Extended Energy Return on Investment of multiproduct energy systems

Abstract

Energy Return on Investment (EROI) is an indicator of how efficient is an energy supply system. In the present study, the conventional approach of EROI assessment is extended to include the equivalent energy investment needed for offsetting the life cycle environmental impacts. Moreover, the issue of allocation of the invested energy among different by-products is addressed. The EROI of multiple products has been specified using different benchmarks of price, energy content, exergy content, and exergy costs. The application of the concept is demonstrated through a case study of an Iranian oil production unit. The overall conventional and environmentally-extended EROI values of the produced oil in Iran is estimated to be 26.8:1, 23.3:1, respectively. Also, when taking the downstream environmental emissions into account, the EROI will be as low as 6.8:1. This shows that the EROI may be overestimated by 75% if the embodied costs are not taken into account. The comparison of the aggregated EROI estimates based on state-properties (price, energy, and exergy) and disaggregated process-property (exergy cost), gives a measure of the error of aggregation. It is shown that this error may be as high as 11.5% in the case of the multi-product energy system of the studied case.