I have a smartsolar 100/20 controller that will be going into a caravan. Would 2 190w panels with a voc of 44.8v connected be oversizing by too much?. They will be mounted flat on roof. Temps would be between 5 and 40 degrees celcius
asked
Oversizing 100/20 controller
@paul-p Depending on your battery voltage it will chop the peak power. 190w x 2 is 380w at 13v on the battery the potential at peak is 29amps. So the 20amp controller will "waste" 9 amps.
That is if your panels produce the full amount when they are warmer they won't.
Yes its a 12v battery. Is the wasting of 9 amps an issue? Would it hurt the controller? They will be connected in series
@paul-p There is no problem there at all. You have not massively over paneled. Heat may be the only issue as a side effect.
https://www.victronenergy.com/upload/software/VE-MPPT-Calc-4_0.xlsm
There is the spreadsheet linked above if you would like to check the low temperature voltage and see if it exceeds the hard limit of 100v in as suggested by @Leslieanne
Hi Paul,
This is no problem whatsoever. I have had 2 × 200W panels with similar OCV flat-mounted into a 100/20 for several years. Sure, the maximum amperage to battery is 20A (lower if very hot and controller derates), but that only ever happens in summer when sun is high in sky in bright sunshine. In these conditions you don't need the extra power anyway! Even in full sun in winter they never get up to 20A to battery, and this is when one is glad to have all the amps available.
One caution...I think series connection is risky. On a cold morning (and your panels may well be colder than the 5deg air temp) the OCV will be higher...by about 0.3 V per deg below 25C, so higher by say 6V per panel. You might then exceed 100V and the magic smoke will appear. I have mine in parallel to avoid this.
Cheers, Leslie
Yes, you will have double the amps from the parallelled panels to the controller, but roughly the same as series connection from controller to the battery, of course. Still well within specifications for the controller.
So you are saying ill have the same output in amps but reduce the risk of going over the 100v max?
Yes, exactly. You are still producing the same power (watts = volts x amps) from your panels - at half the voltage but twice the amps. But then, when the controller converts that power to 12 volts, you end up with the same amps to the battery.
Note that if using "12v" panels in series you might get a little more output in poor light conditions than in parallel, but with an OCV of 44V this effect would be negligible.
