Is Ocean Power a Viable Energy Source?

Pioneer Companies Research the Ocean to Create Renewable Energy

Tidal Energy Bridge
Mmdi/Digital Vision/Getty Images

Dear EarthTalk: Alternative energy sources like wind power, hydrogen and biofuels are getting a lot of headlines these days, but what about efforts to generate electricity from the ocean’s waves?
-- Tina Cook, Naples, FL

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

Is Ocean Power an Option?

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”.

Ocean Wave Power

 

In harnessing wave power, the back-and-forth or up-and-down movement of waves can be captured, 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.

Ocean Tidal Power

Harnessing tidal energy, on the other hand, involves trapping water at high tide and then capturing 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.

Ocean Thermal Energy Conversion (OTEC)

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.

What’s Being Done with Ocean Power?

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. Plus, the corrosive power of sea water generates steep engineering challenges. But as the industry matures, costs will drop and some analysts think the ocean could power a non-negligible proportion 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.

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, New York with electricity through tidal river turbines and has begun installation of tidal power systems in New York City’s East River.

 

EarthTalk is a regular feature of E/The Environmental Magazine. Selected EarthTalk columns are reprinted on About Environmental Issues by permission of the editors of E.

 

Edited by Frederic Beaudry.