Johannesburg - Power utility Eskom said on Wednesday that its upcoming summer season would be challenging as it ramped up maintenance at its power plants, but said it was not issuing any blackout warnings. “We are not warning of blackouts. We are saying that summer is more challenging than winter because we have to take advantage of the space cleared by lower demand to do our maintenance,” Eskom spokesperson Hilary Joffe told Reuters. “We’ve kept the lights on but have warned that we have a maintenance backlog,” she said. Demand peaks in the June to August winter season, so Eskom generally holds back on maintenance then. Eskom faces tight supplies for the next couple of years as it builds new stations to meet accelerating power demand. Rolling blackouts in 2008 cost the key mining sector billions of rands in lost output and hurt the wider economy.