System voltage: 12V vs 24V vs 48V
Higher system voltage means lower current for the same power — thinner cables, smaller losses, but you need batteries in series. Here is when to use each.
Why voltage changes cable size and losses
Power is volts times amps, so for the same wattage, higher voltage means proportionally lower current. Halving the current — going from 12V to 24V for the same load — cuts resistive losses in the wiring to roughly a quarter for the same cable, or lets you use thinner, cheaper cable for the same acceptable loss. Current, not voltage, is what actually drives cable-sizing decisions on a solar system.
Matching the rest of the system
System voltage has to match across the battery bank, inverter and, for most setups, the charge controller's battery-side output — you cannot mix a 12V battery bank with a 24V inverter. Changing system voltage later usually means re-wiring the battery bank's series/parallel configuration and replacing the inverter and controller, so it is worth sizing the system voltage against your realistic future load, not just what you need on day one.