# Energy Balance and Energy Ratio

## Energy balance and energy payback ratio

The terms "energy balance" and "energy payback ratio", or "energy ratio", are used to describe system energy output related to system energy input.

The energy balance can be expressed as

E_{o}= dE + E_{i}(1)

or

dE = E_{o}- E_{i}(1b)

where

dE = energy balance

E_{o }= energy output

E_{i}= energy input

The energy ratio - system energy output to system energy input - can be expressed as

ER = E_{o}/ E_{i}(2)

where

ER = energy ratio

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