After a sharp drop in 2013, U.S. installed windpower capacity rose 8% last year, a new Dept. of Energy report says, but it adds that further increases are uncertain, partly because key federal tax credits for wind expired last year and it’s unclear whether Congress will renew them.

The study, which DOE and its Lawrence Berkeley National Laboratory released on Aug. 10, reports that there were more than 4.8 gigawatts of wind installations, valued at $8.3 billion, in the U.S. last year. That boosted capacity 8% to 65.9 GW. Wind accounted for 4.9% of U.S. electricity demand.

Last year’s installations were up significantly from 2013’s level of about 1 GW but were far below the 2012 peak of roughly 13 GW.

Wind turbines were installed in 19 states, led by Texas, with 1.8 GW.

The report expects more wind capacity gains this year but says prospects for post-2016 growth aren’t clear.  Factors include uncertainty about the wind production and investment tax credits, continued low natural gas prices and “limited near-term demand” for sources like wind from state renewable energy portfolios.

The Senate Finance Committee in July approved a package of tax-break extensions that included a provision to continue the wind production credit for one year.