NOCT
Nominal Operating Cell Temperature -- cell temperature under realistic operating conditions (800 W/m², 20 °C, 1 m/s wind).
Also known as: Nominal Operating Cell Temperature, NMOT
What Is NOCT?
NOCT (Nominal Operating Cell Temperature) is the cell temperature that a solar module reaches under defined, realistic conditions: 800 W/m² irradiance, 20 °C ambient temperature, and 1 m/s wind speed. Typical NOCT values range from 42—48 °C.
Why Is NOCT Important?
The rated power specified under STC (Standard Test Conditions) is measured at 25 °C cell temperature — a temperature that is almost never reached in real operation. NOCT provides a more realistic estimate of actual module performance in the field.
NOCT vs. STC
| Parameter | STC | NOCT |
|---|---|---|
| Irradiance | 1,000 W/m² | 800 W/m² |
| Cell temperature | 25 °C | 42—48 °C (measured) |
| Wind speed | Not defined | 1 m/s |
| Power rating | Wp (rated power) | Realistic power |
Calculating Real-World Power
The NOCT value can be used to estimate the actual cell temperature:
T_cell = T_ambient + (NOCT - 20) x (Irradiance / 800)
At 30 °C ambient temperature, 1,000 W/m² irradiance, and NOCT = 45 °C: T_cell = 30 + (45 - 20) x (1,000/800) = 61.3 °C
Practical Tip
A lower NOCT value is advantageous as it indicates better heat dissipation. Modules with NOCT below 44 °C are particularly well suited for warm locations.
Related Terms
STC (Standard Test Conditions)
Standardised test conditions (1,000 W/m², 25 °C, AM 1.5) under which the rated power of solar modules is measured.
Temperature Coefficient
Metric indicating how much a solar module's power decreases per degree Celsius of temperature rise (typical: -0.3%/°C).
Solar Module
Assembly of multiple solar cells in a weatherproof housing for generating electricity from sunlight.
Efficiency
Ratio of usable electrical energy to incident solar energy -- indicates the effectiveness of a solar cell or system.