How to size a solar inverter

Updated October 2026

An inverter that is too small shuts down when you switch on a heavy appliance. One that is too large costs more and wastes a little power when idle. The right size depends on what runs at the same time and, for off-grid and hybrid systems, on motor surge. See the inverters page for the three types.

Off-grid and hybrid: size by loads

1. List what can run together. Only count appliances that may be on at the same moment.
2. Add the running watts.
3. Find the surge. Motors such as pumps, fridges and compressors draw about 3 times their running watts for a second or two when they start.
4. Add 25 percent headroom to the running total, and check the inverter's surge rating covers the peak.

Worked example

The pump starts at about 3 × 373 = 1,119 W, which adds roughly 746 W on top of the running total, so the peak is about 1,570 W. With 25 percent headroom the running load becomes about 1,030 W. A 1.5 kW inverter with a surge rating of 3 kW or more is a sound choice.

Battery voltage

• Up to about 1 kW: 12 V.
• About 1 to 3 kW: 24 V.
• Above about 3 kW: 48 V, which keeps battery current and cable size manageable.

Grid-tied: size by the array

A grid-tied inverter is sized to the solar array, not to the loads. A DC-to-AC ratio of 1.1 to 1.3 is common. For the 8.2 kW array in our panel guide, 8.2 ÷ 1.2 ≈ 6.8, so a 7 kW inverter fits. Check your utility's limits on export size.

Other things to check

• Choose pure sine wave for motors, fridges and electronics.
• For hybrids, confirm the battery charge current and the backup output rating, which can be lower than the main rating.
• Check the maximum PV input voltage and power if panels connect directly to the inverter.

Next step: size your array and battery, then compare off-grid, hybrid and grid-tied inverters.