NOCT (Normal Operating Cell Temperature) is a characteristic value of the temperature of solar panels under normal operating conditions. This parameter is particularly important when evaluating the performance of solar panels, as their efficiency and output are significantly affected by their operating temperature.
What is NOCT?
The NOCT value is determined under standard environmental conditions:
- Irradiance: 800 W/m² (instead of the usual 1000 W/m² which applies to STC).
- Wind speed: 1 m/s.
- Ambient temperature: 20 °C.
- No load: The circuit is open, meaning the solar panel is not operating under full load.
These conditions are closer to real-life situations than STC (Standard Test Conditions), which use 1000 W/m² irradiance, 25 °C ambient temperature, and zero wind speed under laboratory conditions.
Why is NOCT important?
More realistic performance estimation: NOCT provides a more accurate picture of how solar panels perform under real-world conditions. This helps determine the expected energy production of the system at a given location.
Temperature effects: The performance of solar panels generally decreases as temperature increases. The NOCT value shows the operating temperature of the solar panel when it operates under normal, rather than ideal, conditions.
System design: NOCT helps designers and engineers create solar panel systems that operate with maximum efficiency under specific environmental conditions.
Comparison of NOCT and STC
| Parameter | NOCT | STC |
|---|---|---|
| Irradiance | 800 W/m² | 1000 W/m² |
| Ambient temperature | 20 °C | 25 °C |
| Wind speed | 1 m/s | 0 m/s |
| State | Open circuit (no load) | Operating under load |
Example of NOCT use
If the NOCT value on a solar panel's datasheet is 45 °C, it means that under normal conditions, the cell temperature is expected to rise to 45 °C. This information is useful because solar panel efficiency decreases with increasing temperature. For example, if the power-temperature coefficient of the solar panel is -0.4%/°C, the power loss at 45 °C will be approximately 10% compared to STC conditions.
Important considerations
- NOCT is not an absolute value but a parameter characteristic of the specific solar panel type.
- The NOCT value affects the efficiency of the entire system, so it is worth considering the climatic conditions of the installation site.
- Solar panels with lower NOCT values should be chosen for hot climates to reduce efficiency loss due to heat.
Summary
NOCT is a fundamental indicator that helps determine the performance of solar power systems under real-world conditions. Based on the NOCT value indicated in datasheets, the system can be more easily designed and optimized, taking into account the climatic conditions of the specific location and the temperature sensitivity of the solar panels.