The millions of people who struggled to keep warm in Texas, with blackouts crippling life inside a dominant energy hub, have laid bare the desperate state of U.S. electricity grids. To fix nationwide vulnerabilities, President Joe Biden will have to completely reimagine the American way of producing and transmitting electricity.

Biden wants to overhaul the nation’s grids so they derive all electricity from carbon-free sources by 2035—a major step toward zeroing out net emissions of greenhouse gases by mid-century. Realizing that goal will require building billions of dollars worth of new transmission lines, a challenge that might prove just as difficult as getting his climate agenda through Congress.

Switching to renewables and electrifying vehicles will require rethinking many of the assumptions that underpin the existing grid system. For much of its industrial life, the U.S. relied on power plants in or near the communities they served. If more power was needed, monopolistic utilities were ready to add it by burning more coal or natural gas. A clean grid will probably be more decentralized, powered in part by smaller renewables facilities including rooftop solar as well as batteries. It will also have to be smarter and more flexible.

While Texas built new transmission lines that support renewable energy, its continued reliance on fossil fuels failed the state this month. The cold snap triggered shutdowns at some plants fired by coal and gas that weren’t designed to withstand such extreme temperatures. Some wind turbines also stopped spinning.  The state’s grid is largely isolated from the rest of the U.S., in part for political reasons, and operators unable to call on neighbors for help were forced to implement blackouts.