Media playback is unsupported on your device Media caption David Shukman watches one of China's giant wind farms take shape

China has embarked on the greatest push for renewable energy the world has ever seen.

A key element involves more than doubling the number of wind turbines in the next six years.

Already the world's largest producer of wind power, China plans further massive increases.

From a current installed capacity of 75 gigawatts (GW), the aim is to achieve a staggering 200GW by 2020.

By contrast, the European Union countries together have just over 90GW of installed wind capacity.

The far western province of Xinjiang is one of seven areas designated for wind development.

Against a backdrop of snow-capped mountains, turbines are massed in their thousands over the frozen desert.

New units are being installed in a frenzy of construction in which the pace of work has been accelerated.

Jiang Bo, an engineer with the manufacturer Goldwind, told me: "Seven years ago we could only do one wind turbine in about two days - but our current speed is that we can do two in one day."

However, integrating this surge in wind power has posed a series of challenges.

Image caption Reduced prices could make Chinese-made turbines more appealing to buyers abroad

The windiest regions, such as Xinjiang, tend to be extremely distant from the biggest cities where the electricity is most needed.

And the construction of wind farms has often outstripped the building of the connections needed to link the turbines to the grid.

The grid itself, accustomed to handling the predictable output of power stations burning coal, has struggled to cope with the intermittency of wind.

The result has been that some wind farms have been ordered to shut down even on windy days - a process known as curtailment.

Last year as many as 20%-30% of turbines across China were left idle at particular times but wind industry officials say the problem is now being tackled.

A more fundamental question is the likely contribution of wind power to China's insatiable demand for energy.

The most recent figures, for 2012, show that wind only generated 2% of the country's electricity. Coal, the largest contributor, generated 75%.

However, since China's total generation is more than that of all European Union countries combined, wind's percentage is large in absolute terms.

Liming Qiao, China director of the Global Wind Energy Council (GWEC), said: "Two per cent sounds small but it's not when you consider China's total electricity.

"In fact, last year wind surpassed nuclear to become number three after coal and hydro, and it's got a lot more potential."

The sheer scale of the wind market is encouraging mass production which has lowered prices and fostered innovation.

Until recently, Chinese wind manufacturers produced Western-designed turbines under licence. Some acquired a reputation for turning out inferior products.

Now, the wind boom has led to a flurry of new designs. Goldwind, for example, offers a turbine which does not need a gearbox but instead has a "direct drive" system designed to be cheaper to maintain.

Image caption Workers are putting up two turbines per day at the Xinjiang wind farm

According to Paolo Frankl of the International Energy Agency, developments in China will drive down prices globally.

"As with any other things, what China does has an impact on the whole world and China is contributing to the reduction in the cost of wind in two ways:

"One being the most important market in the world with large deployments and, second, with a very robust and active manufacturing capacity."

Mr Frankl expects reduced prices to make Chinese turbines more appealing to buyers abroad.

"The export ratio of the Chinese producers will increase and they'll find new markets in Asian countries, Latin America and Africa," he said.

The Chinese government has set renewable energy as a strategic priority and supports the push for wind through a system of subsidies.

The crisis in air pollution in many Chinese cities has added a further rationale for renewable energy - beyond the aims of energy security and lower carbon emissions.

Still open is the question of whether wind's costs can ever be driven below those of coal, China's energy backbone.

Image caption The Chinese government has set renewable energy as a strategic priority

Ma Jinru, a vice president of Goldwind, looks forward to a time when fossil fuels will be scarcer and subject to carbon pricing.

"One day in the future when the resources become limited and the price gets higher and pollution gets worse, then society will charge the social cost for that, so in the long term the cost of wind energy can be cheaper than coal.

"And the cost of wind energy will drop through technical innovation, so the wind energy sector will have a huge huge growth in the whole electricity supply."

If any country can industrialise wind power and make it pay, it's China.

And a glimpse of its future can be found beside the Silk Road in Xinjiang: along this ancient trade route stand white metallic forests of turbines, some completed, others waiting to be fitted with blades, and many more planned.