Sizing an inverter

Inverter shopping goes wrong when people size to the wrong number. Daily watt-hours tell you about batteries. The inverter cares about the watts running at the same moment.

Find your continuous peak

The Megawatt battery calculator estimates that peak from the appliances you check. A luxury coach with the AV package on and the air conditioner off comes to 2,300 watts in that table.

Check multi-zone air conditioning and the peak jumps by another 4,500 watts.

Add a margin, then round up

The solar planner multiplies the peak by 1.25 and picks the next size in a list that runs from 1,000 to 6,000 watts.

That 1.25 is a planning margin we use on this site. It isn’t in the old calculator and it isn’t a National Electrical Code rule, so change it if your installer works differently.

Surge is the part the math misses

A roof air conditioner can pull several times its running watts for a moment at startup. The old calculator doesn’t publish a surge column, so we won’t invent one.

Read the inverter’s surge rating and the air conditioner’s startup data in the appliance manual.

Big loads push the voltage up

The same peak watts choose battery voltage in the original widget. Past 3,000 continuous watts it leaves 12 volts, and past 5,000 it leaves 24.

That’s why a residential fridge plus air conditioning pushes a plan toward a higher-voltage bank and a bigger inverter.

Megawatt’s affiliate list has batteries and solar packs. It doesn’t have an inverter yet, and we won’t dress up a battery link as one. These are the banks that pair with the first two voltage steps.

The original solar calculator’s footer still applies: talk to a certified electrician before you modify the electrical system.