We have a DC system going in at a tower site in a very treed area, but to one side of the site is a clear field (part of the tower property) we have eight 120W 12v pv panels, they will be about 20m from the equipment shack. So we need to run them in series in order to get high voltage to overcome I2R loss in the cable back to the equipment shack. I am trying to figure out which MPPT controller I should use. The shack will probably use 24v batteries or 48v batteries, it would be easier to go with a 24v system due to the fact that a lot of the gear is already setup for that voltage and the remaining gear is 12vdc, for which there are loads of buck converters on the market. I have an mppt 150/70 which will handle the current. But I am unsure of the Voc of those 12v panels in series. They are not new so the data plate is gone, but they still will put out near the 900W as I was using them on a 24v system with them in pairs, I recall that they read somewhere about 32-34vdc when feeding the mppt controller. But not sure what the Voc is. Anyone have an idea of what the minimum input voltage should be from panels wired as “96vdc”. I am guessing based on what I saw when running 24v in series that at 96 v I would see something around 148vdc which appears to put it near the 150v limit on the 150/70, any one run panels in that configuration give me some guidance?
Measure them with a multi meter. You can measure an individual or them all in the string.
Voc is easy, connect them all and measure the string open circuit. Add 10 % then that is the headroom you need for VOC max.
If in doubt use a 250/70 mppt
I seem to recall when I had the panels myself (I gave them to a group that is setting up an amateur radio
based microwave network for emergency communications) I had them in two sets of 4 and I recall that
they always showed about 72-78vdc, but that was loaded. With the cable run being between 20 and 30
metres from panels to equipment shack all 8 in series would be better but one of the guys down there
may be able to get the proper size cable for the 4 panel (48v) configuration. with two sets in parallel.
They will have to set them up and take the measurements.
If that was imp then voc in one string will definitely be over 150vdc.