# Thread: Solar system btu output huge!

1. ## Solar system btu output huge!

The past week the sun has been quite anemic, but the last 2 days have been phenomenal. The pool went from 64 to 72 yesterday and then from 71 to 79 today. Clear skies, 75 to 80 deg with minimal wind. Lows in the mid 50s at night solar cover on for all but about about 4hrs yesterday.

Panels are roof mounted facing about 10 deg east of due south...so by 530-6pm, the panels do not get much sun

So i geeked out and figured out the btu input and even forgetting any losses to the ground, radiation and evaporation I come up with 1 800 000btus imput EACH of the last 2 days

The pool is 27000 gallons. If my math is right, multiply that by weight of water (8.34lbs/gallon) equals 225000lbs....1btu raises temp of 1lb of water 1 deg F...so 225 000btu required to raise temp of pool 1deg multiply by 8 and ...1.8million but per day divided by 11 panels equals 167 700btu per panel per day
I have an easy touch and intelliflo. This spring I moved the vacuum breaker from the top corner of the panels to the lower corner (I have 1 more panel than recommended in series...) So I had to keep the pump at or above 2800rpm to keep the system from drawing air in from the vacuum breaker. With it moved, I can now run the system at about 2300rpm...which is about 800watts vs around 1700 at 2800rpm...and we have time of use electricity rates, so this can be significant.
Looking at the specs for the panels, they are rated for only 45 600btu/day... http://www.techno-solis.com/dimensions.html So I got more than 3.5 times the rated output...without accounting for any losses and the water table is high and that water is in the mid to high 40s right now.

So I'm happy...just surprised by the math. Did I miss something? Without looking up the certification criteria, I'm guessing they must factor in a wind speed and cloud cover...

2. ## Re: Solar system btu output huge!

8 Degrees in one day is due to both the panels and the pool surface in proportion to their area. So you have 528 sq-ft of panels but your pool is close to twice the size so about 1/3 is due to the panels. So at 27000 gallons, 8 degree rise is 1.8 MBTU and 1/3 is due to the panels or 0.6 MBTU. So that is about 1100 BTU/sq-ft of panel which is close to average.

3. ## Re: Solar system btu output huge!

Thanks mas985. The pool is 38x20 and clear of shadows 90% of the day this time of year. This is south western Ontario for reference. Anyway, just thought I would share my pleasure. I am considering a 200k but gas heater for night swims and when the sun doesn't play nice.

4. ## Re: Solar system btu output huge!

Ok so the panels should be about 40% of the heat or close to 1400 per sq-ft so pretty good.

5. ## Re: Solar system btu output huge!

So when the air and water temps are close and its sunny, one would get more solar gains to the pool with the cover on rather than off? I didn't think that much solar radiation would penetrate the cover, I know it prevents massive heat loss through evaporation, however.

Thx again

6. ## Re: Solar system btu output huge!

Depends on the cover and the wind but in some cases the gain can be higher with the cover on than off. The sun will heat the cover and then the cover in turn heats the pool via conduction and radiation. Also, some of the heat gets transmitted directly through the cover. There is some loss to the environment but given the cover has eliminated the evaporation loss, that can be better than the heat lost from the cover surface.

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