Spain stops turbines to balance supply

The country's thousands of wind turbines supplied a new record of 54.1 percent of demand early December 23, forcing gas- and coal-fired power plants to run at minimum output to avoid system overload as hydropower companies drained brimming reservoirs.

"High wind output in the early hours of this morning, together with the high level of hydropower generation, due to reservoirs opening up after recent rains, forced the control center to cut thermal power to a technical minimum," Red Electrica said in a statement.

"Due to low demand at the moment this was not enough.... So the control center had to order wind power production to be cut between 4 a.m. and 7 a.m. this morning by 600 megawatts."

Spain has invested heavily in wind power generation over the last decade to cut carbon emissions and reduce its reliance on imported fuel.

It now has over 18,000 MW of turbines installed, out of a total power generation capacity of about 93,000 MW, and first produced over half of its electricity with them early on November 9.

Wind turbines are seen as a key technology for producing electricity without emitting climate-warming carbon. But the Spanish experience highlights the difficulties for grid and other plant operators in balancing the system when the wind blows hard and there is little demand, especially early in the morning.

Greater numbers of electric cars charging up overnight could help absorb some of the extra output in future but there are still too few to make a difference.

Wind power output hit 54.1 percent of demand at around 0350 local time (0250 GMT) on December 23, or over 10,000 megawatts.

Even after the order to cut output the remaining turbines were still producing around 40 percent of Spain's power at around 7 a.m., reducing the contribution of coal and gas plants to under 5 percent in the hours in between, according to Red Electrica data.