Dig into the delicate balancing act of how power grids supply energy to the world and how renewable energy factors into this process. -- In 1967, Homer Loutzenheuser flipped a switch and connected the power grids of the United States, forming one interconnected machine. Today, the US power grid is the world’s largest machine, containing more than 7,300 electricity-generating plants. So how exactly do these power plants work? Henry Richardson digs into the delicate balancing act of how power grids supply us energy. Lesson by Henry Richardson, directed by Anna Benner.