The critical distinction most guides miss: You size a hybrid inverter differently than a pure grid-tied inverter. A grid-tied inverter only needs to match your solar production. A hybrid inverter must also handle your heaviest appliances during a blackout.
The Surge Trap (Sizing for Off-Grid Backup Loads)
Here's the biggest mistake I see DIYers make: They size the hybrid inverter based only on the monthly electric bill, completely forgetting about "In-rush Current."
Starting motors requires 2-3x their running power for 5-10 seconds. A central AC might need 10,000W+ to start. A 3HP well pump needs 8,000W surge.
The Pro Fix: You must size your inverter for your heaviest single appliance. This is why we engineered the SolarInverterUS 8kW and 10kW Hybrid Inverters to deliver 2x surge capacity for a full 10 seconds. A Texas rancher installed our 5kW unit specifically because it could start his 3HP deep well pump during a grid outage.
The NEC 120% Rule (Don't Burn Down Your Panel)
Let me translate this into plain English:
Most modern US homes have a 200-Amp main electrical panel. The NEC says total amps supplying the panel cannot exceed 120% of the busbar's rating.
200A × 1.2 = 240 Amps total allowed 240 Amps - 200A (Your Main Breaker) = 40 Amps
Translation: On a standard 200A panel, the largest solar backfeed breaker you can legally install is 40 Amps (about 7.6kW-8kW inverter). If you want larger, you need a Line-Side Tap or panel upgrade.
