China is building a vast array of new coal-fired power stations, potentially more than the operating capacity of the U.S., even though it knows the plants will probably never be fully used.

The puzzle of why the world’s leading installer of clean energy is investing so much in the worst polluting — and increasingly expensive — fossil fuel shows the depth of Beijing’s concern over the global squeeze in energy supplies. But it also reflects planning for a gradual relegation of coal’s role, from prime power source to a widely available but often idle backup to China’s rapidly expanding renewables fleet.

Work on at least 165 gigawatts of plants powered by coal should begin by the end of 2023, the National Development and Reform Commission told executives at a meeting in September, according to state-backed Jiemian News. The chairman of China Energy Engineering Corp., meanwhile, has forecast the country could add a total of 270 gigawatts in the five years to 2025 — more than currently exists in any other nation.