panel configuration

bundy Registered Users Posts: 10
hi my buddys got 2 strings of 4- 75 watt panels in series 300x2
one string of 2- 165 watt in series 330x1

the 75 watt panels are 4.4 amps rated at 17 volts x4 68 volts
the 165 watt panels are 4.72 at 35 voltsx2 70 volts

he would like to add 290 watt panels x2 is 580
volts would be 70 volts total at 8 amps 580 watts
but i told him its not good to have diiferents amperage of panels together would u guys agree or could he get away with that set up.

if not hears an idea i had for him he has 3 conductor tec cable running to juction box
to charge controller there is one wire not being used on that run he could add one breaker for the two panels and put another charge controller but could he share the same negative wire in that tec cable with that spare wire that is not being used .that would save not having to run another tec cable. i hope i wrote it out as clearly as possible what he wants to do any idea s on this set up thanks


  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: panel configuration

    when you place pvs in series you try to match the currents.
    when paralleling pvs or strings of pvs you will look for matching the voltages.

    generally i recommend a 5% tolerance, but others say up to 10% and it is somewhat arbitrary with you knowing that the farther away in tolerance the more likely losses will increase from mismatching.

    now 68v and 70v is very close for different pv strings and when paralleled their currents should add together just fine.:D