Possible New Projects Including a Stirling Engine
I calculated that running the spa on average 1/2 hour per day, only costs $52 a year for power and gas. For a spa solar heater I would need: two 12 volt 6 amp pumps ($100), 144 watts of solar panels ($200). a heat exchanger ($70), check valve ($20), solar heat collectors ($60), pipe, fittings, insulation and wire ($100). and a ($50) budget buffer. That’s at least $500 for the project. At $52 a year savings it takes about ten years to pay back the investment. It is a cool project but it is hard to justify the money and time spent.The doghouse (computer, frig and power bricks) uses a little less than 200 watts per hour. 24 hours x 365 days = 1728 KWatts/year. We pay on average $0.182 per KW, so the doghouse costs about $315 a year to operate. To get back the 200 watts a day with just eight hours of sunshine, I need 600 watts of panels ($840) and probably four big acid/lead batteries ($400). After 3 years the batteries need to be replaced. Maybe $2000 altogether or payback in about six years.
I have huge trees that overshadow my house on the south side, so solar collectors on the roof are not gong to work. My wife is not comfortable with the aesthetics of solar arrays in the backyard. The garage roof is probably the best place for a solar array but it is about 80 feet from the doghouse. I need to percolate this idea some more...
While researching solar collectors, I ran across George Plhak’s excellent blog on parabolic collectors and also the Tamera SolarVillage Youtube video about using a large Stirling engine to pump water.
I am intrigued by the idea that the temperature difference between solar array fluid and spa water could be used to circulate both fluidic systems. A Stirling engine is essentially a heat exchanger that extracts mechanical work in the process. So, could I build a large cheap Stirling engine and use it in place of the heat exchanger, the electric motors and the photovoltaic panels of the spa solar heating project?
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