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 is on track to add an average of one new coal-fired plant a week until 2020, according to by 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.

As part of its broad policy, China — the world’s biggest emitter of greenhouse gases — that it would try to make 20 percent of its energy renewable by 2030. But given the planned growth in coal power capacity, some environmentalists question that goal.

“China’s worsening coal overcapacity crisis is acting as a dead weight on the country’s ongoing energy transition,” said Lauri Myllyvirta, who wrote the report with Shen Xinyi.

Representatives of China’s hydropower and wind power industries have complained of the glut of coal power plants. The addition of a large number of such plants would make it harder for companies specializing in non-fossil-fuel energy to be profitable because coal-fired plants can more easily secure contracts with the major state-owned electrical grid companies.

Mr. Myllyvirta and other Greenpeace researchers have been trying to calculate the amount of overcapacity of coal-fired power plants in China. Greenpeace East Asia on the topic in November, noting that 155 projects had received a permit in 2015, equal to 40 percent of operational coal power plants in the United States.

In March, Greenpeace revised that number upward, saying 210 new or proposed plants, with a total capacity of 165 gigawatts, had received environmental permits last year. Greenpeace tracked China’s proposed capacity by examining provincial websites for permit approvals.

There are already too many coal-fired power plants in China, as shown by a steady decline in the plants’ average operating hours since 2013, according to official statistics. China also in 2015 compared with 2014, and coal-producing companies across China have complained of a in the industry.

The boom in approval of coal-fired power plants began in early 2015, after the central government said provincial governments could approve projects.

But the central government has tried to rein in the approvals, and it announced a to limit capacity and retire some plants. Under that policy, about 110 gigawatts of proposed capacity would be suspended and 70 gigawatts would be retired by 2020, according to the Greenpeace report on Wednesday.

But plants that would add 200 gigawatts are already under construction, and projects adding 165 gigawatts could get permits despite the new limits, Greenpeace said.

Mr. Myllyvirta said that he and his colleagues estimated there would be 600 new coal-fired units, or boilers, at 290 plant sites.

Greenpeace said that northern and northwestern provinces and regions that are designated new “coal bases” have been trying to approve or build plants as quickly as possible. These include the provinces of Shanxi and Shaanxi and the region of Inner Mongolia, all of which have large coal reserves and whose economies depend on coal.

The industrial burning of coal is the biggest source of carbon dioxide, the main greenhouse gas responsible for climate change. It is also the main contributor to the air pollution in many Chinese cities.