The threat that the U.S. Production Tax Credit would lapse on Dec. 31 prompted developers to complete as many projects as they could last month, the London-based research group said. A record 13.2 gigawatts of turbines were installed last year including 5.5 gigawatts in December, the most ever for a single month. Total wind capacity is about 60 gigawatts.

“It’s clear that the economics, aided by the Production Tax Credit, drove wind growth in 2012,” said Amy Grace, lead analyst on wind in North America for New Energy Finance. “Capacity was built without any near-term state mandated demand. This means that in most areas, utilities are buying wind power because they want to, not because they have to.”

The credit has been extended for a year to cover wind farms that start construction in 2013. Previously it only covered projects that started working by the expiration date.