You can carry forward the energy efficiency tax credit to future years if you use a geothermal pump, solar panels, solar water heater, small wind energy system, or fuel cells.
Energy Incentives 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.
The IRS hasn't yet said how long the tax credit can be carried forward.
It's 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 nonrefundable, which means at the end of the year, you can't get back more than you paid to the government in taxes throughout the year. If you're unable to claim the entire 30% of your purchase for the previous products in one year, you can carry forward the unclaimed portion to future years.
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.