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Summary

The Sandia model uses an empirical exponential relationship to calculate module temperature, with surface temperature calculated first and then cell temperature derived from it. This model was developed at Sandia National Laboratories based on extensive field measurements.

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Inputs

NameSymbolUnitsDescription
Ambient Air TemperatureTaT_a°CDry-bulb air temperature
Wind Speedvwv_wm/sWind velocity
Effective POA IrradianceGeffG_{eff}W/m²Effective irradiance after all optical losses
Sandia Conductive Coefficientaa—Sandia conductive coefficient
Sandia Convective Coefficientbb—Sandia convective coefficient
Cell-to-Module Temp DiffΔTc−m\Delta T_{c-m}°CTemperature difference between cell and module surface
Reference IrradianceGrefG_{ref}W/m²Reference irradiance (typically 1000 W/m²)

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Outputs

NameSymbolUnitsDescription
Cell TemperatureTcT_c°COperating temperature of PV cells
Surface TemperatureTmT_m°CModule surface (back-of-module) temperature

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Detailed Description

The Sandia model uses an exponential relationship, calculating surface temperature first: Tm=Geff⋅ea+b⋅vw+TaT_m = G_{eff} \cdot e^{a + b \cdot v_w} + T_a where:
  • aa is Sandia conductive coefficient
  • bb is Sandia convective coefficient

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Empirically Derived Coefficients

The following coefficients were empirically derived by Sandia National Laboratories for open rack mounting configurations:
Module TypeaabbΔTc−m\Delta T_{c-m} (°C)
Glass/cell/glass−3.47−0.05943
Glass/cell/polymer−3.56−0.07503

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Cell Temperature

Tc=Tm+Geff⋅ΔTc−mGrefT_c = T_m + G_{eff} \cdot \frac{\Delta T_{c-m}}{G_{ref}}

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Time-Series Surface Temperature Option

If time-series surface temperature data is provided, it is used directly: Tm=Tm,series(t)T_m = T_{m,series}(t) Tc=Tm+Geff⋅ΔTc−mGrefT_c = T_m + G_{eff} \cdot \frac{\Delta T_{c-m}}{G_{ref}}

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References

  • King, D. L., Boyson, W. E., & Kratochvil, J. A. (2004). Photovoltaic array performance model. SAND2004-3535, Sandia National Laboratories.