question

taddy avatar image
taddy asked

Open circuit voltage seems to have dropped on PV string

Hi all. I have 2 strings of 4 canadian solar panels. I haven't yet connected them up to the inverter/batteries etc as still waiting on the solar electrician. However, when I first installed the panels in Feb I did a open voltage check at the combiner box and it was reading about 190+V for each string of 4. I checked this a couple of months ago after heavy winds and was still around this mark. However now it is down to 180V which is only 45V VOC per panel. Supposed to be 49V VOC per panel according to candian solar datasheet. The one thing I have changed is that I have put all the solar cables into a single 25mm flexible conduit from panels to the combiner box whereas previously they were separate. Also the weather is hotter atm but I am getting the same readings in morning and evening when it is cooler. Any ideas? Could I have damaged the panels by having them up there but not connected up for 5 months?

Cheers

Tom

Solar Panelvoltagevoltage drop
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

3 Answers
pwfarnell avatar image
pwfarnell answered ·

The higher the temperature, the lower the Voc. The panels datasheet will tell you what the temperature coefficient is. The temperature is not the air temperature but the temperature of the solar panel. This is set more by the solar irradiation rather then the air temperature. Voc can fall by 0.3%/degC, you have dropped about 8% so 27degC warmer then the datasheet rated temperature seems to fit. This is your most likely explanation assuming that you are now coming into northern hemisphere summer.

1 comment
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

taddy avatar image taddy commented ·
Thank you. I've re-checked the datasheet and actually there are two tables - one showing Voc for at Standard Test Conditions (irradiance of 1000W/m2, cell temp 25C) which was the 49V and a second table giving a Voc at nominal module operating temperature (NMOT) with 800W/m2 irradiance and ambient temp 25C and this is 46V which is much closer to what I have now. Strange that I got a higher reading when I first tested the panels though. Maybe I'm remembering incorrectly
0 Likes 0 ·
seb71 avatar image
seb71 answered ·

Could I have damaged the panels by having them up there but not connected up for 5 months?

The PV do degrade when exposed to the Sun (and weather). But not that quickly. Over a long period of time you should expect a decrease of the PV power.

2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

mvas avatar image
mvas answered ·

Also , are the panels dirty?

1 comment
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

taddy avatar image taddy commented ·
A little bit - but not extensively I would say.
0 Likes 0 ·

Related Resources

Additional resources still need to be added for this topic