Like surfers, engineers see plenty of potential in the ocean's waves. In fact, 10% of the world's electricity supply could someday come from this renewable resource, according to a World Energy Council estimate. One way to harness the power of the sea is by offshore wave energy devices. Aside from being environmentally benign, these structures usually sit low to the water, offshore, getting around not-in-my-backyard-type issues.
Wave technology is still young. The first time an offshore wave energy device (the Pelamis WEC) generated electricity and transferred it to an onshore grid was in August 2004. Mirko Previsic of the Palo Alto, Calif.-based Electrical Power Research Institute sees the following devices as among those furthest along.
1. The Pelamis WEC
Invented by Edinburgh, U.K.-based Ocean Power Delivery Ltd., the Pelamis WEC consists of four cylindrical sections linked by hinged joints. The floating device lines up perpendicular to the direction of incoming waves. The force of a wave travelling along it causes the different segments to move like a seesaw. A hydraulic system in the hinges pumps high-pressure oil through motors; these drive generators that produce electricity. Power from the joints is fed down a cord to a junction on the sea bed, where several devices can be connected together and linked to shore through a single cable. The Pelamis P-750 has an installed capacity of 750 kilowatts. In May, the company inked a deal to begin construction on the world's first commercial wave farm off northern Portugal. The firm would not divulge the current cost of the electricity the Pelamis WEC generates, but project engineer Andrew Scott projects future costs of 6¢ or 7¢ per kilowatt hour.
2. The Energetech Australia Wave Energy System
When a wave hits this device, a “parabolic wall” focuses the water into an air chamber. The air is pushed toward the chamber's narrow end, where it powers a turbine. A generator linked to the turbine produces electricity, which a cable feeds to shore. When the water in the chamber falls back down, air gets sucked back through the chamber's narrow end, and the turbine goes for another spin. Randwick, Australia-based Energetech Australia PTY Ltd. developed the device and expects it to produce up to 2 MW, depending on the size of the wave, at a projected cost of between 2¢ to 6¢ per kWh. The firm is currently testing its prototype and expects to have a commercial product by 2007.
3. The Wave Dragon
This device looks like a kite and shares some of the principles of that toy. Attached to the sea bed by a cable, the Wave Dragon adjusts to the direction of incoming waves. Its two arms focus the wave toward a ramp, spilling the wave's water into a reservoir with turbines at the bottom. The water spins the turbines, generating electricity, which is transferred by cable to shore. Danish company Wave Dragon ApS developed and is testing the device, and expects the 2007 commercial version to generate electricity at 18¢ per kWh, with a capacity of 4 MW. Eventually, the firm expects the cost to go down to 6¢ per kWh.