PV loss due to temperature

What this step does

The row measures the loss from the module running warmer than 25 °C, taken from the array energy. For every timestep it records the difference between the module's maximum power at 25 °C and at the computed cell temperature. The Model tab's Cell temperature step sets the cell temperature.

The math

1. Running total
2. Loss at a timestep

$$E_{after} = E_{before} - E_{row},\qquad E_{row} = \frac{\Delta t}{1000\,P_{DC}}\sum_i L_i \tag{1}$$ $$L_i = N\left[P_{mpp}(G_i, T_{ref}) - P_{mpp}(G_i, T_{arr,i})\right] \tag{2}$$

where

Symbol	Meaning	Unit
$E_{before}$	the running total of the loss diagram before this row	kWh/kWp
$E_{after}$	the running total after this row	kWh/kWp
$E_{row}$	the row taken as a loss	kWh/kWp
$\Delta t$	the length of one timestep	hours
$P_{DC}$	the DC nameplate of the system	kWp
$L_i$	the power lost at timestep $i$ over the whole system	W
$N$	the number of modules in the system	—
$P_{mpp}(G, T)$	the maximum power of one module at irradiance $G$ and cell temperature $T$, from the module model	W
$G_i$	the irradiance the module converts at timestep $i$: the effective irradiance on the front plus the bifaciality factor times the rear irradiance	W/m²
$T_{ref}$	the reference cell temperature (25 °C)	°C
$T_{arr,i}$	the cell temperature at timestep $i$	°C

Reading the number

A loss, negative: typically 3 to 8 % of the nominal energy. Roof-mounted modules with little ventilation run hotter and lose more than open-rack utility arrays. The row becomes a gain only where the cells run below 25 °C for most of the year's energy.

References

1. Faiman 2008, Assessing the outdoor operating temperature of photovoltaic modules, Progress in Photovoltaics 16(4) 307–315

API

loss.pv_temperature

Symbols follow the symbol registry.