SOLAR ENERGY: OUTLOOK SUNNY

And yet there is a way of harnessing solar energy that not only evades the collecting-area snag, but that promises to be economically in the ballpark, too. This is, as we have pointed out before, the use of ocean thermal gradients to run electric power stations. Such "solar sea power plants" exploit the difference of some 20°C between the surface and deep (500 m) layers of tropical oceans to run turbines by the vapor of a liquid with a low boiling point, such as ammonia. This liquid is vaporized in a heat exchanger near the surface, and condensed by the cold water pumped up from the deep. The vast area of the oceans is already collecting solar energy, and though the small temperature difference plus the energy lost in pumping reduces the conversion efficiency to a puny 3%, it is 3% of a vast input that has hitherto gone untapped.

Ocean Thermal Energy Conversion (OTEC), as the subject is now called, is being investigated at a number of institutions, primarily at Carnegie-Mellon

University (Dr. Lavi) and TRW, Inc. (Dr. Griffin). At a recent Workshop held at the University of Miami's School of Engineering, several problems were identified, of which the two major ones appear to be biofouling and pumping.

Biofouling refers to the thin layer of bacterial slime that settles on the submerged equipment, particularly on the most critical part, the heat exchanger. Pessimists claim that a layer only .003 ins. thick could reduce the heat flow by a factor of 2 or 3. However, firm data are lacking, and biofouling can be combatted by introducing chlorine or copper ions into the heat exchanger.