Exergy in Photovoltaic/Thermal Nanofluid-Based Collector Systems

Abstract

This chapter focuses on the exergy analysis of photovoltaic/thermal (PVT) systems using nanofluid. The PVT hybrid systems are designed to harness solar energy more efficiently. The thermodynamic theory of exergy in PVT systems is explained in details. The existing researches used various models to perform the exergy analysis for performance evaluation of the PVT systems. These models and formulations are compared with each other to achieve a widely used theory for a better comparison of the results. The exergy analysis is an effective tool to evaluate the performance of PVT systems. The exergy efficiency enhancement in PVT systems and the effect of nanofluid from the literature are presented. The literature survey suggests that the increase in the flow rate increases the exergy efficiencies in collector-based PVT. Using nanofluid as optical filters of solar radiation results in higher exergy efficiencies compared to collector-based PVT systems. According to the recent publications, the long-term thermophysical stability of nanofluid and cost-based exergy analysis still require further investigations.

Exergy optimization of a multi‐stage solar micro‐cogeneration system

“…In the case of the PVT collector, the exergy flow to the system Ex in comes from the solar irradiation. However, solar irradiation is not seen as pure exergy and due to this a conversation coefficient is included in the calculation of the PVT incoming exergy [29]: $$$$\begin{equation}E{x_{in}} = \ A \times {N_c} \times {G_{irr}} \times \left( {1 - \frac{4}{3}\frac{{{T_0}}}{{{T_{sol}}}} + \frac{1}{3}{{\left( {\frac{{{T_0}}}{{{T_{sol}}}}} \right)}^4}} \right)\end{equation}$$$$…”

“…Electrical energy is seen as pure exergy, but the exergy content of thermal energy depends on the temperature at which the heat is made available. In the model, the exergy of thermal ( Ex th ) and electrical ( Ex el ) energy are calculated as follows, respectively [29]: $$$$\begin{equation}E{x_{th}} = \ \dot{m} \times {c_f} \times \left[ {\left( {{T_{out}} - {T_{in}}} \right) - {T_0} \times ln\frac{{{T_{out}}}}{{{T_{in}}}}} \right]\end{equation}$$$$ $$$$\begin{equation}E{x_{el}} = \ {\eta _{pv}} \times {G_{irr}} \times {r_c} \times A \times {N_c}\end{equation}$$$$…”

“…In the case of the PVT collector, the exergy flow to the system Ex in comes from the solar irradiation. However, solar irradiation is not seen as pure exergy and due to this a conversation coefficient is included in the calculation of the PVT incoming exergy [29]:…”

“…Electrical energy is seen as pure exergy, but the exergy content of thermal energy depends on the temperature at which the heat is made available. In the model, the exergy of thermal (Ex th ) and electrical (Ex el ) energy are calculated as follows, respectively [29]:…”