Expanding solar panels

fiddlerkelly Registered Users Posts: 19
When I started my solar system I started with 5-100 watt 12volt panels from a certain company and want to expand with approximately another 500 watts. That company is now no longer in operation so I am forced to get my panels somwhere else . Am I able to have two different types of panels in the one setup.

Now I am not planning on connecting them all in series but rather keep them seperate and bring them to a combiner box. Can I do tbis? I will join all new panels in series for 48 volts and the old ones in 48 volts and then the 2 lines will go to the combiner box and yes I will have to remove one 50 watt panel from old group of panels.


  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    Re: Expanding solar panels

    You can put panels in series that are within ~10% of Imp of each other (i.e., 8 amp Imp for one panel, 7.2 to 8.8 amp Imp for the next panel in series).

    For placing panels in parallel, you can put two 17.5 volt panel in series to give Vmp~35.0 volts. And put that in parallel with a Vmp~38.0 volt panel.

    The other issue to watch for--As you put panel strings in series--The lower Isc/Imp rated strings will probably require a lower rated series protection fuse/breaker (i.e., lower Imp panels may need 7 amp fuse/breaker, and higher current panels may require 15 amp series fuse/breaker).

    There are times when it is pretty much impossible to match "old panels" Vmp/Imp with new panel Vmp/Imp--And you may need a new MPPT charge controller to support the new Vmp/Imp-array values.

    This get into a paper review of costs... It is cheaper to use old panels + New charge controller, or get a whole new set of panels to use with the existing/new controller.

    We get attached to the old panels that may have cost us $5 to $10 per watt--But with new panels costing $2 to $1 per what in "GT Type" 250+ Watt panels (vs 3x as many 80 Watt panels)--Sometimes it does not make much sense to preserve the old array/panels.

    Many times, people can still sell the smaller panels for pretty good $$/Watt pricing (even today, smaller panels still cost more $$$/Watt than large format panels).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • fiddlerkelly
    fiddlerkelly Registered Users Posts: 19
    Re: Expanding solar panels

    Thanks Bill .I ha e considered selling the in the past and may again if price is right. I am upgrading to midnite solar 150.