Per the Energy Star FAQ website:
Can the energy efficiency tax credit be carried over to future years?
Only the tax credit for the following 5 products CAN be carried forward to future years:
The IRS has not issued guidance on how long the tax credit can be carried forward. It is clear that it can be carried forward through 2016, and it appears that it may be able to be carried forward beyond 2016. The energy efficiency tax credit is technically "non-refundable" which means at the end of the year, you can't get back more in credits than you paid to the government in taxes throughout the year. If you are unable to claim the entire 30% of your purchase for the above products in one year, you can carry forward the unclaimed portion to future years.
The Energy Star FAQ will be updated when the IRS issues further guidance. Energy Star is a joint program of the U.S. Environmental Protection Agency and the U.S. Department of Energy.