Panel Array Voltage dropping under high load?

PorkChopsMmm
PorkChopsMmm Solar Expert Posts: 189 ✭✭✭✭✭
I recently doubled by panel array from 1.4 KW to 2.8 KW. Previous to doing some re-wiring the highest watts I saw were 2900 watts (really!) and since re-wiring for a cleaner install I have seen 2500+ watts just passively looking. So everything should work. Recently I haven't been seeing the wattage coming in that I thought I would. We also haven't recent to '0' days since 100% as I thought we would (an Outback indicator being fully reaching the charge and float parameters). I was running some tests today and saw that under high load (testing with a blow dryer and our microwave to pull enough power to max out the panels) the voltage of the panels was dropping.

I recreated the test a few times and took screenshots of the VisualMATE software tool. Is this normal? Maybe indicate I have a wiring issue somewhere? I was using the same amount of panels, same kind of wiring (although I shortened things up!), with the same combiner box and charge controller settings. Nothing has really changed save for the wiring and I think everything is working.

Any suggestions or advice? I tested each breaker in the combiner box and all showed similar voltages based on high bright it was (e.g. each array of 3 panels showed between 80 and 90+ V depending on how sunny it was when I was checking). Panel specs below the screenshots. I also work full-time so it is hard to monitor solar during the day -- I am planning on buying the WattPlot PRO software in a week or two.

Prior to turning in blow dryer (1600 watts) and microwave (1000 watts)
6gjo.jpg

After turning on blow dryer and microwave
l6a.JPG

I guess typing this up I think I should have seen more than 2200 watts -- maybe closer to my cap of 2800 watts? It was very sunny and about 2 PM here. Maybe one of my arrays is messing up?

Here is another screenshot from a few months ago -- right after I put up the new panels. Earlier in the day but with a similar wattage coming in. The voltage of the panels was higher.

ld4m.jpg


I have 4 arrays of 3 panels -- each panel has these basic specs:

Rated Power (Max) 240W
Tolerance +- 5%
Voltage at PMax (Vmp) 30.0V
Current at Pmax (Imp) 8.0 A
Open-Circuit Voltage (Voc) 36.0 V
Short-Circuit Current (Isc) 8.96 A
Nominal Operating Cell Temp (NOCT) 45 +- 2 degrees Celcius
Maximum System Voltage 600VDC
Maximum Series Fuse Rating 15A
Operating Temperature -40 to + 85 degrees Celcius
Fire Resistance Class C
Cell Technology Poly-Si

Any thoughts or tips? Thanks!

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Panel Array Voltage dropping under high load?

    Well ... the first statement that you once got 2900 Watts from 1400 Watts of panel really isn't possible. Do you mean 2900 Watt hours perhaps?

    In terms of what you could expect you'd be looking at maximum current differences:

    1400 Watt array on a 48 Volt system: about 23 Amps max.
    2800 Watt array on a 48 Volt system: about 46 Amps max.

    These would be peak current values and you might never see them depending on battery SOC and load at any given time.

    Watts in/out would likewise vary.

    As far as Voltage and Amperage in to an MPPT charge controller, they will both vary according to what the controller thinks is best for the circumstances at the time.

    The only way to see the maximum potential on a battery based system is to load the output heavily at a time of maximum insolation. 2:00 PM is not likely to be that time if the array is pointed solar South as most are.

    Some things you do need to look at: if the array size has doubled and the new panels share the same conductor to the charge controller as the old, is it large enough to handle the increased current without suffering significant Voltage drop?
  • PorkChopsMmm
    PorkChopsMmm Solar Expert Posts: 189 ✭✭✭✭✭
    Re: Panel Array Voltage dropping under high load?

    Sorry if it wasn't clear -- I went from a 1.4 KW array to a 2.8 KW array. All the wiring is basically new and has supported these watts before. It just seems like something has changed -- unsure of what.
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Panel Array Voltage dropping under high load?

    Your batteries are fully charged it says. So, the controller wants to produce only as much as needed to support loads.

    On the first picture, it increased the voltage way above Vmp to limit production to 500W.

    On the second picture it moved closer to Vmp (probably even below Vmp) because it now needs to produce 2kW.

    These are inner workings of the controller. Nothing to worry about.