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Hello,
Is this PWN controller "BlueSolar PWM-LCD&USB 12/24V-30A" ok for 2 panels with the specs:
Polycristalline, 280W
Open Circuit Voltage(V) 38.5 V
Short Circuit Current(I) 9.54 A
Maximum Power Voltage(V) 31.7 V
Maximum Power Current(I) 8.83 A
Module Efficiency 17.2 %
And charging a 12V battery.
Thank you!
Hi @Sorin T.
That would work, but not very well. Just guessing, to at best 50% of their rated output.
A far better option would be a 100/30 mppt unit. One small consolation to help allay the $ pain is that you could series wire them, so a simpler install.
Hi @JohnC . Working on a similar installation, and wondering why you were saying this would work at best at 50% of the capacity ?
Unless I am mistaken, the MPPT (be it 15 or 30A) will indeed have a max array wattage limit based on the battery voltage . But the PWM if connected in parrallel , would show for this example : Voc = 1x 38,5V : Short circuit C = 2 x 9.54A : 19.08 A.
I am trying to install a very minimalist system on various locations, and cost is the key for the customer . I was thinking of using the same PWM 24V/15A with 2 similar panels in parrallel .
Would be interested if you could develop a bit more your thoughts .
Thanks and regards
With PWM the panel V in production will match Vbat, so the panels must be matched to the batts. Otherwise the Vmp won't even be close to where it should be, somewhere a long way down the efficiency curve. ("50% at best")
Bear in mind I was commenting on a 12V system with '24V' panels, and there pwm wasn't appropriate.
If you have 24V batts then similar panels would be ok. But not necessarily as good as mppt..
Hi @JohnC
Wouldn't 100/15 be ok? I mean .. please correct me if I'm wrong, if the panels are in series ... the amperage remains the same (max 10A) and the voltage is summed, so around 80V for an open circuit.
Thanks
The /15 A rating of the mppt is at batt V, and the most you see there might be ~14.5V. The /30 I suggested might cap out then at ~435W, which is still below your panel specs, but they'll only be reached at the peak of a good solar day.
Might depend on the size of your batts what the best choice is. Say for each 100Ah, 10-15A of charge capacity is a fair design start point.
@JohnC I went on your suggestion with a 100/30 and with 2 panels (in series) and it works great. Will it be ok to add another 2 panels, exactly the same rating, but, of course in a 2 sections in parallel (each section having 2 panels in series). That will be (as total) around 80V / 20A.
Or it is too close to the limit?
Thank you!
Yes, you could do that. Your 100/30 is listed at 35 Isc limit, and each of your strings 9.54 Isc. So well under in total, but you won't harvest the full Wattage of your panels. The influence of bad-sun-days and shade will be lessened though, and it should still work well.
If you ever decided to step up to 24V batts, you'd have a ready-made doubling of peak W.. :)
