Despite popular belief, the power output of a solar panel decreases with the increase of the panels temperature. The listed power of a solar cell is the power measured under ideal laboratory conditions, which prescribes a temperature of 25 °C. However, on a typical hot summers day, it is not uncommon for a solar cell to reach a temperature of 75 °C. The efficiency of some cheap solar cells can decrease more than 0.5% for every 1 °C above 25 °C. This means that on a hot summers day, the efficiency of a solar cell could drop as much as 25%.
It is therefore extremely important to keep your solar panels well ventilated. Make sure the wind is able to cool on all sides, including the underside of the solar panel. Be aware that some solar power installers have been installing solar panels on low profile box aluminium extrusions to roofs. Typically solar panels installed this way will not be able to dissipate high temperatures as well as solar panels installed on purpose built solar framing systems as they do not have more than enough room for ventilation between the back of the solar panel and the roof structure.
Solar Panels and Temperature – The Temperature Coefficient (Pmax)
The temperature coefficient is a characteristic of solar panels that can differ greatly, especially between cheap panels and quality panels. This characteristic however, should not be overlooked. For example on a hot summers day the temperature of your solar panels may be around 75°C, this will equate to a power loss according to the solar panels temperature coefficient. 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 250W REC Solar panels from the manufacturers datasheet. REC solar panels are a quality multi crystalline solar panel recommended by Gold Coast Solar Power Solutions, their temperature coefficient is -0.40% per °C above 25°C. This would equate to a loss of 200W at 75°C just from heat for every 1 kW of solar panels.
However with some cheaper panels offered by other companies the temperature coefficient can be greater than -0.52% per °C above 25°C. This equates to a loss of 260W at 75°C on every 1 kW of solar panels.
So with the cheaper, so called “cost effective” panel this loss alone equates to 60W lower power output from every 1 kW of solar power system that you have installed compared to the higher quality REC solar panel on a good summers day! Imagine the extra power loss on a larger system! That is more than a 10% loss in output over a higher quality solar panel, add to that the peace of mind that comes with purchasing from a reputable brand and knowing that they will be around in the years to come to honour their product warranties.. suddenly the quality solar panels look a lot more appealing.
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