It may sound strange but it is true that with the increase in the temperature the efficiency of the solar panels reduces. With the increase in temperature the flow of the electrons increases causes the current to increase and at the same time the voltage drops. The decrease in the voltage is greater than the increase in the current. Therefore the overall power (Power=Voltage*Current) decreases which make panel to operate at the lower efficiency.
The PV modules are generally tested at the standard temperature of 25ºC. Based on the different locations the heat can reduce the efficiency of the solar panels by 10% -15%.
The change in the efficiency of panel as the temperature varies
How to determine the efficiency ?
Whenever you buy solar panel look at the manufacturer’s data sheet, where you will find the term called temperature coefficient at Pm (Maximum Power). This will give you the idea about the efficiency of the panel with change in the temperature.
Let us suppose a 200 watt solar panel has temperature coefficient of 0.48%.It means that with every 1 degree rise in the temperature above 25ºC , the maximum power of the solar panel reduces by 0.48%.
In a hot sunny day when the temperature is 40ºC (15 degree excess of Standard temperature), the maximum power of the solar panel will get reduce by approximately 7 %.
While on the other hand during spring when there is sunny day with temperature below 25ºC , the output power can be more than the maximum rated power Pm.
So we can understand that the efficiency of the solar modules vary with variations in the seasons
Reducing the effect of the heat on the solar panels ?
What we should to reduce the effect of the heat on the solar panels ?
We can reduce the effect of heat by installing and elevating the solar panels few inches above the roof so as to allow air to pass through and cool the panels. Also, maintain gap between panels in the array.