Epstein makes two attacks on the Model S. First, the low chances of renewable energy supplying a substantial percentage of the electricity going into the car – he calls it "unlikely" and never mentions Tesla's Supercharger network, which uses solar power. Second, Epstein criticizes the amount of natural resources committed to producing the Model S's lithium-ion battery, and argues that the environmental benefits from the car's gas-free life may be completely offset by the battery production and coal sourcing for electricity. Yes, the line arguing the opposite side of that theory is a long one.
That said, Epstein goes on espouse the virtues of coal, applying some sort of idea about people living longer with coal-powered electricity at their disposal than those without that luxury (the cause and effect is a little murky, here, and if you're going to criticize using natural resources, then Epstein's overall logic in this argument is hard to follow). He also takes the opposite side of the global warming argument by saying that coal reduces climate related deaths by supplying the power needed to make things like sturdier homes and weather satellites. You can read the whole thing here.
Of course, Forbes is no stranger to publishing work that attempts to take the wind out of the plug-in vehicle movement. Forbes contributor Patrick Michaels wrote last September that General Motors was inflating Volt sales via discounted lease rates but the publication did give a frustrated Bob Lutz room to refute longstanding EV attacks.