Despite popular belief, the power output of a solar panel decreases as the temperature of the cells inside the panel increase. The listed power of a solar cell is the power measured under ideal laboratory conditions of 25 °C, however on a typical hot summers day in Australia it’s not uncommon for a solar cell to reach a scorching 75 °! The efficiency of some cheap solar cells can decrease more than 0.5% for every 1 °C above 25 °C, which means that on a hot summer’s day the efficiency of a solar cell could drop by as much as 25%!
With high temperatures being such an issue it’s extremely important to ensure your solar panels are well ventilated. Make sure the wind is able to cool the solar panels on all sides, including the underside by making sure the panels are not installed too close to the roof. Be aware that some solar power installers have been installing solar panels on roofs with low profile box aluminium extrusions, and when installed this way the solar panels will not be able to dissipate high temperatures as well as they should. When installed on purpose built solar framing systems solar panels have more space for ventilation between the back of the solar panel and the roof structure, providing you with a greater power yield.
Solar Panels and Temperature – The Temperature Coefficient (Pmax)
The temperature coefficient is a characteristic of solar panels that can differ greatly and should not be overlooked as it can have a dramatic effect on the overall yield of your system. Typically a solar panels temperature coefficient can be found on the solar panels data sheet, usually broken down into the 3 following percentages:
Temperature Coefficient of PMPP
Temperature Coefficient of VOC
Temperature Coefficient of ISC
The Temperature coefficient of PMPP is all we really need to worry about as this is the product of the other two percentages and provides us with the percentage of power lost per oC.
The image above points out the temperature co efficient of 290W REC Solar panels from the manufacturers datasheet. REC Twin Peak 2 solar panels are a quality multi crystalline solar panel recommended by Gold Coast Solar Power Solutions, their temperature coefficient is -0.36% per °C above 25°C. With 1 kW of solar panels operating with a cell temperature of 75°C this would equate to a loss of 180W just from heat for every 1kW of solar panels – with a 5kW solar power system that’s 900W of losses due to the high temperature!
Although 900W of power being lost from heat seems like a huge loss with some cheaper panels the temperature coefficient can be greater than -0.5% per °C above 25°C. This equates to a loss of 250W at 75°C on every 1kW of solar panels – with a 5kW solar power system that would equate to losses of 1.25kW, that’s a 350W higher loss than the REC Twin Peak 2 solar panels.
Solar Panels and Temperature – The Temperature Coefficient of Voc
The solar panel temperature coefficient of Voc shows us how the voltage of a solar panel is affected by temperature. This is very important to note in the design of solar power systems to ensure the solar panel array matches the solar inverter or charge controllers requirements along with any other legislation in regards to system voltages. For more information on this topic visit our post: Solar panel maximum voltage calculator
Solar Panels and Temperature – Conclusion
As can be seen with the cheaper, so called “affordable” panels the losses due to the solar panel temperature alone equates to a lower power output of 350W from a 5kW solar power system compared to the higher quality REC Twin Peak 2 solar panels on a good summers day. Over a full summer’s day with our 5kW example you are looking at a lower yield of around 2.8kWh from cheaper panels; just imagine the difference over the entire year! That is more than a 13% loss in output compared to REC Twin Peak 2 solar panels, and add to that the peace of mind that comes with purchasing from a reputable brand who will be around in the years to come to honour their product warranties.. and suddenly the quality solar panels look a lot more affordable!
Learn more about solar panels with the following articles: