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Understanding the energy metabolism of national economies is nowadays crucial for policymakers in order to define effective policies and to properly set energy efficiency targets. Energy accountings based on the traditional Production-based accounting method (PBA) allows to understand how primary energy is directly extracted, traded, transformed and used within each economy. On the other hand, Consumption-based accounting method (CBA) allows to understand the ultimate economic purposes of such energy flows. The information provided by the joint application of these approaches may provide useful and complementary insight on the national energy metabolism, allowing to identify hotspots for potential interventions from both the supply and demand side. This paper reviews PBA and CBA energy accounting methods, presenting a possible way for the joint use of their results, consistently represented by means of one unique Sankey diagram. This will be useful to have a comprehensive insight on the energy metabolism of national economies, supporting analysts and policymakers in the identification of energy efficiency hotspots. The method is applied to South Africa and to the neighbor country of Botswana, based on data provided by IEA energy statistics and the EORA26 Multi-Regional Input-Output model, taking into account non-renewable fossil energy (raw coal, crude oil and natural gas) and considering the reference year 2013. Results suggest that the joint use of PBA and CBA methods may provide useful information on the hidden energy links among national economies, helping analysts and policymakers in defining alternative energy efficiency policies. For this reason, the Authors argue that results of CBA should be provided alongside energy statistics based on the traditional PBA approach. [ABSTRACT FROM AUTHOR]

Exergy Life Cycle Assessment (ELCA) is proposed by literature to account for the exergy embodied in products of energy systems. In order to make results of ELCA comparable, supply chains that support the life cycle of the system should be analyzed through a unified model: this is one of the main concerns related to Life Cycle Assessment and Industrial Ecology disciplines. In this paper, Hybrid Input-Output analysis is proposed as the computational structure of ELCA: according to this method, national supply chains are modeled through the Monetary Input Output Tables (MIOTs) of national economies, a constantly updated and freely available data source. Then, the adopted national MIOT is expanded to include the detailed model of the considered energy system, hence defining a Hybrid Input-Output model. The (non-renewable) exergy embodied in electricity production and the Exergy Return on Investment (ExROI) are defined as the appropriate performance indicators based on ELCA. The introduced model is here adopted for the analysis of a Waste-to-Energy (WtE) power plant currently operating in the Italian context. It is found that the primary non-renewable exergy embodied in electricity produced by the analyzed WtE is non-negligible for both the construction (127.1 toe) and the operation phases (11.6 toe/y). Nonetheless, the plant is able to produce a net amount of electricity that pays back such primary non-renewable resources requirements about a hundred times. Finally, the joint application of Exergy Analysis and ELCA lead to improve the overall thermodynamic performances of the WtE system, increasing its exergy efficiency by 1%, and reducing the non-renewable exergy embodied in electricity production by 7938 toe. [ABSTRACT FROM AUTHOR]

Due to the rapid increase of the World’s primary energy demand of the last decades, low-temperature processes for the purification of natural gas streams with high carbon dioxide content has gained interest, since they allow to make profitable exploitation of low-quality gas reserves. Low temperature purification processes allow the direct production of a methane stream at high purity and at low-temperature, suitable conditions for the direct synergistic integration with natural gas cryogenic liquefaction processes, while CO 2 is obtained in liquid phase and under pressure. In this way, it can be pumped for transportation, avoiding significant compression costs as for classical CO 2 capture units (where carbon dioxide is discharged in gas phase and at atmospheric pressure), and further uses such as Enhanced Oil Recovery (EOR) or underground storage. In this paper, the three most common natural gas low-temperature purification techniques have been modelled and their performances have been evaluated through energy and exergy analyses. Specifically, the dual pressure low-temperature distillation process, the anti-sublimation process and a hybrid configuration have been considered. It is found that the dual pressure low-temperature distillation scheme reach the highest thermodynamic performances, resulting in the best values of exergy efficiency and equivalent methane requirements with respect to the other configurations. This is mainly due to the distributed temperature profile along a distillation column, resulting in a less irreversible heat exchanging process. [ABSTRACT FROM AUTHOR]

This paper proposes an exergy-based well-to-wheels analysis to compare different passenger vehicles, based on three key indicators: petroleum energy use, CO 2 emissions, and economic cost. A set of fuel pathways, including petroleum-based fuels, compressed natural gas, biofuels, and electricity are considered in five representative national energy mixes, namely Brazil, China, France, Italy, and the United States of America. Results show no fundamental difference in the fossil fuel pathways among the five scenarios considered. Compressed natural gas vehicles and electric vehicles can completely displace oil consumption in the personal transportation sector. Compressed natural gas vehicles also reduce CO 2 emissions by over 20% compared to gasoline vehicles. Emissions from electric vehicles greatly vary depending on the electricity mix. In low-carbon electricity mixes electric vehicles reach almost-zero CO 2 emissions, while the use of biofuels leads to the lowest CO 2 emissions in carbon-intensive electricity generation mixes, where vehicles running on E85 could reduce CO 2 emission by over 50% compared to gasoline vehicles. Hybrid electric vehicles show the lowest overall economic cost, due to improved efficiency and low cost of petroleum-based fuels. Vehicles running on electricity are characterized by significantly higher capital cost and lower operating costs. Thus, different electricity generation costs impact minimally the overall cost. These results can be used to inform decision-makers regarding the multi-dimensional impact of passenger vehicles, including environmental impact, economic cost, and depletion of primary energy resources, with particular focus on petroleum. [ABSTRACT FROM AUTHOR]