On Aug. 14, 2003, a tree branch struck a power line in northern Ohio. Within minutes, 21 power plants shut down due to a series of errors. Fifty million people from Ohio and across the northeastern United States and Canada were affected. Around 100 people died.

Some areas regained power within a few hours, while others waited days. In New York City, people fled subways in droves, walking across bridges to get home. Others waited hours in lines to buy batteries and other supplies. It was one of the largest blackouts in US history and cost the US $4 billion to $10 billion. It began to shed light on how broken the existing system is and how much change is needed.

"I think it's amazing that the system's not worse than it is," says Johanna Mathieu, associate professor of electrical engineering and computer science at the University of Michigan. "Most people don't appreciate how hard it is to keep the lights on." Supply and demand must always be balanced, but increasing strain on the grid is creating new challenges.

Blackouts are becoming more common, as the grid struggles to adjust to the shift to electric vehicles and the increase in the frequency and severity of storms amid climate change. Errors that result in debilitating outages, like the 2003 blackout, exacerbate growing energy demands.