On boundaries and ‘investments’ in Emergy Synthesis and LCA: A case study on thermal vs. photovoltaic electricity

Indicators of efficiency and environmental performance are fundamental to marking progress toward more sustainable patterns of human development. Central to indicator development is a common framework through which the wide range of environmental assessment methods may make comparative analysis. Clear and consistent definitions of system boundaries and input categories are essential to their interpretation, and form a necessary pre-requisite for meaningful comparisons of competing systems. A common framework of foreground and background categories, consistent with both LCA and Emergy Synthesis, is identified and discussed as the basis for the calculation of performance indicators. In this paper a revised operational definition of the Emergy Yield Ratio (EYR) is introduced, in light of the proposed categorization scheme, for consistent application to technological processes. Two case studies, namely CdTe PV and oil-fired thermal electricity production, are investigated. The Unit Emergy Value (UEV) of electricity generated by the thermal plant was calculated as 5.69E5 seJ/J with services and 5.11E5 seJ/J without services. The UEV for electricity generated by the PV system is 1.45E5 seJ/J with services, and 7.93E4 seJ/J without services. The computed EYRs including services are 6.8 for thermal electricity and 2.2 for PV electricity.

► We discuss the pivotal roles of consistent boundaries and input classification in environmental analyses, focusing on Emergy Synthesis and LCA. ► The Emergy Yield Ratio indicator is discussed, and a revised operational definition is provided for it. ► A case study is carried out on thermal vs. PV electricity. ► Results show that PV electricity requires less environmental support per unit of energy output (lower UEV) and per unit of emergy investment (lower EYR).