“The vast majority of solar cells are made of the material silicon,” associate professor of solar cell technology René van Swaaij of TU Delft tells RTL News. The energy of the sun releases electrons from that silicon. “And the bottom line is: heat suppresses that effect a bit. More energy leaks away. The electrical voltage of the solar cell drops.”
In the manual
If you have solar panels on the roof of your house or shed and you have kept the manual, you can look up the power of 1 panel there. “I did that for my own panels. They each have a capacity of 270 watt peak.”
But that is the case under standard test conditions. “It is then assumed, among other things, that the panel has a temperature of 25 degrees.” Now, with an outside temperature of around 30 degrees, the panels are getting much warmer. “They can get up to 60 degrees now.”
If we assume that 60 degrees, then the panels are 35 degrees warmer than in the test environment. For every degree difference, they work a little less well. “In the case of my own panels, that saves – that is also stated in the manual – 0.44 percent per degree. So times 35 is 15.4 percent.”
The warmer it is, the less well the panel converts light into energy. Under test conditions, a panel like the one on Van Swaaij’s roof would have a capacity of 270 watts peak, but at temperatures like now of about 230.
Watt?
Watt peak is the unit in which energy from solar panels is expressed. On the Essent website states: “On average, 1 Watt peak (Wp) in the Netherlands yields approximately 0.88 kWh per year.” A solar panel of 270 watt peak therefore delivers – under ideal circumstances – 237.60 kWh per year.
Wim Sinke, emeritus professor of solar energy at the University of Amsterdam, compares the operation of solar panels to a rain barrel that fills itself not with rain but with sun rays. Heat is then a leak in that barrel, a hole in the bottom. “Water, in this case solar energy, flows away through that leak.”
As soon as the panels cool down again, the leak in the barrel is closed again: “The panels do not sustain any permanent damage due to the high temperatures.” But the fact is, says Sinke: “Nothing is as beautiful for solar energy as a cold day with lots of sun.”
White buildings effect
Incidentally, there are many more factors than just the temperature that determine how much your panels yield. Van Swaaij: “Obviously the amount of light they catch. How are they positioned in relation to the sun? If there is a white building nearby, reflection can ensure that they catch more light and work better. And the wind is one factor, more wind means less warm panels and a better yield. If they are dirty, for example due to sand, then they work less well.”
Finally, the age of the panels also plays a role: “Mine are eight years old and are therefore less effective by 0.44 percent per degree. Nowadays they have been further developed and that effect is smaller per degree.”
All things considered, how annoying are very hot days for the wallet of the solar panel owner? Although panels do their job a little better in winter, it is the months of May and June when they often produce the most energy. “It is then the longest light per day. In addition, the light is more intense.”
Costs no power
Warm or not, it will be a good month at the bottom line: “The yield per panel may now temporarily drop due to the temperature, but there are now so many hours of sunshine and the intensity is so high that the panels still generate a lot of energy. I have ten lying around and on an annual basis they generate more electricity than I use anyway.”
If you keep track of what your panels yield in an app and you see the ‘yield’ falling these days, know: this will not cost you any capital. In euros then, in watts a bit.
2023-06-13 07:35:22
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