Phil Scott does not wax romantic about the moon. Where others see mystery or madness, he ponders megawatts. Twice a day, like clockwork, the moon’s gravity makes the seas ebb and flow. For Scott, a business manager at GE Power Conversion, the tides are the perfect source of renewable energy, more predictable and reliable than wind or solar power. “Some tides off the coast of U.K. clock in at seven meters per second,” he says. “It’s a force of nature begging to be leveraged.”
Spinning With the Fishes: GE engineers have tapped the low and high tides to generate renewable electricity.
GE has already helped to anchor the first tidal turbines on the sea floor around the Orkney Islands off the coast of Scotland. They resemble large ship propellers submerged in 180 to 240 feet of water and use turbines adapted from wind technology. The turbines stand in strategic “pinch points” where the tides rush through a narrow channel between an island and the headland. So far the Orkney turbines have pumped more than 15 megawatt hours of electricity into the local grid.
The GE team is currently talking about supplying power converters and generators for a second 10-megawatt underwater turbine array in northwest Scotland. Engineers estimate that UK’s total theoretical tidal range resource is estimated at between 25 and 30 gigawatts – enough to supply around 12 percent of UK’s power demands. “If you give me the tidal tables, I can tell you what the tide’s going to be doing at a certain point on the planet a hundred years from now,” Scott says.
There are three main ways to tap the power of the tides. Tidal range uses the vertical flow in water as tides rise and fall in one spot. Tidal current captures the water’s horizontal movement as the sea ebbs and flows when the tide changes. Special buoys can also generate power at the surface, from the up and down movement of the waves. This last approach is still being tested. “It happens to be roughly an order of magnitude more difficult to mount and maintain equipment on the surface of the sea,” Scott says. “Companies have put wave systems in only to find them dashed upon the rocks.”
Despite the harsh sea environment, GE wind turbine know-how gave the company a head start in tidal power. Will tidal energy overtake wind power someday? “I think not,” Scott says. But he says that over the next five years there will be “a significant amount of tidal arrays, and probably wave systems too,” connected to the grid in the U.K. as well as the U.S., South Korea, China, Australia and Brazil.