PV Performance Ratio from Stacked Losses
Performance ratio as the product of (1 - loss) over the PVWatts-style derate stack...
Example
You enter
- Soiling 2
- Temperature 8
- Wiring dc 2
- Inverter 4
- Mismatch 2
- Shading 3
You get
- Performance ratio (PR) 0.806
- Total loss 19.4%
Checked against published worked examples from: NREL (A. Dobos).
Details, formula, and sources
ScopePerformance ratio as the product of (1 - loss) over the PVWatts-style derate stack (soiling, temperature, wiring, inverter, mismatch, shading, etc.; PVWatts itself models temperature and the inverter separately, so its default 14% excludes them). A typical rooftop stack lands near 0.75-0.82; attacking the two largest losses moves it most, the multiplicative leverage made visible. A screening stack, not a metered PR.
Formula or tablePR = product over entered losses of (1 - loss_i/100); total_loss = (1 - PR) x 100.
Source and editionThe PV performance-ratio derate stack (PVWatts-style loss categories), by name.
Free accessThe PVWatts loss categories and the multiplicative derate stack are published free by NREL. A screening stack, not a metered performance ratio.
What governsEstimate. AHJ and licensed professional govern.
API field namessoiling, temperature, wiring_dc, inverter, mismatch, shading, pr, total_loss_pct
- Multiplicative stack PR = product of (1 - loss_i); losses compound, not addNREL PVWatts
- Loss categories soiling, temperature, wiring, inverter, mismatch, shading, availability, nameplate, LID, connectionsPVWatts
- Screening, annual an annual-average screen; not a metered performance ratioscope of this tile