Solar PV modules convert sunlight into electricity, and their performance is affected by several factors, including temperature. Generally, as the temperature increases, the efficiency of solar panels decreases. This happens because, while higher temperatures can increase the current slightly, they cause a significant drop in voltage, leading to an overall reduction in power output.
To understand this better, let’s look at the IV (current-voltage) curve of a PV module. The IV curve illustrates the relationship between the current and voltage produced by a solar panel at different levels of irradiance and temperature. At a constant irradiance, an increase in temperature causes the IV curve to shift, showing a mild increase in current but a notable decrease in voltage. This shift translates to reduced power output.
Quantifying Temperature Effects
PV module manufacturers provide temperature coefficients in their data sheets, which indicate how different parameters (like power, voltage, and current) change with temperature. These coefficients help quantify the impact of temperature on solar PV performance.
For instance, the temperature coefficient of power (dP/dT) tells us how the power output decreases with each degree Celsius increase in temperature. Let’s consider a practical example to illustrate this:
Imagine a PV module with a maximum power output of 250W under standard test conditions (STC) at 25°C. If the temperature coefficient of power is -2W/°C, we can calculate the power output at 30°C using the following equation:
P=250W+(−2W/°C)×(30°C−25°C)=240W
As shown, the power output decreases to 240W at 30°C. This example demonstrates how even a small increase in temperature can lead to a noticeable drop in solar panel efficiency.
Understanding Module Temperature
While discussing temperature effects, it’s essential to differentiate between module temperature (or cell temperature) and ambient temperature. The module temperature can differ significantly from the ambient temperature due to factors like encapsulation, heat dissipation, and environmental conditions.
To estimate module temperature accurately, a model called the NOCT (Nominal Operating Cell Temperature) is often used. The NOCT is defined as the cell temperature under specific conditions: an irradiance of 800W/m², an ambient temperature of 20°C, and a wind speed of 1m/s. Using this model, the cell temperature (T_cell) can be estimated based on the ambient temperature (T_ambient) and irradiance (G).
Seasonal Variations and Performance
Temperature effects on solar PV performance vary with the seasons. In summer, although sunlight is more abundant, higher temperatures can reduce the efficiency of PV modules. Conversely, in winter, lower temperatures can enhance performance despite reduced irradiance levels.
A study by the PVMD group at Delft University of Technology analysed the temperature effects on PV module efficiency over a year. The study revealed how efficiency fluctuates with ambient conditions, showing significant deviations from rated efficiency due to temperature variations.
During summer, although the sun shines more intensely, the higher temperatures can cause the solar panels to perform worse than expected. On the other hand, in winter, the cooler temperatures help maintain better efficiency, even if the sunlight is less intense. This seasonal variation highlights the importance of considering temperature effects when planning and optimising solar PV systems.
Module Ideality Factor
To quantify the impact of temperature on PV output more precisely, we use the Module Ideality Factor (MIF). The MIF is the ratio of the actual annual PV yield (considering temperature effects) to the expected yield (without temperature effects). A lower MIF indicates greater temperature impact, which varies with PV technology and manufacturing processes.
For example, if the MIF is 80%, it means that the module has lost 20% of its annual energy yield due to temperature effects. Different PV technologies and manufacturing processes result in varying temperature coefficients, which affect the MIF.
Conclusion
Temperature plays a vital role in the performance of solar PV systems. Understanding its effects can help homeowners optimise their installations for maximum efficiency. By considering temperature coefficients, using accurate models to estimate module temperatures, and recognising seasonal variations, you can ensure your solar system performs optimally throughout the year.
For more insights on optimising your solar PV system or personalised advice, contact Blue Electrics today. Stay tuned for more tips on harnessing solar energy effectively!
