Terraintegra’s use of the word “efficient” or “efficiency” describes the conversion efficiency of energy. This can be described as the ratio between the useful production of a technology as against its required energy input. The useful output may be mechanical energy, combustion energy or heat, or electricity. Efficiency can be affected by the practical usefulness of the energy output. A car engine may be 35% efficient with most of the energy lost as heat. The same engine can be put to work in a biogas plant with 80% efficiency as the waste heat is used to drive a Racine Cycle turbine generator, to heat water in local buildings and to provide building airspace heat.