Capacity Factor = annual AC energy ÷ (DC nameplate × 8760 h) —
fraction of time the system runs at full rated output; 10–20 % is typical for fixed-tilt PV.
Performance Ratio = annual AC energy ÷ (annual POA irradiation × DC nameplate) —
how efficiently the system converts available sunlight into delivered energy
(accounts for temperature derating, inverter losses, and system losses); 0.75–0.85 is typical.
Calculation Method
The solar PV calculations in this tool follow the
PVWatts® Version 8
algorithm developed by the National Renewable Energy Laboratory (NREL). There will be differences between the results from this tool and PVWatts® due to differences in the underlying weather data and minor differences in the implementation, but the general trends and magnitudes should be similar.
The JavaScript implementation is ported from NREL’s open-source
SSC (SAM Simulation Core)
library.
Key sub-models:
Sky-diffuse irradiance —
Perez, R., Ineichen, P., Seals, R., Michalsky, J., & Stewart, R. (1990).
Modeling daylight availability and irradiance components from direct and global irradiance.
Solar Energy, 44(5), 271–289.
doi:10.1016/0038-092X(90)90055-H
Incidence-angle modifier (IAM) —
De Soto, W., Klein, S. A., & Beckman, W. A. (2006).
Improvement and validation of a model for photovoltaic array performance.
Solar Energy, 80(1), 78–88.
doi:10.1016/j.solener.2005.06.010
Cell temperature —
Steady-state NOCT model per
IEC 61215 / Fuentes, M. K. (1987).
A Simplified Thermal Model for Flat-Plate Photovoltaic Arrays.
SAND85-0330. Sandia National Laboratories.
[OSTI]
Inverter —
King, D. L., Gonzalez, S., Galbraith, G. M., & Boyson, W. E. (2007).
Performance Model for Grid-Connected Photovoltaic Inverters.
SAND2007-5036. Sandia National Laboratories.
[OSTI]