Temperature is the key factor that impacts the output power of solar panels and it needs to be within the specified limits. Behaviour of different solar PV modules changes with their operating ambient temperature resulting in decrease of the output power with every increase in temperature.
Sun’s radiation consists of two components – heat and light. An increase in temperature does not change solar energy reaching the panels, however, it reduces the amount that can be converted into electricity from the solar panel.
Energy that the solar panels produce is a function of power, further power is the product of current and voltage (P= I x V). So, while an increase in temperature slightly increases the current in solar cells, the voltage is decreased by a greater amount which results in reduced power output.
Effect of module temperature on the output of the PV plant can be clearly seen from the below graphical representation, which have been observed from actual plant operation at sites for two different months- September and March:
The Temperature Coefficient
Every PV modules has its different unique temperature coefficient value (Pmax) in the data sheet provided by the manufacturer. This is in the form of negative percentage and it reveals the temperature effect on the PV module.
Solar Panels are rated at 25oC and therefore the temperature coefficient percentage depicts the change in efficiency with each degree up and down in temperature. For instance, if the temperature coefficient of a panel is -0.45%, then for every 1oC rise, the panel’s maximum power will reduce by 0.45%.So, on a hot day, when panel temperatures may reach 45oC, a panel with a temperature coefficient of -0.45% would result in a maximum power output reduction of 9%.
On the other hand, on a sunny winter’s morning, solar PV modules will be much more efficient. The optimal operating condition for the solar panels is the cold and sunny environment. Unfortunately, these regions near the globe have weaker sunshine and shorter days, so the insolation value which is the main strength of the sunlight hitting the ground will decrease closer to the poles as the sun comes in at a lower angle. The solar tracking system can bring positive effects in such climate because of its ability to adjust its angle in such a way to get more irradiation that will ultimately add up to the generation.
Temp coefficients of module from some of the leading OEM’s is tabulated as below:
|OEM||Rating Wp||Module Technology||Temp Coefficient %/oC|
|First Solar||82.5||Thin Film||-0.25|
- Both Monocrystalline and Polycrystalline cells have a temperature coefficient, Pmax, of between -0.45% to -0.50%.
- Amorphous based or cadmium telluride (First Solar) based thin film panels have temp coefficient between -0.20% to -0.25%.
What can be done to stop Panels from getting too hot?
There are different methods to control PV module temperature. Some of them have been detailed further.
Firstly, intrinsically in the process of making the panels, companies use a thermally conductive substrate to help vent excess heat from the glass layer.
Externally, a few methods of cooling the panels such as dousing them with water may be available to improve power efficiency, though economic efficiency would depend on whether water is inexpensive and plentiful. In case of ground mounted solar PV plants, the MMS design will try to ensure there is a free flow of air above and below the solar panels when they are mounted, by elevating the panels a few inches above the ground. Also, having a layer of grass or weeds under the panels is a way to ensure slightly lower temperatures than bare soil / sand underneath the panels.
In addition, for roof mounted systems, it is possible to add ventilation systems or fans to the solar PV system to help assist the movement of air around the panels to keep them cool.
We, at Susten, have an experience of 900+MW portfolio across India and across PV modules of different makes. Continuously benchmarking of modules across various performance parameters and detailed analysis of such trends help us to optimise our site operations and in turn result in improved plant performance.