I have three Renogy Solar Panel 200 Watt 12 Volt connected in serise and the open circuit volatge is 23 volts each, do I buy a charge controler thats 23 volts or combine the open circuit volatge together (69) and buy a 70 volt charge controler ?.
Thats where the MPPT calculator comes in handy
If you put the panels in series then the voltages add up. A 75V MPPT might be too close, might need a 100V, but the calculator will rell you