High Solar Panel Temperature Effects

Jakachira

This is a very technical question but I hope I will get much help here.

Recently, on two very hot days, my solar panels behaved very strangely. But now that I have done research I kind of like know what happened during those days.

My Steca Controller charged my battery up until a voltage of 15.0V (I think it was an equalization stage). Just when it reached that mark, the controller showed a dramatic decrease of current going into the battery (0.1A) and stayed there. The voltage at that stage was now showing the Open Circuit Voltage (19.6V) and the Solar Panel Current was now showing the Short Circuit Current, meaning nothing was being produced. This was at midday. My understanding is the current should slowly decrease as the controller turns to floating charge. The battery was not yet full. Since then I have realized that it should be the TEMPERATURE of the solar panels that is causing a big voltage drop and the panels cannot meet the equalization charge voltage which is around 15.5V. My panels’ voltage at Max. Power at 25degrees C is 16.9V and the Open-Circuit Voltage is 21.9V. I showered the panels with a bucket of water and they started charging again but after an hour they stopped. I switched on my loads and it started to charge again. Heat seems to be ungrateful animal when it comes to the max. power voltage of the solar panels.

The temp co-efficient shown are for Open-Circuit Voltage and Short-Circuit Current. Does high temperature affects these or the maximum voltage and current values? I’m trying to figure out if my panels are the one to blame under these conditions or my wiring. I have a 12 Gauge (4mm^2) cable that runs 6 metres (+ and – total distance). Maximum current for the panels is 10A. I have a broken solar panel but it still performs very well, I even disconnected it to see if it was the culprit but no. It’s still giving the maximum voltage as require but at very less current. When I use one small 50Watts panel the controller began to put some charge into the battery merely because the battery voltage might have decreased as the other two panels were now off. I was contemplating replacing the controller thinking it might be the problem but I do not think so.

How can I limit the temperature of the panels to pass through an equalization stage?

Ralph Day

Re: High Solar Panel Temperature Effects

Was this a first attempt to eq charge? If so, what is the time setpoint for eq duration? |Maybe the voltage setpoint is reached, but there is a zero time duration as default and you need to change that?

Ralph

Jakachira

Re: High Solar Panel Temperature Effects

Ralph Day wrote: »

Was this a first attempt to eq charge? If so, what is the time setpoint for eq duration? |Maybe the voltage setpoint is reached, but there is a zero time duration as default and you need to change that?

Ralph

It was the first attempt. The time set is 2 hours.. and the maximum voltage for that can be reached during equalization is 14.8V as stated in the manual but i saw it kicking to 15.0V probably attempting to reach 15.5V for equalization. Somehow it looks like the panels voltage can't reach that point when it's too hot outside.

The Steca PR3030 Controller have factory settings, cannot change them.

BB.

Re: High Solar Panel Temperature Effects

Not quite sure I understand the 19 volts Voc... That is still OK but a bit low.

In the end, equalization may only be able to be performed on a cooler day. Very hot panels (hot day, full sun, no breeze) can reduced the Vmp of the panels significantly. However, I am not sure it would do it down to 0.1 amps.

What is the battery bank Amp*Hour capacity? And what type (Flooded Cell, AGM, etc.?). Does the battery "bubble" a lot while equalizing? Have you measured the specific gravity of each cell (if not a sealed battery)?

-Bill

mike95490

Re: High Solar Panel Temperature Effects

Avoid that bucket of cold water on hot panels. Unless you like tempting fate to break the glass from thermal shock.

And, while the PV voltage droops as the panels heat up, it should be gradual. A sudden decrease could mean a bad panel. Treat them carefully, rinse off in the morning before they get hot, and give them a good inspection, look for discolored areas on the cells or backsheet.

SolaRevolution

Re: High Solar Panel Temperature Effects

You said your array was getting hot. Are your charge controller and battery subjected to the high tempuratures too?
The Steca 3030 has built in temperature correction and overtempurature protection.

Here is a theory:
It starts charging in the morning when it is not too hot and the battery voltage rises to the highest setpoint (15 v). Around mid-day the ambient tempurature at your charge controller increases and the controller "corrects" the charging voltage by lowering it below the actual battery voltage. It would be proper operation for the charge controller to open the PV circuit to prevent overcharging the hot battery.

To fix the situation you should put the battery and charge controller where it is protected from the high temps. As with most small charge controllers the Steca 3030 does not have a remote temp sensor so it "corrects" bassed on the ambient temp of the controller, not the battery.

Also; it is not good to EQ your batteries when they are already hot. High heat is very stressful for them.