Inverter Sizing — Method
The inverter must continuously supply the sum of AC loads that run together, with headroom for motor in-rush. Take the total continuous load, add a margin (≈25%), and round up to a standard rating. For grid-tied PV the inverter is also matched to the array through the DC/AC ratio (array DC kW ÷ inverter AC kW), normally 1.1–1.3: a modest over-sizing of the array captures more energy in weak light while keeping clipping losses small.
Frequently Asked Questions
Add up the continuous AC loads, multiply by about 1.25 for surge margin, and round up to a standard inverter rating. For grid-tie also check the DC/AC ratio against the array.
For grid-tied PV, 1.1-1.3 is typical: the array DC kW is slightly larger than the inverter AC kW, which improves utilisation with little clipping loss.
Yes for motor loads (pumps, fridges, AC). Their locked-rotor/start current can be several times the running current, so the inverter peak/surge rating must cover it, not just the continuous rating.
Yes - a DC/AC ratio above 1 is normal. Going much above ~1.35 starts to clip peak production; check the inverter clipping curve and any export limit.
String inverters suit unshaded arrays of similar orientation; microinverters or optimisers suit shading and multiple roof planes. Both are sized to the connected module power and the AC load.
Solar Inverter Sizing Explained
The inverter converts DC from the panels/battery into AC for loads or the grid. It is sized from two angles: the AC load it must run, and the DC array it is matched to.
Load side
Sum the continuous loads that operate together and add surge margin for motors. The continuous rating must never be exceeded; the peak rating covers brief start-up surges.
Array side
For grid-tie, the DC/AC ratio (array ÷ inverter) is typically 1.1-1.3 so the inverter runs near capacity in good sun without large clipping losses. Combine with array sizing and string sizing to confirm the MPPT voltage window.
Related: Panel Sizing, Battery Bank, PV String.