solar collector 1

a while ago we decided to start using the power of the sun to at least partially power/heat our house. next to installing a 2 kV PV solar array on the roof i also planned on building a solar collector to provide hot water.

after doing some research i went for a non pressurized flow back system using only water. i found an excellent example to work from right here http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm. in this system the water in a large insulated tank is pumped through a collector sitting on the roof and thus heated by the sun. inside the tank there is a large (100 meter) coil of tubing acting as a heat exchanger. the tap water absorbs the heat of the water in the tank through the coils side walls. the heavily insulated tank is capable to hold its heat for days-weeks depending on water use and outside temperatures.

there's an additional set temperature tankless gas boiler in the water circuit to provide hot water when the sun hasn't been out for a while.

the reason i decided to go for a DIY project is cost and return. compared to electricity producing PV arrays solar collector hot water systems are very expensive and give only a modest return on investment. the goal is to spend 1500 euros - not including the gas boiler - on the installation as opposed to the 5000-7000 that would be spend on an of-the-shelf system (also not including the boiler).