This is an article written by Doug Kalmer about his DIY solar hot water heater:
"This Photovoltaic (PV) pumped hot water system has been working well, with no maintenance, for years on my house.I am now past the point where the money I invested in the solar water heater equals the money I would have spent on electricity to heat water. Most of the year, we have more free hot water than we can use. Consider the fact that in the next five to eight years you are going to pay the cost of a solar water heater,whether you buy one or not. I kept costs down by doing all of the work myself, and buying a used collector panel, but still created a long lasting, efficient, high quality system.
I started by looking in the yellow pages under "Solar", and found a plumber in the nearest large city, with spare collector panels. I bought a 3`x13` aluminum collector with copper tubing and tempered glass cover for $100, guaranteed not to leak, but I tested it first, anyway. Assuming the collector needs to be freeze protected, a non-toxic antifreeze, usually propylene glycol, is pumped through the collector, to the heat exchanger tank. The simplest way to circulate the anti-freeze is with a 12 volt pump directly wired to a small photovoltaic panel, this eliminates the need for controls of any kind. When the sun is heating water, the pump runs. I bought a matched set of a 10 watt 12 volt solar electric panel, and bronze magnetic drive circulation pump from Zomeworks. The most expensive single component was the Heat Exchanger (HE) tank. I looked at what is available, and most are built around the ordinary glass lined steel water heaters, which have a limited lifetime. For less money, I had a stainless steel tank built with 50' of 3/4" soft copper tubing in the lower half as my Heat Exchanger. It holds 85 gallons, and acts as a preheater for the regular electric water heater. Non ferrous stainless will outlast me.
Proper sizing of the system is important. Plan on at least 20 gallons of storage tank size for each of the first four people and 15 gallons for each additional person per day. You should have at least 40 square feet of collector area for the first two family members, then add 12-14 square feet for each additional family member. Keep tank size at a ratio of 1.5 gallons or more to one square foot of collector area to prevent overheating.
Besides the pump, panel, HE tank, there are a few other parts to the system:
1) A pressure gauge (0-60psi) will let you know the closed loop has not lost it`s charge of antifreeze.
2) A solar expansion tank allows the solar solution to expand as it heats.
3) A check valve above the tank to prevent thermosyphoning at night.
4) A pressure relief valve.
5) A hose valve at the lowest point for filling and draining. It really is a reliable, efficient system, we do no maintenance to it. I can read water temperature going in to my electric water heater, and most of the year, it is above the 120* setting of the thermostat.
It's your choice-you can invest in solar now, demonstrating your support for sustainable energy, and getting free hot water after your payback period, or continue to pay ever-increasing energy bills, which indicates your support for maintaining the status quo."