Energy Sustainability Analysis (ESA) of Energy-Producing Processes: A Case Study on Distributed H2 Production

Abstract

In the sustainability context, the performance of energy-producing technologies, using different energy sources, needs to be scored and compared. The selective criterion of a higher level of useful energy to feed an ever-increasing demand of energy to satisfy a wide range of endo- and exosomatic human needs seems adequate. In fact, surplus energy is able to cover energy services only after compensating for the energy expenses incurred to build and to run the technology itself. This paper proposes an energy sustainability analysis (ESA) methodology based on the internal and external energy use of a given technology, considering the entire energy trajectory from energy sources to useful energy. ESA analysis is conducted at two levels: (i) short-term, by the use of the energy sustainability index (ESI), which is the first step to establish whether the energy produced is able to cover the direct energy expenses needed to run the technology and (ii) long-term, by which all the indirect energy-quotas are considered, i.e., all the additional energy requirements of the technology, including the energy amortization quota necessary for the replacement of the technology at the end of its operative life. The long-term level of analysis is conducted by the evaluation of two indicators: the energy return per unit of energy invested (EROI) over the operative life and the energy payback-time (EPT), as the minimum lapse at which all energy expenditures for the production of materials and their construction can be repaid to society. The ESA methodology has been applied to the case study of H2 production at small-scale (10–15 kWH2) comparing three different technologies: (i) steam-methane reforming (SMR), (ii) solar-powered water electrolysis (SPWE), and (iii) two-stage anaerobic digestion (TSAD) in order to score the technologies from an energy sustainability perspective.

Trends in Scientific Literature on Energy Return Ratio of Renewable Energy Sources for Supporting Policymakers

“…The study showed an energy index equal to 4.19 and 4.31 per kilogram of diesel and gasoline, respectively. In this context, the research findings highlight that, since 2011, there has been a tendency to consider, apart from EROEI or EROI, some sustainable indices such as carbon footprint (CF) (Zupko 2019;Manouchehrinejad et al 2020;Roles et al 2020), energy payback time (EPBT) (Perez et al 2011;Bhandari et al 2015;Koppelaar 2017;Pickard 2017;Walmsley et al 2018;Gómez-Camacho and Ruggeri 2019;Goel et al 2020), energy return on carbon invested (EROC) (Liu and Van den Bergh 2020), energy sustainability analysis (ESA) (Gómez-Camacho and Ruggeri 2019) or carbon-equivalent payback time (CPBT) (Perez et al 2011). In fact, 26 documents consider these indices connected with EROEI values, indicating an increasing interest towards both energy efficiency and sustainable aspects of RES.…”

Tools for Measuring Energy Sustainability: A Comparative Review

“…Different sustainability studies must go beyond economic analysis due to the intrinsic and complex nature of economic markets. For example, a photovoltaic system installed in Europe, but produced abroad, has an energy burden for society in terms of energy [54][55][56].…”

Monitoring the Physiological State in the Dark Fermentation of Maize/Grass Silage Using Flow Cytometry and Electrooptic Polarizability Measurements

“…Alternatively, the liquid effluent of carboxylic acids and solvents from the DF process can be fed into different processes (see Fig. 1), thus increasing value addition and improving the sustainability of the process [8,9]. This can be achieved by additional energy production as it occurs in microbial fuel cells (MFCs) [10], algae and microalgae cultivations [11], and other multi-cascade reactor configurations [7], as well as in the synthesis of valuable chemicals [12].…”

“…Enzymatic systems suffer from sensitivity to O 2 [8,14] and H 2 , which reduces the efficiency of these systems, although novel approaches are actively being researched to overcome this drawback [15]. Pure fermentative cultures (natural or engineered strains) require high sterilization costs that are currently unsustainable [9] and can lead to a negative net energy balance [8]. Open mixed fermentative cultures, such as those used in DF, are preferred due to their high production rates and their simplicity of operation [15].…”