In this chapter:

The term “defined fuel source” means any of the following:

(A) Petroleum.

(B) Natural gas.

(C) Coal.

(D) Coke.

The term “energy-efficient maintenance” includes—

(A) the repair of military vehicles, equipment, or facility and infrastructure systems, such as lighting, heating, or cooling equipment or systems, or industrial processes, by replacement with technology that— (i) will achieve energy savings over the life-cycle of the equipment or system being repaired; and (ii) will meet the same end needs as the equipment or system being repaired; and

(B) improvements in an operation or maintenance process, such as improved training or improved controls, that result in energy savings.

The term “hybrid”, with respect to a motor vehicle, means a motor vehicle that draws propulsion energy from onboard sources of stored energy that are both—

(A) an internal combustion or heat engine using combustible fuel; and

(B) a rechargeable energy storage system.

(4) The term “operational energy” means the energy required for training, moving, and sustaining military forces and weapons platforms for military operations. The term includes energy used by tactical power systems and generators and weapons platforms.

(5) The term “petroleum” means natural or synthetic crude, blends of natural or synthetic crude, and products refined or derived from natural or synthetic crude or from such blends.

The term “renewable energy source” means energy generated from renewable sources, including the following:

(A) Solar, including electricity.

(B) Wind.

(C) Biomass.

(D) Landfill gas.

(E) Ocean, including tidal, wave, current, and thermal.

(F) Geothermal, including electricity and heat pumps.

(G) Municipal solid waste.

(H) New hydroelectric generation capacity achieved from increased efficiency or additions of new capacity at an existing hydroelectric project. For purposes of this subparagraph, hydroelectric generation capacity is “new” if it was placed in service on or after January 1, 1999.

(I) Thermal energy generated by any of the preceding sources.

(Added Pub. L. 112–81, div. B, title XXVIII, § 2821(a)(1), Dec. 31, 2011, 125 Stat. 1689; amended Pub. L. 115–91, div. B, title XXVIII, § 2831(c)(6), Dec. 12, 2017, 131 Stat. 1858.)