An undersea cable that provides 40% of San Francisco’s electricity is offline for most of the summer.
Since 2010, the Trans Bay Cable has delivered energy across the bay from Pittsburg into San Francisco — the result of efforts to improve electricity reliability in San Francisco after the entire city lost power in a 1998 outage.
But in recent years, underwater erosion has exposed parts of the buried 53-mile-long cable on the bay floor, leaving it susceptible to damage, according to the company. In some places, the cable had dropped as much as 15 feet from its original burial depth, a consultant for the company said at a public permitting meeting. Repairing it involves installing new protective sleeves and 9- to 12-inch-thick concrete coverings on top of the cable to rebury it…