Promoting New American Energy Act of 2008 - Amends the Internal Revenue Code to classify as three-year property for depreciation purposes: (1) any industrial steam and electric generation and/or distribution system, electric utility nuclear or steam production plant, electric utility transmission and distribution plant, or electric utility combustion turbine production plant fueled by natural gas that is described in the Internal Revenue Service (IRS) Revenue Procedure 87-56; (2) certain pollution control equipment; and (3) certain solar energy property.