My solar water heater is an over achiever on clear sunny days. The fact is, I only need a couple hours of sun to heat the water I use in a day. So, when the days are long and the sky is clear or partly cloudy, I get 80 gallons of water at 160 degrees or higher. I can easily go 3 days with no sun. Unfortunately, having super heated water in my house when I’m trying to keep it cool inside, is not really a good thing. Even with heavily insulated tanks, the hotter the water, the faster the heat escapes.
Well, I got the idea to make a cover for the heating panel to keep the sun from heating it so efficiently. I figured I would have to uncover the panel for a couple hours to heat my water, but it turns out that the panel still keeps my main storage tank (40 gallons) above 130 degrees; as long as the sun is shining. I don’t use as much hot water in the summer, but it still amazes me that I have excess hot water, even when I’ve shielded the collector plates from the sun.
The good news is that the water isn’t getting nearly as hot, the circulation pump doesn’t run as much, and I don’t have to take the cover off to heat my water. I’m in my 3rd year, using only solar for my hot water. So far, it’s working out great. It hasn’t paid for itself, yet, but I’ve saved roughly $20/month for the past 27 months. Since I paid for the system out of pocket. Every month with free hot water feels like profit. However, it will be about 5 more years before the system has paid for itself.