Do Working Solar Panels Run Hotter or Cooler than Disconnected Ones ?

[Stinsy]

Conservation of energy, init?

The conversion is light into electricity. A byproduct of which is heat.

[Oliver90owner]

I doubt there would be any discernible difference. Energy striking the disconnected panel will reflect back into the atmosphere, more than the one connected. Reflected radiation does not heat the panel. There will be some heat generated in the connected panel due to resistance.

That makes me think that the ambient conditions will affect the panel temperature more than its electrical conversion properties.

How one measures the temperature is also questionable. An IR gun may well provide erroneous results as the recorded temperature may be influenced by the less IR reflection. Contact thermometers may be affected by the incoming insolation, so likely the panels need covering entirely on the rear side and the temperature measured at the back of the panel by some form of contact thermometer.

[nowty]

Excellent, now we have all three possible answers guessed, so at least one of you is correct.

To wet your appetites, here was the test setup. I did two test setups and took readings with an IR thermometer many times in heavy cloud, in bright but cloudy and in full sun conditions. I tested individual cells close up and general temp further away.

I do take the comment by Oliver90owner about using an IR thermometer seriously but I also did measure the temp from the undersides (i.e. the backsheet) and got the same result.

I will say that the answer to my original question re-copied below, was very consistent and clear cut.

So, in full sun, with identical panels and same orientation, what do you think the answer will be ?

1) Both panels are the same temperature,
2) The disconnected one with no current flow is cooler.
3) The disconnected one with no current flow is hotter.


The first test was using 3 identical Suntech panels, same age and had very similar irradiation during their lifetimes. The two panels on the left are connected and generating. The single panel on the right is disconnected. They have all been on the decking area since early morning.



In full sun the two 250w Suntechs were pushing over 7 amps.



In a second experiment I tested two side by side identical 335w Panasonic panels with higher efficiency. Here I did not disconnect either of the panels but placed a decking board across the one on the right to pretty much shut down any meaningful current flow. All the connected panels are connected via TIGOs so the forced shading did not affect the operation of the unshaded panel.

[Joeboy]

Have you used threaded rod for the stands to angle the panels?

[Stig]

Conservation of energy, init?

The conversion is light into electricity. A byproduct of which is heat.

Yep, and the energy that isn't converted into electricity (when it's disconnected) has what by-product?

[Tinbum]

Energy in has to equal energy out, conservation of energy.

(In) Sun =
(out) heat + electric

No electric therefore heat is more. (approx 20% more but as the panel heats up to a higher temp it looses more to the surroundings so it won't measure 20% more but will be more than a panel supplying electric ).

[nowty]

Have you used threaded rod for the stands to angle the panels?

I used 10mm x 200mm stainless steel coach bolts with 2 x stainless steel nuts and oversized washers at the panel end. I will try and remember where I bought them from as I guess your thinking of your winter decking panel string.

[spread-tee]

I think No3 as well but only just too. Incoming light will have photons of various wavelengths, the panel will select only the short wave ones to knock out an electron from the crystal lattice which will use a bit of energy over and above the amount of leccy enregy generated,

Now I'm confused............

speer rad

[Joeboy]

Have you used threaded rod for the stands to angle the panels?

I used 10mm x 200mm stainless steel coach bolts with 2 x stainless steel nuts and oversized washers at the panel end. I will try and remember where I bought them from as I guess your thinking of your winter decking panel string.

Low impact domed end, nice!

[AE-NMidlands]

How one measures the temperature is also questionable. An IR gun may well provide erroneous results as the recorded temperature may be influenced by the less IR reflection. Contact thermometers may be affected by the incoming insolation, so likely the panels need covering entirely on the rear side and the temperature measured at the back of the panel by some form of contact thermometer.

Very good point. I used to do this in a lab, and in working environments, and it is a job for a professional by itself! If you want to measure air temperature you need to screen your sensor from solar or other radiant gain (by a reflective ""tin"-foil sleeve) and if you want surface temperature you need to look at exactly what your sensor is seeing and how it works, and whether it is actually seeing the surface or looking at the radiant heat source warming it up!
A