Pick the system voltage (12, 24 or 48 V)
The battery voltage sets the DC bus. For the same power, doubling the voltage halves the current, so cables, fuses and losses all shrink. That is why larger systems use 48 V.
How
- Use the inverter size you expect (step power-13) as a guide. Victron's wiring guide suggests 12 V up to about 3,000 VA, 24 V up to about 5,000 VA, and 48 V for 5,000 VA and above.
- See the current difference: a 3,000 VA inverter at 12 V can draw around 500 A at peak, which needs very heavy cable. At 48 V the same power draws a quarter of that.
- Choose 12 V only for small cabins, vans or shed systems. Most whole-house off-grid systems use 48 V.
- If a few devices need 12 V, use a DC to DC converter rather than running the whole system at 12 V.
- Fix this decision before buying batteries, controllers and inverters, because they must all match.
Sources
- Wiring Unlimited: DC wiring. Victron Energy, accessed 2026-11
- Stand-alone system sizing (AE 868 Commercial Solar Electric Systems). Penn State University, John A. Dutton e-Education Institute, accessed 2026-11