The folks at Google have a $4.4 trillion plan to remake America’s energy landscape by 2030, eliminating coal from the picture and shaving emissions of greenhouse gases by 95%. Unlike some other ambitious plans to rejig America’s energy mix, it comes with detailed prescriptions and pricetags—but how realistic is it?

The plan has three big pillars: energy efficiency to reduce demand for new electricity; a massive renewable-energy push to replace coal; and an accelerated rollout of plug-in cars that can displace about half the...