California's solar energy efforts have been so successful that renewable energy has powered 100% of the state's main grid for at least 15 minutes on most days over the past month. But now, the state and its grid operator are facing an unusual situation. With an abundance of solar energy integrated into the grid, during bright spring days with reduced demand, electricity prices plummet into negative territory. The surplus of solar power results in gigawatts being "curtailed" or effectively wasted