The plants are more than 25 years old and have turned uneconomical, said S.D. Dubey, chairman of the Central Electricity Authority, the planning wing of the power ministry. They will be replaced by super-critical units, which are more efficient, at the same sites, he said, without giving a timeline.

“Our first concern is emissions,” Dubey said in New Delhi. “We also want plants to be more efficient in use of resources.”

The plan reflects Prime Minister Narendra Modi’s attempt to balance energy security with the need to protect the environment. Coal, whose use is declining in several parts of the world because of emission concerns, accounts for about three-fourths of India’s electricity generation and will probably remain the nation’s dominant fuel for at least two decades, the government estimates.

In December, the environment ministry issued norms to curb emissions, such as particulate matter, sulphur dioxide and nitrogen oxides, from power plants amid rising concern over air pollution in Indian cities. The norms also capped the use of water by plants.

A majority of the old capacity—22 gigawatts—is controlled by provincial governments, while 13,000 megawatts belongs to companies of the central government, such as NTPC Ltd, Dubey said. About 2 gigawatts of capacity belonging to non-state producers is also being considered for shutdown, he said without naming the plant owners.

The Central Electricity Authority will hold talks with plant owners and electricity buyers to prepare a roadmap for phasing out the old capacity, he said.

Coal fires 62% of India’s 298 gigawatts generation capacity, according to the government’s data. The aging plants being considered for a shutdown account for about 12% of the country’s total capacity. Bloomberg