Size the inverter/charger
The inverter turns battery DC into AC for your appliances. It must handle the highest continuous load and the starting surge of motors, and in most off-grid systems it also charges the batteries from a generator.
How
- Add up the AC loads that could run at the same time (step power-1). The inverter's continuous rating must exceed this, with room for future loads.
- Check the surge rating against the biggest motor start (well pump, compressor) running on top of the other loads.
- Use the inverter sizing calculator on this page. A rating in VA is not the same as watts: Victron notes a 5 kVA generator gives about 4 kW, and inverters work the same way.
- Choose a pure sine wave inverter. Sensitive electronics and many motors need a clean sine wave.
- Match the inverter DC input to your system voltage and the AC output to your country (for example 230 V 50 Hz or 120/240 V 60 Hz).
- If you have a generator, choose an inverter/charger with a generator input, automatic transfer and an adjustable charge current.
- Check the idle (no load) consumption, because it runs 24 hours a day and belongs in the load audit.
- Check whether the inverter/charger has an automatic ground relay, which makes the neutral-earth link while inverting (power-19).
Sources
- Balance-of-System Equipment Required for Renewable Energy Systems. US Department of Energy, Energy Saver, accessed 2026-11
- Wiring Unlimited: DC wiring. Victron Energy, accessed 2026-11
- Wiring Unlimited, chapter 7: Ground, earth and electrical safety. Victron Energy, accessed 2026-11
- MultiPlus FAQ: generator sizing. Victron Energy, accessed 2026-11