Exergy Analysis
Exergy as an available useful work needs to be analyzed from the point of view of the second law of thermodynamics. It derives from Carnot’s thermal efficiency, which is responsible for high-grade energy. Exergy plays an important role in life-cycle cost
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Exergy Analysis
Abstract Exergy as an available useful work needs to be analyzed from the point of view of the second law of thermodynamics. It derives from Carnot’s thermal efficiency, which is responsible for high-grade energy. Exergy plays an important role in life-cycle cost analysis (LCCA).
Keywords Energy analysis Exergy analysis Energy matrices CO2 emission Carbon credit
19.1
Introduction
Current progress in the concepts, design, developments, and manufacture of solar energy technologies is very rapid. New solar-energy technologies are now predicted to play a major role to meet the energy demand by human being for good living comfort. This is most important areas in undeveloped/developing countries. The energy output from solar-energy technologies can be classified as follows: (i) Thermal energy(low-grade energy): Solar thermal systems The energy analysis of thermal energy (low-grade energy) output is based on the first law of thermodynamics as performed in Chap. 14. However, the concentrating collector operating at high temperature should be analyzed on the basis of the second law of thermodynamics. (ii) Electrical energy(high-grade energy): Photovoltaic systems The energy analysis of high-grade energy (photovoltaic) is based on the second law of thermodynamics and is known as “exergy analysis.” (iii) Both thermal (low-grade energy) and electrical energy (high-grade energy): Photovoltaic thermal systems In this case, either thermal energy is converted into high-grade energy using the concept of Carnot’s efficiency, or electrical energy is converted into low-grade © Springer Science+Business Media Singapore 2016 G.N. Tiwari et al., Handbook of Solar Energy, Energy Systems in Electrical Engineering, DOI 10.1007/978-981-10-0807-8_19
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19
Exergy Analysis
energy by dividing it by power plant‒conversion factor (Eq. 14.1) as performed in Chap. 14.
19.2
Exergy Analysis
As mentioned in Chap. 3, an exergy analysis of any system incorporates all of the irreversibilities and inefficiencies that lead to the destruction of exergy. In this chapter, since we are dealing with exergy analysis, thermal energy (low-grade energy) will be converted into exergy (high-grade energy) as follows. First method If the operating temperature is very high, say, approximately 400–500 °C in the case of a concentrating system for power generation, then thermal energy will be converted into exergy as _ ¼ Q_ u 1 Tfi þ 273 Ex Tfo þ 273
ð19:1Þ
where Q_ u ¼ m_ f Cf ðTfo Tfi Þ is the rate of thermal energy (low-grade energy) at temperature Tfo (°C); and Tfi (°C) is the inlet temperature at the surrounding air temperature. Second method Unlike a solar concentrator, the flat-plate collector operates at medium temperature range, say, approximately 100–150 °C. The second method of exergy analysis incorporates entropy losses in the system. For a solar thermal collector system, if Tfo and Tfi are, respectively, the outlet and inlet fluid temperature (K), and m_ f is the _ c Þ of the system is expressed as mass flow rat
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