Natural-gas replacement would be cheaper and faster. A combined-cycle natural-gas plant takes about two years to build, says David Eppinger, vice president for the power group at Irving, Texas-based Fluor Corp. Much of a natural-gas plant is built on the assembly line, cutting both delivery time and the construction schedule, he says.

Eppinger says the growing availability of liquefied natural gas makes gas plants an option for utilities worldwide.

There is a downside to relying too heavily on natural gas, however. Some predict the abundance of shale gas will stabilize the price of natural gas, now at about $6/MMBtu, until 2025. Beyond that, though, no one is comfortable in estimating a price, says Aneesh Prabhu, director of U.S. utilities, power and project finance for Standard and Poor's. (Standard & Poor's and Engineering News-Record are both owned by the McGraw-Hill Cos.)

The price of natural gas could skyrocket, leaving utilities with an expensive resource. It's nave to think that gas isn't volatile, Sielger says.

While coal is now out of favor, its use for base-load power isn't disappearing. For three to four to seven years, realistically, gas [will be] the fuel of choice. There's not a whole lot of options, Gabriel says. But in five to 10 to 15 years, we'll have clean coal and integrated gasification.

While it is now technically feasible to build plants to capture carbon dioxide and gasify coal, the cost to build such plants on a large scale is prohibitive, say David Harris, vice president, and Rich Chapman, strategic projects director for clean coal technologies, both of Black & Veatch. Such plants are tied to the price set on carbon dioxide, through either a carbon tax or a cap-and-trade system.

The speed of how it progresses is dependent upon how much money is made available, Chapman says. There's no commercial reason for utilities to do this in the absence of regulatory requirements.

Worldwide, China, India and other countries are still building lots and lots of coal plants, some with the intention of retrofitting carbon-capture technology when it is commercially available, says Jeff Merrifield, vice president of Baton Rouge-based The Shaw Group's power group.

If an economic recovery bumps up U.S. demand, plans to retire coal burners might get pushed back. I think [coal-fired plants] will have surprising resiliency, Gabriel says. Harris agrees, especially if utilities have difficulty relicensing their nuclear plants. They may reconsider their coal-plant retirements.

Our vision is that the world will have no choice but to burn coal cleanly and use nuclear [power] safely, says Pierre Gauthier, Alstom U.S. and Canada president and CEO.