pv panel/roof cooling?

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christian09
christian09 Registered Users Posts: 22 ✭
in Solar Beginners Corner #1
I have been investigating many ways to cool solar panels, and at the same time cool my roof. I figured this would decrease cooling costs, increase array output by 5-10%, and extend the life of the panels and the roof. I live in Florida, usa, and we use a/c 6 months of the year, and the bills can be high. I have an array that greatly suffers from the Florida heat. I have been looking into using micro irrigation sprayers on the back surface of the solar panels, the water would then stream off onto the roof, thus cooling the roof and panels. I have run tests and know the roof misting gives me a net gain in savings, as I save about $30/mo. in cooling and only use $7 in water.
Couple of questions:
1. Is it ok to mist the back of these panels? It seems like it would be ok, since we get torrential rains that splatter water on the backs of all the outer perimeter panels.

2. If it is ok, since my panels are angled, should I just spray say the top half of each panel, and let the water flow down the rest of the panel?

Thank you.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #2
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    Re: pv panel/roof cooling?

    I would not do it... Panels and jboxes are difficult to seal anyway--Adding water only makes things worse.

    You have the losses from water pumping and issues with mineral deposits/corrosion too.

    Are you going to recycle water, dump it to a garden? Do you have "unlimited" water available? Will you have problems with moss/mold on the constantly wet roof/panels?

    All told, I would just add "10%" more panels and scrap the whole water cooling idea.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
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    Re: pv panel/roof cooling?

    In case you're wondering, people have in fact tried this. Net result has always been the same: more trouble than it's worth.

    The power required to pump the water up to the roof and spray the panels will exceed the amount gained by the slightly cooler panels. Spraying the back of the panels will not effectively cool them because it is the front that gets hot and there's quite a thermal difference between the two (as well as conductivity difference in the materials). The water will attract dirt to the panels. The water may 'lens' and focus sun on spots causing greater insolation and increased current in those spots.
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  • christian09
    christian09 Registered Users Posts: 22 ✭
    #4
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    Re: pv panel/roof cooling?
    BB. wrote: »
    I would not do it... Panels and jboxes are difficult to seal anyway--Adding water only makes things worse.

    You have the losses from water pumping and issues with mineral deposits/corrosion too.

    Are you going to recycle water, dump it to a garden? Do you have "unlimited" water available? Will you have problems with moss/mold on the constantly wet roof/panels?

    All told, I would just add "10%" more panels and scrap the whole water cooling idea.

    -Bill
    Thanks Bill. I will not spray the backs...What do you think about "watering the roof" every half hour or so, to reduce cooling loads on my house....I have tried this, and roof temp has gone from 150+ to the 90's for up to 1/2 hour. Since here in FL we use a lot of A/c, I am thinking this may help significantly. I have found that running water on the shingles under the panels(not touching the panels) also decreases the panel temp significantly from 150sh to 110/120...I have an unlimited supply of water (well) If I use a pump, it will cost me around 5$/mo. If I use city water, it will cost around 7$/mo. and I just use the incoming pressure. What do you think about this?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
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    Re: pv panel/roof cooling?

    Cover the roof with solar panels. Cools the roof, increases the PV production. No joke.
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  • smatthew
    smatthew Registered Users Posts: 15 ✭
    #6
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    Re: pv panel/roof cooling?

    Spraying florida well water on a roof would quickly lead to mineral buildup, unless you sprayed enough continually so that the run-off was able to carry away the minerals. Otherwise, every time that water evaporated, it would carry away heat, but leave behind some nice white crystals.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #7
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    Re: pv panel/roof cooling?

    here is a company that provides PV-T Hybrid Collectors.

    http://www.solimpeks.com/pv-t-hybrid-collectors/
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
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    Re: pv panel/roof cooling?

    You know what the basic problem there is? For hot water you want the panels up over 140F. For good PV you want the panels at about half that temp. So ... compromise is required. Whether it's worth the money is up to you.
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