How Many Solar Panels to Heat a Pool?

The simple answer is, divide the square footage of your pool in half, and thats how many square feet of solar panels you will need to heat your pool. For example, if your pool covers 100 square feet, you will need 50 square feet of solar panels to heat it.

Obviously, once you get into the specific installation and setup things may change a bit depending on how much sun you get, what direction the panels face, and other details. But if you are looking for a general rule of thumb, the 50% rule is a good one to go by.

Alternatively, you can setup a pool heating system where the pool water runs through the panels themselves, rather than the panels powering an electric heater. There is a great book called “Homeowner’s Guide to Solar Heating and Cooling,” by William M. Foster. He gives more details about how to setup a proper solar powered pool heating system that runs the water through the solar panels themselves (see diagram). I’ll quote an excerpt of the book below:

“The next system has an automatic control system, using a differential thermostat specifically designed for swimming pool applications. Although an automatic control adds to the initial cost of the installation, I feel most homeowners would not devote the time to manually operate the controls. And without almost constant monitoring, you could end up cooling the pool water rather than healing it.

“…The solar panels are connected in a parallel arrangement, taking the pool water directly after it has been filtered, then heating it and returning the heated water to the main line. This solar-heated water may be fed directly into the pool, if no supplementary heating is provided.

“If you presently have a gas-fired heater and can get fuel, the solar installation would then feed directly into the heater. A typical operation cycle of the automatic system with an auxiliary heater is:

The swimming pool pump runs either on a time clock or continuously, as preferred. The pump operation is completely independent of solar panel controls.
Sensor T1, is basically a miniature solar panel. When a thermostat attached to the panel needs a temperature 5’F higher than the pool water, solenoid valve V2 is closed, forcing the pool water through the solar panels.
Sensor T2 monitors the pool water temperature and opens valve V2 when the temperature difference (T) is 2 degrees F. That is when the temperature difference (AT) is 2’F. That is when the sensor T1 is only 2 degrees hotter than the pool water is sent directly into the gas heater.
The gas heater has it own individual thermostat, and it will operate if the water temperature entering the unit is below the thermostatic setting.
When the pool pump is stopped, float-type air vent valve v2 opens allowing air to enter the line and draining the water from the panels and distribution piping. V2 remains open when the pump is stopped.

“It is important to remember that solar swimming pool panels have different operating conditions than collectors for water heaters or room heating.

“The swimming pool (which is your storage tank) has a very large volume. A small quantity of high- temperature water flowing slowly in the pool would make only a small contribution to the overall temperature of the water in the pool. Remember your objective
is to raise the temperature only 10 degrees, a rapid flow of pool water through the panels does this most efficiently. Refer to the efficiency curve and you can see how it pays to keep the water
flowing rapidly and the temperature difference small. Plastic collectors should be cool to the touch with pool water flowing through them at the proper rate. To keep the flow rate high, be
sure the pump is of adequate size and that the panels have a low pressure drop (OR MINIMUM restriction to the flow of water). Insufficient flow may also be caused by a dirty filter or piping that is too small in diameter.

“Self draining of the panels is an important feature to prevent freezing, as well as overheating if the pump becomes inoperative on hot days. Water in the panels can freeze at night, even with
with air temperature above 32’F, due to radiation losses. Water expands as it freezes and will most assuredly burst pipes, rupture panels, and ruin your system unless protection is provided.