BEIJING — The Chinese government is trying to slow down the approval of new coal-fired power plants because of overcapacity, but projects already in the pipeline, as well as loopholes in policy, mean China is on track to add an average of one new coal-fired plant a week until 2020, according to a report released on Wednesday by Greenpeace East Asia.

The construction boom would result in about 400 gigawatts of excess capacity and would waste more than one trillion renminbi, or $150 billion, on building unneeded plants, the report said.

China now has 910 gigawatts of coal-fired capacity and is expected to retire 70 gigawatts of that. The new construction means the country would increase capacity at a time when additional coal-fired power is not needed, Greenpeace said.