Heatwaves can crimp power output across Europe

France, which relies on atomic power plants for 80 percent of its electricity, is especially vulnerable to heat waves. With 14 of its 19 nuclear plants located by rivers, rising temperatures over a longer period of time can trigger cooling problems due to local laws that prevent plants from discharging water in rivers above certain temperature levels.
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Forecasts for warmer temperatures this week in parts of Europe raise the possibility of summer heat waves that can heavily strain the ability of the energy sector to keep supplies flowing.
The following are overviews of how some countries have fared in the past during heatwaves.
FRANCE
 French temperatures have been at above 30 degrees Centigrade in some regions and are expected to remain at those levels until the end of the week. Forecasts show tempertures will dip by around 5 degrees next week.
 France, which relies on atomic power plants for 80 percent of its electricity, is especially vulnerable to heat waves. With 14 of its 19 nuclear plants located by rivers, rising temperatures over a longer period of time can trigger cooling problems due to local laws that prevent plants from discharging water in rivers above certain temperature levels.
 Lower output from reactors located near rivers because of cooling problems usually coincides with surging demand as people crank up air conditioners during the summer.
 France has five plants located by the sea and EDF (EDF.PA: Quote, Profile, Research, Stock Buzz), the state-owned utility which operates all of France's nuclear plants, tries to avoid carrying out maintenance operations during the summer on these facilities because they do not suffer from cooling problems.
 During the heat wave of 2006 France was forced to import 2,000 megawatts of extra power - roughly equivalent to the capacity of two average-size nuclear reactors - to meet surging demand and to offset lower output.
 EDF warned earlier this month France may need to import up to 8,000 megawatts of power by mid-July in a heat wave as a 10-week long strike by nuclear workers during the traditional maintenance season has delayed the restart of many reactors.
 Only two thirds of French reactors are currently producing - the lowest level seen since 2003 - but power grid RTE predicts availability to climb to 72 percent next week, to ease back to 68 percent in the week starting July 13 before rising back again to 76 percent in the week of July 20.
GERMANY
 Temperatures in Germany are running between 26 and 31 degrees Centigrade with slow winds, the met office DWD said in its daily report. These conditions are expected to last through the week.
 Germany's power sector responded to extreme heat waves in 2003 and 2006 by reducing load flows at some of its 17 nuclear power stations.
 Some of the plants are on small rivers, which means the ability to draw cooling water from the rivers is reduced when water levels decline in heatwaves.
 Hot water emissions into the river from the plants' operations also poses a problem because of environmental limits on water temperatures aimed at keeping the rivers from getting too warm in order to protect wildlife.
 Swing supplies of wind power with a maximum 23,900 MW capacity can also stop entirely in heat waves.
 Low water on the main shipping arteries such as the Rhine in hot weather can restrict supply of coal to power stations. This can also affect the output of run-of-the-river hydro plants.
 A varied power generation mix and flexible maintenance schedules allow German power operators to shift between various fuels if individual plants are affected during heat waves.
 A worldwide recesssion that has curbed industrial demand has also led to full German gas stores even though the winter was a cold one.
BRITAIN
 Forecasts for hot temperatures across Britain prompted the Met Office on Monday to issue the first heat watch of the summer, warning that temperatures could hit 33 degrees Centigrade during the week, some of the highest temperatures since 2006.
 During that heatwave, Britain was forced to call on expensive oil-fired stations to meet soaring demand as the heatwave coincided with maintenance shutdowns at several large plants.
 Britain gets much of its electricity from gas-fired power plants, which need to reduce output in hot weather.
 Because the country's nuclear power plants are located near the sea, the issue of cooling down water is not as big a problem as in France.
(Reporting by Muriel Boselli in Paris, Vera Eckert in Frankfurt and Michael Kahn in London; editing by James Jukwey)