How do Solar Water Heating Systems Operate?

Before calling an installer, it is best to understand the various types of solar systems. And although there are various types for you a homeowner to consider, you will probably choose from one of the following: Direct-gain systems (which encompasses batch collectors or open loop) and heat exchange systems (which offer closed-loop or drain-back system).

Direct-gain with Batch Collectors

Batch collectors, also known as integrated collector storage (ICS), form the easiest type of solar heating. They work by collecting water in a large 40-gallon tank, which is located on the roof where it is supported by large copper rods. The stored water is then heated by direct sunlight and distributed throughout the home. If the solar collector is insulated, clean drinking water can also be distributed via the home’s water pressure.

Direct-gain with open loop

This method also allows water to be heated by the sun directly through the use of solar collectors on the roof, but the large water tank (typically of the 80, 120, or 125 gallon capacity) is located inside the home or basement. When the differential controller detects a higher temperature in the solar collector than the water tank temperature, it causes the pump to push the water out of the tank and into the solar collectors. The pump will also activate if the temperature is detected at lower than 40 degrees Fahrenheit. This is an advantage on direct-gain with open loop system, as it prevents the pipes from freezing and bursting. A disadvantage to this system is that the tank loses heat easily, which makes this system ineffective in cold climates that have freezing winter nights.

Heat exchange with closed loop

If freezing pipes are an issue, you may want to consider a heat exchange with closed loop system, as it comes with separate piping which is filled with anti-freeze solution that continually runs between the solar collectors via the home to the tank. The anti-freeze solution is ideal in these situations as glycol (a main component of anti-freeze) is able to remain fluid even at -50 degrees Fahrenheit. In actuality, the pump will only activate when the differential controller detects a higher collector temperature than the tank temperature. One caveat to this system, however, is that it does not do well in extremely high temperatures (175 degrees Fahrenheit). To prevent overheating expansion tanks and valves are built into the system that can release pressure. Alternatively, this type of system can also include high quality digital controllers that can activate the pump at night for cooling the tank quickly.

Heat exchange with drain-back

The drain-back system can avoid the freezing and overheating that a pressurized fluid can cause by isolating the heat exchange fluid in a closed-loop when there is no solar heat being absorbed. Similar to the pressurized system, the differential controller activates the pump to circulate the fluid. Drain-back systems can be installed where the pipes can flow downhill to the drain-back tank, which will prevent the water from freezing.