One potentially useful alternative to conventional economic analysis is net energy analysis, which is the examination of how much energy is left over after correcting for how much of that energy (or its equivalent from some other source) is required to generate (extract, grow or whatever) a unit of the energy in question. Net energy analysis is sometimes called the assessment of energy surplus, energy balance, or, as we prefer, energy return on investment (EROI or sometimes EROEI) [2-7]. EROI is calculated from the following simple equation, although the devil is in the details [5-7]:
EROI = Energy returned to society / Energy required to get that energy

Since the numerator and denominator are usually assessed in the same units (an exception we treat later is when quality corrections are made) the ratio so derived is dimensionless, e.g. 30:1 which can be expressed as ╥30 to one╙. This implies that a particular process yields 30 Joules on an investment of 1 Joule (or Kcal per Kcal or barrels per barrel). EROI is usually applied at the mine-mouth, wellhead, farmgate, etc. We call this more explicitly EROImm, and is not to be confused with conversion efficiency, i.e. going from one form of energy to another such as upgrading petroleum in a refinery or converting diesel to electricity. It is only loosely related, at least in the short term, to the concept of energy return on monetary investment.