Definition of CONSERVATION
1: a careful preservation and protection of something; especially : planned management of a natural resource to prevent exploitation, destruction, or neglect.
2: the preservation of a physical quantity during transformations or reactions.
Many people use this term, not realizing that it means only to maintain or preserve, when our goal is maximum gains.
Definition of EFFICIENCY
1: the quality or degree of being efficient.
2a : efficient operation.
b (1) : effective operation as measured by a comparison of production with cost (as in energy, time, and money) (2) : the ratio of the useful energy delivered by a dynamic system to the energy supplied to it.
http://www.merriam-webster.com/dictionary/efficiencies