Using Solar Heat for the Pool

Many customers have asked us about solar heating for our therapy pools. Solar heating has some great advantages such as using a free energy source and requiring very low maintenance costs. However it tends to be much slower than electric or gas heaters, needs a lot of room to install, and is not the most effective or reliable heating method.

Solar panels come in different sizes such as 2×20’, 4×12’, or 4×20’ with prices per panel ranging from $100 to $500.00 or more. The sun generates about 300 BTU per square foot per hour. We have a great article here that goes into how much BTU you need to warm your therapy pool, but suffice to say for a smaller iPool or Fitmax Therapy Pool you would need at least roughly 18,000 BTU minimum per hour.

Unfortunately, solar panels do not run at 100% efficiency. The Solar Rating & Certification Corporation has a great listing of different solar panel efficiencies to give you a better idea of how well a solar panel runs on optimal conditions. Some companies claim their panels have a 75% efficiency in sunny weather. Generally speaking using a 50% collection efficiency is a good ballpark for estimation keeping in mind solar panels are only really viable in sunny open states such as Arizona, Texas, or Florida. Unfortunately at best you may only be able to add a few degrees to your pool even in the sunny states, solar heating is insufficient to heat up a therapy pool on its own.
If you had a 50% efficiency solar panel it would require at least 120 square feet of space or two 4×20’ sets to collect your needed 18,000 BTU per hour. This does not include the panel add on kits you would need to attach them all together as well. Unfortunately during mornings or cloudy days, solar panel efficiency drops to roughly 10-25% and is pretty much 0% at night.

Moreover, getting your pool up to 85 degrees Fahrenheit in the morning can’t happen due to surface temperature heat loss. Let’s take a typical morning scenario. For example, if it is 45 degrees outside with minimal wind and your pool was originally 85 degrees:

4 (btu/hour surface heat loss factor) x 40 (difference between pool temperature and outside air) x 70 (surface area of pool in ft squared)
= 11,200 BTU Drain / Hour

You will be losing 11,200 BTU per hour during a cloudy morning when you are only generating 4,500 BTU to begin with (the solar panel efficiency on a cloudy morning) basically this means your pool only gets colder instead of warmer. This is extremely inconvenient for many of our customers who want to enjoy a morning swim or an evening soak since the pool would not be warm during those time periods, and might only be available during noon on the weekends when it is already pretty warm to begin with.

The chart below shows that you need it to be roughly 70 degrees outside, all other things remaining equal, to really benefit from a solar heater. Once you drop below 70 degrees the heat loss is so significant that the heater cannot reliably warm the pool.

Although solar heating may be a useful option for kiddie pools they are only designed to heat swimming pools up eight to ten degrees in ideal conditions. A much better investment would be pool insulation that can reduce reheating time significantly, is a lot cheaper, and does not require as much upkeep and maintenance as solar panels. The iPool and Fitmax Therapy Pool are designed to be used year round and with the proper set up it is a pool that the whole family can enjoy.

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