Political attacks on renewables range from attempts to place moratoriums on new wind development in states such as New Hampshire and Vermont, to efforts to repeal or significantly roll back targets in North Carolina, Kansas and Ohio. Other states, including Connecticut, are looking at watering down their mandates by allowing electricity from large-scale hydro to be used to meet the requirements.
"This year, we saw bills introduced across the country that would have wiped out nearly 50% of the demand created through state policies," a Vestas spokesman told Windpower Monthly.
In all, according to a database compiled by the law firm Keyes, Fox & Wiedman, there have been at least 35 bills to weaken renewable portfolio standards (RPS) proposed in 16 of the 29 states that have them on the books.
Activity to undermine the standards has been increasing, said Jeff Deyette, assistant energy research director at the Union of Concerned Scientists.
"It is more pervasive this year than in years past," he said.
Deyette and other renewable energy advocates attribute the surge in activity to the involvement of the American Legislative Exchange Council (ALEC), a conservative-leaning national organisation that has more than 2,000 state legislators as members.
ALEC has made the reversal of RPS policies a priority for 2013, arguing that the free market is a better way to determine the most cost-effective source of power. It typically releases model legislation for state lawmakers to use as a blueprint when drafting bills and last autumn joined forces with the Heartland Institute, a conservative think tank, to develop one such model bill, the Electricity Freedom Act, aimed at repealing state mandates.
Other groups have also entered the fray, including Americans for Tax Reform and Boston-based Suffolk University's Beacon Hill Institute, which produced what Deyette called questionable economic analyses to bolster arguments that the policies raise power prices and cost jobs.
"This is, I think, a co-ordinated attack to try to undermine the progress the renewable energy sector has made, the momentum that's been created," said Deyette.
These opponents have yet to make much progress in their efforts, added Deyette, but they have forced renewable energy advocates to expend valuable resources defending their positions.
"If you measure success by outright repeal of these standards, they may be successful with one or two. I don't think they are going to get much more than that," he said.
"But if you measure success in a different way, in that they are slowing our ability to do what we should be doing, which is going out and expanding these policies and creating larger markets for renewable energy, then I think they have been successful."