Anyone outthere with some reallife experience in active cooling of PV panels
to enhance energyproduction?
regards,
Zwerius Kriegsman
Holland
Hello Zwerius, all;
One year ago I had a 5 KW system installed (4.2 KW STC). I noted that
the panel specs indicated that there is a .5% per degree C loss. Under
full insolation (Nothern California), the temperature rise on my
panels is 25 to 35 C (roof mounted, 6" space on underside). Spraying
the panels with a garden hose (at mid day) produced the expected ~10%
increase in power output - for about 10 mnutes until the panels warmed
back up.
It appeared to me that it might be possible to squeeze another 10% out
of my system without too much trouble. At ~$7 per watt installed, this
indicated that an expenditure of up to ~$3000 (.1 x 4200 x $7) might
be justified.
Continously flooding or spraying the panels is not an option for me.
Water use would be excessive and my water rates are too high to make
this viable.
My first inclination was to utilize evaporative cooling - spraying a
fine water mist (fog) into the space behind the panels. My
calculations indicated that the evaporation of approximately 50
gallons of water per day would be adequate to reduce the panel
temperatures by ~15 to 20 C. The objective was to have the applied
water fog evaporate completely and avoid the maintaince complications
of wet surfaces. The costs would be: the water cost, the equipment
(fog nozzles, distribution plumbing, and high pressure pump), power to
run the pump, and installation. The total system would cost
approximately $700.
I performed a "proof of concept" test using a group of 6 panels (~ 6
square meters) and quickly found that it DID NOT work as expected.
There was simply not enough air exchange on the backside of the panels
to allow the water mist to completely evaporate. The air quickly
became saturated and the fog simply deposited on the backside of the
panels. The cooling effect was minimal, a few degrees at most.
Once I recognized my oversight, a quick calculation indicated that I
needed an air flow velocity of ~20 miles per hour on the back side of
the panels to provide enough air for the water mist to evaporate. And
this is in California where the relative humidity is relativley low.
The required air flow would be much greater in more humid locations.
Since the fog nozzles and instrumentation were already in place, I
installed a number of fans along the edge of the test array to
provide the necessary air flow. The cooling effect did increase, but
not by as much as desired, a total temperature drop of only 4 to 5
degrees C was achieved. A calculation of the power required for the
fans indicated that the majority, if not all the "extra" power from
the panels would be consumed by the fans. Just the fans alone helped
reduce the panel temperatures - but not enough to satisify their own
power usage.
Bottom line is that you can increase the power harvested from your
solar panels by active cooling, but it is unlikely to be economical
(solar power itself has questionable economics).
If you have access to large quantities of cool, clean water (and don't
have to pump it very far) and can continously spray the panels, then
you might get a small net increase in power.
All in all, an interesting learning experience but not part of a
solution to global warming
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I would think that the best cooling would be to have some way to circulate water
against the back of the panel. Since lower water temps would improve
performance, the best use I can think of for the resulting warmed water would be
for a hot water preheater and heating a hottub or a pool. Might as well use the
captured heat for something useful, but heating water enough to replace a water
heater might be too hot to increase the PV performance.
