Adding additional panels

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