Marine solar panel repairs

[howthom]

I have 3 100w panels regulated with a Heliotrope controller to charge 3 AGM batteries on my boat. The system has been working great for 8 years but I recently changed the old batteries for new. After hooking everything up, I notice there was no contribution from the panels. I tested the voltage from the panels where it connected to the controller and it read 19.6v then went to immediately reading 1. I tested again at the connector box at the panels and got the same reading. I spoke with a tech from where I purchased the system and he told me I did something to short out the panels during the battery install. He said I had diode failure. I've removed the panels and there are no diodes on the back of the panels. Did I destroy these panels somehow or are the repairable?

[ewarnerusa]

Maybe fried controller. Did you disconnect panels from the controller prior to disconnecting and swapping batteries?

[howthom]

No. I did not disconnect the panels from the controller prior to swapping the batteries. I'm sure I did some damage to the panels.I was told diode failure, but don't see any on the panels. What fried? Are they garbage now or can they be repaired?

[ewarnerusa]

I'm suspecting controller damage, not panels. I don't actually know anything about the failure mechanism. But my controller warns against having any PV hooked up without being hooked to a battery or load. I think this is a common precaution. No power should be coming into the controller without it having somewhere to route it to.

[howthom]

I suspect I fried the controller too. But, when I measure the voltage at the panels that are disconnected from the controller, I get a reading of 1v. I think that means something inside the panels is cooked. Can that actually happen without fried wires or some other visual indication? The panels look fine. Can I repair them?

[inetdog]

I suspect I fried the controller too. But, when I measure the voltage at the panels that are disconnected from the controller, I get a reading of 1v. I think that means something inside the panels is cooked. Can that actually happen without fried wires or some other visual indication? The panels look fine. Can I repair them?

If there is a terminal box attached to the panel, it likely contains two or three bypass diodes. A high reverse voltage can cause those diodes to break down and short circuit. Or running a string of panels into a short circuit with partial shade on the panels could also fry those diodes.
If you can, disconnect them (clip the leads if necessary) and then measure the voltage. If it is still ~1V then the panels are probably beyond repair.

If there is no junction box that contains the bypass diodes they are probably internal to the panel and cannot economically be replaced.

[howthom]

Thanks, I didn't see any diodes in the junction box. They must be internal and the panels junk. Another lesson learned.

[Sunking]

Test your panels VOC and ISC. Then you will know exactly what is wrong. A 100 amp battery panel Voc should be around 20 volts and Isc around around 6 amps.

[PNjunction]

I suspect I fried the controller too. But, when I measure the voltage at the panels that are disconnected from the controller, I get a reading of 1v. I think that means something inside the panels is cooked. Can that actually happen without fried wires or some other visual indication? The panels look fine. Can I repair them?

Yes that can happen if the panel has no bypass diodes, and they get differing amounts of shade across them. The shaded cells are reverse biased, and if left long enough that way in a shaded condition with the rest of the panel trying to push current through them, they burn up. Most quality panels have a bypass diode for each string of about 18 cells approximately. At least ONE across the panel would be a minimum, especially in a multi-panel setup.

Note that we are not talking *blocking* diodes, but bypass diodes.

The trick is that the panels would do just fine without any bypass diodes as long as there is no differing amounts of shade across them. But in your environment there is plenty of opportunity for shading to cross the panels.

Another possible scam is getting panels second hand from dealers who trade panels that have KNOWN defects, and should have been replaced under the manufacturer's return policy. The Kyocera 120 panels had an initial bad run, and Kyocera made good with replacements/upgrades, but there are still a bunch floating around that should have been returned, and are now floating around online sales sites. Ideally they should have been destroyed to prevent this endless scam (from shady dealers, not Kyocera who made good in short order).

Btw, "shorting" a panel doesn't kill it. In fact, many early charge controllers did just that towards the end of charge (weakly emulating modern pwm, with "ping pong" type relays). In a multi panel system a short may burn up poor wiring infrastructure, but a short across the panel won't hurt it. (It is a current source, and not a voltage source for advanced readers.

Just to be sure, follow Sunking's advice and go directly to the junction box with everything else disconnected to make a last set of measurements to be sure you have removed all variables.

[howthom]

Thanks for the advice. I will test the panels as described by Sunking. What is the chance that the controller is still good? Is there a way to test it?

I'm thinking worst case I have to replace the panels and controller. I have 315AH with 3 agm batteries that I never let get below 80% charge. I figure I need to replace approx 63 AH at 20% battery drawdown. 63A x 12 V= 756 w / 5 hrs/d= 151w.Adding in a 20% contingency that means 181 w panel would do it. Is this math correct or am I missing something? Do the panels need to be matched to a controller or can any MPPT controller for AGM batteries work? Any and all advice is very much appreciated. Thanks.

[Mike90250]

Panels need to be matched within 5% of each other for Vmp & Imp for any MPPT controller to work well with them.

But you have not added in enough loss, Panels produce 20% less then nameplate power, and the batteries have a 5% (AGM) - 15% (flooded) loss for recharging
So bump your loss factor to about 30% and you would be good for unshaded panels. Less than optimum solar angle also adds some loss, depending on how far off perpendicular you are.

[soleram]

Was just curious, did you test your panel?
Having also solar panels on my boat, would be interested to learn what was the problem.
The cabling is also important to take into consideration, especially on a boat.
Depending on the conditions, a solar installation on a boat can be on much greater stress than RV (sea water corrosion, constant motion, etc.)
To monitor my battery bank, I installed a small and cheap gadget https://goo.gl/BWgYjP
Probably not the most accurate, but for less than $20, I can get a quick look on the current situation of my solar system.