As an advocate of sustainable development, and renewable energy technology, I was excited to see the January 19th article “An Idea Whose Tide Has Come” in The Day (New London, CT) . The article presents a case for placing turbines in the tidal currents off of Connecticut and Long Island, New York, specifically off of Race Point and Plum Gut. I am skeptical of the estimates put forth by Natural Currents Energy Services, which were described in the article.
The article’s suggestion that a turbine of 3 ft by 3 ft by 8.5 ft will generate 10 megawatts (MW) of power, allowing 100 turbines to produce 1,000 MW, violates the conservation of energy principle. The theoretical power available from the kinetic energy of the water, that which is realized as it flows, is equal to the product of one half of the mass flow rate and the square of the velocity. Assuming the turbines have a 3 ft X 8.5 ft intake, the maximum allowable by the given dimensions, and a sustained supply current of 7.5 knots, the upper limit given, just under 68 kilowatts (kW) may be produced. This is far below the 10 MW suggested. Basic laws of Thermodynamics, as well as the cyclic nature of tidal currents, ensure far less will be realized by a practical device. It is likely many more turbines would be required to produce the 1,000 MW suggested.
In July 2007 New York’s Department of Environmental Conservation reported a 1,000 kW hour per day output from turbines installed for the Roosevelt Island Tidal Energy (RITE) project. This equates to an average power output of just under 42 kW. Assuming such turbines were used over 23,000 would be required to produce 1,000 MW.
This should not discourage those researching ways of bringing renewable energy to the area. I applaud Natural Currents Energy Services for proposing the plan, and The Day for running articles drawing attention to this important and promising technology. (This information in this post has also been included in a letter to the editor of The Day). – MJP
