Cold Springs and Solar Ponds as Natural Power Generators
Cold springs can be used to cool the cold side of Stirling Generators that when even air cooled have been shown by Sandia Labs to be more efficient than the most efficient photovoltaic cells. With a temperature differential of 40-50 degrees with the air the thermal differential of the cold springs could boost this efficiency significantly. If the hot side of the solar Stirling generators uses concentration by either reflectors or refraction this increases by a factor of 20X or more depending on the materials and type used. Besides the typical kind of above ground mirror concentrator it is possible to use in ground concentrators either from settling ponds such as used for phosphate mining, retention ponds or make new ones.
Besides reflectors we have found that water can be used to make very large refracting concentrators. This is done by using transparent plastic and filling it with the appropriate amount of water. Refractors of this type can be made very cheaply and offer concentration of three to four times that of reflectors with easy focal adjustment by merely tightening or loosening the plastic container.
Another method to use for the hot side of the solar Stirling is a solar pond. Some springs are brackish and make the formation of solar ponds relatively cheap and easy. All bodies of water absorb heat from the sun. Normally, heat is lost as warm water rises to the surface and cools by evaporation. But water is a VERY poor conductor of heat and if this circulation can be stopped, the heat can be trapped in the bottom of the pond. A salt pond managed so that the water on top is of (relatively) low salinity and the water on the bottom is of very high salinity, will not circulate to release heat because the water on the bottom is so heavy with salt it cannot rise. The deep water gets to over 100c degrees in the right circumstances 80c degrees is common in the tropics. The main management problem is to extract heat at the right rate so the pond does not boil or 'turn over' and lose its heat this is accomplished by sensors and computer controlled valves.
Solar ponds can also be used without Stirling generators by using a sealed metal cylinder or cylinders in the pond filled with fresh water within which vertically mounted power turbines are placed. These turbines are moved by convection currents created in the fresh water as they are trying to stabilize with cold water being on the bottom and the hottest being on the top, the exact opposite of the solar pond. Heat from the solar pond is absorbed through the metal cylinder and heats the bottom layer of the fresh water causing it to rise rotating the upward turbine. The water on the top of the cylinder cools and falls to the bottom moving the down fall turbine. The turbines in turn drive power generators.