Solar Hot Water Preheater Idea?
I'm thinking about making a solar collector and placing it on the roof of the home, as large as I can afford (caravan is 12 wide) and feeding that into a heat exchanger inside an old 47kg LPG gas cylinder (I have access to several old cylinders and believe it can hold around 110 litres, so could even use 2?) and having the mains inlet at the bottom and outlet to the boiler at the top.
For the heat exchanger, I'm thinking cut both ends off and drop a coil through from top to bottom and weld back up but i'm open to suggestions.
I want to a heat exchanger instead of having the mains water go round the solar collector, as it can get cold in the UK at night, even in the summer and I dont want it freezing in the winter (i'll have enough worry of water pipes freezing anyway), so will use some form of copper friendly anti-freeze.
I'll need a pump for this, as the collector will be on the roof, above the cylinder, so thinking to run it on a light sensor, but how complicated would a thermal switch be, so when the temp in the collector ir warmer then the cylinder be to make? If anyone knows of a place for the circuits (or of the shelf product), I can see if it's something i'm competent enough to take on.
One last thing, Would having the cylinder painter black and left in sunlight be a good idea. Would it get hot enough to cause problems with the water mains pressure?
Look forward to your feedback and advise.