How to Build a Solar Pool Heater
Even during hotter months, stepping into a warm pool is a wonderful feeling. But powering all that heat from your gas or electric system can get ridiculously expensive. Free photons to the rescue! A solar powered heater can boost the temp of your swimming water all year long, and after the installation, these extra degrees won't cost you a thing.
Step 1 - Assemble the Panels
Warming a pool with solar heat requires a few solar panels hooked up to the filtering/circulating system. These panels can be made from sheets of 3/8” (9 mm) plywood boxed-in with 2x4s around the perimeter (Fig. 1).
Dril two holes in opposite corners of the box through the sides and not too far from the corner, for the inlet and the return. A good coating of exterior black paint inside and out will help draw the heat to warm up the pipes.
The box will accommodate 400 ft (122 m) of 1/2” (12 mm) black polyethylene pipe, but before starting, some accessories should be prepared and ready for use. They can be made from 3/4” x 2 1/2” (19 mm x 64 mm) strapping. You'll need two pieces that are 48” (1220 mm) to make “spacers.”
Eight more pieces about 18” (450 mm) long, and six (or more) at 12” (300 mm) long will be used to hold down the pipe and keep it from collapsing. The two spacers will be positioned parallel to the long sides at about 16” (400 mm) from the edge and centered with the ends at about 22” (570 mm) from the end walls. They should only be temporarily fastened in position so that they can be relocated later.
Step 2 - Attach the Pipe
Handling the pipe is a lot easier if the tubing is warm, since a cold pipe will have a tendency to form kinks when shaping it around the corners. One end of the 1/2” (12 mm) pipe should first be inserted through one of the holes in the corner of the box, with at least 10” (254 mm) of the end sticking out. The tubing should then be placed against the long wall first, then arcing around the corner and following the end wall into the next corner where it keeps going around, careful not to create a radius too tight as to kink the tubing. The 18” (450 mm) strapping is required to hold down the pipe as the work progresses. This is done by “bridging” one end on the pipe and the other end on top of the 48” (1220 mm) spacers, screwing in place with one screw only in its center.
Since the pipe is very soft from the heat, care must be taken not to screw in too tight to avoid flattening and damaging the pipe. While proceeding at coiling the tubing inside the collector panel, the spacers will have to be adjusted and relocated to suit the needs, and usually, more will have to be added, including the shorter pieces, wherever the pipe tends to slide out or overlap. They must be screwed carefully by placing the screws between two pipes, making sure to separate the two pipe so the screw doesn’t touch and damage the pipe.
The coiling of the tubing around inside the solar panel should continue winding towards the center until all the tubing fits snug and neat looking. Some permanent spacers and hold-downs can then be made more accurately to their proper size, to replace the temporary ones, and re-positioned in their most beneficial locations on the solar panel. Those permanent braces should be primed and painted black prior to installation.
Step 3 - Connect to the Filter
The completed solar panel will hook up to your pool’s filtering/circulating system. The method showed here to hook up provides the pool with hot water from the solar collector as long as the pump is running (Fig. 2). The inlet of the solar panel takes its feed from the Tee fitting on the 1 1/2” (38 mm) return pipe from the pool filter. The outlet of the solar panel will then run back to the pool passing over its side (Fig. 3). By installing a valve on the main return line between the Tee fitting to the solar panel and the pool’s return (Fig. 4), enough pressure can be built up by partly closing the valve, to create a flow through the solar collector installed on the roof.
The valve is adjusted by feeling the circulation in the pool return outlet. Before the initial start-up, however, the valve could briefly have to be fully closed, depending how high the solar collector panel is installed, so most or all the pressure pushes the water through to fill the 400’ of pipe with water, and at the same time clearing out the air from inside the system.
When there are multiple units installed, their inlets should all be hooked up in parallel to the same return line from the filter. As long as the return pipes of each solar panel feed directly into the pool, or into a larger pipe that runs back to the pool to avoiding creating a bottleneck restricting the flow, it will work smoothly. In the latter case, the combined surface area of all the smaller pipes should connect to a larger pipe with a surface area equal or larger surface area of all the solar panels’ return pipes.
Step 4 - Glaze the Panel
Another thing with solar panels is that they are sensitive to the ambient temperature around them. If it gets cooler out, whatever warmth was gathered in the pool all day will drop as long as the water runs through the solar panel. If there is a breeze, the wind passing over the pipes will also contribute to a significant heat loss. This can be corrected by glazing the solar panel.
This is done by covering the box with a heavy gauge clear plastic or vinyl thus creating a chamber for the pipe layout (Fig 5). A Temperature Control Switch Thermostat (Fig. 6) is then added to the solar panel to deactivate an N/C (normally closed) solenoid valve (Fig 7) installed along the line running to the solar panel cutting the water flow.
This will ensure that when the water in the solar panel cools down, the flow is stopped. This is where the benefits of solar heat panels are really appreciated.