How to size a solar inverter
An inverter smaller than the array is normal and usually correct. Understanding why makes the trade-off deliberate.
The DC to AC ratio compares array capacity with inverter capacity. A 6 kW array on a 5 kW inverter is a ratio of 1.2, and that is a perfectly conventional design.
Step-by-step
- Enter your array size.
- Enter candidate inverter sizes.
- Read the ratio and the estimated clipping.
Why undersizing is normal
An array almost never produces its rated output. That figure assumes full irradiance at 25°C cell temperature, and real conditions rarely coincide. A 6 kW array might peak at 4.8 kW on a good day.
Sizing the inverter for a peak that occurs for a few minutes a year means paying for capacity that is idle almost always. A ratio of 1.1 to 1.3 is the usual band.
Clipping, and what it actually costs
When the array does exceed the inverter's capacity, output is capped — clipped. It sounds wasteful and is usually trivial: at a ratio of 1.2 the annual loss is commonly under 2%, because it only happens near midday in the clearest conditions.
Against that, a smaller inverter is cheaper and runs closer to its efficient range more of the time. Inverters are less efficient at very low loads, so an oversized one performs worse on the many days when production is modest.
When to go higher or lower
- Higher ratio (smaller inverter) suits east-west arrays, which never peak all at once, and cloudy climates.
- Lower ratio suits cool sunny climates where the array genuinely reaches its rating, and cases where a grid export limit is the binding constraint.
Frequently asked questions
Should the inverter match the array size?
Usually not. A ratio of 1.1 to 1.3 DC to AC is conventional, because arrays rarely reach their rated output and sizing for a rare peak wastes money.
How much does clipping cost me?
At a ratio of 1.2, commonly under 2% of annual output. It only occurs near midday in the clearest conditions, so it affects few hours a year.
Can an inverter be too large?
Yes. Inverters are less efficient at low loads, so an oversized one performs worse across the many days of modest production, and costs more to buy.
Open the inverter sizing tool →