Carbon capture is finally heading toward big numbers.

The Department of Energy and private investors will sink approximately $3 billion ($979 million from the DOE, the rest from industry) into three relatively large-scale carbon capture projects. Although carbon capture has been debated for years, only a few experimental sites have been built. Blame it on high costs, a lack of easy technological solutions, and the challenge of ensuring that the carbon dioxide will remain captured for hundreds of years. Despite the obstacles, with coal providing about half of the energy in the U.S. and even more in China, carbon capture, many believe, is inevitable.

Each of the projects will tackle the problem slightly differently. In New Haven, W.Va., American Electric Power (AEP) will build a capture system next to a 1.3-gigawatt power plant that will capture 90 percent of the emissions from a 235-megawatt flue gas stream at the plant and then chill the emissions with ammonia to compress them. The carbon dioxide will then be permanently stored in two saline aquifiers 1.5 miles underground. In Alabama, Southern Company Services will capture carbon and both store it underground in saline reservoirs and also try to use some of the gas for enhanced oil recovery. Another project in Texas will capture 90 percent of the gases from a 400-megawatt plant for enhanced oil recovery.

Whether enhanced oil recovery and persistent storage is better than trying to turn carbon dioxide into fuel or things like baking soda remains a debate in greentech. Many startups, such as Skyonic, have been formed to try to turn carbon dioxide into chemical solids. Others, though, say that the high price of turning a somewhat inert molecule like carbon dioxide into something valuable combined with the volumes that will need to be sequested tip the balance toward persistent storage. At the Western Energy Summit at NASA Ames in Mountain View, Calif., Steve Koonin, undersecretary for science Department of Energy, has said he favors persistent storage. 

Carbon capture and sequestration has the potential to account for 220 to 2,200 gigatons of CO2 over the next century, says the Intergovernmental Panel on Global Change (IPCC). It's a nice vague number. In a single year, Europe generates about 4 gigatons. About half of the CO2 generated worldwide comes from stationary sources like power plants that could potentially be equipped with CCS.

The total cost for CCS depends on when it is built as well as the volumes and technological breakthroughs of the future. Experimental CCS plants will be able to sequester and store CO2 at a cost of $80 to $120 per ton (€60 to €9), according to a McKinsey report on CCS. That includes capture, transport and storage. Capture accounts for about two-thirds of the cost.