READ IMPORTANT UPDATE BELOW:
I built a solar water heating system. In this video I show you how I built the water heating solar panels. My current system of twenty panels have the capability to collect 500,000 BTU per sunny day. typically I collect about 300,000 BTU, Still that is enough to easily heat our house for a day
The panels cost about $450 to $500 each to build. Still that is much cheeper than buying them off the open market.
UPDATE: The second set of solar panels has been plagued with leaks. The joints between the header and the 1/4 I/D tubing keeps springing leaks. I do not know why this set keeps leaking, and the first set (after three years of use), has not. For a DESIGN IMPROVEMENT I now wrap rings of 8 or 10 guage copper house wire around the joints before soldering. This holds a fillet of solder at each of the joints and dramatically decreases the leakage opportunity. I plan to make a video of this improvment when I get time.