In Quest for Bigger Batteries, California Mulls Century-Old IdeaJun 06 2019, 10:00 AMJun 06 2019, 12:07 PMJune 06 2019, 10:00 AMJune 06 2019, 12:07 PM(Bloomberg) -- As the sun sets on California’s solar farms, a backup energy source deep in the Sierra Nevada Mountains springs to life.Disclaimer