kurupetos wrote:bill cobbett wrote:kurupetos wrote:@ BillC
The color of the water storage tanks doesn't really matter, because radiation heat transfer occurs through the flat plate collectors which are facing the sun.
And yes the collector assembly is usually black, whereas the water storage tank only needs to be well insulated to minimise heat losses.
Simples, dear goblin...
Yes, ok... but what if there were no black flat plate collector assembly and no insulated copper cylinder.... just the uninsulated plastic water storage tank, would the water in it get hot/hotter and hopefully stay warmish overnight if it was painted black...???
No, because in this case you would have heat losses when there is no sunshine (e.g. evening) and the water would reach ambient temperature within an hour or so.
Also it's a solar water heater, and not a thermal water heater, which is a different thing and cannot reach temperatures high enough for domestic water heating. The metal (e.g. copper) does all the heat transfer effectively because it has a high conductivity, whereas plastic has negligible conductivity.
Have a look here...
http://en.wikipedia.org/wiki/List_of_thermal_conductivities@GR! Go back to the closet.
Bill Yes it would get warmer but not a lot and would probably cool down overnight. The solar heating system works ( even with tanks in the roof) because by and large the collectors make enough hot water throughout the day to ensure there is enough for normal usage, which usually requires a few litres a time for washing etc., plus enough capacity to retain enough heat overnight for early morning usage.
It is in fact possible to make simple collectors out of black plastic hose, or plastic pipe painted black and there are some designs for the DIY'er to build themselves, using flattened beer tins to make collecting fins.
I am thinking of adding a second collector at home better angled for the winter sun., I.e. Slightly more upright.
For the systems needing pumps as eg the tank is lower than the collector one needs to assess how fast the warm water naturally flows out of the collector through convection as if the pump is a bit quick one risks filling the tank with lukewarm water.
I am a firm believer in trying to use solar power as much as is possible, preferably in small scale schemes , to reduce reliance on centrally supplied power. Solar thermal in the home is probably under used: build a big enough collector and put in a big enough tank and one can even run a small heating system. After that solar PV, bearing in mind it is expensive to make and fit the panels. Bearing in mind how hot PV panels get! and as they warm up they lose efficiency, so one should look at hybrid systems to use water coolers to extract the waste heat . Kill two birds with one stone. Electricity and free hot water out of one panel.
