Solar is so cheap, we need to build far, far more than we need.

That was the surprising conclusion Marc Perez, a doctoral student in engineering at Columbia University, arrived at in 2014. Perez was trying to design the world's cheapest electricity grid. By using a decade of satellite data to calculate solar power potential across the globe, he designed the optimal grid for producing the most power at the lowest cost.

Perez found overproduction was not a problem. Unlike a coal or natural gas plant, renewable fuel is free. And switching off a solar panel's output could be done electronically, compared to the expensive process of spinning down a turbine. "Wasting" the energy carried few costs.