The availability of reliable electricity and heat sources for community guarantees a better living environment in terms of education, healthcare and economy. Two main parameters should be considered in heat production which are the cost of this production and the performance of the devices used to produce this heat. In this work, a thermodynamic analysis based on energy and exergy analyses as well as economic analysis are presented to analyze the performance of parabolic trough solar collector (PTC). A multiobjective swarm optimization (MOPSO) technique is used to find out the maximum exergy efficiency and the minimum heat production cost of PTC. The optimum results show that the exergy efficiency, energy efficiency and heat cost are 29.22%, 35.55% and 0.0142 $/kWh. The effect of PTC geometrical parameters such as length, focal length, width and internal absorber diameter on the performance of PTC and heat production cost are investigated. Energy efficiencies of the system at different times during the day are calculated and they are in good agreement with the experimental results available in literature. The proposed system of PTC is located in Tehran, Iran.

Introduction

Solar energy is one of the abounded renewable energy resources distributed in the world. Utilization of solar energy can be used based on its application at low, intermediate and high temperature (Jebasingh and Herbert, 2016; Yousefi and Ehyaei, 2017). One of these applications is Concentrated Solar Power plant (CSP). CSP depends on the reflected sun ray from the concentrator to the receiver in order to increase the temperature of the working fluid (Jebasingh and Herbert, 2016; Yousefi and Ehyaei, 2017). There are two types of CSP which vary based on the shape of optical concentrator namely point or line focusing. Point focusing produces higher temperature than the line focusing and it requires two axis tacking. Both power tower and parabolic dish CSP are considered as point focusing, while Parabolic Trough (PT) and Fresnel CSP are considered as line focusing (Fuqiang et al., 2017). Parabolic trough concentrated solar power (PTCSP) can be integrated easily with conventional power plant such as steam turbine (Rankine cycle) or gas turbine (Brayton cycle). This integration is carried out to achieve higher integrated system efficiency at low environmental impact t (Jebasingh and Herbert, 2016; Yousefi and Ehyaei, 2017). There are many configurations of PTCSP used in power plants, these configurations vary based on many parameters such as type of integration, type of working fluid, thermal storage system, shape of receiver, types of tracking system and reflector, and receiver (absorber) materials (Ehyaei et al., 2019; Fern andez-García et al., 2010).

Hydrogen, as a clean fuel, can provide all the requirements and characteristics of a clean and reliable energy carrier in the long term as a suitable alternative to fossil fuels. In this paper, a power generation system using hydrogen storage has been investigated. For this purpose, 64 photovoltaic modules with area of 2.16 m 2 for each module and 329 PW and 5.5 kW PEM fuel cell and electrolyzer were used in this hybrid system. The day product of hydrogen day has been calculated as 158 kg. The system has been subjected to exergy analysis and, hence the efficiency and destruction of exergy components have been calculated. The annual average electrical production by photovoltaic system is 4850 W. The average annual exergy efficiency of each component including compressor, electrolyzer, fuel cell, and photovoltaic cell has been calculated as 75.9%, 11.2%, 32.8%, and 10.8%, respectively. The energy and exergy efficiencies of the system have been calculated for different days and its average annual values have been obtained 20.4% and 21.8%, respectively. Cost of electricity is 0.127 $/kWh, which is compatible with solar thermal and wind turbine offshore electricity costs. Finally, according to the advanced exergy analysis in all equipment’s except the photovoltaic cell, the highest exergy destruction has been related to exogenous unavoidable.

Introduction

Hydrogen as a clean fuel can be a suitable alternative to fossil fuels due to the fact that it has the characteristics of a clean and safe energy carrier in the long run, in addition to its highest energy per unit (Mitlitsky et al., 1998). The fuel cell and electrolysis unit’s combination has become a new strategy for suppling the required hydrogen to the fuel cell for power generating unit. This combined system is the main source of power and applications in several units (Rekioua et al., 2014). Hydrogen production for the use in fuel cells has been widely investigated. Bilgen (2004) examined various methods to produce hydrogen from renewable energy resource. A similar study was done be Levene et al. (2007) and Smaoui et al. (2015). Integration of photovoltaic (PV) system with fuel cells has been recently investigated for the purpose of hydrogen production (Babayan et al., 2019). A new PV system integrated with polymer electrolyte membrane (PEM) fuel cell using phase change material (PCM) as a storage medium has been presented (Babayan et al., 2019) to produce hydrogen in a filling station of hydrogen. The study showed that the use of PCM resulted in an improvement of energy and exergy efficiencies of the proposed system. Ashari et al. (2012) investigated a system consisting of PEM fuel cell, reformer, burner, and heat exchanger to provide the required electricity, heat and domestic hot water for a residential building. The study revealed that an 8.5 kW fuel cell could meet all the building loads requirements. Residential electricity cost was calculated to be 0.39 $/kWh which is considered to be a high electricity cost. This type of fuel cell was also investigated by Saidi et al. (Saidi et al., 2005a; Saidi et al., 2005b).

This study presents an analysis of a biogas engine-powered cogeneration system using four different thermoeconomic methods. The most important parameter is the thermoeconomic cost of work produced by the gas engine for each method. The aim is to compare the results obtained from each of those methods. The first method is the exergetic cost theory, which introduced the exergetic cost concept to the thermoeconomic field for the first time. An incidence matrix is defined to show the interaction of flows and components within the system. Exergetic cost theory defines the main rules and delivers a result of 110.065$/h for the work produced by the gas engine. A second method, modified productive structure analysis, is applied to the system and cost balance equations are formed for each component. Exergy destruction is clearly defined and tabulated. At the end of the analysis, the cost of gas engine work was found to be 85.536$/h. A third new method described in published literature, Wonergy, is used to determine both the cost of work and the heat utilized in the cogeneration system. Wonergy gives the same thermoeconomic cost for the components which help to produce work. The smallest value obtained was 72.5$/h. The fourth method, SPECO (specific exergy cost), was the final analytical method used on the system. It defines fuel and product rules to obtain auxiliary equations. The thermoeconomic cost of work produced from the gas engine was determined to be 141$/h which was the highest value obtained in comparison to the others.

Introduction

In the analysis of the production processes of complex energy systems, the economic profitability and the productivity displayed in resource consumption should both be considered. Performing this analysis, thermodynamics enables us to calculate the efficiencies of the subcomponents that make up the system and determine the locations and amounts of system irreversibilities that occur in the process. However, thermodynamic analysis cannot assess the overall production process in an economic context. Thermoeconomic analysis, by contrast, is a combined discipline that directly assesses the cost of consumed resources, i.e., money and system irreversibilities, within the total production process. While a thermoeconomic analysis shows a variety of ways to use resources more effectively, it also describes the concept of monetary irreversible cost as the economic impact of inefficiency, and it aims to increase the cost efficiency of production processes. Thus, in a detailed thermoeconomic analysis, it becomes possible to understand the flows in the subcomponents and the entire production process, from the perspective of cost, from the raw material sources entering the system to the final products. Thermoeconomic methods are generally divided into two groups: cost accounting [1e5], and optimization techniques [6e12]. Cost accounting is the process of determining the total cost of the production per unit of each output of a thermal system, such as electricity, steam, hot water, chilled water, etc., while optimization methods are applied to finding the optimum design or optimum set of operation conditions. All initial investment and operating costs for establishing and operating a thermal system should be allocated to the final product. Principally, there are two costs that must be defined for each product: (i) Direct costs, which include the cost of resources and materials that are clearly attributable to the product cost throughout the production process, and (ii) Indirect costs. In a comprehensive thermoeconomic analysis, the aim of cost accounting is to establish a logical framework for evaluating the profitability, starting from the determination of the rational costs of the products, to organizing and evaluating the decisions made in accordance with this framework. Valero et al., in their initial work on exergetic cost accounting, developed the basic ideas of their thermoeconomic approach and presented a strong theoretical background. That study, which consisted of two parts, has been accepted as one of the pioneering studies in the thermoeconomic field. In the first part, they identified exergetic and thermoeconomic costs for a relatively simple thermal system and presented the basic conditions for conducting the thermoeconomic analysis of a more complex system [13]. In the second part, they developed the mathematical background for three different applications of the thermoeconomic analysis method described in the first part [14].

تحلیل دقیق اکسرژی سیستم های قدرت حرارتی گردنده با جمع کننده های خورشیدی تشتک سهمی وار در این مقاله معرفی می گردد . برق یا با استفاده ازچرخه رانکین بخار ( ORC) یا با چرخه ترکیبی تولید می شود که چرخه رانکین بخار در آن یک چرخه راس می باشد و چرخه رانکین آلی یک چرخه ته می باشد . هفت ماده سرد کننده برای چرخه رانکین آلی مورد بررسی قرار گرفتند : R134a, R152a, R290, R407c, R600, R600a و آمونیاک . پارامترهای کلیدی اکسرژی مورد سنجش قرار گرفتند : کارامدی اکسرژی ، نرخ اتلاف اکسرژی ، نرخ فرسایش سوخت ، نسبت برگشت ناپذیری و پتانسیل بهبود . در تمامی موارد بررسی شده آشکار گردید که وقتی تشعشع خورشیدی افزایش می یابد ، کارآمدی اکسترژی افزایش می یابد . چرخه ترکیبی R134a در میان چرخه های بررسی شده در واقع بهترین عملکرد اکسرژی را با حداکثر راندمان اکسرژی 26 درصد نشان می دهد که با چرخه ترکیبی R152a با راندمان 25 درصد همراه گردید . متناوبا ، چرخه ترکیبی R600a از کمترین راندمان اکسرژی یعنی 20 تا 21 درصد برخوردار بود . این بررسی آشکار می سازد که منبع اصلی اتلاف اکسرژی یک جمع کننده خورشیدی می باشد که در انجا بیش از 50 درصد اکسرژی دهانه از بین می رود یا از جهات دیگر بیش از 70 درصد اکسرژی منهدم شده بوده است . بعلاوه ، بیش از 13 درصد اکسرژی دهانه در تبخیر کننده منهدم می شود که با حدود 19 درصد اکسرژی منهدم شده برابر می باشد . در نهایت ، این بررسی آشکار می سازد که در انجا پتانسیل بالقوه اکسرژی 75 درصد در سیستم های بررسی شده وجود دارد .

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