By Scott DiSavino

(Reuters) PJM Interconnection is the biggest U.S. electricity grid operator. If their fuel supply drops below certain levels, they could limit the amount of coal-fired power plants that can be operated this winter. This will ensure there’s enough coal to go around in case of a severe freeze in the east.

Global energy prices have reached multi-year peak levels as oil and coal supplies run low. These are causing outages across China and Europe, while utilities around Europe and Asia scramble to get fuel for winter heating.

PJM stated that it might restrict the operation of steam units (which are usually coal-fired) if there is less than 10 days (240 hour) fuel availability. This will help to ensure that power plants can be used when they need them.

In the past, PJM permitted plants to run until there was only 32 hours fuel availability. If the area experiences extreme winter weather, or any other reliability issue, plants can run several days.

PJM manages the United States’ largest electricity grid, which serves 65 million customers in 13 Mid-Atlantic States (Illinois to New Jersey) and the District of Columbia.

Michael Bryson (PJM’s senior vice-president of operations) said that he was concerned about the coal supply chain and inventories going into winter. He supported temporary adjustments to regulations governing minimum fuel requirements, which took effect Thursday.

He said that PJM has made it a priority to maintain a reliable electricity grid.

According to data from the U.S. Energy Department, 24% of America’s electricity comes still from coal plants.

U.S. power companies cut their coal stockpiles in September after shutting down many coal plants for carbon dioxide reduction. Federal data shows that this is the lowest monthly level since March 1978.

The federal government projects that coal plant stocks will plummet to 62.7 millions short tons by February. This is the lowest level of recorded data since 1973.