Within the rapidly expanding renewable energy sector, wave energy farms like the one tested in Portugal are still a novelty. But not for long. As the push to develop clean alternatives to greenhouse gas-emitting, nonrenewable fossil fuels accelerates, most money, research, and development remain focused on wind and solar technologies. But marine power, particularly wave and tidal energy, might also eventually provide consumers with large amounts of affordable, renewable electricity. Essentially, the science, art, and costs of marine energy are where wind power was two or three decades ago. "It's not ready for prime time—it needs five to 10 years of technical development," says Dick K. P. Yue, a professor of ocean engineering at the Massachusetts Institute of Technology. "But it could have a huge impact in 20 years."
About 70 percent of the Earth is covered in water, and this water is the globe's biggest repository of solar energy. One need only watch waves crashing onto a rocky shore to appreciate the seas' might. If just 2 percent of the oceans' energy were converted to electricity, it would meet the world's entire power needs, according to the Northwest National Marine Renewable Energy Center in Oregon. Moreover—unlike wind and sunlight—waves, currents, and tides are highly predictable, which makes ocean power more grid friendly. With an increasing swath of the world's population living within 50 miles of the seas, marine power would not need to be transmitted great distances. The converters used to harness water power are generally environmentally benign and unlikely to harm marine life. Indeed, the environmental group Greenpeace has been lobbying heavily for ocean energy.
Far from shore. So why has it lagged other renewables, particularly wind? Mainly for technical reasons that are now largely solved. The open sea can be unforgivingly harsh, and salt water is corrosive. Creating machines that could withstand those elements for years and years was a challenge. Accordingly, most government research money and industrial investment went instead to wind and solar projects. But oil and gas companies have in recent years devised technologies that enable them to put their rigs farther from shore into deeper, rougher waters. The marine energy industry now can use that knowledge to ensure that its own devices are likewise robust. That's a big reason behind more financial support going to marine energy now.
Wave energy, more than tidal, offers the most accessible sea power. (Tidal energy uses the currents in seas, while wave energy draws power from the rise and fall of waves on the surface.) The Electric Power Research Institute conservatively predicts that wave energy could provide around 6 percent of America's electric needs (about the same as the hydropower drawn from dams), while tidal energy could provide an additional 3 percent.
Wave devices come in a variety of designs, but all work to transform the energy from the rolling motion of waves of water to electricity, usually converting aquatic motion to mechanical energy that runs a turbine or generator. The machines used in the Portugal wave farm were designed by the Pelamis Wave Power company of Scotland. Worldwide, there are around 100 competing designs for wave and tidal energy converters. But as the industry matures, there will be a necessary shakeout of the most impractical and costly designs, leaving only a handful of commercially viable machines.
Another wave energy device undergoing tests is the Oyster, developed by Aquamarine Power, also based in Scotland. Designed to capture the energy of near-shore waves, it's essentially a hinged flap connected to a base that rests on the seabed. As a wave passes over the top flap, it pushes the flap down, driving hydraulic pistons that shoot water at very high pressure through a pipeline to an onshore turbine. "The beauty of the machine is its simplicity. There are only seven moving parts," says Martin McAdam, Aquamarine's chief executive. Oyster's design also shows that it's not necessary to capture all the energy in each wave, especially if it's a massive storm wave that might otherwise overload the machine. Excess wave energy streams over the top of the flap once it is submerged. Aquamarine and the utility company Scottish and Southern Power plan to install over the next few years six to eight wave farms that together could provide 1,000 megawatts of electricity from around 1,200 Oyster devices. (One megawatt is a million watts, enough electricity to power up to 900 American homes for a year.)