A system of systems approach to energy sustainability assessment: Are all renewables really green?

Renewable energies are emerging across the globe in an attempt to slow down global warming and to improve national energy security in face of the depleting fossil fuel reserves. However, the general policy of mandating the replacement of fossil fuels with the so-called green energies may not be as effective and environmental-friendly as previously thought, due to the secondary impacts of renewable energies on different natural resources. Thus, an integrated systems analysis framework is essential to selecting optimal energy sources that address global warming and energy security issues with minimal unintended consequences and undesired secondary impacts on valuable natural resources. This paper proposes a system of systems (SoS) framework to determine the relative aggregate footprint (RAF) of energy supply alternatives with respect to different sustainability criteria and uncertain performance values. Based on the proposed method, the RAF scores of a range of renewable and nonrenewable energy alternatives are determined using their previously reported performance values under four sustainability criteria, namely carbon footprint, water footprint, land footprint, and cost of energy production. These criteria represent environmental efficiency, water use efficiency, land use efficiency, and economic efficiency, respectively. The study results suggest that geothermal energy and biomass energy from miscanthus are the most and least resource-use efficient energy alternatives based on the performance data available in the literature. In addition, despite their lower carbon footprints, some renewable energy sources are less promising than non-renewable energy sources from a SoS perspective that considers the trade-offs between the greenhouse gas emissions of energies and their effects on water, ecosystem, and economic resources. Robustness analysis suggests that with respect to the existing performance values and uncertainties in the literature, solar thermal and hydropower have the most and least level of RAF robustness, respectively. Sensitivity analysis indicates that geothermal energy and ethanol from sugarcane, have the lowest and highest RAF sensitivity to resource availability, respectively. (C) 2014 Elsevier Ltd. All rights reserved.