Originally Posted by Jmooney
Don, based on my configuration ( 2 100w panels in parrellel. ) would you covert to a MPPT controller?
You would get a larger benefit from adding an extra panel over an MPPT controller.
You may realize some gains if you have small wiring and are experiencing large voltage losses. You would have to wire your panels in series to up the voltage and reduce amps which the MPPT controller could take advantage of.
For example. Lets use the SC2030 PWM controller I have for $129 usd and the Renogy MPPT shown above for $209 and lets use four 100 watt panels.
Connected in series for 72 volts and 5.3 amps for the MPPT controller. Volts*amps=watts = 382W
Connected in parallel for 18 volts and 21.2 amps for the PWM controller. =382W
Let’s assume that the batteries are discharged and will accept all the amps we can provide and that both systems were wired properly and voltage losses are equivalent.
It is a cold morning and the panels are producing their optimal output voltage of 18 volts. From the manual we know that the max efficiency is 92% so we are getting….
382*.92=351 watts to the batteries at 14.6 volts (bulk charge) = 24amps going into the batteries.
Same cold morning for PWM…..
21amps getting to the controller but the controller has to clip the output to 14.8 volts (voltage adjusted to match charge specs)
14.8*21.2amps= 313 watts going to the batteries.
So……Cold panels and dead batteries and MPPT has an 10% advantage. Pretty good.
What about after the panels warm up from the sun and it starts to get hot out. Now the voltage output is 15 volts from each panel
20°C above standard conditions (25°C) and panel efficiency drops ~8%. Voltage is reduced to 16.5 volts per panel
MPPT is 66.2 volts * 5.3 = 351 watts
PWM is 16.5 volts * 21.2 = 350 watts
MPPT efficiency loss of 8% and we are now at 323 Watts and 22amps.
PWM efficiency is now better (around 10%) and we get the same 313 watts and 21 amps.
So equivalent at this point. No benefit with MPPT.
If your batteries are not depleted and can’t accept the 20+ amps the panels can provide then you are wasting energy with either system.
Let me know if you see any holes in my logic or math.