Blue Efficiency: Ocean Energy Overview

Blue Efficiency: Ocean Energy Overview

Tidal and wave technologies convert the kinetic energy of moving water into electricity. Ocean thermal systems tap the solar heat absorbed by marine waters to generate clean energy. In theory, these three ocean-based renewable resources could meet the world's energy requirements many times over, but they remain largely undeveloped at present.

Tidal Energy
Tidal energy takes advantage of the daily ebb and flow of tides and of more localized examples of water in motion. The gravitational pull of the moon drives tidal flows, while persistent currents and large-scale circulations such as the Gulf Stream are influenced by solar heating, water chemistry, and other factors. Most tidal current technologies employ a turbine to transform kinetic energy into electricity.

In Massachusetts, tidal waterwheels supplied mechanical energy to early settlers. Today, many tidal, coastal, nearshore, and offshore environments harbor resources with development potential, but no modern ocean energy technologies suitable for use in these settings are commercially available.

Two main types of tidal energy systems exist. Emerging tidal current technology does not alter the natural ebb and flow of water, whereas tidal barrages operate like conventional hydropower facilities. Many tidal current technologies are being developed, and one promising design is being tested within the tidal reach of the Merrimack River along the Massachusetts-New Hampshire border. Tidal barrage systems have been installed in Canada and overseas, but they offer limited applicability and are unlikely to gain public acceptance within the Commonwealth.

Wave Energy
Waves are powered largely by the wind and the tides. The majority of the more than 1,000 patents relating to wave energy technology are for devices that harness kinetic energy associated with the up-and-down motion of the water column as waves pass through it.

Hundreds of patents exist for wave energy technology, and a variety of prototype devices have been tested. However, only one commercial wave power station has been developed-a 500-kW plant, sited on the shoreline in Islay , Scotland . Demonstration projects are being examined for various locations in New England.

Ocean Thermal Energy
Ocean thermal energy conversion (OTEC) systems exploit temperature differences between warmer, surface layers and colder, deep layers of the ocean. All OTEC designs require a large-diameter intake pipe to pump cold water to the surface. There, they employ a variety of heat-exchange cycles to drive a turbine and generate electricity. OTEC technology is further from commercial application than wave and tidal systems. Small-scale OTEC units and individual system components have been tested successfully in waters off the coast of Hawaii.

Tapping ocean energy resources provides Massachusetts with opportunities to reduce reliance on fossil fuels and other conventional sources without producing pollution or greenhouse gases

Blue Efficiency: Ocean Power for San Fransicso

Blue Efficiency: Ocean Power for San Francisco

The blue waters churning beneath the Golden Gate Bridge could become a source of green power for the Bay Area if one researcher gets his way.

Four-hundred billion gallons of water four times a day - 2.5 billion cubic meters of water every six hours - pass beneath the Bridge every day. That flow of water under the one-mile span could provide 1500 megawatts of power day-in, day-out as long as the moon is in the sky, according to Peter O’Donnell in his report Tidal Current Technology Generation. O’Donnell is Senior Energy Specialist with the Department of the Environment for the City of San Francisco.

O'Donnell's ocean power vision includes two tidal fences constructed as part of jetty for areas near the Bridge. Similar to those being developed by Blue Energy, each tidal fence utilizes a number of vertical axis turbines submerged and mounted in caissons that together make up a pier, or fence, with its topside only 12 feet above the water. Turbines would be connected by shaft to above-water electric generators. In concern for environment, large marine mammals instinctively shy away from the turbines and can swim under the fence, according to O’Donnell.

Aside from the tidal fence project the report author has other projects in mind for the area including water farms. Not unlike wind farms, water farms would use numerous submerged water turbines in areas of reliable currents to generate electricity for the nearby power grid.

The biggest hurdles right now are cost and faith. Tidal current technology (as well as other ocean energy technologies), though in use around the world, is scarce. With scarcity comes high cost. Scarcity can also mean unproven and risky in the eyes of those who must finance a project. But in the end San Francisco voters might decide. Last year they voted to approve $100 million in renewable energy bond measures. This year they are voting to approve a municipal power company for the City. Next year could they approve tidal power for their city? Visit Blue Energy at http://www.bluenergy.com/ , the San Francisco Department of the Environment at http://www.sfgov.org/sfenvironment/.