A federally backed, $2.2 billion solar project in the California desert isn’t producing the electricity it is contractually required to deliver to PG&E Corp., which says the solar plant may be forced to shut down if it doesn’t receive a break Thursday from state regulators.

The Ivanpah Solar Electric Generating System, owned by BrightSource Energy Inc., NRG Energy Inc. NRG, -1.99% and Alphabet Inc.’s GOOG, -2.37% GOOGL, -2.41% Google, uses more than 170,000 mirrors mounted to the ground to reflect sunlight to 450-foot-high towers topped by boilers that heat up to create steam, which in turn is used to generate electricity.