Coal-fired power plants in the United States are facing a serious backlog of coal inventories, as low gas prices and renewables expansion eroded coal-fired power's competitiveness.

Over the past two years, U.S. utilities and power producers have accumulated a total of 138 million short tons (125.17 million tonnes) of unused coal inventory in their power plants, according to data from the Energy Information Administration (EIA).

The inventory, worth $6.5 billion, has caused financial impacts for power plant operators, according to the Institute for Energy Economics and Financial Analysis (IEEFA).

U.S. coal plants burned just 1 million short tons of coal per day, half as much as in 2015, and it will take more than four months to burn through existing stocks, the IEEFA reported.

The EIA expected inventories to remain high, above 100 million short tons through 2025, and also forecasted that coal production will fall to 469 million short tons by 2025, from 505 million short tons in 2024 and 578 million short tons in 2023, as power plants burn less coal.

Utility-scale wind and solar generation will surpass coal for the first time this year, reaching 665.8 TWh, according to the EIA's November Short-Term Energy Outlook.

Natural gas generation has become the dominant fuel since 2016 and now accounts for more than 40% of the nation's electricity generation, continuing to squeeze coal out of competitive electricity markets.

IEEFA estimated that by 2025, an additional 13 GW of the remaining 173 GW of coal-fired capacity will be retired or converted to natural gas, further reducing the market for coal.