Solar Panel Question

[Fatbob]

Perhaps someone has had the same issue and knows the answer.

I have two 100W solar panels wired in parallel and run to a PWM solar controller. On a sunny day, I can see that only 2.5 amps is coming into the boats system from the solar panels. If I take my clamp meter to the panels and measure DC amps, one panel is making 2.5 amps and the other is making .05 amps. If I disconnect the "low producing" panel and short it out (plug the panel's positive lead into its negative lead), it now measures 2.5 amps as well. When I reconnect that panel in parallel, it seems to work properly and the entire system is measuring 5 amps (2.5 from each panel). Several days later....same fault will occur and shorting the panel out seem to fix it again.

Any ideas why the panel does this?

Thanks for the help.

Drew

[rslifkin]

Sounds like you have a bad connection on that panel and the disconnect / reconnect cleans things up just enough for it to work for a few days.

[Bill O]

Your panel output seems low for a 100W or 200W total.

Not sure if you have flexible or hard panels, but a typical 100W hard panel should be around 5 amps/each in full sunlight.
What brand of panels do you have or do you have the specs off the back of the panel?

Can you test the short circuit amp output to confirm that each panel meet specs?

[Fatbob]

Originally Posted by Bill O

Your panel output seems low for a 100W or 200W total.

Not sure if you have flexible or hard panels, but a typical 100W hard panel should be around 5 amps/each in full sunlight.
What brand of panels do you have or do you have the specs off the back of the panel?

Can you test the short circuit amp output to confirm that each panel meet specs?

The panel is a Aurinco Compact Panel. It is an odd panel that looks like a thin (flexible) panel that is mounted on an aluminum plate. It is from the factory this way and not a "home grown" solution.

The sticker under the panel reads:

Pmax: 100W
VMPP: 18V - IMPP 5.6A
VOC: 22V - ISC 6.2A
STC: 1000W/m2 - AM 1.5 - 25C

I measured 20.4 V and 3.4 Amps in nearly direct sunlight without any shadows on the panel.

Regards,

Drew

[Fatbob]

Originally Posted by rslifkin

Sounds like you have a bad connection on that panel and the disconnect / reconnect cleans things up just enough for it to work for a few days.

You think it is a bad connection where the panel plugs into the boat wiring or a bad connection internal to the panel somewhere?

It is definitely a case that disconnect/reconnect seems to reset something. The odd thing is that if I have no amps when the panel is plugged into the system, then when I unplug/short it I get amps and when I plug it back into the boat wiring I have amps. To me, this wouldn't seem to be a connection between the panel and the boat wiring but perhaps something internal to the panel that I am resetting....but I could be wrong.

[rslifkin]

Originally Posted by Fatbob

You think it is a bad connection where the panel plugs into the boat wiring or a bad connection internal to the panel somewhere?

It is definitely a case that disconnect/reconnect seems to reset something. The odd thing is that if I have no amps when the panel is plugged into the system, then when I unplug/short it I get amps and when I plug it back into the boat wiring I have amps. To me, this wouldn't seem to be a connection between the panel and the boat wiring but perhaps something internal to the panel that I am resetting....but I could be wrong.

I'd consider the connection you're disconnecting / reconnecting to be the first suspect. I'd expect it's making poor contact or has slightly burned contacts and once you've messed with it, it at least temporarily makes better contact.

[Fatbob]

Originally Posted by rslifkin

I'd consider the connection you're disconnecting / reconnecting to be the first suspect. I'd expect it's making poor contact or has slightly burned contacts and once you've messed with it, it at least temporarily makes better contact.

Thanks, I'll change the connectors and hopefully that fixes it.

[StuM]

Originally Posted by Fatbob

The panel is a Aurinco Compact Panel. It is an odd panel that looks like a thin (flexible) panel that is mounted on an aluminum plate. It is from the factory this way and not a "home grown" solution.

The sticker under the panel reads:

Pmax: 100W
VMPP: 18V - IMPP 5.6A
VOC: 22V - ISC 6.2A
STC: 1000W/m2 - AM 1.5 - 25C

I measured 20.4 V and 3.4 Amps in nearly direct sunlight without any shadows on the panel.

Regards,

Drew

With a PWM controller and 20.4 V you are losing a lot of that power. I'd replace it with a MPPT controller.

[goboatingnow]

Originally Posted by StuM

With a PWM controller and 20.4 V you are losing a lot of that power. I'd replace it with a MPPT controller.

Just be aware that max power point can have upto -0.4% per degree C , so if the panel is hot the Vmp point can be lowered a lot to the points where a mppt controller can do little. This is especially the case with low voltage panels wired in parallel

Victron covers this in a very good write up
And shows for hot cells the advantage can be minimal


https://www.victronenergy.com/upload...WM-or-MPPT.pdf