Electrifying role possible for Great Salt Lake
| Logan, Utah
Not a drop to drink -- too salty. No fishing -- there are no fish. No diving either -- unless you brought weights to help you sink. Beyond its value to mineral companies and as an odd curiosity for tourists, the Great Salt Lake is relatively useless.
Or is it? Scientists here at Utah State University (USU) are looking at the possibility of tapping the lake's natural talent as a first-class solar collector.
"The analyses tell us that if the nitty-gritty mechanical things can be worked out, the energy potential is there," says Dr. J. Clair Batty, a professor of mechanical engineering.
The scheme is simple. Water at the bottom of the lake, laden with salt, gathers heat from the sunshine because it is unable to rise to the surface and cool off. Water at the top, which is less saline since it is continually fed by fresh- water streams, remains cooler through evaporation. Thus the lower layers of water are trapped and continue to gain heat. (Temperatures have been measured close to the boiling point.)
A quirk in the history of the Great Salt Lake, in fact, may make the lake an ideal catch basin for the sun's rays. When a wooden railroad trestle that crossed the lake began deteriorating in the 1950s, a causeway was built in its place.
The causeway split the lake into a north and south arm and, in effect, created two legs with different characteristics. Three rivers feed the south arm with fresh water, turning the north arm into a mammoth evaporation pond with a lower water surface (some two feet below the south arm) and higher concentrations of salt. The extra salts in the north arm yield heavier water -- which is forced, by the greater pressure gradients, back through the culverts in the causeway and through seepage in the embankment, to the south arm.
Once heated by the sun, the water at the bottom of the south arm can be 60 degrees C. hotter than the water at the top.
To generate electricity the heat would vaporize a liquid agent, such as Freon or ammonia, which would drive a turbine generator.
The idea is already in use. In Israel, a 150- kilowatt system takes its energy from similar characteristics -- but no causeway -- in the Dead Sea. Scientists there already are planning a new project that by 1981 will generate 50,000 kilowatts -- enough to provide power for city of 10,000 people.
The energy contained in the Great Salt Lake may be easier to tap since the lake is shallow -- an average 14-foot depth compared with 1,000 feet in the Dead Sea. The shallow depth means it requires less energy to actually "pump" the heat to the surface.
"If solar pond technologies can be developed anywhere in the world, the Salt Lake is as good a place as any," says J. Paul Riley, a USU professor of civil engineering.
Measurements show that the surface of the lake receives some 16.5 megajoules of insolation. Dr. Batty calculates that with a 10- percent conversion rate of that energy into electricity (a figure that may be optimistic), the 1,700 -square-mile lake could yield 15,000 megawatts of power. The current installed capacity of Utah Power and Light Company, which provides electricity to most of the state, is 20,000 megawatts.
There are problems. Chief among them are the environmental consequences of developing the lake's shoreline and interior. One proposal involves sectioning off the lake into even smaller solar ponds.
Other problems involve wind, which can stir up the lake and destroy the heat inversion, and cooking organic materials in the lake with excessive heat, which may result in too much gas. "The whole lake begins to burp," Dr. Batty says.
A $750,000 study already is under way to determine the feasibility of a similar project in the Salton Sea in southern California, which receives more solar insolation in its warmer climate but is at least seven times less saline than Great Salt Lake.