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Wave and Tidal Power: Energy from the Seas

Five Fun Facts

Energy analysts believe there is enough accessible energy in the ocean waves to provide up to 2 terawatts of electricity.
In the Pacific Northwest alone, wave energy could produce 40–70 kilowatts (kW) per meter of coastline.
On December 18, 2007, Pacific Gas and Electric Company announced its support for plans to build America's first commercial wave power plant off the coast of Northern California. The plant is scheduled to begin operating in 2012, generating up to 2 megawatts of electricity. Each megawatt can power about 750 homes.
In less than three years, U.S. energy regulators have received nearly five dozen applications for water-related energy projects from South Florida to Washington state. (LA Times; Mar. 10, 2007)
The modern scientific pursuit of wave energy was begun in the 1970s by Professor Stephen Salter of the University of Edinburgh. In small scale controlled tests, his invention, Salter's Edinburgh Duck, stopped 90 percent of wave motion and converted 90 percent of that to electricity. However, the machine has never gone to sea, primarily because of its complex hydraulic system.

Oceans cover 70 percent of our planet and hold 97 percent of the Earth's water. For centuries humans have relied on this abundant resource for food, transportation, commerce and recreation.

However, we have only recently started to capitalize on the energy potential of the seas.

With over two billion people living within 60 miles of a coast, marine energy could become an important part of a clean energy future.

The Promise

Waves are constant, predictable and have high energy density. Maximum ocean energy can reach 100,000 watts per square meter, compared to 1000 watts per square meter for solar energy.

Wave energy can be harnessed from a variety of devices, including those, such as buoys, that float on the ocean surface.

As waves move the device up and down or side to side, the motion converts the kinetic energy of the waves into electricity, often by pressurizing water or hydraulic fluid within the device to drive a turbine. The electricity is then carried back to shore on undersea cables.

The energy of tides can also be captured by a variety of methods.

At the world's largest tidal energy project under development, in the South Korean province of Wando, large turbines will be suspended underwater from bridge-like structures which rotate twice a day to capture the energy of incoming and outgoing tides. The projected output from the fast, powerful currents will equal the output from a medium-sized traditional power plant.

Wave and tidal energy projects are under development from the Pacific Northwest to Western Europe to the Far East. While Europe has a head start, legislators from California, Oregon and Washington are pushing to allocate millions of dollars towards wave energy research and development.

The Challenge

The ocean energy industry is in its infancy compared to other renewable energy technologies. While progress is being made, challenges remain.

Like many renewable energy sources, wave and tidal power potential varies greatly from region to region. While there are vast areas, such as the Pacific coast, where marine energy is abundant, it may prove difficult to harness in places where the tidal current is slow or waves are quiet.

All wave and tidal energy projects must be built to survive the harsh conditions and forces of the sea and to withstand corrosion and storm damage. Maintenance and retrieval of malfunctioning equipment pose major challenges.

Modernizing energy transmission lines and expanding capacity would benefit all energy sources. But the nature of marine energy—which is abundant only in some coastal areas and must be economically delivered via undersea cables to the coasts and then to population centers—makes transporting the power of the seas a unique challenge.

Marine energy also raises concerns about fisheries and ecosystem health. At commercial scale, wave or tidal energy facilities will cover large areas.

Some fishing communities worry that their fishing grounds could be disturbed. Toxic hydraulic fluids might leak. The devices' anchors and cables might damage critical ecosystems like salt marshes, estuaries, and near-shore reefs, or alter the natural processes that maintain ocean and coastal ecosystems, such as the movement of sand, silt, animals, and larvae.

Regulatory agencies, ocean technology developers and environmental groups are working together to address these concerns.

The Federal Energy Regulatory Commission (FERC) and other agencies are requiring environmental impact assessments before issuing test permits for marine energy technologies.

Companies are designing their equipment to minimize the dangers of pollution and ensure that marine life does not get caught, displaced or destroyed.

Environmental Defense Fund is bringing ocean energy industry leaders together with policymakers and other NGOs to develop performance standards for this nascent industry, and monitoring the development of marine energy in Oregon.

In Cuba, where EDF recently co-sponsored an international scientific conference on ocean energy, we are developing a scenario for systems in Caribbean countries to maximize social and economic benefits and minimize environmental impacts.

Wave and tidal energy technologies are new and unproven at commercial scale. Portugal is planning the world's first commercial wave farm, though installation has been delayed.

Other plans for wave farms include a 3 megawatt array in the Orkneys, off northern Scotland, and a 20 megawatt development off the north coast of Cornwall, England.

The Future

The potential of ocean energy is immense. The Snohomish County Public Utility District north of Seattle, WA, estimates that the tides in just seven areas under consideration for ocean energy development in Puget Sound could provide power for 70,000 homes.

In places around the world where waves are big, fast and continuous, ocean energy could be generated 80–90 percent of the time. The Electric Power Research Institute estimates that ocean energy could provide power for up to 10 percent of US households.

As the cost of the global warming pollution from the burning of fossil fuels is factored into the market, energy from the ocean could take its place next to solar, wind, biomass and geothermal energy as a viable and productive clean energy resource.