Solar Inverter Sizing Calculator

Add up the running watts of all appliances you'll run simultaneously. That's your continuous load. Add 25% safety margin. Also check each appliance's starting (surge) watts — motors like refrigerators, AC units, and pumps draw 2-3x their running watts on startup. The inverter must handle the surge load too.

Continuous watts is the power an inverter can supply indefinitely. Surge (peak) watts is the maximum power it can supply for a brief period (usually 1-3 seconds) during motor startups. Most inverters are rated for 2x their continuous rating as surge capacity. Always check both specs for your loads.

Pure sine wave inverters produce AC power that matches the utility grid quality, compatible with all appliances including sensitive electronics and motor loads. Modified sine wave inverters are cheaper but can cause buzzing in audio equipment, reduced efficiency in motors, and incompatibility with some electronics. For most residential solar, pure sine wave is recommended.

Inverter efficiency (typically 90-97%) means that some power is lost as heat during the DC-to-AC conversion. A 95% efficient inverter loses 5% of the energy passing through it. This loss is factored into system sizing. High-quality MPPT inverter-chargers combine the inverter, battery charger, and sometimes MPPT charge controller in one unit.

String inverters are simpler and lower-cost but are limited by the worst-performing panel in each string. Microinverters (one per panel) or DC optimizers paired with a string inverter allow each panel to perform independently, better handling shade and mismatch. Hybrid inverters add battery storage capability to grid-tied systems.