Spain’s windmills produced a record amount of electricity on Thursday, underlining the growing importance of renewable energy to Europe and the challenges of matching new and sometimes erratic power sources to the continent’s demand.

At 11.09am, the windmills were producing 11,203MW – the highest output ever – equivalent to 29.5 per cent of Spanish demand at that time, according to Red Eléctrica, the national grid operator. For much of the day, wind was Spain’s single largest source of electricity. Before dawn, when demand was low, wind turbines contributed up to 42 per cent of electricity supply.

Spanish investment in subsidised wind energy has been so intense – hilltop ranks of huge white windmills can be seen across the country – that Red Eléctrica has been forced at times to shut some of the turbines because the grid can’t cope with the excess supply.

“Wind is no longer a marginal supplier for us,” Luis Atienza, Red Eléctrica’s chief executive, said recently in one of its control rooms in Madrid, eyeing huge, illuminated displays showing power flows and wind speeds. Over the year, wind already supplies about 12 per cent of Spain’s electricity, more than hydropower.

“It’s going to catch coal in the next few years and it represents a special challenge,” he said, referring to the difficulty of reducing the output of coal and other thermal power stations to compensate for strong winds at night when demand is low. “Renewables are very demanding in terms of networks,” he said.

Iberdrola of Spain, the world’s biggest wind energy generator by installed capacity, said on Thursday that this winter had been particularly blustery, contributing to a 37 per cent increase in the company’s domestic electricity production from wind.

“Wind is not only a good clean alternative,” it said, “but is getting close to becoming competitive with conventional energy sources in terms of production costs.”

The European Wind Energy Association said that in 2008 more wind power capacity was installed in the European Union than any other power source. Of the 23,851MW of new EU capacity, 36 per cent was wind, 29 per cent gas and 18 per cent solar photovoltaic cells.

By year-end, Spain expects to be producing almost a quarter of its electricity from renewable sources.

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