My inverter is rated lower than my panels — is that a mistake?

Almost certainly not a mistake: panel arrays are routinely oversized 10–30% relative to the inverter (a DC/AC ratio of 1.1–1.3). Panels rarely deliver their nameplate rating in real conditions, so a smaller inverter runs closer to its efficient operating range for more of the day, at a lower cost per installed kW.

Why installers do this

A panel’s rated power is measured in lab conditions — 25°C cell temperature and full perpendicular irradiance — that a rooftop almost never sees. Real output is trimmed by heat, haze, morning and evening sun angles, and gradual degradation. An inverter sized for the panels’ nameplate would spend most of its life loafing at partial load.

Oversizing the array instead means the inverter reaches its rated output earlier in the morning and holds it later into the afternoon — a fatter, fuller production curve. The cost is a clipped plateau on the few perfect days when the panels could briefly exceed the inverter’s rating (see the answer on flat midday output). Across the year those clipped kWh are typically small compared with the gains, and with east-west roofs or partial shading the effective ratio is even more conservative than the paper one.

What to do

1. Calculate your DC/AC ratio — total panel kWp divided by inverter kW. Between 1.0 and 1.3: textbook. Above ~1.4: worth asking your installer to justify (it can be fine for east-west layouts, less so for a single south-facing string).
2. Check the warranty terms — reputable inverter makers explicitly permit oversizing up to a stated ratio; staying inside it keeps the warranty clean.
3. Judge by annual yield, not by the midday peak — a forecast for your exact configuration models clipping, so you can see whether the design costs you 1% per year (normal) or meaningfully more.