Clean coal-fired power plants have been touted as a remedy for an environmentally challenged age, offering the promise of turning cheap but dirty coal into a pollution-free energy source. Don't turn off those wind turbines yet.

At least eight clean coal plants, more than a third of those on the drawing board, have been canceled, delayed or rejected by regulators this year [1].

Developers cite soaring construction costs, technology hurdles and uncertainty about regulation of greenhouse gases.