Adding additional panels

BJ_OR

Sorry if this has been covered before but ..
Im adding what I plan to be 600 watts 12v panels to my Rv that already came with 2 100 watt panels wired to a old pwm controller 12 years or more old
Can i just leave them in place Add my 6 -100 watt panels =600watts ...wired 2 ea in series then parallel to a mppt controller Will the old system interfere with the new one? What are my options as I know I cant put the old panels in with the new ones (mismatched)

BB.

Yes, you can do what you ask... Old panels+old controller wired directly to battery/battery bus... And new panels+new controller directly to battery bus (fuse/breaker in + lead for each controller to battery bus).

• 600 Watts * 0.77 panel+controller derating * 1/14.5 volts charging = 31.9 amps amps typical maximuim

So, a 30 Amp MPPT controller will just work (efficiently--Safety wise, good quality MPPT controller will limit to 30 amps maximum rated output just fine). Or you can step the next size up (typically 45 amps).

You can mix/match panels behind a single new MPPT controller--If the Imp and/or Vmp is "close" or within 10% maximum difference. Typically "12 volt" panels have Vmp~18 volts + 0.5 volts--So you can put the two old panel in series, and then put them with the rest of the panels in parallel (2 new panels in series, then 4 total parallel strings). The size of the controller should be (minimum):

• 800 Watts * 0.77 panel+controller derating * 1/14.5 volts charging = 42.5 amps amps typical maximum

If you do not have the new 100 Watt panels yet--you might look at getting >> 140 Watt panels... 200+ watt panels tend to be much less $$$/Watt vs the smaller "12 volt 1xx Watt" panels. The smaller panels may be $1.80 per watt vs less than $1.00 per watt for the large format panels. Check panel sizes (fit roof)... Also note that panels >>140 Watts tend to require truck shipping--And packing/shipping a few large panels can be very expensive if you cannot purchase them locally.

Get 4x ~200 Watt panels in parallel (Vmp~30 volts) behind one MPPT controller--And you are good to go (again, check price delivered to your front door).

-Bill

BJ_OR

Thanks for the reply I got a deal on the 12 volt panels 100 watts for a little over a hundred ea .. And they fit the space I have perfectly so that's set. And it looks like the existing panels won't go to waste!
thanks I'm new to this and how all the pieces interact with ea other. Now to pick my controller ( thanks for the info) and get my Labor Day week work planned !