A solar pool heater can reduce or totally eliminate the need for grid power to heat a swimming pool. The sunlight is absorbed into the black coils of pipe within the panel, and the heat is transferred to the pumped water. The average backyard pool owner can build a solar pool heater in about an hour.
Secure four 2-by-4's to a section of plywood to create a shallow "box." The 2-by-4's should be fastened on their edges with wood screws from the rear of the plywood, by turning the screw clockwise. This shallow box is the primary panel.
Drill two holes into opposing corners of the box, on the sides of the 2-by-4 walls. The holes are the inlet and output of the water pipes, and should be slightly larger than the actual pipe.
Run pipe through one of the holes and across to the opposite side of the panel. Attach a 90 degree pipe adaptor, then a short section of pipe, and another 90 degree adaptor. The result is a 180 degree bend in the pipe. Run a piece of pipe from this adaptor to the opposite end of the panel and attach two more adaptors in the same manner. This will run the pipe into a radiator pattern on the inside of the panel. The final straight section of pipe should exit out of the second hole. Reducing the length of the shorter pipe sections will maximise the amount of water in the panel, and allow the pipe to line up with the exit hole.
Paint the inside of the panel black. Spray or brush all interior surfaces with several coats of flat black paint, and allow it to dry completely.
Attach a sheet of Plexiglas to the top of the panel, sealing the pipes inside. The Plexiglas can be pre-drilled for small screws, or held with adhesive.
Connect the water pump to the input pipe on the panel by turning it's pipe adaptor clockwise, or using adhesive. The pump input hose should go into the deep end of the swimming pool, where the water is coldest. The pump should have its own power cable, or the pool's filter pump can be run through the panel if no extra pump is used.
Connect the exit pipe on the panel to a hose and place it into the shallow end of the pool.
Place the panel in direct sunlight, and turn on the water pump. As the water is drawn into the panel, the sunlight is absorbed by the black pipes and heat is transferred to the water. As it exits, it warms up the shallow end, which circulates to the colder water at the deep end, warming the entire pool.
Use caution when connecting several heaters together, the water could reach dangerous temperatures.
Do not touch the panel in direct sunlight, it gets very hot.