Ideal EROI (energy return on investment) deepens the understanding of energy systems

This article presents a new EROI (energy return on investment) factor named the ideal EROI, or EROI_ide, that provides the theoretical upper boundary of the EROI of a given system. The EROI_ide is the ratio between the inputs within the EROI_stnd boundaries and the theoretical maximum output from a given system; i.e, all losses are omitted and the maximum theoretical energy output of the system is used. EROI_ide resembles the concept of the idealised Carnot heat engine. Although the EROI of a given system can never be equal to EROI_ide, the EROI_ide can be used to estimate the potential for improvement; e.g., if the difference between the EROI_ide and EROI_stnd is small then little improvement can be expected from further research funding. Calculations using EROI_ide can add a valuable depth to the overall results of an EROI study, benefitting policy makers involved in energy policy planning. Three application examples of EROI_ide are provided, one for a hydroelectric power plant, one for a geothermal power plant and one example for a hypothetical wind farm. The calculations show that the hydro power plant could improve approximately 3 fold, whereas the geothermal plant had a potential of 27 fold improvement over its lifetime.