I am exploring some self-sufficiency ideas to go along with our solar electric system. A big one apparently has been using propane to keep a 40 gallon water heater running. I installed a 7 KWatt flash heater a while back and shut down the gas water heater. This heater will raise 1.5 GPM (enough for one shower) by 40 degrees F. This is actually enough for comfortable 105 F showers during spring, summer, and fall in San Diego. In fact I had to turn the flash heater current down in the summer time, or it got too hot. That problem was solved recently by installing a replacement Black and Decker flash heater that has a thermostat you can set to a maximum temperature.

But it still has a problem getting hot enough during the winter. So I am building a solar water preheater system for it. The goal is to store enough heat so tap water gets up to at least 70 F as it passes through a heat storage tank. Then the flash heater can do the rest. If I can preheat the tap water to 105 F, that would require no more energy from the flash heater.

Even now, with no solar input, I am still running a surplus on my grid power usage, but we are going to be switching from propane cooking to electric and I would like to keep generating a surplus. So the plan is to use a DIY 24 square foot panel constructed with CPVC, aluminum fins, polyisocyanurate foam insulation (R 7-8), and an old sliding glass door as glazing. It all gets painted black as it goes into service. That feeds by thermosyphon into a 250 gallon IBC heat storage tank. A submerged coil of copper tubing will transfer heat into tap water as it makes it's way to the flash heater. There is no direct contact between the tank water and the tap water, All that gets transferred is heat, and even if the tap water only gets 10 degrees hotter, that will be enough.

I've got the panel built, minus the plumbing. I've got all the needed parts. including the IBC and enough PEX to hook it all up. I have some chain link fence panels I can use to build a fence around and it and keep it "helpful" dog free, .like my solar electric array. As you may be able to tell, I enjoy DIY engineering projects like this. Hours of hot water every day is just a bonus.

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