12v MPPT and 24v MPPT vs 24v PWM Test
Got a chance to try out comparing amps to the battery using MPPT vs PWM on a 24v battery bank and comparing those with the usual MPPT on 12v with my 230w panel. The bank is four 6s, so it was easy ...
Forum Discussion
jrnymn7 wrote:
PWM CHARGE CONTROLLERS can be used with either 12v or 24v panels, provided it's 12v panel to 12v battery, or 24v panel to 24v battery.
PWM controllers pass thru Isc.
Using the panel specs of two particular panels found on 2solar.com...
The 24v 250w panel has an Isc of 8.39a.
Two of the 12v 135w panels, adjusted down to 125w, in series, have an Isc of 7.38a.
8.39/7.38 = 1.1369... that's 113.7% Therefore, the 24v panel would deliver 13.7% more current to the pwm, and 24v battery.
With PWM, what you are saying is that the Isc : Watt ratio of the 250W panel is 6.7% and the 135W panel is 5.9%. Therefore when charging a 24V bank, then 6.7/5.9 is 1.13, or the 250W panel is 13% better than two 125W(using your adjusted Isc). Now when charging a 12V bank, the 250W ratio is only 3.3% whereas the two 125s in parallel are better at 5.9%.
Conclusion: when using PWM, try to get the most Isc : Watt!
Now with MPPT, you ignore all of that. You want the Vmp to be in excess of charging Volts while the keeping Voc less than the controllers Voc spec.
Conclusion: much more flexibility in choosing panels and assembling panel arrays. It really doesn't matter if you use the 250W or the two 125Ws. Plus it doesn't matter if the 125W are series or parallel.
HTH;
John
