12 Volt, 24 Volt or 48 Volt - which system should I choose?

Question: Should I choose a 12 volt, a 24 volt or a 48 volt stand-alone power system?

Reply: In short, your energy consumption should determine the voltage of your power system so continuous currents ideally do not exceed 100 amperes.

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Basics

  • Power (Energy) (P) = Watts
  • Current (Flow) (I) = Amps
  • Voltage (Pressure) (V) = Volts
  • Cell = Single component of a Battery
  • Battery (Battery Bank) = Collection of Cells wired in series or parallel

Power - Current - Voltage

  • 1,000 watts = 83 amps @ 12 volts
  • 2,000 watts = 83 amps @ 24 volts
  • 4,000 watts = 83 amps @ 48 volts
  • 20,000 watts = 83 amps @ 230 volts

The higher the current the larger the wiring and circuit protection components need to be, both of which are expensive. By doubling the voltage (I = P/V), the same amount of power is achieved with half the current.

Dealing with currents over 100 amperes is costly and potentially dangerous. As a perspective, a standard household extension cord is rated for a maximum current of 10 amperes. 100 amperes would melt it and could start a fire!

System Size

12 volts used to be a standard for extra low voltage power systems. The cost of an off-grid system could be reduced by limiting the inverter size, which was achieved by using 12V or 24V appliances lighting that run directly from the battery without the need for an inverter. Over time, inverters, AC appliances and solar panels have become more efficient and affordable, while 12V or 24V appliances and lighting have become more difficult to source and often dearer.

Nowadays most off-grid households run on 48V systems including a 230V AC inverter that runs all the loads. The wiring of the house can be the same as any other grid-connected household and cabling cost is greatly reduced.

12V and 24V are still relevant in cases of minimal power usage, like in a caravan, campervan or shed.