solar cover on/off for best heating?

[steveinaz]

I can give you a direct example: With my cover left on during day/night I get about 2.5 degrees a day (10,000 gal IG). With the cover on only at night and off during the day, I get about 1-1.5 degree increase. Keep in mind I'm in a very sunny, very dry climate. So, yes, leaving the cover on will get you higher temps--at least in my experience, at my location.

Lately, due to cool evenings, I can't seem to break the 82 degree barrier. Our daytime temps have been 88-92 degrees, with nights around 58-65 degrees. I usually loose about 1-1.5 degrees at night, even with the cover on, at the cooler temps. But the pool recovers quickly and by 1:00pm, it'll be back at where it was the day previous.

Like it or not, evaporation is everything; you loose 70% of your heat through evaporation. I think this is why even on a sunny/hot day you'll probably gain more heat with the cover on.