MPPT in high temperatures

Re: MPPT in high temperatures

With all of the different panel and PWM/MPPT charge controller options out there, plus the fact that people can configure different charger to the same battery bank--the questions get confusing fast...

The simple answer is that for an MPPT charge controller, adding parallel strings need to have the same Vmp (i.e., if one string is 35 volts Vmp, then the rest of the added parallel strings should be around 35 volts DC-- roughly +10% bminus 10% of each other--for example 31.5 volt to 35 volts range OR 35 volts to 38.5 volt range). The farther the way from that 10% range a panel string is, the more likely that the MPPT charge controller will harvest less than the "total available power"... More or less like paralleling a 12 volt + 24 volt battery together (with blocking diodes). You get the current from both batteries at 12 volts but only the 12 volt power. Or at 24 volts, you only get the current/power of a single battery at 24 volts.

MPPT charge controllers are not designed or tested to figure out how to get the maximum power from widely differing Vmp voltages on one MPPT input--plus it is physically impossible to get "maximum power" from a 12 volt and 24 volt panel paralleled together.

If you have a bunch of different panels--you can put two or more MPPT controllers in parallel on one battery bank. Each MPPT controller connecting to its own Vmp Array (12 volt, 24 volt, etc.). Remember that MPPT (or PWM controllers) cannot up convert voltage (a 12 volt panel cannot charge a 24 volt battery bank).

Also, when putting panels in series (to increase voltage)--the current should be withing 10% of each other for optimum performance. The farther away the panels are from Imp matching, the more power is lost (like placing a 1.5 volt D Cell flashlight battery in series with a 12 volt car battery--you will get 13.5 volts, but be limited to the current supplied by the much smaller flashlight cell).

-Bill