SAN LUIS OBISPO, Calif. — After 40 years, Rochelle Becker's fight is coming to an end. Under an agreement reached in June by Becker; labor and environmental groups; and California's largest utility, Pacific Gas and Electric Co., the Diablo Canyon power plant, the state's last nuclear generating station, will close in 2025. It's a big win for Becker and coastal advocacy groups long transfixed on the goal of convincing state officials that closing Diablo Canyon is the only way to deal with alarming safety concerns. The nuclear reactors represent 7 percent of the state's emissions-free electricity, which today helps keep California from feeding its voracious energy appetite with dirtier fuels. But to Becker, Diablo Canyon's outsized role in California's energy portfolio stands in the way of a state goal to get most of its power from wind, solar, energy efficiency and energy storage technology developed in Silicon Valley.