Do I wire my solar panels in series or parallel?

Wire solar panels in series when you need higher voltage: string inverters and long wire runs both prefer it, and current stays low so the wire stays small. Series is the default for grid-tied roofs.

Wire in parallel when you need shade tolerance or must stay at battery voltage. Parallel strings keep producing when one panel is shaded, at the cost of higher current and thicker wire.

Series-parallel combinations are normal on bigger arrays: match voltage within each string, then parallel the strings.

Hard limits apply. Your inverter or charge controller has a maximum input voltage, cold weather raises panel voltage above nameplate, and mismatched panels drag each other down. Design to the equipment's window.

Then size the conductors with the NEC solar DC wire calculator, which applies the PV-specific 125 percent factors.