NOCT
Nominal Operating Cell Temperature: the temperature a PV module cells reach under 800 W/m², 20 °C ambient air and 1 m/s wind on an open rack.
NOCT describes how hot a module runs in realistic sunshine, complementing the laboratory STC rating. The defined test conditions are irradiance of 800 W/m², ambient temperature 20 °C, wind speed 1 m/s, open-circuit electrical state and open-back rack mounting at 45° tilt. IEC 61215:2016 replaced it with NMOT (Nominal Module Operating Temperature), measured with the module at maximum power, which gives values 1–3 °C lower.
Typical values: 41–46 °C for glass-backsheet modules, slightly higher for some glass-glass designs. Datasheets also give the module power at NOCT, usually 74–76% of the STC rating.
Example: NOCT 45 °C, ambient 30 °C, G = 1,000 W/m² gives Tcell about 61 °C. Combined with the power temperature coefficient, this estimates thermal derating.
The simple formula assumes open-rack mounting. Real cell temperatures depend strongly on mounting and wind: flush roof mounts can add 10–20 °C, while floating or high-wind sites run cooler. Simulation tools therefore use more detailed thermal models (Faiman, Sandia, PVsyst U-value model) calibrated per mounting type.
Related terms
All terms →- Temperature coefficient
The percentage change in a PV module power, voltage or current per degree Celsius of cell temperature away from 25 °C.
- Standard Test Conditions (STC)
The reference conditions for rating PV modules: 1,000 W/m² irradiance, 25 °C cell temperature and an AM1.5G solar spectrum.
- Performance ratio
Ratio of actual AC energy output to the theoretical output implied by plane-of-array irradiation and nameplate capacity; a location-independent quality metric for PV plants.
- Floating solar
PV arrays mounted on buoyant platforms on reservoirs, lakes, ponds or sheltered coastal waters instead of on land or roofs.