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Hi everyone. I have Victron solar panels; each is 24V rated 200W, they have 72 cells instead of the normal 60, and I have four pairs of them. Each pair is in series to give 48V nominal and each pair has its own MPPT. When I read PV from the MPPTs the starboard side shows 60V on one pair and 65V on the other. This is a little high I think but the port side reads over 80V on both, which is concerning. Does anyone know why this might be happening and how concerned I should be?? Thanks in advance.
You need to check the open circuit voltage of the panels. This may be abbreviated to Voc. Should be a sticker on the panels giving the numbers
This gives the max value you should see at the panel.
But it sounds as if you have a cabling error.
In essence, yes.
Voc is for standard conditions. Very bright days may result in a higher voltage. But as bright days usually mean higher temps, maybe not.
I guess your next step is to find out why you're not in the 80V region all round. Be careful disconnecting. The connectors should not be connected/disconnected under load. They'll arc and be damaged. Most likely illumination differences, though. If it was me I'd check uneven illumination, very likely on a boat, and leave it there.
80 Volts could indicate that, those PV Panel have no load. How many amps is flowing from those PV Panels?
Sounds like you are measuring the solar voltage off-load (Voc). Putting panels in series adds the voltage together so a max of 88v is quite correct for your panels - but obviously, the voltage should never exceed the MPPT max input voltage level of your charger. As regard different panel maximum currents, so long as the voltages are correct for your system it would actually not matter too much since banks of panels give different currents depending on what exposure they have to sunlight - one bank could be more in the shade at certain times and consequently output lower currents. The total voltage will also lower considerably when under charging load from the MPPT.
Since the series string of panels are all connected to a common bus bar, the current each set delivers would add together at that point. Panels are normally fitted with a diode so current can only flow away from the panel and only go into the charger.
Hope that may help.
Indeed as @kaypea has indicated. An single photovoltaic solar cell can produce an “Open Circuit Voltage” ( VOC ) of about 0.5 to 0.6 volts at 25oC (typically around 0.58V) no matter how large they are. This cell voltage remains fairly constant just as long as there is sufficient irradiance light from dull to bright sunlight.
So your 60 (or 72) cells should be in the range of approximately 60V (72V) or slightly higher as you indicated above for the two panels. Obviously I am not referring to losses or efficiencies of mppt etc.
From the spec sheet I posted, it would also appear that your SERIES voltages are correct, that is if I correlate your data (irrespective of 3a or 4a) with the +- 210W panel in the spec sheet.
