Wave power: how it works

SmartPlanet is launching a new, occasional series aimed at dissecting some of the complex topics we cover on a daily basis. ”How It Works” will provide primers on the important issues — in energy, power, technology, health and more – that affect our ever-changing world.

First up: wave power.

What is wave power?

Wave power is renewable energy derived from ocean waves. It is the kinetic energy of wind interacting with water and creating waves, said Peter Asmus, a senior analyst with Pike Research, a clean tech market research and consulting firm.

Wave energy is generated by the wind, said Paul Jacobson, ocean energy leader of the Electric Power Research Institute, a nonprofit that studies the electricity sector. That distinguishes wave power from tidal energy, which is derived from underwater equipment that captures the ongoing movement of ocean currents powered by gravity and the Earth’s rotation.

Where in the world can wave power be used?

The best wave energy environments are along western coastlines because the largest, most consistent winds come from the west, Jacobson said. In the United States, wave power hotspots are California, Oregon, Washington and Alaska, Asmus said. (There are limited wave power opportunities in the East, when the shape of the land can sometimes yield energy resources.) Globally, he said, wave energy leaders include the United Kingdom, Portugal, Australia and New Zealand. Northern Canada and southern Africa are other wave power hotspots, according to the U.S. Department of Energy.

Construction on what would be first commercial wave farm in the United States began recently off the Oregon coast, Asmus said. The project was developed by the New Jersey-based Ocean Power Technologies. Portugal is home to the world’s first commercial wave farm, Aguçadoura Wave Farm, but the project has reportedly been suspended due to financial and technical difficulties.

How does wave power work?

Most of the energy comes from the rising and falling water level and requires exposure to the waves, Jacobson said. There might never be a dominant technology for harnessing this power, he said, because of the differences in potential wave energy sites throughout the world.

Currently, there are three basic technological paradigms for wave energy and various companies are pursuing their own designs in these areas, said Ted Brekken, assistant professor in energy systems at Oregon State University. They are:

• Oscillating body: The device, either submerged or on the surface, is moved up and down or back and forth by waves. Its motion is used to drive an electric generator. Pelamis Wave Power is developing a snake-like oscillating body that would rest on top of the water, while other devices look more like buoys.
• Oscillating water column: Air enters a chamber through a hole and is compressed and decompressed by wave movement. A high-powered turbine catches the air as it’s decompressed.
• “Over topping device”: A large structure, shore-based or in the ocean, that channels waves into a basin. When the basin’s water level becomes higher than the ocean’s, the basin is drained. The technology is similar to a hydropower system, in which draining water runs a turbine.

Because they’ll sit in the ocean amid major storms, wave power technologies must be developed with strength in mind, Asmus said. “The key to wave power is making designs that are robust enough to withstand weather conditions,” he said.

How effective is wave power?

Currently, wind is our biggest renewable energy source, Asmus said. But, he added, all ocean energy resources, including wave power, would combine to create energy 800 times more powerful than wind. According to the Department of Energy, experts believe there could be enough ocean power to provide up to two terawatts of electricity.

While solar energy might yield 150 watts per square meter on a sunny midday and wind power could produce 300 watts during a similar time period, wave energy has the potential to create 30,000 watts per square meter, Brekken said. “It’s very power dense,” he said. “That’s one of the reasons why people are attracted to it.”

Which companies are the major players in the wave power industry?

Experts listed these companies as among the major players:

• Pelamis Wave Power, a Scotland-based company whose name references the Greek sea snake because of its cylindrical converter technology
• Ocean Power Technologies, a New Jersey company that is installing wave farms off Oregon’s coast and off Spain’s northern coast
• Columbia Power Technologies, through a partnership with Oregon State University, this company develops wave energy harvesting devices
• Pacific Gas and Electric Company, the California utilities company that is advancing the WaveConnect program, a pilot study to test various wave energy converter devices
• AWS Ocean Energy, a Scotland-based company that develops ocean energy technology
• Aquamarine Power, also in Scotland, this company developed a hydroelectric wave energy converter called Oyster (and recently unveiled Oyster 2)
• Oceanlinx, the Australian firm behind the oscillating water column

What are the benefits of wave power?

Because wave devices tend to be on the surface and don’t have propellers, as tidal power technologies do, some believe they will create less environmental damage than other renewable energy technologies, Asmus said. Jacobson added: “There are advantages compared to wind in that the devices are smaller and don’t have the visual profile that wind turbines have.”

Also unlike wind and solar, wave energy “occurs around the clock,” Jacobson said. “It’s much more predictable because the waves are propagating across the oceans from long distances,” he said. Wave energy reaching a wave farm can be predicted about 48 hours in advance and with increasing accuracy, he said.

From a business perspective, wave power provides the greatest opportunity of the ocean energies because so much of it is available, Asmus said. Once a wave farm is built, operation and maintenance costs run low because their fuel, water, is free, according to the energy department.

What are the downsides and challenges of wave power?

Wave power, like other early energy sources, is expensive, Brekken said. While coal might be priced at five to 10 cents per kilowatt hour of energy, he said, wave energy costs reach 20 to 30 cents. “The question is, “How quickly does that come down?’” Brekken said. In the United States, Asmus said, wave power companies need more research and development funds and greater subsidies. Wave energy companies need more time to develop technologies that can withstand the harsh ocean environment, Jacobson said.

Another thorny issue is property. Unlike building a power plant on land a company owns, the ocean is common space, Asmus said. And although some believe the environmental issues related to wave power are less so than with other technologies, there are still environmental unknowns, Jacobson said, such as how ecological systems will be affected by wave technologies and how shipping and fishing activities will be affected by device placement.

What’s next in wave power?

Watch for companies to install several devices in the water over the next five years to test for failures - and spot successes, Brekken said. It’s important to get prototypes out of the lab and into the water, Jacobson said, so engineers can get operations information and resource agencies can assess potential environmental effect.

According to the research firm Cleantech Group, venture capital investments in hydro and marine technologies jumped from $14 million in 2005 to $82 million in 2007. In 2009, however, investments sank to $27 million.

Image: Pelamis wave power device in Portugal / U.S. Department of Energy