Inverter Sizing and the DC:AC Ratio Explained
The array is usually bigger than the inverter — on purpose. The DC:AC ratio is the design lever that trades a little clipped energy for a lot more useful output.
Why oversize the array
An array only hits its nameplate kWp for a few hours around solar noon on clear days. For most of the day it produces well below rating. Sizing the inverter smaller than the array (DC:AC > 1) lets the inverter run at or near full output for more hours, raising total energy yield and improving the inverter’s efficiency and economics.
The ratio
| Ratio | When to use |
|---|---|
| 1.05–1.15 | High-irradiance sites, cool climates, west-facing arrays |
| 1.15–1.30 | Typical — most rooftop systems, tropical climates |
| 1.30–1.50 | Low tilt, diffuse climates, heavy shading, self-consumption caps |
Clipping
When array DC power exceeds what the inverter can convert, the surplus is “clipped” (the inverter shifts operating voltage to limit power). At a 1.25 ratio, annual clipping loss is typically only 0.5–2% — far less than the extra yield from the larger array.
Also match the windows
- Array open-circuit voltage (Voc) at the coldest expected temperature must stay below the inverter’s maximum DC input voltage.
- Array operating voltage (Vmp) at the hottest expected temperature must stay within the MPPT tracking window.
- String current must not exceed the MPPT’s maximum input current.
EngEst Pro’s Solar PV Calculator sizes the inverter to a target DC:AC ratio, checks the array voltage against the MPPT window at your site temperatures, and lists the inverter with the matching protection in the BOM.
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