Guides / System Design & Sizing
12V, 24V or 48V? Picking Your System Voltage
Why system voltage matters, how it changes the current and cable size, and which voltage suits a shed, workshop or home.
Before you buy a battery, an inverter or a charge controller, you need to pick your system voltage. Almost everything else has to match it, so it's one of the first decisions in any off-grid or backup system.
1. Why voltage matters: it's all about current
Power is volts times amps. For the same power, a higher voltage means less current. Less current means thinner cable, smaller fuses and less energy lost as heat in the wiring.
- 2,000W at 12V is about 167A.
- 2,000W at 24V is about 83A.
- 2,000W at 48V is about 42A.
Those figures are before inverter losses, so the real battery current is a little higher again. At 167A you need very heavy cable and every connection has to be perfect. At 42A the wiring is far easier to handle.
2. When 12V makes sense
- Small sheds and cabins running lights, a radio, phone and tool battery charging.
- Systems that run mostly 12V gear directly, without a big inverter.
- Inverters up to roughly 1,000 to 1,500W, with short, heavy cable runs.
12V gear is cheap and easy to find, because it's what caravans and 4WDs use. If that's your world, see Wired For The Wild.
3. When 24V makes sense
- Workshops running a 1,500 to 3,000W inverter for power tools.
- Longer cable runs between the panels, batteries and loads.
- A middle ground: the cable is half the current of 12V, and parts are still easy to get.
4. When 48V makes sense
- Larger off-grid homes and workshops with inverters of 3,000W and up.
- Systems you expect to grow.
- Most larger off-grid inverter-chargers and lithium battery banks are built around 48V.
A 48V lithium bank charges to the high 50s of volts, which is still classed as extra-low voltage DC. It can still deliver a huge current into a short circuit, so it needs proper fusing and isolation (see Fuses, Breakers and Isolators for 12V to 48V Solar).
5. Watch the panel side too
Panels wired in series add their voltages together. A string of panels can easily reach well over 120V DC, which is no longer extra-low voltage and can give a dangerous shock. Check the open-circuit voltage on each panel's label, and check it against your charge controller's maximum input voltage, allowing for the voltage rising on cold mornings.
6. A simple way to decide
- Work out the biggest load you'll run through the inverter at once.
- Up to about 1,500W: 12V is usually fine.
- About 1,500 to 3,000W: 24V is usually the better choice.
- Over about 3,000W, or a system that will grow: go 48V.
Whatever you pick, buy the battery, inverter and charge controller to match. Changing system voltage later usually means replacing most of them.
Safety: in Australia, any work on 240V AC wiring, including connecting an inverter, battery or solar system to a home's switchboard or fixed wiring, must be done by a licensed electrician. Grid-connected systems also need approval from your electricity network.