Install Solar Panels to Heat a Pool

Heating a pool with inexpensive, unglazed plastic solar panels can be a relatively easy and low cost project you can do yourself. Although these black plastic solar panels are less efficient per square foot than high-cost, high-efficiency solar panels, they may require less energy to manufacture and transport than panels using steel, aluminum, glass, or copper. Certainly the heat gain per dollar of investment and ease of installation are compelling benefits.

Steps

  1. Before you begin, consider your climate and reduce your expectations. Nighttime temperatures tend to undo daytime gains, even during sunny weather. A pool blanket is absolutely essential at night as this is when the majority of heat loss takes place - when the air temperature is much cooler than the water. An in ground pool will lose heat faster than an above ground pool as the ground area below 3' in most areas is cold even during the summer. Do you have space for solar panels to receive direct sun most of the day? Will you remove the panels prior to high wind storms and perhaps each winter? Will the reduced water flow still clean your pool or is running your pump for more hours acceptable? That said, the low cost and ease of installing your first panels may make it feasible for you to experiment. In most situations plastic solar panels will increase your comfort during the regular swimming season however they are not likely to increase the length of the swimming season unless you supplement with gas heating also. No prior planning can substitute for the experience of trying it out.
  2. Install a 3-way pool valve after the pump and filter (in the return line) so water can be directed to the panels or to the pool (bypassing the panels). Proper pool valves are not cheap, but they never block the return flow and can be adjusted to direct all, part, or no water through the panels. Consider a pool valve that will accept an automatic valve controller if you may want to later control the valve from another location or with a clock.
  3. Install a T pipe fitting near the 3-way value in the same return line on the pool side. Water returning from the panels will reenter the return line below the valve. Water is then free to return from the panels to the pool. It is helpful for winterizing the system in the future to buy valves that have unions so that you can open and drain the system.
  4. Maintain the same pipe size as the return pipe (usually 1-1/2" or 2") for the two lines to and from the solar panel location. If the panels will be installed on the roof, plastic conduit pipe hangers will hold the pipe securely to walls and the eave. At the roof edge install a union fitting on each pipe to make it easy to remove the panels seasonally, or for wind, or to replace the roofing. Even for solar panels on the ground, union fittings will make seasonal removal easier. Consider burying the rigid pool pipes to keep your yard looking neat.
  5. Plastic solar panels come in several sizes, but 2'x20' is common. Purchase no fewer than two. Each panel costs roughly $150. You may want to try two before adding more. Enough panels to equal the area of your pool would be ideal, if you have the space for them. An 18' diameter round pool has a surface area of about 254 sq ft / 40 sq ft per panel = 6 panels. But fewer panels are OK and it may be best to keep your investment modest until you are convinced that all the considerations and benefits are worthwhile. More panels require more pump power, so this is another consideration you will understand better after you have tried two panels. It is common to need to increase the size of the pump by 1/4hp in order to accommodate any lifts higher than a single storey or longer than 100'.
  6. Fastening the panels to the roof may be your greatest challenge and a reason to consider placing them on the ground. Use stainless steel hanger bolts ordered on the internet, if your local hardware does not carry them. Consider your roof rafter spacing and locate hanger bolts slightly wider than the 2-foot width of the panels. A generous dob of roofing polymer or "tar" around each hanger bolt is required to prevent leaks. A strap or aluminum bar with a hole at each end fits over the panel and two hanger bolts. Secure with stainless steel washers and wing nuts to make removal of the panels quick and easy. In most communities you will need to submit drawings, comply with codes, and obtain a permit before making any roof installation. These considerations may make installing panels on the ground an attractive alternative.
  7. Once the solar panels are in place, connect them to each other and to the union fittings. Pay particular attention to which end of the panel pipe is IN or OUT, so that the water flow will always be entering IN and exiting OUT. Air will be trapped in the panels if they are installed backwards. When panels are installed on a slope, the OUT end of the panel should be higher.
  8. After the pipes are connected, turn on the pump and open the valve to the panels. Check for leaks. Theoretically, the greater the flow, the more efficient (because the cooler water in the panels absorbs more heat from the sun). You will probably find that the water returning from the panels is just two or three degrees higher, but over a period of a day this will heat your entire pool by a few degrees. If your nights are not too cool, you will gain a few degrees each day. Even a small pool will take about a week to be noticeably warmer. We've been conservative to help keep your expectations realistic, but I have only three panels on my South Florida pool and they are wonderful. With no electric or gas heating, I can enjoy a pool at 80 degrees or more for about half the year. This year I'll add two more panels for a total of five to extend my season. Happy swimming!
  9. If you live in an area that experiences sub zero temperatures be sure to install a drain at the lowest point of the system or plan to pressurize the system with air to prevent freezing damage in the winter.
  10. A solar controller system can be purchased for around $400 which includes temperature probes, valves and actuators to automate the system.

Tips

  • Most pools require about six hours to ensure cleaning. Solar panels will usually extend this time to take advantage of all the sunny hours. A warmer pool will require more cleaning than a cool pool.
  • If panels are subject to freezing, you will need to drain them. An extra fitting to let air in at the top could make this easier.
  • Don't circulate the water through the panels until it is cloudy bright or sunny. The panels may actually cool your pool in the evening and at night.
  • Solar pool controllers are available to sense the temperature in the pool and at the panels to open the valve whenever there is the potential to heat your pool and close it whenever conditions might cool the pool. The controllers come with or without a clock to control your pool pump, too, but cost about $500 and require both 120V and 24V wiring and the temperature sensor wiring.

Warnings

  • Do not send concentrated chlorine through a solar heater. You should always introduce the chlorine after the heater.
  • Don't undertake plumbing, wiring, or roof work if you don't have the confidence, skills, and knowledge to do so safely. Get qualified help.
  • Although polymer solar panels are light weight when empty, they are heavy filled. Don't place them on the roof unattached so that a wind might blow them down.
  • Most communities will not allow anything to be installed on your roof without a plan and a permit. Local codes will determine what and how panels are fastened to the roof.

Related Articles

  • Install Solar Panels to Heat a Pool
  • Use Solar Energy to Heat a Pool
  • Appreciate the Benefits from Free Solar Energy
  • Create-an-Eco-Friendly-House
  • Install Wind Booster Throttle Controller
  • Create Your Own Swimming Pool Solar Heater

Sources and Citations

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