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Most energy conversion systems, and especially electricity generation plants, do not operate at nominal conditions throughout their useful life: periodic, semi-periodic and stochastic changes in the availability of the resource affect solar (thermal and PV), wind, hydraulic, and geothermal plants, which in reality operate at off-design conditions for most of their life. To a smaller extent, fossil-fuelled plants may also be plagued by fuel availability problems and no longer easily predictable demand oscillation. In spite of the ever growing net connectivity, since the demand curve in even larger geographic regions displays a typical quasi-sinusoidal shape, fleet load modulation is unavoidable. Naturally, off-design operation and load cycling affect the cost of the generated kWh. This paper presents a general thermoeconomic method to evaluate the economic and environmental effects of energy system integration, taking into account life cycle concerns (supply chains) and the effect of inefficiencies due to off-design operation of the systems. The method here is applied to a realistic case study of an Italian regional utility: an analysis of the implications of the variation of the productive mix between a photovoltaic power plant (PV) and a standard commercial, non-cogenerating gas turbine plant (GT) on the final cost of the electrical kWh. The demand curve is prescribed, and the effect of different mixes is assessed, both on the monetary and on the exergy cost of the electricity. The economic cost assessment is performed by standard thermoeconomic techniques, whereas the exergy costs are evaluated using both the Extended Exergy Accounting (EEA) and the Thermo-Ecological Cost (TEC) methods. The results show that a purely monetary cash flow accounting and thermo-economics lead to contrasting results, and also that the EEA and TEC cost indicators generate different rankings among the studied alternative GT/PV mixes. [ABSTRACT FROM AUTHOR]

Highlights: [•] The model proposed aims at minimizing local impact of energy systems. [•] The model is meant to minimize the impact starting from system thermodynamics. [•] The formulation combines exergy analysis and quantitative risk analysis. [•] The approach of the model is dual to Thermoeconomics. [ABSTRACT FROM AUTHOR]

In the last decades, thermoeconomic analysis emerged as a combination of exergy analysis and cost accounting principles, widely used for multiple purposes: to account for the exergy and economic costs of energy systems products, to derive the structures of such costs for the design optimization purpose, and to perform system diagnosis quantifying the source and the impact of malfunctions and dysfunctions within the analyzed process. Traditionally, thermoeconomic analysis is referred to as Exergy Cost Analysis or Exergoeconomic Cost Analysis. The former is based on the so-called Exergy Cost Theory, focused on the evaluation of exergy cost of the system products, while the latter is focused on the evaluation of monetary cost following the same theory. Currently, many practical approaches are available in the literature for the application of thermoeconomic analysis and Exergy Cost Theory to energy conversion systems, while a comprehensive classification, benchmarking and comparison of such approaches is missing. This paper aims to fill this gap through the following activities: first of all, a brief but comprehensive literature review related to the theoretical developments and applications of thermoeconomic analysis method is performed. Secondly and for the purpose of benchmarking, the main practical approaches identified for the application of Exergy Cost Theory are presented and formalized, including the fundamental aspects related to the definition of auxiliary relations and the reallocation of the exergy cost of the residues. Finally, the identified approaches are comparatively applied to the standard CGAM problem, and the advantages and drawbacks of each approach are discussed. It is found that the definition of the functional diagram and the numerical solution of the system through input-output analysis seem to be more straightforward with respect to the other approaches, leading also to the formalization of an unambiguous method to reallocate the exergy cost of the residual flows. [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]

In this work, the primary resources assessment of four different soil erosion remediation technologies, Geo-nets , Bio-mats , Geo-cells and Deep Rooting Plants (DRP), is performed applying the approach of the Exergy Life Cycle Assessment (ELCA). The ELCA provides a comprehensive framework to assess the primary resources requirements of products by means of the conversion of primary flows of energy and raw materials absorbed by a production process into exergy. The soil erosion technologies described in the work are analysed according to two complementary indicators: the annual average soil loss and the life cycle primary exergy requirements. The primary exergy requirement of the different applications is measured by means of three ELCA indicators: the Cumulative Exergy Demand (CExD), the Thermo-Ecological Cost (TEC) and the Cumulative Exergy Extraction from Natural Environment (CEENE). The specific context of the application is a highway slope of the size of 1 hectare situated along the A1 highway, near the town of Fabro (TR), in Italy. The results indicate that DRPs are the most suitable solutions. However, TEC, CExD and CEENE indexes of these technologies suggest the existence of hidden impacts related to land use. The same result characterises also Bio-mats, the technology with the highest contribution of renewable material along the life cycle phases. In conclusion, this work shows that the use of exergy based impact indexes for the environmental impact assessment supplies a wider framework and deeper insights of the environmental performance of production processes and products. [ABSTRACT FROM AUTHOR]