Solar Heater 270,000 BTU

Insolation Data:


Right now for your location, incident energy is around 2200 BTU/sq-ft/day on average, depending on the angle of the panels. For 480sq-ft panel area, that is about 1M BTU/day but panel efficiency is not included. If one assumes 60% panel efficiency, that drops to 600k BTU/day or about 3F per day.

I have a full heat transfer model that can be used to more accurately estimate both heat gain and heat loss. I started the model here:


The model assumes multiple days at the input weather conditions and explicitly calculates the heat loss of the panels and pool so the multi-day heat rise with vs without solar is about 8F but that is without a cover. A cover on top of solar increases the temperature by 13F over just solar alone. The cover makes a huge difference but can be difficult to deal with.

There are a lot of input variables that can affect the heat gain and loss so your results may vary.

Hypoxic said:

Thanks for the great info! I followed the most of the suggestions from here Solar Pool Heaters - Further Reading when I designed and built my heater. I have Aquatherm Ecosun panels that are advertised at 93% efficiency.

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Manufacture's published efficiency numbers are under specific operating conditions (water temp, air temp, sky temp, etc) which are almost never typical. The efficiency numbers in the model are calculated for the actual conditions specified in the model so tend to be more accurate than the manufacture numbers.

Hypoxic said:

I’m at 43 degrees north with my panels mounted at 30 degrees. I was able to get a 5 degree rise in pool temperature from 10C to 15C that day. I didn’t have the solar cover on since I was cleaning the pool.

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The lower the water temperature, the higher the temperature gain and the higher the efficiency. If I put in 50F as a starting morning temperature into the model, by the end of the day it is over 59F (@ 89% efficiency) which is pretty close to what you are measuring. Also, keep in mind that some of that heat gain is due to the direct solar gain into the pool and has nothing to do with the panels.

Hypoxic said:

Thanks for the great info! I followed the most of the suggestions from here Solar Pool Heaters - Further Reading when I designed and built my heater. I have Aquatherm Ecosun panels that are advertised at 93% efficiency. I’m at 43 degrees north with my panels mounted at 30 degrees. I was able to get a 5 degree rise in pool temperature from 10C to 15C that day. I didn’t have the solar cover on since I was cleaning the pool.

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Average heat increase with a properly sized (80% coverage) system is 5-7 degrees per day. Average heat loss is 3-5 degrees at night. Both without a cover. It hasn't changed in the 34 years I have in the pool industry. Regardless of all the calculations, if you expect anything different you may well be disappointed. I've seen it, but it is extremely rare.

Hypoxic said:

I asked Chat GPT to calculate the btu’s required to heat the water from 12C(54F) to 18C(64F) at 50gpm. It came up with 270,000 btu per hour. I’ve got ten 4x12 panels.

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Assuming a 10 degree F temp rise from inlet to outlet at 50 gpm, the heat power is 50 x 60 x 8.34 x 10 = 250,200 btu/hr.