Solar generation has been exceptionally strong for several weeks and offered solid support to France's power mix, as a heatwave and drought forced 13 nuclear reactors offline, marking the highest level of power shutdowns in the country since 2015, according to an AFP analysis based on data from French state-owned utility EDF.

Real-time data from French grid operator RTE showed nuclear output at around 32 GW on the morning of August 14, compared with about 45 GW on a typical day in March. The EDF expects output to decline at more nuclear plants in the coming days, with forecasts indicating a maximum capacity loss of 12.47 GW between August 14-September 1. 

Other generation sources are also under strain. Five gas-fired plants in the UK have cut production, while low water levels in Italy's Po River have threatened thermal plants, and coal-fired plants in Serbia and Poland have scaled back operations. Hydropower has also suffered, with seven of the EU's eight largest producers recording generation below five-year averages.

However, solar generation has remained robust during the period, accounting for up to 35% of France's electricity generation mix. Energy thinktank Ember said in a study published August 13 that solar output ran above normal levels across several European countries during recent heatwaves, rising up to 17% daily in France and Hungary.

Even as solar helped stabilize grids when other sources struggled to operate normally, the main challenge comes after sunset, when demand remains high due to air conditioning but photovoltaic output falls to zero, forcing reliance on dispatchable gas-fired generation, according to Chris Rosslowe, an analyst at Ember.

Average daily power prices during earlier heatwaves rose 119% in Hungary, 44% in France, 13% in Italy and 7% in Spain, with notable spikes in early evening. Rosslowe said battery storage could take over in the evening, combining with solar as one of the cleanest ways to make the European electricity system more resilient during hot summers.