Various Types of Solar Hot Water Heaters to Heat Water for Off Grid Homes
United States – There are many options for solar water heaters that range from inexpensive home-made jobs to high-end state of the art commercial models.
If you switch to a solar water heating system, your use of electricity or propane will drop significantly; that number will approach zero rapidly if your backup heating system is a wood stove or firebox with a water jacket rather than occasional use utility electricity.
The home-made options are typically not suited for use during times of the year when temperatures dip below freezing. You would need to winterized them before any threat of fall or winter weather arrives. There are probably hundreds of variations that may be found on the internet. They range from coils of black plastic pipe on one’s roof to coils of copper inside a box with outer glass cover (creating a greenhouse effect).
Some of these utilize a DC electric circulating pump. It pushes the heated water into a storage tank and bring fresh cool water into the heater. This pump may be activated by a switch that is temperature controlled. But some are directly connected to a solar panel and only run when the sun is shining (precisely the same times that the water is being heated and needs to be circulated).
Evacuated Tube Solar Hot Water Heaters
Evacuated tube models are composed of numerous rows of glass tubes with another smaller tube inside each of the larger tubes. A vacuum is pulled between each of the two tubes which greatly lessens the loss of heat to outside weather. Water or an antifreeze solution is then circulated through the inner tubes.
The advantages of evacuated tubes lie in greater efficiency and less heat lost. So they work quite well even during surprisingly cool temperatures. However they are somewhat fragile and may not be as suited to areas with a great amount of snow and ice due to the potential for breakage from buildup.
Flat Panel Solar Hot Water Heaters
These heaters look much like solar electric panels but contain tiny water passages which enable a great amount of surface area to come in contact with the heat from the sun. While not as efficient as evacuated tubes, flat panels still work very well and are certainly more rugged when faced with heavy snow and icy conditions.
Typically an antifreeze solution is circulated through the tubes or panels and the hot fluid is routed inside to a heat exchanger which transfers the heat of the fluid to the home’s hot water. There are some varieties of evacuated tube heaters that are called drain down systems, which do not require the use of antifreeze because the water drains away from exposed areas once the water cools off.
Thermo-Siphon Solar Hot Water Heaters
It is possible to set up a solar water heating system that doesn’t require an electric circulating pump. This would be called a thermo-siphon system, operating on the principle that heat rises.
This was the type of system we planned to install for our cabin in the summertime. The disadvantages would be the amount of work involved in installation, significant cost of commercial systems, and reliance on an electric circulating pump (unless it is set up as a thermo-siphon system).