On behalf of California’s five largest electric utilities, E3 evaluated the challenges, costs, and potential solutions for achieving a 50 percent renewables portfolio standard (RPS) by 2030. Using our Renewable Energy Flexibility Model (REFLEX), we performed detailed operational studies of power system dispatch flexibility constraints under high levels of wind and solar generation. We found that achieving a 50 percent RPS is feasible and that California’s power system can remain reliable as long as renewable resources can be dispatched in response to grid needs. Our study recommended strategies for integrating higher levels of renewables, including greater regional coordination, renewables portfolio diversity, flexible generation capacity, flexible loads, and energy storage. We found that deploying these strategies would reduce the need to curtail renewables, lowering the cost of reaching 50 percent RPS.