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Solar panel cooling

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Benihanas

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Feb 20, 2021
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Would it be absurd to add some heavy duty waterproof 12v fans to cool underneath my panels on the roof in the summer ? I’d love feedback on if this is dumb or might actually do me some good. South Florida is getting to record temps and my panels I’m sure are super hot
 
Interesting concept. Probably not. If you don't pay for water usage, you could spray the backsides of the panels with water to cool them down.
 
Benihanas said:
Would it be absurd to add some heavy duty waterproof 12v fans to cool underneath my panels on the roof in the summer ? I’d love feedback on if this is dumb or might actually do me some good. South Florida is getting to record temps and my panels I’m sure are super hot
Click to expand...

Yes.

Fans use power. Fans always use more power than they output. Let's say you used a 20W fan to cool your panel. Pretty much impossible that you'd get enough cooling from it to generate 20W let alone an additional amount beyond the 20W to run the fan.

Panels are designed to run at 40-50°C. Check the NOCT or NMOT rating on your panels. If they're performing at that level, and they have sufficient clearance to radiate to the ambient air, not much you can do to improve things besides hosing them down with water every 5 minutes.
 
I wonder about having a pumped water tank on the back of the solar panel. This water would cool the panel and give you warm water.
 
sunshine_eggo said:
Fans use power. Fans always use more power than they output. Let's say you used a 20W fan to cool your panel. Pretty much impossible that you'd get enough cooling from it to generate 20W let alone an additional amount beyond the 20W to run the fan.
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I don't think we can apply the thermodynamics "no free lunch" answer to this situation. If a panel is very hot, it's quite possible that a 20W fan could remove far more than 20 watts of heat from the back of it. Forced convective flow across a hot surface can greatly improve heat transfer

The electric fans blowing through a car's "radiator" (really, "heat exchanger") remove heat at the rate of thousands of watts, but the fans typically use about 800 watts (about 1 HP).

The important question is whether removing the heat from the PV panel will improve its performance enough to make up for the 20 watts used by the fan. I don't know the answer to that, but we can see that folks aren't normally doing it, so that's one indication that its not worth it.

Now, we can cheat and install a tiny PV panel to power the fan. In that case there's no doubt that we'll improve the performance of the previously existing PV panels, but we also installed more PV capacity.

Mark
 
Could always use those heat powered fans like they use on wood stoves. Use the heat of the sun to drive it.?
 
xsilvergs said:
I wonder about having a pumped water tank on the back of the solar panel. This water would cool the panel and give you warm water.
Click to expand...

There are solar panels with this already built onto them I believe.
 
Vigilant24 said:
Now, we can cheat and install a tiny PV panel to power the fan. In that case there's no doubt that we'll improve the performance of the previously existing PV panels, but we also installed more PV capacity.

Mark
Click to expand...
But what's the payback time!?
 
Johneb said:
Could always use those heat powered fans like they use on wood stoves. Use the heat of the sun to drive it.?
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They need way more heat than the sun could provide ? i have one and it barely runs on an electric oil filled heater in my shed and that's so hot you cant touch it, wood stoves get very hot !
I do have a large collection of aluminum CPU coolers, i had thought about gluing them on the frame of a panel to see if it made a differance ?
 
dirt diggler said:
They need way more heat than the sun could provide ? i have one and it barely runs on an electric oil filled heater in my shed and that's so hot you cant touch it, wood stoves get very hot !
I do have a large collection of aluminum CPU coolers, i had thought about gluing them on the frame of a panel to see if it made a differance ?
Click to expand...

You're thinking too small, we think big around here!!

Full-capacity-test-a-success-for-concentrated-solar-power-plant-in-China.jpg
 
You're right. I shouldn't have approached from the thermodynamics angle. I should have approached it from the efficiency angle...

For every 1000W/m^2 hitting the panel, 800W of it is going into heating it with only 200W of it going to production. To keep panel AT ambient, you need to shed ~800W/m^2 of energy INTO ambient with your fan.
 
Measure the temp on the backside of the panel at midday without a fan, then put some random fan up there to blow air behind the panels for half an hour and see if the temp changes. If it does you can use the temp coefficient to estimate the effect on power output. An interesting and fun experiment, at least until you fall off the roof.
 
What if we increase the angle of the panel, and put giant heatsinks on the back of it, and let the hot air rise naturally. Surely that will solve this dilemma!
 
dirt diggler said:
Pump or fan it still takes power to run? a pump more so but at least youd get hot water ?
Click to expand...
You wouldn't need a pump with a thermosyphon setup. The heated water in the pipes rises to the top due to differential density. It automatically stops at the end of the day when the temperature of the tank water is higher than the temperature in the heated tubes.

In anyplace where temps get below freezing during the year, a fan moving air is going to be a lot more reliable and less trouble. Better to keep the solar hot water system as its own project unless you just don't have any more sunny real estate for collectors.
 
Doggydogworld said:
Measure the temp on the backside of the panel at midday without a fan, then put some random fan up there to blow air behind the panels for half an hour and see if the temp changes. If it does you can use the temp coefficient to estimate the effect on power output. An interesting and fun experiment, at least until you fall off the roof.
Click to expand...
Or, just monitor the output of the panel directly with and without the fan. It's simple then to know if the watt bill for the fan is worthwhile, at least under that set of conditions (outside temp, etc).
 
Vigilant24 said:
Or, just monitor the output of the panel directly with and without the fan. It's simple then to know if the watt bill for the fan is worthwhile, at least under that set of conditions (outside temp, etc).
Click to expand...
Should really use two panels, one with fan and without. We want the data to be as accurate as possible.
 
You could experiment with potential power gain using a garden hose. Assuming you have the ability to monitor your system closely note the volts and amps before you cool them off with hose then note them again. Pick a cloudless day of course.

Logically water will cool them off better than a fan so keep that in mind when making a decision about how far down the fan idea road you'd want to go.
 
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Here's an interesting article that may be of interest.
Enhancing the performance of photovoltaic panels by water cooling



I just became interested in the possibility when I recently noticed my solar output was about 55% of what the best output was last summer on a clear sunny day.

That may not seem like much but the recent conditions were deplorable. The solar angle was very low. The sun was partially blocked by trees and it was a hazy day at best but it was cold out (arounf 38 F).
I was surprised to see any output at all let alone 55 % of best case recorded to date.
I intend to try an experiment this coming summer.
I already have a custom made ground water based air conditioning system. The ground water is about 53 F direct from the ground. The discharge water is around 62 F.

I intend to try a simple lawn sprinkler on the roof fed by my discharge water. No additional pump should be needed so this setup should cost me nothing more than I’m already paying for AC.

If I’m still alive, I’ll report my findings on this forum.
 
I haven't watched one of Wills videos since he damn near killed himself by running a drill bit through a lithium battery.
I hope he wasn't following your advice.
 
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Spraying water isn't feasible all day long and is a scarce resource.

Adding cooling via fans, heat sink or water exchangers are orders of magnitude more cost than the panels themselves.

In all cases, just adding panels to compensate for climate effects on net energy generation is the lowest cost and most long term reliable option.
 
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