(Bloomberg) -- Swedish utility Vattenfall AB turned on some of its reserve diesel generators to supply power on an island in the Baltic Sea as a cold spell caused demand and prices to surge. 

Wholesale electricity costs in the Nordic market jumped to their second highest on record on Monday as temperatures plunged below -40 degrees Celsius in northern Scandinavia. The two diesel units have a total capacity of 35 megawatts and are located near Visby on the island of Gotland. 

“At these high price levels we are obliged to offer this capacity to the market,” Markus Fischer, a spokesman for Vattenfall said. “When there is such high demand that prices surge they will operate for short period of time.”

On the mainland, an oil-fired winter reserve plant was also fired up for a few hours on Monday morning. 

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Local prices in southern Sweden surged to 626.06 euros per megawatt-hour between 4-5 p.m. in day-ahead auction on Nord Pool. 

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