The Fuentes cell temperature model is a first-principles energy balance model that, unlike most PV thermal models, includes the effect of thermal transience. It was originally developed for the PVFORM simulation software and was later adopted by PVWatts (most notably versions 1 and 5).
In addition to the usual plane of array irradiance, ambient temperature, and wind speed inputs, the Fuentes model includes several parameters describing the array configuration:
- INOCT: the “installed” nominal operating cell temperature, which characterizes the thermal properties of the PV module and its mounting configuration
- PV module emissivity and absorption coefficients
- PV module surface tilt, width and length, and mounting height above ground
- Height at which the wind speed was measured
PVWatts uses INOCT values of 45 °C for arrays with free-flowing air and 49 °C for arrays with restricted air flow like rooftop arrays.
The model’s inclusion of thermal capacitance and radiative cooling set it apart from other common PV temperature models. Thermal transience causes the estimated cell temperature to lag and be less dynamic than predictions from a steady-state model are, especially in datasets with variable irradiance conditions and short time steps. Radiative cooling causes, among other effects, the estimated cell temperature to fall below ambient temperature at night.
These effects are demonstrated in the figure below. Relative to a steady-state model, the Fuentes model’s transience more closely recreates the short-timescale effects present in a measured back-of-model temperature dataset.
The Fuentes temperature model is implemented in pvlib-python with pvlib.temperature.fuentes.
References
[1] M. K. Fuentes, "A Simplifed Thermal Model for Flat-Plate Photovoltaic Arrays," 1987. SAND85-0330, Sandia National Laboratories, Albuquerque NM.
[2] A. Dobos, “PVWatts Version 5 Manual”, 2014. NREL/TP-6A20-62641, National Renewable Energy Laboratory, Golden CO.
[3] Anton Driesse, Marios Theristis, and Joshua S. Stein, “PV module operating conditions and temperature measurements: an open dataset for PV research. SAND2023-01949.