Re: solar panel out puts
If you are using a PWM controller or attaching the panels (through a diode) directly to the battery bank, they will each supply current based on their I*V Curve...
The 18 Volt panel charging a battery bank to 14.4 volts will be near maximum current.
The 15 volt panel as it gets warmed up, will probably not supply its maximum current to the battery bank once the battery is much over 13 volts or so (as solar panels heat up, their Vmp drops--that is why a "12 volt" panel has Vmp=~17.6 volt or so and to support ~1-2 volts of controller/wiring voltage drops too).
20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.