Solar Panel Troubleshooting Help

[Captain Bill]

I just got back from 16 days in the Bahamas on a friend's Mainecat 30. While there we noted that his battery charge state was not up to its usual high level. After looking at some readings from his solar panel controller we noted that even though it was near noon on a totally cloudless day his panels were putting out only about 5.8 amps instead of the nearly 11.5 he usually gets on a sunny day. The boat has 4 55 watt Siemens solar panels charging a 12 volt system. A quick coverup test showed that the port solar panels were not putting out any amps. We suspected a bad connection. The way the boat is wired the two port panels are wired together in parallel and a single pair of wires runs through a chase in the hard top and are wired in parallel to the starboard panels. All connections are in small plastic junction boxes on the bottom side of the Solar panels. A quick inspection of the connections showed no signs of corrosion. Proper pre-tinned wire was used throughout the installation. We remade all of the connections just in case. Still no power from the port panels. We then isolated each panel individually and measured the open circuit voltage. The result was that the panels on the starboard side showed a little over 20 volts and the port side only about 18 volts. We attributed the difference to the fact that when we lifted the starboard panels to get at the connections they were pointed more towards the morning sun and the port panels away from the sun, but maybe we shouldn't have. When the panels are connected together and to the controller we see roughly battery voltage. I'm giving these rough voltages because my buddy likes analog volt meters. What can I say. Our next thought was that the cables crossing over the hard top to the other panels might have a high resistance break crack that allowed us to read voltage but wouldn't carry any current. In that case I would have expected to see something like open circuit voltage at the port solar panels rather than battery voltage when everything was connected, but we decided to test the wires any way. We only had one wire long enough to jump to the starboard panels so we jumped the power and ground wires individually. There was still no amperage from the port panels. At this point we are stumped. There is still the possibility that both wires from the port to starboard side went bad at the same time. My friend is now in Georgetown Exuma and is picking up enough wire to jump both wires. I doubt this will change anything. The ends of the wires are in pristine condition and run through a tube it the hard top that has no signs of water or any other contamination. It just seems unlikely to me that these wires are the issue. At this point the only thing I can think of is that both port panels have developed a high resistance internal connection problem that prevents the panel from generating any amps though it can show voltage under a no load condition. There is no visible damage to either panel. It seems odd that this would happen to both panels at the same time. Does anyone know enough about Solar panel failure modes to offer any suggestions?

[ChuckSK]

To determine the health of a solar panel both open-circuit voltage and short-circuit current should be measured. I would isolate the panels again and measure the short-circuit current for each. The current should be around 3 amps in full sun.

Then start chasing wiring.

Regards
Chuck

[Captain Bill]

Thanks for the reply chuck. We thought about doing the current test, the only issue was the VOMs we had available were both limited to 600 ma. We thought about other load tests we could do. We had a 12 volt fan and a 2 million candle power spotlight. The fan would only draw about .5 amps and the spotlight draws about 10 amps. we were concerned about having too much load with the spot and not enough with the fan. I am going to assume that since there is a short circuit rating that there is really no danger of burning anything out if tested for a short period. Our concern was that we at ony 1/3 of the amperage required available that we might not get much out of the spot light thus not be able to tell if we were actually getting anything out of the panel. Unfortunately I had to catch a flight before we got that far. There were stil a couple of hundred boats in Georgetown, maybe he can borrow an ammeter with sufficient capacity. I'll pass on the advice on the current test.

[chala]

Captain Bill
I think that you should own a test lamp.
A test lamp has been used by electrician’s way before they could afford electrical meters. The advantage of a test lamp is that it put a load on the supply but you know that. “We had a 12 volt fan and a 2 million candle power spotlight. The fan would only draw about .5 amps and the spotlight draws about 10 amps”.
My 12V test lamp come from a car wreck. In your case you will require a globe (globes) that create enough load on your 55w solar panel and in the same time check the voltage with a multimeter. 3 amps should see around 15.5V. (compare between the 4 solar panels)
In your thread you make no mention of a voltage regulator or a blocking diode. At least one blocking diode is required in the circuit to prevent the battery draining into the solar panel during the night. Locate the blocking diode; check the voltage under load with your test lamp before and after the blocking diode if nothing happens, checks the solar panel at his output.
I do not know how long a 12V globe will last at more than 14V so get few spare or limit the time the globe is connected to the solar panel.

[schoonerdog]

hmm, its an interesting question. I would check the open circuit voltage of each again, as mentioned. Then check the voltage where they are coming together in a single run to the battery regulator. Also check the gauge of wire coming from each side to ensure it's adequate. If you're seeing voltage drop from the panels to the junction box, it's probably the wire gauge is insufficient. Also, your port and starboard pair should come together in the middle of the boat with equal legs before being joined together in parallel and coming to the battery charger so they have equal voltage drop. If your port panels had a large run to the starboard side and where it was then being joined together for the common run back, I'm guessing that the panels with the longer run would have a lower voltage due to voltage drop and then the panels with the higher voltage would basically be the only panels to actually be putting electricity back to the charger. I remember working with a marine electrician on this very issue and he mentioned too that higher voltage wins (think of water pressure if one side of a plumbing channel has 10 lbs of water pressure and the other side has 8 lbs of water pressure, then when they are combined the side with 10 lbs of water pressure will be the only one to actually be contributing). Last I would do the following if your battery charger can step down battery voltage from 24 volts to 12 volts (if it's an MPPT the odds are it can), I would wire them in series on each side and then in parallel going back. It will double the voltage coming from each panel and thus help reduce any voltage drop in the cables prior to them being connected again for the common run back to the battery charger. Each side will then be one large 24 volt panel (or from your meter probably putting out around 36 volts open circuit).