energytooutput

Energytooutput (ETO) is a performance metric used to quantify how much energy is required to produce a unit of useful output in a given system. It is typically expressed as energy input per unit of output, such as kilowatt-hours per unit produced or joules per joule of useful work. In many contexts, ETO is the reciprocal of energy efficiency when both input and output are measured in the same energy form.

Calculation involves setting a system boundary, measuring total energy input over a defined period, and measuring the useful output generated in the same period. The ratio is ETO = energy input / useful output energy. Lower ETO indicates higher energy performance. For electrical motors, for example, if a motor delivers 0.90 kWh of useful work for every 1.00 kWh drawn, the ETO is 1.11 kWh per kWh of output. This reflects the energy cost of producing a unit of useful output and is useful for cross-system comparisons.

ETO is used to compare technologies, optimize processes, and track improvements over time. It informs decisions on equipment replacement, process integration, and energy-management strategies. It complements other metrics such as energy efficiency, energy intensity, and exergy efficiency, which emphasize different aspects of performance.

Limitations of ETO include dependence on how useful output is defined and the system boundary; it does not account for energy quality (exergy) or losses outside the defined scope. It can be sensitive to operating conditions and measurement accuracy. For that reason, ETO is generally used alongside other indicators and in life-cycle assessments.