Extreme heat and the threat of looming blackouts are putting the nation’s power grid under special scrutiny, with many blaming the major transformation from traditional to renewable resources for the reliability problems.

Peaking electricity demand and slim reserve margins are behind the power crunch straining grids across Texas and swaths of the country. Many, especially Republicans in Congress and fossil fuel interests, are assigning blame to the aggressive campaign to displace legacy coal-fired plants or other sources, such as natural gas, with “intermittent” or variable sources, especially wind and solar.