Energy conversion efficiency

Energy conversion efficiency is the ratio of useful energy output to energy input in a process or device, usually expressed as a percentage. It measures how much input energy reaches a specified useful form rather than being dissipated or diverted.

First law of thermodynamics: Energy is conserved: it can move between systems or change forms, but cannot be created or destroyed. It requires accounting for all input energy, including energy that does not become useful output.
Thermal efficiency: The ratio of useful work or energy output to heat supplied to a thermal process. It applies the general ratio to engines and other heat-driven systems.
Energy return on investment: The ratio of energy delivered by an energy source to the energy required to obtain it. It compares energy gains over a supply chain, not useful output to input within one conversion.
Jevons paradox: The phenomenon in which efficiency improvements lower the cost of a resource service and can increase total resource consumption. Efficiency gains can raise demand enough to offset some expected energy savings.
Second law of thermodynamics: The entropy of an isolated system cannot decrease, constraining the conversion of heat into work. It explains why real energy conversions cannot turn all input energy into useful work.
Electricity generation efficiency: The ratio of electrical energy produced by a generator or plant to its energy input. It measures how much fuel or other primary energy becomes electricity.
Capacity factor: The ratio of actual energy production over a period to the maximum possible production at continuous rated output. It measures how intensively a plant operates, not how efficiently it converts energy.
Rebound effect: An increase in use of a service that reduces some of the energy savings expected from efficiency improvements. It describes how lower operating costs can erode projected savings without necessarily eliminating them.
Energy balance: An accounting of energy entering, leaving, and accumulating in a system over a defined interval. A consistent boundary and accounting period are needed to calculate the ratio.
LED efficacy: The luminous flux produced by a light source per unit of electrical power, measured in lumens per watt. Lighting is commonly evaluated by useful visible light per electrical input, rather than energy alone.

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