tl;dr: solar, mostly The short answer is that average generation in CA is: - 51% solar - 22% natural gas - 21% other renewables (hydro + wind + geothermal)

tl;dr: solar, mostly The short answer is that average generation in CA is: - 51% solar - 22% natural gas - 21% other renewables (hydro + wind + geothermal) - 6% nuclear - 0.1% coal sources: - https://www.eia.gov/state/print.php?sid=CA https://www.eia.gov/state/print.php?sid=CA - https://www.gridinfo.com/california https://www.gridinfo.com/california - caiso.com is also good The medium answer is that trains run during daylight hours, so they probably consume more solar and less natural gas than the averages suggest. The long answer is that counterfactual modeling of electricity generation is surprisingly subtle. E.g., the Diablo Canyon nuclear power station is going to run regardless of whether Caltrain electrifies, and no more nuclear is being built either way, so really Caltrain is "responsible" for none of the nuclear generation in the state, even if the trains are consuming power at the same time that Diablo Canyon is generating. In this analysis frame, you tend to look at the marginal plant being built, which likely further pushes toward solar but depends on tons of factors in reality.