Office of Energy Efficiency & Renewable Energy

How are Ocean Waves Converted to Electricity?

April 19, 2017

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Before they break on shore, ocean waves pack immense energy. The energy of a single wave, for instance, could power an electric car for hundreds of miles. Researchers are working to harvest and convert that energy into cost-effective and reliable electricity. With 50% of the U.S. population living within 50 miles of coastlines, America can lead a new energy industry and meet a huge energy demand with reliable and forecastable clean energy. But how are ocean waves converted to electricity, exactly? It’s a process that begins with the sun:

1. Wind blows across the ocean, creating waves

The sun heats up air at different places around the globe, which creates wind that blows over ocean surfaces. The wind creates surface waves, like those that crash on a beach. The waves range in sizes (from ripples to nearly 100 feet tall) and can travel thousands of miles before they reach land with almost no energy loss.

2. Waves approach land

Regular waves, like radio or light waves, have a constant frequency and amplitude (see picture below). Ocean waves, on the other hand, interact with each other, the environment, and the weather. By the time a wave approaches land, it’s unlike any other. This is where researchers aim to extract the energy.

light wave.jpg

3. Waves encounter machines

Ocean waves are converted to electricity with wave energy converter, or WEC, devices. Researchers expect typical full-scale WEC devices to be anchored miles offshore in deep water where wave energy is strongest. Because WECs extract energy from waves of all sizes that move in multiple directions, identifying the type of machine that can most-effectively do this work is a key goal of the U.S. Department of Energy.

The Wave Energy Prize, an 18-month competition that advanced the energy capture potential of WECs, highlighted a variety of promising devices. Grand-prize winner AquaHarmonics, for example, designed a point absorber, which demonstrated a five-fold increase in energy capture potential. Point absorbers are usually a two-part device. One part rides surface waves and the other is a static or slower moving part below the surface or that’s connected to the seabed. The surface portion moves faster than the submerged part, and the WEC converts that relative motion into electricity.

4. Machines convert waves into electricity

In short, ocean waves will move a WEC and that motion drives a generator that creates electricity. How machines take this motion of low-speed ocean waves with high energy content and convert them into the high-speed motion required for generators is not fully understood. Neither is how to do this economically and reliably, while also surviving harsh ocean conditions. Early-stage research supported by the Water Power Technologies Office is working to answer these questions.

5.  Electricity is applied to the grid or other needs

Wave energy could power swaths of coastal homes and businesses. In fact, developing just a third of the available wave energy near Pacific states with U.S.-made equipment could support 33,000 jobs and meet up to 30% of West Coast electricity demand. Wave energy is highly predictable and can be developed close to load centers to reduce transmission needs and ease integration onto the grid. Additionally, wave energy could power distributed applications in the near term, like desalination plants—which remove salt from salt water to benefit water-insecure communities and military bases.