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Originally Posted by cel
Not being very knowledgeable in the subject I will ask the experts. Would it be economically feasible to generate enough electricity for a small house in the Houston area using the earth as a heat sink and solar panels as a heat source with propane as the transfer medium. A piston type motor would drive the generator.
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Depends on your definition of "enough electricity." With no modern appliances, you may barely make the mark.
I ran the numbers for using a small Lister diesel engine, biodiesel, and a generator for making electricity. The expense, complexity, and labor lost out to grid power at 11 cents/KW. I also considered buying an outhouse and diesel fired boiler to heat water and my home. Despite cost savings using homebrew biodiesel, it still could not match the cost of natural gas.
Sure, if I was off-the-grid, it would be more attractive, but I was faced with sacrificing time for no cost savings. Hard to justify the investment with infinite payback time.
The problem I see with your idea is you'd need significant pressure to move that piston. Or, you could make the piston larger, but then you'd need more vapor. More vapor = more solar panels. Your theory is very similar to solar vacuum tubes used for water heating. The tubes are placed under vacuum to minimize heat loss and increase efficiency. The medium is vaporized by the heat of the sun. The vapor rises and condenses on a manifold at the end of the tube. That heat is eventually transferred to water. Solar water heating should receive greater focus in America. It's proven, efficient, and can immediately reduce energy usage, particularly in the sunny Southern US.