How would you like to have all of the free hot water you could use? I have, and you can if you live in a place you are going to stay for at least five to eight years and have good southern exposure, even if it's just on the roof. The payback period will vary with your situation, water use, energy now used to heat water, and whether you need to hire out the work done.

Why heat with the sun?

There are four main reasons why heating your domestic hot water with the sun makes so much sense:

1. It is a proven method. There were about 50,000 solar water heaters in use in Miami, Florida alone from the late 1930s to the early 1950s. Most were replaced by pipelines bringing in expensive natural gas.
2. It is a year round application. Your family uses hot water every day. A typical family of four spends about 40% of its utility costs on water heating.
3. Solar energy gathered during the day can be stored in an insulated tank to provide hot water long after the sun has gone down.
4. It is cost effective.

Solar water heaters are either passive (no pumps) or active (pumped). Two types of passive systems are "batch" and "thermosiphon." A batch uses line pressure to send water to and from a solar-heated tank located in an insulated box outside the house. A thermosiphon system calls upon water heated in the collector to rise by convection into a tank that must be placed at least 18 inches above the collector. Passive systems have no automatic freeze protection.They must be drained manually or left idle in freezing weather.

The three active water heating systems are draindown, drainback, and closed-loop antifreeze. A draindown system pumps drinking water under line pressure through the solar collectors. A drainback system pumps water from a small tank through the collectors and a heat exchanger. A closed loop antifreeze system pumps a non-freezing fluid through the collectors to a heat exchanger in a sealed system. Draindown and drainback systems rely on solenoid valves or pump controls for freeze protection. Equipment malfunctions can be expensive.

If there is an attached sunroom or greenhouse, it would be a great location for the collector, as you would not need to take precautions against freezing.

Closed-loop antifreeze systems are freeze-proof and reliable in all climates. It is the recommended system where there are more than 15 freezing nights per year. It is preferred in hard water areas where corrosion or mineral buildup would reduce the efficiency of the collectors.

System size

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.

Many good, used collectors are still available. I just called plumbers listed under "solar" in the yellow pages of the nearest large city. 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.

Antifreeze

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 antifreeze 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.

The entire collector loop must be made of copper or brass. Solar tanks have heat exchangers in the form of copper tubing bonded to the lower half of the tank wall. They are expensive, and being glass-lined, subject to failure eventually. I had a stainless steel tank built with 50' of 3/4" soft copper tubing inside the lower half as the heat exchanger. While this cost me $500, it is forever and still costs less than one that will corrode.

Just seven parts, counting the pump

Besides the pump, there are only six parts in the system:

1. a pressure gauge (0-60psi) will let you know the closed loop has not lost its 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;
6. a bypass valve around the check valve to allow the heat to thermosyphon back to the roof collector at night, to prevent the tank from overheating if you are away.

Solar hot water can be added to existing structures, as I did to my house nine years ago. 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. 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. 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.