Heat wave brings photovoltaic systems in Germany into full swing

Interview: Meteorologists have predicted a new heat wave and temperatures of up to 40 degrees Celsius in parts of the republic in the coming days. Good news for the operators of photovoltaic systems, even if the heat can have a slightly negative effect on the performance of the modules. However, the temperature coefficient of the modules has much less impact than if the inverters are curtailed due to the high heat, as Bruno Burger, Head of Department Advanced Devices and Technologies Division Power Electronics, Grids and Systems and responsible for the Energy Charts at Fraunhofer ISE, says in an interview with pv magazine. He also explains why Germany actually needs a much greater expansion of photovoltaics.

pv magazine: Germany is facing the next heat wave. How does this affect the generation of photovoltaic systems in Germany?

Bruno Burger: First of all, it's a fact that the heat wave is also synonymous with a lot of sun. In view of the extremely high irradiation, a lot of solar power generation is also to be expected for the coming days. The negative temperature coefficient for the modules is only of secondary importance. This can also be seen, for example, in today's generation data. We have already reached 32 gigawatts, which is only slightly below this year's record value of 33.5 gigawatts from May.

At what temperature does the performance of the modules decrease?

In the laboratory, the performance measurements for the modules are carried out at 25 degrees Celsius. Depending on the technologies, the temperature coefficients differ. In the case of monocrystalline solar modules, we see a decrease in output of 0.4 percent per Kelvin or degree Celsius, i.e. at ten degrees more, the photovoltaic systems generate around four percent less. For highly efficient modules, the effects are more likely to be three percent at ten degrees more, and slightly higher for older polycrystalline modules at just under five percent. It can therefore be said that the more efficient the crystalline modules, the less susceptible they are to temperature. At the same time, at temperatures below 25 degrees Celsius, an increase in module performance in these areas can also be measured.

The outside temperature does not necessarily correspond to the temperature of the modules that are directly exposed to solar radiation. What differences can be observed?

That's right. In modules installed on flat roofs or open spaces, we see that the modules are around 20 degrees hotter than the air temperature in full sunlight. With pitched roofs, they often become 30 degrees warmer. In roof-integrated photovoltaic systems with an insulated module back, cooling is only provided by the front. Here it can even be 40 degrees more.

Is there anything operators can do to actively counteract this effect?

I would recommend operators not to do anything with the modules. They also work very well in the heat. If you want to do something, you should check where your inverter is located. In this case, it is advisable to install it in a cool place, such as in the basement. If inverters are located in the attic, for example, which gets 50 degrees hot in midsummer, it can quickly happen that the inverters significantly limit their output. This effect can then be much greater than that of the temperature coefficient in the modules.

How are electricity prices on the market developing at the moment after being relatively low in June?

At the moment, we are seeing rising prices on the electricity exchange again. This is also always a sign of greater demand or low supply. We haven't quite reached the level of last summer yet. Nevertheless, it is not foreseeable whether we will not face similar effects. In view of low water levels in the rivers and high water temperatures, the curtailment or shutdown of fossil fuel power plants cannot be ruled out this summer either. Then we need photovoltaics all the more to fill the gap.

But is the installed photovoltaic capacity in Germany sufficient for this?

Although the expansion picked up again last year, we still installed 15 gigawatts too few photovoltaics compared to wind. This is all the more true if we will see many more such heat waves in the future in view of climate change. In Germany, too, more and more people will certainly consider buying an air conditioner. Especially for their consumption – usually during the day – photovoltaics is the perfect partner. For the energy transition and the German government's goal of providing 65 percent of electricity generation from renewable energies by 2030, we need an annual photovoltaic expansion of ten gigawatts. In recent years, this has been two to three gigawatts.