Solar Thermal Engine
Solar thermal power plants use the same kind of
superheated steam as conventional oil, coal, or nuclear
power plants. Unfortunately it's almost impossible to build and install a
practical high temperature power plant for a single residential
How about the low temperatures available from flat plate collectors? Can they supply enough heat to drive a solar thermal engine?
A flat plate collectors might reach a temperature of 240 F in bright sunlight if no fluids are circulated through the collector flow tubes. When water is circulated to collect heat this high temperature drops off rapidly and approaches the temperature of the heat storage vault. A Stirling engine , invented in 1816, is capable of generating electricity with temperature differences as low as 20 degrees F so it should be an easy matter to generate power from a heat storage vault temperatures of 150 degrees F and a heat sink of 100 F. Good Sterling engines can be pricey and not very powerful. An alternative to the Sterling engine is the steam engine run with a low boiling point liquid that's condensed and reused.
In1904 Henry E. Willsie developed the concept of thermal storage. His choice of a vaporizing liquid was sulfur dioxide because of its low boiling point and high specific gravity. The exhausted gas was then reused by liquefying it inside a condensing tube and pumping it back into the boiler. Willsie used the stored hot water as a boiler and made no attempt to salvage the condensed heat from the steam engine.
The solar hybrid engine that I'm now working on takes a low boiling point gas like CO2 and pumps it into the flow tubes of a collector under pressure where it boils. The gaseous CO2 is then used to drive a turbine. I am sorry I can not share with you the project details at this time, but with a little luck projects like this will be commonplace in the coming years. If successful the integrated solar: HEATING, HOT WATER and POWER system should be able to supply most of the energy needs of people in a dwelling at an affordable price. It sure would be nice to use rather than waste the energy that falls on our roofs. Just something to think about. Hopefully low-temperature , power producing systems like this will become more popular after our planets supply of oil has been consumed. If not practical low temperature differential Stirling engines may soon come to the rescue.