Exergy and exergoeconomic analysis of sustainable direct steam generation solar power plants Amin M. Elsafi Mechanical Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia article info Article history: Received 25 February 2015 Accepted 22 June 2015 Keywords: Direct steam generation Exergy and exergoeconomic Reheating Solar power plant abstract Solar direct steam generation is considered as a promising technology for steam production in thermal power generation due to high temperature levels that can be achieved compared to other technologies that use indirect steam generation. This paper demonstrates exergy and exergoeconomic analysis of commercial-size direct steam generation parabolic trough solar thermal power plant. For steam power cycles, reheating might be necessary to avoid great wetness of steam which shortens the lifetime of the turbines. Therefore, two configurations have been considered in this study; the non-reheating config- uration as well as reheating by steam–steam heat exchanger. For each component, exergy and exergy-costing balance equations have been formulated based on a proper definition of fuel–product–l oss. Exergy results show that particular attention should be paid to solar field, condenser, low pressure turbine and high pressure turbine (in a descendant order) as they constitute the major sources of exergy destruction. Results from exergoeconomic analysis, however, show that the condenser should be the fourth component in the order of importance after the solar field and low/high pressure turbines. Increasing the temperature at the inlet of the low pressure turbine by 100 K using steam–steam reheating is shown to result in 9.1% increase in the vapor fraction at the exit of turbine. This increase in steam qual- ity, however, would be achieved by drop less than 1.5% in thermal and exergetic efficiencies, and about 2% increase in cost of electricity. Moreover, the effect of degree of reheating on exergetic exergoeconomic parameters has been investigated. The results revealed that there is a specific value of degree of reheating for which the exergetic efficiency would be on it’s lowest value. This point would be of importance during optimization procedure of reheating direct steam generation solar plants. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction The growing concerns about energy savings led to the develop- ment of exergy concept. Exergy is considered as a powerful tool in analyzing thermal systems to pinpoint the locations and magni- tudes of irreversibilities in processes based on the second law of thermodynamics. It is important to realize that in the endeavor to save waste energy that some of system irreversibilities cannot be eliminated. Nevertheless, a detailed study of the system and its components in the light of the second law of thermodynamics helps in specifying the opportunities to save energy with high quality. Increasing energy demand and exhaustible natural resources make system design with minimized costs to be one of the most challenges that faces engineers [1]. Exergoeconomic emerged as useful tool that combines exergy analysis of the system with economic constrains which provides information not avail- able through conventional thermodynamic and economic analysis [2]. This systematic approach, therefore, allows engineers to asses the cost of consumed resources, money and system irreversibilities in terms of the overall production and enable them to exploit these resources effectively. By allocating costs to flow streams in each process, exergoeconomic helps in the assessment of economic effect of irreversibilities. Exergoeconomic not only helps in locating inefficiencies and their economic effect during plant operation, but it can also be used in optimizing the design of the new plants and assessing rational prices of plant’s products. Therefore, it is for these reasons that exergy and exergoeco- nomic analysis are being implemented to asses the performance of thermal plants and to investigate improvement potentials. Shokati et al. [3] presented comparative exergoeconomic analysis for absorption Rankine power cycle using specific costing method. Vuc ˇkovic ´ et al. [4] evaluated the performance of industrial plant using advanced exergy and exergoeconomic analysis based on real plant data. They [4] concluded that 80% of the total exergy destruc- tion mainly occurs in steam boiler, and 83.5% of this destruction is unavoidable. Memon et al. [5] developed regression model that http://dx.doi.org/10.1016/j.enconman.2015.06.066 0196-8904/Ó 2015 Elsevier Ltd. All rights reserved. E-mail address: amin_elsafi@yahoo.com Energy Conversion and Management 103 (2015) 338–347 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman