HONG KONG—The Chinese government has halted the expansion of wind power in its northern provinces where a large number of turbines are churning out power that's being wasted. The move underscores the challenges facing China as it works to fulfill its clean energy ambitions.

Chinese regulators said the windswept regions of Inner Mongolia, Jilin, Heilongjiang, Gansu, Ningxia and Xinjiang will suspend the approval of new wind projects in 2016, according to a March 17 statement published on the website of China's National Energy Administration. The six regions have installed nearly 71 gigawatts of turbines, more than the rest of China combined. It's at least the fourth time in five years that Beijing has ordered wind operators there to slow down growth.

The decision highlights a growing concern among energy analysts that China's spectacular growth in renewable energy is bumping up against the reality of grid constraints and shrinking electricity demand. Solar panels and wind turbines were virtually nonexistent in China a decade ago, and now the country leads the world in installing both.

Wind power installations, in particular, have exploded over the last five years as part of the country's ambitious push to combat climate change and bring down dangerous levels of air pollution from its massive coal consumption. Already the world's wind energy giant, China installed an additional 33 gigawatts of wind turbines in 2015, more than half of new installations worldwide, as developers rushed to build as many projects as possible to meet a year-end deadline for subsidies.

But too much of that energy is being squandered. In 2015 alone, 33.9 billion kilowatt-hours of wind-powered electricity was wasted, government statistics show—equivalent to the electricity consumed by 3 million American households a year. That was about 15 percent of China's total wind power generation, up from 8 percent a year earlier.

Some of the wind-generated electricity had no place to go because there's no transmission infrastructure to carry the power to population centers. In other cases, developers couldn't compete with coal for contracts to connect to the grid.

"Energy waste on wind farms in China has already become a major problem impacting the healthy development of the wind power sector," the National Energy Administration said in its statement. "Unless we take tougher measures to cut waste, the rate of wasted wind power will continue to get worse this year."

Xie Guohui, an analyst at the State Grid Energy Research Institute, an influential think tank based in Beijing, echoed that there is little prospect for immediate improvement.

"Even though China will not approve new projects, the scale of existing wind power installations is huge, leaving the grid struggling to cope with it," Xie said. "In the best-case scenario, this policy will help China's wind power curtailment maintain the same level as it was last year."

China's grid has long been a challenge for wind power producers and other renewable energy developers. Because the country's strongest gales, brightest sunlight and most powerful rivers are inland and far from its energy-guzzling coastal provinces, China must rely on transmission lines to deliver the clean electricity hundreds of miles from where it's produced. Although the country has extended transmission networks in recent years, the number of new renewable energy installations has been rising far faster than new lines have been built.

The intermittent nature of renewable energy also poses safety challenges for grid operators. Overcoming that requires financial resources and profound improvements to electricity lines. Further, until late last year, China's government-regulated power allocation scheme gave coal priority on the grid by guaranteeing each coal plant a certain amount of operating hours and leaving renewable energy developers struggling to compete.

At the same time, China's demand for energy has been growing at a slower pace than in previous years, due to its economic slowdown and improved energy efficiency across its economy. Data from the China Electricity Council show that the country's consumption of electricity increased by only 0.5 percent in 2015, the smallest increase this decade.

"The main cause of idling turbines is an overcapacity in China's power generation," said Lin Boqiang, director of the China Center for Energy Economics Research at Xiamen University. "China's power supply currently surpasses its demand by 20 to 25 percent. All the electricity producers in the country are going through a tough time, and wind power developers are not an exception."

According to a new government regulation issued in November, China will give wind power generators and other cleaner electricity producers priority ahead of coal in selling their output to distributors and large industrial users—though detailed guidelines have yet to come. Earlier this month, Beijing slapped a quota on regions' non-hydro renewable energy consumption, requiring Chinese grid operators to ensure that at least 5 percent of the electricity in their transmission network comes from wind, solar or biomass. But critics complain that the requirement is too easy to meet, and that there's no penalty for not complying.

For some analysts, China's move to suspend the approval of new projects in wind-curtailed regions has a silver lining, because it will force wind project developers to shift their attention from building in northern Chinese regions, which have the strongest winds but the worst grid problems, to other regions.

"Projects approved [in the north] prior to 2016 can still be built. However, we believe most developers will slow the construction in those curtailed regions in 2016," said Zhou Yiyi, a Shanghai-based analyst from market research firm Bloomberg New Energy Finance. Instead, she said, the developers will build wind power projects in the south, where fewer idled turbines exist and increased profits are available to developers.

What does this all mean for China's goal of putting up at least 20 gigawatts of new wind capacity this year?

Zhou said that across China 48 gigawatts of permitted capacity is in the pipeline waiting to be built, and roughly 40 percent of that, or about 20 gigawatts, is in non-curtailed regions that are closer to transmission lines and don't have energy waste problems.

"In other words, 20 gigawatts is still an achievable target," Zhou said.

While it remains unclear whether the policy will leave a mark on China's long-term renewable energy growth and climate targets, experts say the country is on the right track.

One reason: Coal plants, the main source of China's carbon pollution, may be worse off than wind farms and turbines.

"The government has imposed even tougher restrictions on coal-fired power generation," said Lin of Xiamen University. "With low electricity demand and more generation capacity coming online, [the implication] this year is that one out of four coal-fired power units could stand idle, while that figure could be one out of five for wind turbines, on average."

"Chinese policymakers are still doing their best to back up the renewable energy industry," Lin said.