Do you cool your solar panels to get more power?

[noelex 77]

The solar panel manufacturers all provide a wealth of information on their panels' performance.

From the temperature characteristics you can work out the magnitude of improvement that would be produced.

If you produce a 10°C reduction in cell temperature (approx an 18°F at the temperatures we are considering) with say liquid cooling, which I think would be achievable if you crunch the numbers, you come up with about a 3-5% gain.

You have to consider the draw of the pump. Typically this might be 1A or so for a small pump. The solar array would therefore have to be producing around 25A to break even.

From these numbers, I cannot see a way to significantly improve solar panel efficiency with liquid cooling, at least not without a passive system that would circulate the water with little or no energy. Even then, the gains are small for the complication involved. I would love to be proved wrong, as more solar output would be great.

The goal of producing "free" hot water where the gain in solar panel production runs a pump which creates warm water for showering, is a more realistic one. Even if there was a net loss of power, the warm water would be helpful.

Note: leaving an air gap for passive air cooling is important. This of costs no power and without this there is a danger the Vmp can drop below the battery voltage in some circumstances with 12v panels. If this happens the power output will drop dramatically.

[SimonV]

NO.

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[El Pinguino]

Originally Posted by SimonV

NO.

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OH.....

My tank water is typically warmer than the air temp so I think I will just live with what I have...

[noelex 77]

Originally Posted by El Pinguino

OH.....

My tank water is typically warmer than the air temp so I think I will just live with what I have...

Solar cell temperatures are significantly higher than air temperatures on a sunny day. 45°C on a 25° C day is typical. 45° C is too hot for shower water without mixing in cold.

Domestic solar hot water units that serve a houshold are only the size of couple of our panels. The solar hot water units are optimised to heat water but our boats use much less hot water than a house and even a significantly less efficient system would give us a lot of hot water.

I think pumping water under the solar panels in tubes it would produce enough shower temperature water in summer. Even in winter, in a moderate climate, I think it would reduce the engine run time required to heat the water. Whether it is worth the trouble and complication is another matter.

[GrahamHO]

I always have my solar controllers rated much higher (double for me) than the panels they control as I believe the panels rating is a nominal figure which must vary according to daytime conditions. The panel wattage output must also vary according to the state of the battery it is charging. I guess you are measuring the controlled output i.e. after the controller. The voltage before the controller can easily be double the battery voltage. As the panels are designed to be used with controllers, I suggest their nominal wattage is what you should expect in average conditions downstream from the controller. Definitely have an air cooling gap underneath them. Maybe the color of the deck under the panel makes some difference too. Walk barefoot on a dark deck and you can burn your feet. Pick up a spanner that's been lying in the summer sun and you can burn your hand.

[Wanderlust]

Originally Posted by noelex 77

You have to consider the draw of the pump. Typically this might be 1A or so for a small pump. The solar array would therefore have to be producing around 25A to break even.

Not necessarily. If the pump cycled on to just wet the panels, it could then cycle off and evaporation would continue to cool the panels. So maybe the pump could run for say, 5 seconds once or twice a minute.

Nevertheless,that further complicates the system and it seems hardly worth the benefit.

[irwin37]

Hot water loop or collector under the panel is not new, we tried it years ago when I worked for Solarex. The problem you run into is too much heat. What happens when your hot water tank is at 180 Deg and you can no longer shed heat from the back of the panel or and other part of the system. You have now limited the radiation of heat from the back as you have tubing and possibly collector plates on the back. You dont dare stop the pump as the temperature of the cell and the water in the tubes behind will spike causing the water to possibly reach boiling and create steam. Things could get nasty after that. By the way the cells are almost transparent to inferred light, so heating the water would not be a problem.

Here,s another tid bit, those Blue and Black cells, they are not really Blue or Black, they are silver with an anti reflective coating (Titanium Dioxide). The thickness of the coating causes the light to refract like a Prism, blues and dark blues (black) are bent outwards while the Greens/Yellows/Reds bent towards the cell surface.

We made cell of any color you wanted by changing the thickness of the coating.

[mstrebe]

If you want an inherent solution you could attach aluminum water blocks to the underside of the panels and then run a copper tubing loop to any shaded location on the boat that is higher than your panels, perhaps up the mast a few feet. Copper tubing will lose plenty of heat in contact with the side of an aluminum mast, just go up with a straight run and down with curves like a still.

Fill the system with an 3M novec 7000, a heat transfer fluid with a boiling point of 34F. That will boil off the bottom of the panels in the water blocks and rise as vapor to your cooling block/tubes on the mast, then drain back down to the panels as fluid. No pumping needed, no moving parts, no maintenance. Won't even corrode. You're exploiting the heat of the system to perform the fluid transfer and you are fixing the cooling temp at 34F. Plus it's non-toxic and not a greenhouse gas.

The only problem is that if the entire system goes over 93F/34C, it'll pop somewhere and vent your novec, which costs about $50/gallon.


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[senormechanico]

How much gain are we talking about here? Not much it seems.
Better just to add a panel and let 'em get hot.

[mstrebe]

About 25 additional watts on a 500 watt system. So yeah, almost certainly not worth bothering with.


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[s/v Beth]

This thread has been interesting, but the brick wall every one is hitting is that of complexity and cost. Hot water? Easier to just hoist a black water bag. The threat of frying expensive equipment should the cooling system go down is a real one.
One advantage of having water cooling over your cabin is that it would be a lot cooler inside during the summer.
I think I might try it on my next house though...

[GrahamHO]

Extending mstrebe's idea further. You could turn it into an illegal whisky still. Then you wouldn't need the hassle of going sailing.

[MarkJ]

Originally Posted by hamburking

You could keep the panels cooler by putting them in the shade.

ROTFLMAO

Indeed!

Interestingly enough you and the OP are right. Cooler panels produce MUCH more.

I have just come up from the Caribbean to New York and the difference is startling and confusing. In the tropics it's often cloudy around the islands where we anchor but still hot. In NY it's cooler but when the sun is out it really zaps.

I doubt pumping water.on them would be economical but it's interesting to see the difference.

Also.longer sunlight hours in the higher latitudes.. and the wind here isn't easterly so panel orientation is different.

All this stuff does affect your daily amps in.

[mstrebe]

Originally Posted by GrahamHO

Extending mstrebe's idea further. You could turn it into an illegal whisky still. Then you wouldn't need the hassle of going sailing.

Pour beer in, get barley whiskey out. I like it!

[SimonV]

Do you think, if cooling your solar panels made a noticeable difference the manufacturer would be pushing it .

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