Wave, tidal and ocean energy technologies are just beginning to reach viability as potential commercial power sources. While just a few small projects currently exist, the technology is advancing rapidly and has huge potential for generating power.

 

Potential

Worldwide potential for wave and tidal power is enormous, however, local geography greatly influences the electricity generation potential of each technology. Wave energy resources are best between 30º and 60º latitude in both hemispheres, and the potential tends to be the greatest on western coasts.

 

 

Wave Energy Technologies

There are three main types of wave energy technologies. One type uses floats, buoys, or pitching devices to generate electricity using the rise and fall of ocean swells to drive hydraulic pumps. A second type uses oscillating water column (OWC)devices to generate electricity at the shore using the rise and fall of water within a cylindrical shaft. The rising water drives air out of the top of the shaft, powering an air-driven turbine. Third, a tapered channel, or overtoppingdevice can be located either on or offshore. They concentrate waves and drive them into an elevated reservoir, where power is then generated using hydropower turbines as the water is released. The vast majority of recently proposed wave energy projects would use offshore floats, buoys or pitching devices.

 

The world’s first commercial offshore wave energy facility will begin operating by the end of 2007 off the Atlantic coast of Portugal . The first phase of the project, which Scottish company, Ocean Power Delivery (OPD) developed, features three ‘Pelamis’ wave energy conversion devices and generates a combined 2.25 MW of electricity. OPD plans to expand the facility to produce 22.5 MW in 2007.5

 

 

Tidal Power Technologies

Until recently, the common model for tidal power facilities involved erecting a tidal dam, or barrage, with a sluice across a narrow bay or estuary. As the tide flows in or out, creating uneven water levels on either side of the barrage, the sluice is opened and water flows through low-head hydro turbines to generate electricity. For a tidal barrage to be feasible, the difference between high and low tides must be at least 16 feet. La Rance Station in France , the world’s first and still largest tidal barrage, has a rated capacity of 260 MW and has operated since 1966. However, tidal barrages, have several environmental drawbacks, including changes to marine and shoreline ecosystems, most notably fish populations.

 

Wave energy research was pursued intensively during the 1970’s and early 80’s, especially in Britain . Interest in it was then revived in the mid 90’s as one of the options to reduce fossil fuel dependency and address global warming. During these last 30 years a large number of devices such as the nodding duck, the Osprey, tethered buoys, bottom standing oscillating water columns, over-spilling systems, floating bags, articulated rafts, submerged pressure chambers, and many others have been tried with varying degrees of success. However, wave technology is now slowly maturing, and the day of commercial viability is approaching.

There are two basic types of wave technology: fixed onshore and floating offshore. Up to very recently most of the research and development has been focused on fixed devices onshore or in shallow waters. Now, however, there is increasing interest in the much greater offshore resource with a variety of floating devices being developed.

The greatest wave energy resource is in the mid-latitudes, between 40 and 60 degrees N & S. This is where winds blow most consistently, while in more tropical areas there are often long periods of calm weather in between severe storms.

Global Highlights

  • The World Energy Council has estimated the global wave energy potential to be 2,000 GW. (New Scientist, Sept.20, 2003)
  • The economically recoverable wave energy resource for the UK has been estimated by the Ocean Power Delivery Company to be 87 TWhrs/year.
  • A 500 kW fixed device called the Limpet has been operating on the island of Islay off the coast of Scotland since November 2000. It was built and installed by Wavegen, and was the first commercial-scale grid-connected wave energy device installed anywhere. Its output is being sold to the local utility for 5.95 pence/kWhr. (Environmental Science & Technology, No.3, 2001)
  • In February 2004 ocean testing began of the 750 kW Pelamis, also called the Sea Snake, which is the first deep-water grid-connected wave power generator in the world. It is 120m long, 3.5m wide and weighs 750 tonnes. It is built and operated by the Ocean Power Delivery Company of the UK


 

 

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