When it comes to keeping the lights and air conditioning on this summer, how much of a safety margin do we need?

After all, summertime is when electricity demand surges, as an entire nation reaches for the thermostat in the midst of a heat wave. Overall, our grid is getting older, and the demands are getting higher.

The North American Electric Reliability Corporation, the agency that’s paid to worry about the power grid in the United States and Canada, says we’re reasonably good shape for the summer—except for Texas and maybe California. Of course, given how large Texas and California are, a worst case scenario could leave some 60 million Americans sweltering in the summer heat.

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