It's like oil: at some point before it's totally depleted it will take more oil to power the extracion operations than is produced. At that point, oil ceases to be an energy source and becomes an expensive input to the chemical industry.

Remember the plan to build a nuclear power plant in order to get oil out of the Canadian oil sands?

A society committed to the notion that government is always bad will have bad government. And it doesn't have to be that way. — Paul Krugman