Wave energy’s enormous potential, along with growing emphasis on development of clean, renewable energy technologies, has caused some companies to take a serious look at harnessing the ocean’s power.
By Teresa Hansen, Associate Editor
The energy in ocean waves holds enormous potential for pollution free electricity generation. Research reveals that wave energy is a suitable renewable energy resource for certain coastlines in Australia, the United States, the United Kingdom, the Pacific Islands, Japan, China, western Europe, South America and Africa. The International Energy Agency (IEA) estimates the worldwide potential for electricity production from wave energy technology to be 10 percent to 50 percent of the world’s yearly electricity demand of 15,000 TWh, depending on the expected load factor and wave regime.
A recent EPRI study concluded that by harnessing just 24 percent of the available wave energy resource base in U.S. waters (2,300 TWh/year) at 50 percent conversion efficiency, a quantity of electricity equal to the amount currently generated by conventional U.S. hydropower (270 TWh/year) could be generated. Another study recently compiled by the U.K. Department of Trade and Industry (Dti) and Carbon Trust predicts that by 2050, 200,000 MW of wave and tidal energy power will be installed. Wave energy’s enormous potential, along with growing emphasis on development of clean, renewable energy technologies, has caused some companies to take a serious look at harnessing the ocean’s power.
The energy bill recently signed into law by President Bush is expected to increase interest in wave energy in the United States even more. The bill not only extended the production tax credit (PTC) for renewable energy resources that are online by December 31, 2007, it also added resources that were not previously covered, including wave energy.
How Wave Technologies Works
Wave energy technologies extract energy from the movement of the ocean’s waves, which are created by wind interacting with the ocean surface. Wave energy technologies should not be confused with tidal energy technologies, which use the powerful water currents created by the rise and fall of the tides. Although not yet quantified, tidal technologies’ overall availability is much less than wave energy because it is only feasible in areas where the tidal currents are strong enough to run turbines efficiently. Tidal energy, however, does show significant promise in certain locations.
Wave energy is abundant and, while not as predictable as tidal energy, is much more predictable than wind or solar. Although the amount of energy that can be created using wave technologies varies from site-to-site and from day-to-day, depending on location and weather conditions, wave energy can be accurately predicted within a window of a few days. For example, waves resulting from storms that occur off the coast of Japan will take a few days to reach the northwest coast of the United States. Thanks to modern technology, their arrival time, along with their potential energy, can be fairly accurately predicted several days before they arrive. This predictability is helpful to grid operators.
OPT PowerBuoy in operation at Marine Corps Base Hawaii, Island of Oahu. Photo courtesy of Ocean Power Technologies.
According to an EPRI Electricity Innovation Institute (E2I) Global Project Team that studied offshore wave energy feasibility, the average power from a wave energy device in the winter can be six times more than the average power from the same device in the same location in the summer. Power output may vary by a factor of 100 with random storms. In addition, the energy potential in waves differs widely around the world. Waves are bigger and more powerful along the western edge of the earth’s continents because of the prevailing west-to-east winds.
Because conditions on and near the oceans’ surfaces can be harsh, wave devices, much like wind turbines, must be designed to operate at conditions that far exceed average operating conditions. Of course, this adds to the devices’ costs and makes some designs too expensive to be practical. Devices designed to operate under the ocean’s surface, called subsea devices, such as the Archimedes Wave Swing (AWS), can withstand inclement weather easier than surface devices and typically require less maintenance.
There are three major wave technology designs:
- Wave devices that ride on the surface of the sea. These devices convert the movement of waves to electricity through movement of different parts of the system. They operate in areas with high wave energy, but must be designed to withstand extreme conditions.
- Subsurface wave devices. These devices use pressure changes that are created as waves pass over the structure to generate electricity.
- Shoreline or seabed mounted wave devices. Although these devices are mounted on the seabed, they usually operate in relatively shallow water. They use the water’s movement as the waves pass to create an oscillating or reciprocating motion in a vane or semi-buoyant structure to create electricity.
E2I Study and Conclusions
In January 2004, the E2I Global Project Team began a study of offshore wave energy feasibility within the territorial waters of the United States. The team identified potential sites, assessed eight potential wave conversion devices, assessed the economic viability of the technology and the wave energy source, and identified and assessed the environmental and regulatory issues associated with implementing the technology.
The team determined that wave energy potential off the coast of the United States is significant and it has substantial promise. It reported that wave energy is a large and, to date, untapped energy resource that is too important to overlook. Roger Bedard, an EPRI wave energy expert, believes the technology is ready. “What has to happen now is a large market has to be created. Everyone understands the power of the ocean, it is the last big natural resource left.”
Completed LIMPET on the Isle of Islay (sea view). Photo courtesy of Wavegen.
The team evaluated five offshore sites during the study: San Francisco; Oahu, Hawaii; Cumberland, Maine; Boston; and Douglas, Ore. The team predicts that wave energy in the United States will become commercially competitive with the current 40,000 MW of installed land-based wind energy at a cumulative production of 15,000 MW in Hawaii and northern California, about 20,000 MW in Oregon and about 40,000 MW in Massachusetts. Maine was the only state in the study whose wave climate would prevent wave energy from economically competing with a good wind energy site.
Oregon State University (OSU) has identified significant opportunities and benefits from wave energy, prompting the formation of an engineering team at OSU to investigate ocean wave energy devices. Currently, OSU’s team is engaged in the United State’s only university research program funded from federal resources in ocean wave energy extraction. The university is investigating three direct-drive prototypes.
While EPRI and OSU are investigating the possibilities of wave energy in the United States, the private and public sectors in the United Kingdom are leaders in wave energy technology research. The British Isles’ long and varied coastlines make it an ideal location for marine development. In fall 2004, Britain pledged $100 million to wave energy development. Most leading wave energy developers have some involvement there.
Completed LIMPET on the Isle of Islay (land view). Photo courtesy of Wavegen.
Another testament to the United Kingdom’s commitment to wave energy came in October 2004 when the European Marine Energy Centre (EMEC), based in Orkney, Scotland, was opened. The £5 million facility is among the first of its type in the world, providing a one-stop facility for the industry to test potential wave energy generators.
In addition, because many elements unrelated to energy capture and conversion, such as siting, mooring and other logistical concerns, must be addressed when implementing marine energy devices, the United Kingdom’s long history with North Sea oil and gas exploration and production, along with its growing experience with offshore wind projects, give it an edge in marine renewables development.
Wave Technology Companies
Several companies (many based in the United Kingdom) are working on innovative wave technologies:
Ocean Power Delivery
Ocean Power Delivery (OPD), Edinburgh, Scotland, has produced a full-scale preproduction wave energy converter (WEC). The 750 kW Pelamis machine is a floating device designed for installation in 50 to 150 meters of water. It is 120 meters long by 3.5 meters wide and weighs 700 tons. Of the eight devices evaluated by E2I EPRI, the Pelamis was the only device identified as ready for deployment in a U.S. project.
Launched in February 2004, the Pelamis is now undergoing sea trials at the EMEC in Orkney. Electricity generated from the Pelamis trial was delivered to the grid in August 2004.
Wavegen’s breakwater turbine. Photo courtesy of Wavegen.
OPD recently announced its first equipment contract with a Portuguese consortium led by energy firm Enersis. The initial phase of the Portuguese scheme will be the installation of three Pelamis machines (2.25 MW total installed capacity) 5 km off the Northwest coast. The consortium issued OPD a letter of intent for 30 additional machines (20 MW total) upon satisfactory performance of the first stage.
According to Des McGinnes, OPD’s business development manager, once commercially viable, OPD will be able to install a 30 MW wave farm in a 1 km2 area. McGinnes said that the Pelamis is still not competitive with other proven renewable technologies. “We are still a ways off from obtaining lenders who will finance commercial projects,” McGinnes said. “We are still relying on venture capital, but we expect to enter the market at 10 to 15 pence (15 to 22 cents) per kWhr with a 40 MW installation.”
Wavegen Ltd., Inverness, Scotland, installed the U.K.’s first grid-connected wave power station, the Limpet power plant. Limpet (land installed marine powered energy transformer) is a shoreline energy converter sited on the island of Islay, off Scotland’s west coast. The current Limpet device – Limpet 500 – was installed in 2000 and produces power for the national grid.
The Limpet unit on Islay has an inclined oscillating water column (OWC) that couples with the surge-dominated wave field adjacent to the shore. The water depth at the entrance to the OWC is typically seven meters. It’s optimized for annual average wave intensities of between 15 kW and 25 kW per meter. The water column feeds a pair of counter-rotating turbines, each of which drives a 250 kW generator, giving it a nameplate rating of 500 kW.
In Mutriku, Spain, a small town not far from Bilbao, Wavegen is performing wave tank testing of “breakwater turbines” for EVE, the Basque Energy Board. This is the first of a number of similar projects Wavegen has planned to secure early demonstrations on its OWC technology.
Ocean Power Technologies
Ocean Power Technologies (OPT), a New Jersey-based company, is developing the PowerBuoy, a shallow water device where the movement of a buoy relative to its seabed mooring is used to generate electricity. The PowerBuoy is an offshore wave energy converter that is submerged more than one meter below the water’s surface. Inside, a piston-like structure moves as the PowerBuoy bobs with the rise and fall of the waves. This movement drives a generator on the ocean floor, producing electricity, which is sent to shore by an underwater cable.
The company has six 1.5 MW units operating off the coast of Hawaii at the Kaneohe Marine Base (Oahu). Under a U.S. Department of Defense Small Business Innovation Research grant, the Navy is partnering with OPT to assess the technology’s technical and economic feasibility. The Hawaiian Electric Co. is monitoring the project, serving as the Navy’s technical advisor.
In addition, OPT signed an agreement last year with Spanish electric utility Iberdrola to build a 1.25 MW station made up of several buoys off Spain’s northern coast. OPT also has a small buoy operating off the New Jersey coast, installed in 1997. A second pilot is underway off the New Jersey coast, partially funded by a $500,000 grant from the state’s Board of Public Utilities.
AWS Ocean Energy Ltd.
AWS Ocean Energy Ltd. is a Scottish company established in May 2004 to commercialize the Archimedes Wave Swing (AWS) technology, originally invented in Holland in 1994 by Fred Gardner.
The AWS wave energy converter consists of a large air-filled cylinder that is submerged beneath the waves. As a wave crest approaches, the water pressure on the top of the cylinder increases and the upper part or ‘floater’ compresses the air within the cylinder to balance the pressures. The reverse happens as the wave trough passes and the cylinder expands. The relative movement between the floater and the fixed lower part or ‘basement’ is converted directly to electricity by means of an innovative linear generator.
The AWS pilot plant partially submerged at sea. Photo courtesy of AWS Ocean Energy Ltd.
The complete system was tested at full-scale in a pilot plant off the coast of Portugal. On October 2, 2004, the AWS pilot plant exported power to the shore, making it the most powerful grid-connected offshore wave energy generator in the world, with a rated capacity of 2 MW. According to Simon Grey of AWS Ocean Energy, the system test verified the AWS theory and provided much information that can be applied to future AWS designs. The company hopes to have funding for the next prototype by the end of this year and have the prototype constructed and demonstrated by the third quarter of 2007, Simon said. “Commercial discussions are well advanced with launch customers and the company plans to have the first commercial wave farm in service by third quarter 2008.”
Armstrong Technology Ltd.
Armstrong Technology Ltd., North Shields, England, is a partner in the development of the 237-ton prototype Wave Dragon, a slack-moored device consisting of two reflectors that focus waves toward a ramp. The ramp is positioned above a reservoir and the water pours from the ramp through a number of variable speed axial turbines to produce power. The prototype has been operating at the Danish Wave Energy Test Station for some time and upon successful completion of the trials, a device five times larger than the test device will be developed for use in the North Sea.
The Wave Dragon wave energy converter uses proven principles from traditional hydropower plants in an offshore floating platform. The Wave Dragon overtopping device elevates ocean waves to a reservoir above sea level. Water is let out through a number of turbines, generating electricity in a three-step energy conversion process. The reservoir contains approximately 8,000 cubic meters of water that must be released through the turbines between two waves.
Energetech Australia Pty Ltd.
Energetech Australia Pty Ltd. is developing a shoreline energy device, the Energetech Wave Energy System. The device is suitable for deep-water coastal locations, such as harbor breakwaters and rocky headlands and cliffs. It uses about 40 meters of coastline.
The system employs a parabolic wall to focus wave energy on to an oscillating water column (OWC) chamber. The rising and falling motion of the waves causes an oscillatory water motion within the chamber, which in turn forces a high-speed airflow past a turbine. The turbine drives an induction generator to produce electricity.
The Energetech technology was installed and operated at Port Kembla, Australia, during a planned test period in June 2005, indicating the primary system works as designed. While the incident waves during the deployment period were low, the parabolic wall clearly amplified the waves. The air velocities past the turbine and the overall system efficiency indicators exceeded expectations. During further testing, the wave energy unit generated power that was sent to the local grid. Final installation in the near future will incorporate the technical improvements defined during this initial test phase.
It is important to recognize that the companies mentioned are not the only companies involved in wave energy technologies. Many companies are researching, developing and testing technologies to harness the power of ocean waves.
Mark Draper, OPT’s UK and Europe chief executive, spoke in Aberdeen, Scotland, at the Wave and Tidal Technology Symposium (WATTS) in May 25. He discussed some of the key challenges of deployment. Draper said that gaining site consent is one of the biggest challenges, and he emphasized the need for collaboration with environmental groups. Connection to the grid is another big issue. Other factors that must be considered include establishing safety systems, proximity to a local service port, establishment of a local fabrication facility, servicing facilities (once the project is installed) and 24-hour monitoring services. Also, the logistics and costs associated with cable installation, mooring installation, vessel availability and diver availability must be considered. And, last, a weather window when work can be carried out must be established.