DEAR EARTHTALK!

Q: Alternative energy sources like wind power, hydrogen and biofuels are getting headlines these days, but what about efforts to generate electricity from the ocean’s waves?  ~ T. Cook, Naples, FL

A: As any board or body surfer will tell you, the ocean’s tidal currents pack considerable wallop. So why wouldn’t it make sense to harness all that formidable power, which is not too unlike that of the rivers that drive hydropower dams or the wind that drives wind turbines, to make energy?

The concept is simple, says John Lienhard, a University of Houston mechanical engineering professor: “Every day the moon’s gravitational pull lifts countless tons of water up into, say, the East River or the Bay of Fundy. When that water flows back out to sea, its energy dissipates and, if we don’t use it, it’s simply spent.” According to Energy Quest, an educational website of the California Energy Commission, the sea can be harnessed for energy in three basic ways: using wave power, using tidal power, and using ocean water temperature variations in a process called “ocean thermal energy conversion” (OTEC).

In harnessing wave power, the back-and-forth or up-and-down movement of waves can be harnessed, for example, to force air in and out of a chamber to drive a piston or spin a turbine that can power a generator. Some systems in operation now power small lighthouses and warning buoys. Harnessing tidal energy, on the other hand, involves trapping water at high tide and then harnesses its energy as it rushes out and drops in its change to low tide. This is similar to the way water makes hydroelectric dams work. Already some large installations in Canada and France generate enough electricity to power thousands of homes.

An OTEC system uses temperature differences between deep and surface waters to extract energy from the flow of heat between the two. An experimental station in Hawaii hopes to develop the technology and someday produce large amounts of electricity on par with the cost of conventional power technologies.

Proponents say that ocean energy is preferable to wind because tides are constant and predictable and that water’s natural density requires fewer turbines than are needed to produce the same amount of wind power. Given the difficulty and cost of building tidal arrays at sea and getting the energy back to land, however, ocean technologies are still young and mostly experimental. But as the industry matures, costs will drop and some analysts think the ocean could power nearly two percent of U.S. energy needs.

Several companies now work at the cutting edge of ocean power technology. Scotland’s Ocean Power Delivery Ltd. has a wave system called Pelamis that it hopes to install in waters off of California’s wave-battered central coast. And Seattle, Washington’s Aqua Energy has installations off the coasts of Oregon, Washington and British Columbia and is in talks with utilities about providing the Pacific Northwest with hundreds of megawatts of ocean energy within the next decade.

Tidal energy pioneers are also hard at work on the U.S. Atlantic coast. The New Hampshire Tidal Energy Company is developing tidal power in the Piscataqua River between New Hampshire and Maine. And a company called Verdant Power is providing Long Island City, NY with electricity through tidal river turbines and has begun installation of tidal power systems in New York City’s East River.

CONTACTS: Ocean Power Delivery Ltd., www.oceanpd.com; Aqua Energy (Finavera Renewables), www.finavera.com/wave; Verdant Power, www.verdantpower.com.

Dear EarthTalk is from the Editors of E/The Environmental Magazine. Send your environmental question to: EarthTalk, c/o E/The Environmental Magazine, P.O. Box 5098, Westport, CT 06881 or e-mail: earthtalk@emagazine.com. Read past columns: www.emagazine.com/earthtalk/archives.php

Appeared in the April/May 2007 issue of Innerchange.