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NREL's PVWatts manual uses what default value for total system losses when estimating solar output?

PVWatts defaults to 14% total system losses.

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  1. 14% ✔
  2. 2%
  3. 30%

Why: Real systems lose some output to soiling, shading, wiring, inverter mismatch and downtime. PVWatts combines these into a default 14% loss.

Huh, didn't know that: The losses combine by multiplying, not by simply adding them up.

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References

Answer: 14%. Real systems lose some output to soiling, shading, wiring, inverter mismatch and downtime. PVWatts combines these into a default 14% loss.

  1. NREL: PVWatts Version 5 Manual www.nrel.gov/docs/fy14osti/62641.pdf
    Total system losses are specified as a percentage, with a default value of 14 %.
    Checked 2026-10-10.
  2. NREL PVWatts Version 5 Manual www.nrel.gov/docs/fy14osti/62641.pdf
    It is important to note that the total loss is not the sum of the individual losses.
    Checked 2026-10-10.

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