NOCT (Normal Operating Cell Temperature) is a characteristic value of the temperature of solar cells under normal operating conditions. This parameter is particularly important in evaluating the performance of solar cells, as the efficiency and performance of solar cells are significantly affected by their operating temperature.
What is NOCT?
The NOCT value is determined under standard environmental conditions:
- Radiation intensity: 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 in an open state, which means the solar panel is not operating under full load.
These conditions are closer to real-life conditions than STC (Standard Test Conditions), which uses 1000 W/m² irradiance, 25°C ambient temperature and zero wind speed in laboratory conditions.
Why is NOCT important?
More realistic performance estimates: NOCT provides a more accurate picture of how solar panels perform in real-world conditions. This helps determine the expected energy production of the system at a given location.
Temperature effects: Solar panel performance generally decreases as temperature increases. The NOCT value shows the operating temperature of the solar panel when it is operating under non-ideal, but normal conditions.
System Design: NOCT helps designers and engineers design solar systems that operate at maximum efficiency under given environmental conditions.
Comparison of NOCT and STC
| Parameter | NOCT | STC |
|---|---|---|
| Radiation intensity | 800W/m² | 1000 W/m² |
| Ambient temperature | 20 °C | 25 °C |
| Wind speed | 1 m/s | 0 m/s |
| Status | Open circuit (no load) | Operates under load |
Example of using NOCT
If a solar panel datasheet lists a NOCT of 45°C, this 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 a solar panel has a power-temperature coefficient of -0.4%/°C, the power loss at 45°C will be approximately 10% compared to STC conditions.
Important information
- NOCT is not an absolute value, but a parameter specific to the type of solar panel.
- The NOCT value affects the efficiency of the entire system, so it is worth considering the climatic conditions of the installation location.
- 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 systems under real-world conditions. The NOCT value indicated in the data sheets makes it easier to design and optimize the system, taking into account the climatic conditions of the given location and the temperature sensitivity of the solar panels.