OCEAN THERMAL ENERGY CONVERSION

     Sunlight warms the top layers of the ocean. In some parts of the world, surface water temperature is 80°F or higher.

     But the lower layers of water, hundreds of feet below the surface, are untouched by the sun’s rays. Water at such depths usually has a temperature of about 40°F.

     This difference in temperature can be used to drive a turbine-generator power plant. Here’s how the process works, in simplified form: Let’s say the power plant uses ammonia as the working medium (this is not the same as household “ammonia,” which is really ammonium hydroxide). The process begins with the ammonia in liquid form, at a temperature of 40°F. (See diagram on page 16.)

     1. Warm seawater at the surface heats the liquid ammonia in the evaporator to a temperature of 80°F. This heating turns the ammonia into an expanding gas.

     2. The expanding gas rushes through the turbine, making it spin. Since the turbine is connected to an electric genera- tor, the generator also spins, thus producing electricity.

     3. Cool seawater, from the deep, chills the ammonia gas in the condenser and turns it back into a liquid. The liquid ammonia is then pumped back to the surface.

     4. Same as step 1 . . .the cycle starts all over again.

     Although this process could generate much electricity, building a large ocean thermal energy conversion plant would be very difficult and expensive. Still, the concept holds promise in the warm parts of the world.