Energieratio

Energieratio, or energy ratio, is a dimensionless metric used to assess the efficiency of energy conversion in a device, system, or process. It compares the amount of usable energy produced to the amount of energy consumed or required to operate the system.

Calculation and boundaries are central to its interpretation. energieratio = E_out / E_in, where E_out is the energy delivered for end use and E_in is the energy supplied to or consumed by the system within a defined period. When expressed as a percentage, the ratio is multiplied by 100. The choice of boundaries (what counts as input, what counts as output, and the time frame) strongly influences the value.

Examples illustrate its application. In a combustion engine that generates 40 MJ of mechanical work while consuming 150 MJ of chemical energy, the energieratio is about 0.27. A heat pump delivering 15 kWh of heat from 5 kWh of electrical input has an energieratio of 3.0. For technologies like solar photovoltaics, a life-cycle calculation of energy invested in manufacturing and maintenance versus energy produced is often discussed in terms related to energy payback or energy return on investment (EROI), which is a broader concept but related to the idea of energieratio.

Relation to other metrics is important. Energieratio is related to, but distinct from, energy efficiency, which typically focuses on instantaneous performance, and from EROI, which emphasizes energy returns over a system’s lifetime and broader boundaries.

Limitations include dependency on how system boundaries and time horizons are defined. Comparisons across technologies require consistent definitions and context to be meaningful.