WASHINGTON -- Energy Secretary Steven Chu said the U.S. should invest in technology to reduce the carbon produced by burning coal, but he said it will take at least eight years to be sure such systems work.

"It absolutely is worthwhile to invest in carbon capture and storage because we are not in a vacuum," Mr. Chu told reporters Tuesday following an appearance at an Energy Information Administration conference. "Even if the United States or Europe turns its back on coal, India and China will not," he said. Mr. Chu added that "quite frankly I doubt if the United States will turn its back on coal. We are generating over 50% of our electrical energy from coal."

As for so-called clean-coal technology, Mr. Chu said "it would take probably a minimum of eight years or more to really have confidence that these technologies will work in a cost-effective way." As a result, "energy efficiency, energy conservation are where the greatest gains will be."

Coal-producing states are lobbying the Obama administration to keep coal -- abundant and cheap -- a part of the country's energy mix. Coal backers have looked to clean-coal technology, which aims to store emissions from coal-burning power plants underground. If the U.S. aims to transition away from coal, a question is whether such technology is worth the investment.

Last week, Baard Energy, which is developing a project to create fuel from a coal and biomass mixture, withdrew from the Energy Department's loan-guarantee program after disclosing that the government said it would consider environmental lawsuits when conducting risk evaluation of a project.