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SESK: Stuff Everyone Should Know · sesk.info/solar-dcac-ratio

NREL's current PVWatts (Version 8) uses a default DC-to-AC ratio of 1.2. What does that mean?

The array DC rating is a bit larger than the inverter AC rating.

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  1. Array DC rating is a bit above inverter AC rating ✔
  2. The inverter is much bigger than the array
  3. Both are always exactly equal

Why: Arrays are often sized larger than the inverter. With a 1.2 ratio, a 6 kW DC array pairs with a 5 kW AC inverter.

Huh, didn't know that: The older PVWatts Version 5 used a default DC-to-AC ratio of 1.1.

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References

Answer: Array DC rating is a bit above inverter AC rating. Arrays are often sized larger than the inverter. With a 1.2 ratio, a 6 kW DC array pairs with a 5 kW AC inverter.

  1. NREL Developer Network: PVWatts V8 API developer.nrel.gov/docs/solar/pvwatts/v8
    dc_ac_ratio, decimal, default 1.2, DC to AC ratio.
    Checked 2026-10-10.
  2. NREL PVWatts Version 5 Manual www.nrel.gov/docs/fy14osti/62641.pdf
    the photovoltaic array is often sized so that its DC rating is higher than the inverter's AC rating
    Checked 2026-10-10.
  3. NREL PVWatts Version 5 Manual www.nrel.gov/docs/fy14osti/62641.pdf
    The default value of the new DC-to-AC ratio input is 1.1.
    Checked 2026-10-10.

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