Cost-minimized combinations of wind power, solar power and electrochemical storage, powering the grid up to 99.9% of the time

► We modeled wind, solar, and storage to meet demand for 1/5 of the USA electric grid. ► 28 billion combinations of wind, solar and storage were run, seeking least-cost. ► Least-cost combinations have excess generation (3× load), thus require less storage. ► 99.9% of hours of load can be met by renewables with only 9-72 h of storage. ► At 2030 technology costs, 90% of load hours are met at electric costs below today's.