Damage to PV panels when they are disconnected long term (say, for months at a time)?

Fenachrone · July 28

I've seen a bit of talk about this topic here and there, but would like more clarity on the issue. The question is how much do panels suffer from not being connected, that is, just sitting out there in the sun on a roof, or rack -- no load on them, and breakers off at combiner.

Some commenters say that the panels will be significantly damaged over the long term when out in the sun if not hooked to a load; others speak of minimal or no degradation.

So just how much, really, is the degradation, if any? I've also heard that CdTe-based panels, or thin-film amorphous types, are most at risk, but silicon-based not much.

Thanks for any insights!

BB. · July 28

The chatter has always been that Cadmium thin film solar panels should never been left in the sun disconnected (more than a few weeks--Fuzzy memory from long ago?).

Since they were always "pushed" for utility solar farms (more efficient, cheaper, better high temperature performance, etc.)., it seemed be more of a theoretical discussion.

I went trolling through the internet and looked for First Solar spec sheets, and the only limitation I could find was they the panels needed to be installed in portrait orientation only:

https://www.firstsolar.com/-/media/First-Solar/Technical-Documents/Series-6-Datasheets/Series-6-Datasheet.ashx

There are lots of "standard" solar panel warnings such as "don't disconnect MC4 connections under load, keep connections clean and dry, don't throw rocks at solar panels, etc.), do not disconnect/connect MC4 connectors more than 10 times (connectors can wear out/fail)... First Solar panels are around 280 Voc (high voltage DC), so avoid electrocution, don't submerge panels in water, etc.

First solar series 6 installation manual:

https://www.firstsolar.com/-/media/First-Solar/Technical-Documents/User-Guides/Series-6-User-Guide.ashx?la=en

Image: https://us.v-cdn.net/6024911/uploads/editor/c0/wghcrx5b2qkj.png

Turns out that First Solar panels appear to not have "bypass diodes" and can be easily damanged/ruined in certain shading conditions:

Image: https://us.v-cdn.net/6024911/uploads/editor/9i/mdvkrltwor4r.png

Marketing documents suggest that these CD thin film panels be used for mobile and "variable load" situations (such as car charging stations, etc.). And remember that for DC battery charging, the charge controllers draw near zero amps when the battery bank is full...

At this point, I can find no "official" documentation on CD-thin film panels must not be left out in the sun disconnected. But there are other issues with shading that could be a big problem with variable shading damaging panels--Which standard silicon panels are protected against with bypass diodes.

So is the "don't leave unconnected" CD-thin film panels a myth? Anyone else find "mfg's documentation" on this issue?

-Bill

JRHill · July 28

Well, I'll let you know. I've got 4 panels on a pole mount that used to power our water well. They haven't been connected since the bank of batteries went dead three years ago and I just plugged the pump into the house system. I am finally going to move three of them them to the house roof before fall. Otoh...

Fenachrone · July 29

My system doesn't use Cadmium thin film panels, but that's the type I read were vulnerable.

But again, there's nothing definitive I can find about others. You're right about all the warnings about connections, breaking connections under load, shading, etc.

I posed this question initially because I have a place I close up for winter. I'd prefer to not leave electronics on without supervision, so panels are basically "off" at the combiner box until I open the place up in the spring.

BB. said:

The chatter has always been that Cadmium thin film solar panels should never been left in the sun disconnected (more than a few weeks--Fuzzy memory from long ago?).

Since they were always "pushed" for utility solar farms (more efficient, cheaper, better high temperature performance, etc.)., it seemed be more of a theoretical discussion.

I went trolling through the internet and looked for First Solar spec sheets, and the only limitation I could find was they the panels needed to be installed in portrait orientation only:

https://www.firstsolar.com/-/media/First-Solar/Technical-Documents/Series-6-Datasheets/Series-6-Datasheet.ashx

There are lots of "standard" solar panel warnings such as "don't disconnect MC4 connections under load, keep connections clean and dry, don't throw rocks at solar panels, etc.), do not disconnect/connect MC4 connectors more than 10 times (connectors can wear out/fail)... First Solar panels are around 280 Voc (high voltage DC), so avoid electrocution, don't submerge panels in water, etc.

First solar series 6 installation manual:

https://www.firstsolar.com/-/media/First-Solar/Technical-Documents/User-Guides/Series-6-User-Guide.ashx?la=en

Turns out that First Solar panels appear to not have "bypass diodes" and can be easily damanged/ruined in certain shading conditions:

Marketing documents suggest that these CD thin film panels be used for mobile and "variable load" situations (such as car charging stations, etc.). And remember that for DC battery charging, the charge controllers draw near zero amps when the battery bank is full...

At this point, I can find no "official" documentation on CD-thin film panels must not be left out in the sun disconnected. But there are other issues with shading that could be a big problem with variable shading damaging panels--Which standard silicon panels are protected against with bypass diodes.

So is the "don't leave unconnected" CD-thin film panels a myth? Anyone else find "mfg's documentation" on this issue?

-Bill

Damage to PV panels when they are disconnected long term (say, for months at a time)?

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