Earth, The Sequel by Miriam Horn

Author:Miriam Horn
Language: eng
Format: epub
Publisher: W. W. Norton & Company
Published: 2008-08-10T16:00:00+00:00

THE INNOVATIONS THAT ARE IN THE WORKS fall into three broad categories. Each technology carries its own mix of advantages and potential environmental impacts. And most illustrate, once again, the importance of scale in evaluating renewable-energy technologies. A pilot project—whether Finavera’s experiment at Makah Bay or Wave Dragon’s demonstration project off the Welsh coast, described below—may seem to have a small impact when compared to existing technologies. But a single, 1-megawatt coal plant would not have a large environmental impact either. The concerns emerge at commercial scale, as the combined impact of many generator units potentially affects important ecological processes. Ultimately, alternative technologies must be judged on their impact at the scale of the conventional energy-generating operations they hope to replace.

Shoreline and near-shore devices are relatively easy to install and maintain and do not require underwater cable, but the waves they tap are less powerful because their energy has diminished as they come close to shore, absorbed by the seabed and dissipated through turbulence and friction. A leader in this category is Wavegen, which has operated a grid-connected wave energy plant near its home base in Scotland since 2000. Wavegen was purchased in 2005 by the German water energy joint venture Voith Siemens Hydro Power Generation. Called Limpet (an acronym for “land-installed marine-powered energy transformer”), Wavegen’s power plant is centered on a capture chamber—the first was excavated directly out of a rocky shoreline; others have been built into man-made breakwaters. As waves enter the chamber, they compress a pocket of air, which is forced through a turbine at the back; as they leave, they suck the air back out through the turbine, which is specially designed to capture the flow in both directions to create electricity. Using air instead of the moving water itself to spin the turbine blades keeps corrosive saltwater away from the moving parts. This method of capturing energy with rising and falling water is called an “oscillating water column.” There is no need to lay a seabed cable—eliminating worries about the impact on bottom habitats and organisms. On the other hand, these facilities have a footprint on coastal lands, where many different kinds of environmental pressures often collide.

Wave Dragon, a Danish-born company that moved to Wales in 2007, uses a completely different technology. The Wave Dragon is a seaborne hydroelectric dam, a large floating barge that stretches out collector arms toward oncoming waves to guide 330 yards of wave front up long, curved ramps; after climbing the ramps, the water flows over the top of the barge and into a reservoir, then drops down through turbines as it returns to the sea. With an expected capacity of 4 to 7 megawatts, the Wave Dragon is the largest onshore wave energy plant in development.

Offshore plants exploit the more powerful waves in deep water. The one AquaBuOY has to beat is the Pelamis from Scotland’s Ocean Power Delivery, an articulated “sea snake” that floats partially submerged in the ocean, moored with weights that swing it to face oncoming waves.

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