Ecosaver 20 panel from Amazon. 20'x2.5' 50 square feet. $140 + ship. I bought one of these knowing I'd need more than one, just to try it out and see what it would do. I posted about this before I bought it and heard I may need 2 or 3. I'm finding out with some measurements and math I'd actually need around 6 for my almost completely shaded pool. (It says on the box one is good for an up to 24' aboveground LOL)
I've seen recomendations that one should have 50-100% their pool square footage as solar. 6 panels would be just over 100% for me, complete shade will do that to a pool I guess.
Got this setup last thursday, yesterday a week later was the 1st day of real sun we had.
The construction of it is 22 ~3/8" tubes flowing water 20 feet one direction and 22 more tubes flowing it back the other direction tubes have plastic between them holding them in groups of 11. 880 feet of tube in all.
I am running it with a real weak (dedicated to solar) pump and small restrictive 3/4" 30 foot long hoses to get it where the sun is. I know high flow, low temp-delta is what you really want to shoot for but keep reading.
Here's how I arrived at my 6 panels-needed #:
Pool water was 76, water coming back into pool from panel in full-sun was 82 so it was adding 6 degrees.
82f water coming out of panel return hose filled a gallon jug in 15 seconds so 4gpm, 240gph, 1920 pounds per hour.
If a btu is 1 degree f added to 1 pound of water, adding 6 degrees to 1920 pounds over an hour is 11520 btu/hr
Pool is 7000 gallons, 56000 pounds.
11520 / 56000 = 0.205 11520 btu/hr will heat 56000 pounds of water by .2f every hour.
Doing some googling for "solar btu square foot" has lead me to a few sites saying that the max solar radiation you could ever pick up with some theoretical 100% efficient god-panel that's never been made is 320 btu/hr per square foot. 50 square feet = 16000 btu/hr on a "perfect panel" which is perfectly positioned + perfect flow. I got 11520, 72% of that perfect # using cheap panel, weak pump, small hoses and having it lay flat on the ground. 72% of perfect is pretty good I'd say. If it were the perfect panel, 16000 btu/hr would heat the pool by .285f every hour instead of .205 and I could do it with 5 of them instead of 6.
Now I wonder how much of my 28%-less-than-perfect comes from the cheap panel and how much comes from the low flow.
I want to be able to heat whole pool by up to 10 degrees any given day. If I had 6 panels it would heat by 1.2F every hour giving me the 10 (well 9.6) degree temp change over 8 hours I'm looking for. I don't have the room for that or the $700 for 5 more when I see used gas heaters selling for $300 sometimes less on CL.
I also can't see 6 of these panels at a cost of $840 lasting long enough to pay for themselves vs. paying for gas. A proper solar heating system yes. (and we want the 16'x32' intex next year would need about 12 of these panels for that)
2 or 3 of these panels I still think may be good for people with wamer pools already in the sun needing a bit of a boost.
So, I'm going to be watching craigslist for cheap gas heaters for next year, I did the math on that and a 100kbtu one should heat up this pool 10 degrees in about 6 hours. To feed it, the .6mbtu gas for one 6 hour run is about [s:tnzjghjh]$2.25[/s:tnzjghjh] $4. (and we won't have to rely on the sun being out.)