The Kemper County project is estimated at $US5.2 billion ($A5.6 billion).

If successful, the project could boost the fortune of coal, which has lost favour to cheaper and less environmentally damaging alternatives.

Sceptics have been quick to raise issue with the project. Many environmentalists have questioned whether the carbon captured will remain underground.

In 2011, carbon dioxide from a natural reservoir blew out of the oil field where Kemper’s gas was to be pumped, leaking for days.

They also question whether the plant will run as advertised after attention from media and environmental groups have waned.

The 582 megawatt Kemper project, the only major coal plant being built in the US, is the first to showcase modern technology, but has a hefty price tag to match.

It will cost more than double the initial estimate.

According to a Sierra Club analysis, Kemper is the most expensive power plant ever built for the watts of electricity it will generate. The plant will end up costing more than $6,800 per kilowatt.

In comparison, a natural gas plant costs about $1000 a kilowatt, according to the US Energy Information Administration. A nuclear plant costs $5500.

The plant will also come under the spotlight as a prodigy of the Obama administration’s effort to spur development of clean-coal technology.

The Environmental Protection Agency’s first greenhouse-gas regulations, proposed in September, rely on this plant to legally justify the set standard.

Kemper is the only major clean-coal power plant funded by the Department of Energy that has so far broken ground.

When the Kemper plant is operating, the coal will be ground up and dropped into a high-pressure, low-oxygen chamber, where it will be transformed into composite gases. Leftover coal ash will be dumped out the bottom.