**Abstract**

Exergy is the very useful tool to evaluate energy systems besides energy analysis based on the first law of the thermodynamics. In contrast to energy, exergy is not conserved and always decreases. There are many types of exergy analysis involving exergoeconomic, exergoenvironmental, advanced exergy-based analyses, extended exergy analysis etc. In this study, an application of the extended exergy analysis is performed. In extended exergy analysis, not only energy related system is considered but also all materials and energy flows' exergy, non-energetic and immaterial fluxes (capital, labor and environmental impact) are turned into exergy equivalent values and utilized in the analysis, which are calculating for local econometric and social data. These methods can be applied to societies or energy based or nonenergy-based system. In this study, dynamic exergy analysis and extended exergy application of electricity generation from photon enhanced thermionic emitter is conducted. According to results, some important values can be listed as; extended exergy destruction, conventional based exergy destruction, extended exergy efficiency, conventional exergy efficiency, extended sustainability ratio, conventional sustainability ratio, extended exergy-based depletion ratio and conventional exergy-based depletion ratio are 542106006 MJ, 542084601 MJ, 0.01094, 0.01094, 1.011, 1.011, 0.978 and 0.989 respectively.

**Keywords:** exergy analysis, extended exergy analysis, photon enhanced thermionic emitter, dynamic performance evaluation, solar energy

### **1. Introduction**

Energy is a concept transferred from an object to another in form of work or to heat. Energy is a conserved quantity; the law of conservation of energy states that energy can be converted in form, but not created or destroyed [1]. From an economic and social perspective, energy is the most important factor that ensures progress in world living standards and country development. Together with the great developments and changes in the industrial field, the increase in the world population at the same time reveals the need for energy [2]. 87 percent of the energy produced in the world is provided by fossil fuels, 6 percent from renewable sources, and 7 percent from nuclear energy sources. "About 64.5% of the world's

electrical energy production is realized by fossil resources (38.7% coal, 18.3% natural gas, 7.5% oil)" [3]. Turkey has no significant energy resources in petroleum and natural gas reserves. In addition, it is a market country that has an important place between Europe and Asia. About 27% of current energy needs in Turkey are known to be met by domestic energy production. When the distribution of Turkey installed power in the energy sector on the basis of resources is examined, natural gas 26.5%, hydraulic energy 32%, coal 21.3%, wind energy 7.7%, solar energy 5.3%, geothermal energy 1.4%, 5.8% share belongs to other resources [4].

The total monetary size of Turkey's energy market is around 84 billion dollars. 60.1 billion dollars of this amount was imported. Renewable energy is the biggest resource that can close a deficit of approximately 24 million dollars. Solar Energy is the biggest renewable energy source. Turkey is a country rich in solar energy [5]. In terms of number of installed solar power plant in Turkey is 556 pieces. Turkey's solar energy installed capacity of 5095 MW in 2018. Turkey ranks 12th in the world in terms of installed capacity [6]. Solar energy is nowadays used in air conditioning (heating–cooling) of residences and workplaces, cooking, supplying hot water and heating swimming pools; in agricultural technology, greenhouse heating and drying of agricultural products; In industry, solar cookers, solar furnaces, cookers, salt and fresh water production from sea water, solar pumps, solar cells, solar pools, heat pipe applications; It is used in a controlled manner in transportationcommunication vehicles, signaling and automation, electricity production [7].

Photon enhanced thermionic emission (PETE) combines photovoltaic and thermionic effects into a single physical process to take advantage of both the high per-quanta energy of photons, and the available thermal energy due to thermalization and absorption losses [8]. It can be described by a simple three-step process: first, photoexitation of the valence electrons into a conduction band. Second, thermalization and diffusion of the conduction electrons throughout the cathode; and finally emission of the thermalized electrons into a vacuum and collection by the anode [9]. PETE cells have an advantage in efficiency over purely thermionic cells because the presence of electrons in the conduction band from photovoltaic effects reduces the effective work function of the material, making it easier for electrons to escape into the vacuum. Similarly, PETE cells do not suffer from the problem of low efficiency at high temperatures as standard photovoltaic cells do. This is because the degradation effect is specific to the two-layer semiconductor junction design of standard photocells. Further, since a PETE cell can operate efficiently at high temperature, it can be run in conjunction with a heat engine attached to the anode [10].

Exergy is the property of the system, which is the maximum work potential cand be distracted from a system, once it reaches to equilibrium state with a reference state [11]. Unlike energy, exergy is not conserved, and it's perpetually depleted due to irreversibilities (entropy generation). Some of the exergy is destroyed due to irreversibilities at within the system, and a few of it's thrown into the surroundings from the system boundaries (loss of exergy) [12]. If the exergy losses or destruction decrease, in other words, if the exergy efficiency increases, resource consumption and loss exergy emissions within the method can decrease inversely [13].

Extended Exergetic Accounting (EEA), provides a route to formally convert immaterial and non-energetic commodities into exergetic equivalents [14, 15]. According to EEA, material, energy carriers and externalities (capital, labour, and environmental remediation) represent resource expenses and are expressed in exergy as a unified metric. EEA has incorporated some elements of preexisting theories such as: cumulative exergy analysis, thermoeconomics and life cycle analysis, etc. and combines them into a consistent and expanded formulation (Extended Exergy) [16]. There are fundamental similarities between EEA and exergy methods. Like thermoeconomics, EEA results in a system of cost equations in which though

*Dynamic Extended Exergy Analysis of Photon Enhanced Thermionic Emitter Based Electricity… DOI: http://dx.doi.org/10.5772/intechopen.96716*

inhomogeneous quantities like labour, material and energy flux, capital are all homogeneously expressed in primary exergy equivalents. Like Cumulative Exergy Consumption, EEA computes the cumulative primary exergy "embodied" in a product over its entire production process. Like Exergy Life Cycle Assessment, EEA computations cover the entire life cycle of the considered system [17].
