Europe's installed wind power capacity has reached the landmark 100 gigawatt level even as doubts about the industry's future growth potential persist.

The European Wind Energy Association said Thursday the European Union passed the milestone this month.

It said 100 gigawatts is enough generating capacity to meet the total consumption of 57 million households and is the equivalent to the power production of 39 nuclear power plants.

The group noted that speed with which the European Union has reached the level compared with the slow going of the industry in earlier years, pointing out that while it took the European wind energy sector 20 years to install its first 10 gigawatts, it only needed 13 years to add an additional 90 gigawatts.

That means half of the total European wind power capacity has been installed over the past six years.

"It would require burning 72 million tons of coal annually in coal-fired power plants to match Europe's annual wind energy production," EWEA Chief Executive Christian Kjaer said. "Loading that amount of coal on trains would require 750,000 wagons with a combined length of (7,145 miles) -- the distance from Brussels to Buenos Aires."

The European Union passed the 100 gigawatt wind power mark with the addition of several new projects, including the 400 megawatt Anholt offshore wind farm off the coast of Denmark and the 48 megwatt Linowo effort in Poland, the group said.

But whether the wind power industry can keep up anything like its recent growth in the near and medium terms is questionable given investor jitters over greater perceived risks in the face of shifting political attitudes and regulatory challenges.

Due to the debt crisis and reduced electricity demand from the recession, EU member governments are cutting subsidies for wind power as they institute austerity measures, thus putting their future in doubt.

The EU and key member nations such as Britain have yet to commit to any binding decarbonization targets past 2020 -- something backers say is needed to fuel investor confidence in the long-term viability of the industry, the EWEA says.

Plus, it added, plans for the establishment of an EU-wide "single energy market" by 2014 -- which is meant in part to benefit an influx of new renewable generation sources -- isn't like to meet the deadline.

In December, the 27 EU members committed themselves to completing a single market for electricity and gas by January 2014, under which Europe's piecemeal energy markets would be integrated and made more transparent for consumers at an anticipated savings of $17 billion annually.

Also worrying potential investors are less-than-hoped-for power production figures from existing wind farms, the Swedish renewable energy journal Recharge reported.

Financiers attending a London renewable energy conference last week complained wind power developers have routinely overestimated the amount of electricity production from wind farms, thus driving up the cost of financing new projects.

"When a wind consultant tells us what we can expect to come from our wind farms, our tendency is not to believe them," Andrew Marsden, managing director in Europe for GE Energy Financial Services, told the publication. "The only place where the wind has been significantly better than we expected is Hawaii."