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Wave and tidal power: huge potential market

时间:8/10/2007 9:35:35 AM  来源:IEC
 

Waves and tides capture coastal energy

By Jeanne Erdmann

From Portugal to Scotland to the United Kingdom to the United States, countries all over the world are using the pull of the tides and the rhythm of the waves to generate power. In fact, marine energy technology has shown so much recent growth that the IEC is enlisting energy experts worldwide to begin developing standards for wave and tidal energy systems. The IEC’s new Technical Committee, 114, Marine Energy – Wave and Tidal Energy Converters, will facilitate efforts by the International Energy Agency to develop best practices for marine energy. Standards will also help integrate wave and tidal energy converters into the International marketplace, especially as more and more governments mandate efforts for sustainable energy.

Sustainable energy source
World energy demand shows no signs of slowing. Humans now use huge amounts of energy every year. Developing economies continue to grow and thus require more energy. Meeting these energy demands by burning fossil fuels already accounts for most of the human-generated carbon dioxide in Earth’s atmosphere and the worst damage from greenhouse gases. Although clean, renewable energy sources, such as ocean energy technology, won’t clear carbon already in the atmosphere, technology of this sort is more environmentally friendly.

The need for sustainable energy has spurred recent growth in wave and tidal energy systems, explains Ken Street, Business Manager of offshore energy systems for Converteam Group SAS, a company headquartered in France. Converteam supplies electrical system solutions for wave and tidal generation devices of all types. Harnessing the forces of nature for energy is nothing new; windmills have been around for a long time. Using the predictability of waves and tides helps turn those forces into energy grid requirements. “First, wind alone cannot satisfy the targets set by international governments, and second, wind, because of its fickle nature, cannot be allowed to become more than 10 - 15% of the grids' supply. Waves are much more predictable than wind, they are more constant compared to wind. Tidal power is obviously even more predictable than wave and will provide a sizable contribution of the power generated by the sea but wave will dominate - there is just so much more of it,” comments Street.

Oh, buoy. Power!
In general, wave systems have many different devices with different shapes. The movement of the waves causes a design in the device to drive an electrical generator, which then transmits power to shore via a cable. Device designs fall into several categories, explains Street:

  1. Oscillating water columns, which are floating or shore based. These columns use wave movement like pistons to push air through a turbine to drive the generator.
  2. Point absorbers either float above or below the surface; these represent a popular type of device. Wave motion causes point absorbers to reciprocate, which in turn operates a linear generator that directly converts motion to energy or uses a similar method, such as hydraulics.
  3. Overtopping devices can be floating or shore based. For overtopping, waves crash over a ledge and are trapped and return to the sea via a turbine driving a generator.

The amount of ocean real estate taken up by wave devices relates to the amount of power needed. “Like any fuel source, such as coal or oil, which have a certain energy value, waves are no different. So to capture a meaningful amount of power you need to absorb that from an area of sea,” explains Street. Waves have a certain kW/metre, explains Street. For California’s north coast that power translates to 30 - 40kW/m. To extract say 500kW, you need a device around 40m in diameter. The area taken up by the device is also a factor of its anchoring system. How different designs are moored determines how much space they need. Also, spacing needs to account for boat access and to avoid creating an energy shadow for the device behind the craft.

“Yes wave devices are large - they need to be,” comments Street. Although wave power, compared with a fossil fuel, provides low levels of energy, this energy is “free”, self-sustaining and comes in unlimited quantities.

Ocean Power Technologies (OPT), a company based in the United Kingdom, designed the PowerBuoy®, a wave generation system. A 10MW power station needs about 30 acres of ocean area, which accounts for the spacing between the buoys, explains John Baylouny, OPT’s senior vice president of engineering. To determine how many PowerBouys are needed, OPT figures an average worldwide household usage at about 1kW. The 10MW of installed capacity will provide a yearly average of about 3 to 3.5MW of power, he says, so 10MW of ocean power can provide energy for 3 000 to 3 500 homes.

Banking on the tides
On most shorelines the tides go in and out twice a day, and tidal power stations can capture energy from this movement. Initially, the costs of tidal power plants run relatively high compared with other types of power plants but the benefits include low operating and maintenance costs, and, since no fuel is necessary, they do not generate emissions.

Many countries today want to increase spending on alternative energy sources. Korea is looking to the tides for those sources by constructing a tidal power plant at Lake Sihwa, one of several such efforts around the world. A dam built in 1994, secured agricultural water for the region around the lake, helped develop industrial and agricultural lands near the metropolitan area, and secured irrigation water. Unfortunately the dam blocked tidal currents. The rapid increase of population and industrial waste loads from factories in the neighborhood caused the water quality of Lake Sihwa to deteriorate. This pollution though, brought an opportunity. Because of rapid socio-environmental changes and the lowering of water quality in Lake Sihwa, government officials opened the lake to seawater. The Sihwa Tidal Power Station, which is currently under construction, will capture the power of nearby tides by taking advantage of the differing tide water levels between the sea and the artificial lake.

Capturing a world market
The market for wave and tidal power is expected to continue growing. For now, Street explains that the wind market is already mature with many players, growing rapidly with demand outstripping supply. “Wave and tidal power have a long way to go before they achieve a similar position. There are very few devices actually deployed at full-scale and even fewer who can claim to have a fully proven system both technically and from a survival aspect.” Securing funding to bring prototypes to market proves difficult and wind and tidal power are still seen as risky for venture capital. “Those who did manage to raise capital on the share market have had, understandably, an unexciting/disappointing performance, and where government funding is available it is insufficient and too thinly spread to be effective. The enormous pressure for sustainable power will eventually allow more developers to get devices in the water and over the next 5 - 7 years we will see more and more,” says Street.

"Still, wave and energy technologies do have the potential for a large market size — $150 billion a year", says Baylouny.

 
(August 2007)

 

 


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