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Heat wave challenges power supply
Rising temperatures put pressure on power plant cooling processes and decrease efficiency of photovoltaic systems

The high 2018 summer temperatures are impacting electricity generation and putting energy production in Europe to the test. The constant heat primarily burdens power plants’ cooling systems, affecting hard coal, gas-fired and nuclear power stations alike. Even renewable energy production is suffering. In these extreme conditions, a diverse energy mix ensures security of supply.

Fans, air conditioning systems and refrigerators are running at full power across large parts of Europe. Ice cream is beginning to sell out in supermarkets. Farmers are facing crop failures. Lawns and parks are parched. But the heat is not just a challenge for man and nature, power plants are struggling too, a topic that has recently been covered extensively by the press and media.

Energy consumption soars when temperatures are extreme. In extreme heat, it is mainly the demand for electricity that goes up. Consumption in Germany is currently at about 1.36 billion kilowatt hours (kWh) per day, six percent more than the average of the past two summers. According to Imperial College London, the additional consumption in the UK on days with temperatures as high as recently is equivalent to the average demand of 2.5 million homes – roughly the number of households in Scotland.

Elchin Mammadov, energy supply analyst at Bloomberg Intelligence in London, had already emphasised in June that “despite the boom in renewables, Europe still needs conventional power plants” and had warned of rising electricity prices as a potential consequence of the heatwave.

Some plants forced to ramp down

The major problem is that long periods of heat drive up rivers water temperatures. Thermal power plants, such as hard coal-fired and nuclear power stations, need cooling water to operate, usually supplied by nearby rivers. To protect the waters and the fish that inhabit them, power plants are only permitted to discharge the water heated by the cooling process up to a specified maximum temperature. If this temperature is exceeded, plant operators must reduce cooling water quantities. The only way of doing that is reducing output, as many plants across Europe have been doing over the last couple of days. Especially in France, where 58 nuclear power stations generate about 70 percent of the electricity, high water temperatures are a problem almost every summer.This year, four reactors in three French nuclear power plants had to be temporarily taken off the grid due to the persistent heat, as a spokesperson of French utility Électricité de France confirmed. Apart from record temperatures, the heat also meant a reduction of power plant output in Scandinavia.

As the German newspaper Die Welt recently reported, the heatwave could “tighten supply particularly in the south of Germany, which is structurally undersupplied with power plants (…).” Exceptional permits to continue operations despite exceeding the maximum cooling water temperature, as they are currently being applied, are one remedy for this. However, with rivers such as the Rhine running low, freighters cannot be fully loaded, which may lead to shortfalls in hard coal supply becoming a critical issue. Hard coal is sourced from the global market and delivered via the North Sea ports of Antwerp, Rotterdam and Amsterdam. Gas-fired power stations are also facing problems: Their operational readiness is affected by a loss of efficiency when external temperatures rise.

Lignite-fired power plants are more heat-resistant. They are cooled with sump water from the depths of the opencast mines, which has a constant temperature of about 20 degrees centigrade all year round. Thanks to this “inexhaustible coolant”, lignite-fired power plants are, once again, proving to be “a pillar of the supply system,” as Die Welt puts it.

It’s not just conventional generation that’s struggling

It is a common misconception that photovoltaic systems produce massive amounts of electricity when the sun is constantly blazing. Currently, they are only producing 24 to 28 gigawatts of the total installed capacity of 44 gigawatts in Germany. This is mainly since their efficiency goes down as the temperature of the solar modules goes up. Photovoltaic systems are more likely to reach record production levels on a sunny spring day than in the midst of a heatwave.

This is also why, according to figures provided by National Grid and Sheffield University, UK photovoltaic systems are performing at top levels: average temperatures in the UK are markedly below those in continental Europe. At up to 17 percent at times, the share of solar energy in the UK energy mix is particularly high – the average share last year being just one percent.

As heat and drought are often linked to high-pressure weather conditions, they also have an effect on electricity generation from wind turbines. “Under these weather conditions, there is practically no wind,” as the German Federal Association of the Energy and Water Industries (BDEW) points out. According to energy provider Uniper, hydropower is running at the usual summer level and still holding up to the current drought.

The more diverse the mix, the better the security of supply

Thanks to the balanced mix of conventional and renewable energy, however, there is currently no need to fear bottlenecks. A spokesperson of the German Network Agency confirmed that there is no reason to worry: “We’re in the green,” he responded when asked by “Deutsche Presse-Agentur”. The same applies for the UK, where the additional demand is not expected to cause problems, as news agency Reuters reports. In conclusion, what the current situation shows is that every energy source has its strengths and weaknesses, making it all the more important to have a broad energy mix that covers every type of generation in order to ensure security of supply across Europe.

Photo credits: Edmund O’Connor,; Bundesnetzagentur – (licensed t under CC BY 4.0)

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