Elsevier

Renewable Energy

Volume 173, August 2021, Pages 942-952
Renewable Energy

Optimum matching of photovoltaic–thermophotovoltaic cells efficiently utilizing full-spectrum solar energy

https://doi.org/10.1016/j.renene.2021.04.031Get rights and content

Highlights

  • A novel concentrated solar spectrum PV-TPV hybrid system is proposed.

  • Effects of key parameters on the systemic performance are investigated.

  • Maximum efficiency and other corresponding parameters are calculated.

  • Optimum selection criteria of key parameters are provided.

  • Performances obtained are largely improved compared with other related systems.

Abstract

The production of redundant waste heat limits the performance of photovoltaic cells, so removing waste heat and converting it back into electricity is a promising way to improve the utilization of solar energy. A new concentrated solar spectrum photovoltaic-thermophotovoltaic hybrid system mainly is proposed. Full-spectrum solar energy is split into different parts according to specific requirements. Expressions for the efficiency and power output of the system are derived. The effects of the voltage output and area ratio of the two subsystems, the bandgap energy of semiconductor in the photovoltaic cell, and the solar concentration factor on the system performance are analyzed comprehensively. By optimizing several key parameters, the problem of the optimal matching between two subsystems is solved. The performance characteristics of the system are revealed, and the maximum efficiency and corresponding power output density of the hybrid system are calculated numerically, reaching 47.74% and 31.13W cm−2, respectively, which are 9.190% and 19.25% higher than those of a single photovoltaic cell. The optimal selection criteria of several key parameters are provided. By comparison with other PV-based systems, the proposed system not only maintains a high energy conversion efficiency but also produces a relatively larger power output density.

Introduction

With the depletion of conventional energy sources such as oil and coal and the deterioration of the living environment, the search for clean and abundant renewable energy [1] has been a concern for decades. Solar energy [2] is an excellent candidate because of cleanliness and richness. The photovoltaic (PV) cell [3] that can directly convert solar energy into electricity is attracted extensive attention and application. However, a mass of incident solar energy is dissipated into the environment in the form of low-grade heat, which greatly reduces the performance of PV cells [4].

How to discharge the waste heat in PV cells and further convert it into electricity has become a hot issue of recent concerns [5,6]. An effective solution is to combine the PV cell with thermoelectric devices to reuse the waste heat. Some related investigations about the PV-based coupled systems have been developed, especially focused on the PV-thermoelectric generator (TEG) coupled systems. For instance, Soltani et al. [7] experimentally investigated a coupled system composed of a PV cell and a thermoelectric module using five disparate cooling skills on the TEG cold side, and evaluated the performance of the entire system. The results indicated that the power output of the hybrid system using SiO2 and Fe3O4 nanofluids cooling technology can be increased by 5.7% on average compared to the case of pure water-cooling technology. Li et al. [8] established an uni-coupling TEG model for the PV-TEG system, and analyzed the influence of the geometrical size of the TEG device on the system performance, in which the temperature-dependent characteristics of thermoelectric material were considered. The results show that the system efficiency of 16% can be attained when the areas of N- and P-type in the TEG are the same. Rejeb et al. [9] developed a three-dimensional statistical concentrated PV-TEG system, analyzed the influences of the product of solar irradiance and concentration factor, ambient temperature, and the intrinsic properties of the TEG on the electrical efficiency, and found that the maximum efficiency can reach 17.45%. Liao et al. [10] proposed a PV-TEG hybrid system, evaluated and compared the system characteristics of three especial work states by solving the energy balance equation. A significant result was obtained: the maximum efficiency of the hybrid system is 22.9%, which was better than that of the PV cell under the same condition. Yin et al. [11] established a tandem concentration PV-TEG hybrid system, experimentally took a comprehensive feasibility analysis including the optimization of several key parameters, and provided a lot useful design principles based on the analytical results. There is an 8.7% improvement of the maximum power output of the hybrid system larger than that of the concentrated PV cell. Although the performances of these coupled systems are improved compared with those of the individual PV cell, the contribution of the TEG to the overall performance of the system is a little finite [12,13]. The main cause is that in the PV–TEG systems directly coupled by the PV cell and TEG, the performance of the PV cell deteriorates with the temperature increase of the PV cell so that the TEG is only operated at a small finite temperature difference. Yang et al. [14] built an updated model of concentrated solar spectrum PV-TEG system so that the TEG module could be operated at a large temperature difference. They discussed the influences of the cell voltage, the cut-off dimensionless current of the TEG and the area ratios of different components on the system performance, and calculated out that the maximum efficiency of the proposed system is 40.2% for the concentration factor of 100, which is higher 2.19% than that of the single PV system. Yin et al. [15] designed a new approach to optimize the concentration spectrum splitting PV-TEG hybrid system, that is, to optimize the solar energy distribution in the hybrid system on the premise of maintaining the optimally operating state of each subsystem. They investigated the performance characteristics of the system to reach the optimum design, and found that the maximum system efficiency attained 30% when the GaAs PV cell was used and the figure of merit in the TEG was equal to 1.

Some investigations have shown that under a large temperature difference, the thermophotovoltaic (TPV) cell proposed in 1956 [16] can more efficiently convert heat into electric energy than the TEG [17]. For example, Datas et al. [18] reviewed the historical and latest development of the TPV cell, and showed that as a device that can directly convert heat into electricity, thermal photovoltaic cells have high efficiencies (∼25% in current devices and potentially 40% in the future) and can produce higher specific power than thermoelectric devices and solid-state thermion converters. Dong et al. [19] evaluated the performance of an updated solar TPV cell with the consideration of various irreversible losses, provided a comprehensive analysis of the effects of the cell voltage, area ratio of the absorber to the emitter, and the bandgap energy of semiconductor on the system performance. The results showed that the optimized solar TPV cell can obtain a relatively high efficiency (23.1%) at the concentration of 800. Kazim et al. [20] studied various factors that influence the performance of the concentrated solar TPV system, especially the importance of incorporating a back-surface reflector, and investigated the effects of the reflection coefficient, external quantum efficiency of the cell, and emitter temperature on the system efficiency. It is shown that the TPV cell with a perfect reflector can attain an efficiency exceed 30% under high emitter temperature (>2000K). Chubb and Good [21] theoretically simulated the performance of a coupled TPV-TEG system, in which TEG and TPV cell are combined using a thermal conduction blocking method to solve the temperature mismatch problem between them. The research results showed that the performance of the coupled system was significantly improved at high temperature and enabled to produce more power. Yang et al. [22] established a novel direct carbon fuel cell (DCFC)-TPV cell coupled system, and analyzed and calculated the critical boundary values of optimized parameters. The maximum power output density of the DCFC-TPV hybrid system can attain 734.7 W m−2, which is superior to other DCFC-coupled systems at differently operating temperatures. Liao et al. [23] proposed a Schottky junction-based thermionic-TPV device, which enables to simultaneously convert emitted electrons and photons into electricity, solved the optimal matching between two subsystems, and provided the optimized criteria of key parameters of two subsystems. The results showed that choosing a high-emissivity cathode material can significantly improve the performance of the device. The above examples indicate that the TPV–based hybrid system consisting of the TPV cell and other devices is an efficient approach to enhance the utilization of solar energy.

In this paper, a novel solar concentrated spectrum splitting hybrid model consisting of a PV cell and a TPV cell is presented, which is not considered before. The spectral distribution is optimized by using a spectrum splitter according to specific requirements, which reduces the generation of waste heat and improves the effective utilization of solar energy. The theoretical expressions for the efficiency and power output of the system are derived. The influences of the voltage outputs and area ratio of the two cells, bandgap energy of the semiconductor in the PV cell, and solar concentration factor on the systemic performance are comprehensively investigated in detail. The temperatures of the emitter, TPV cell, and PV cell are determined by solving energy conservation equations. By optimizing several key parameters, the problem of optimal matching between two subsystems is solved. The maximum efficiency (ME) and power output density (POD) of the PV-TPV system are calculated. The optimal selection criteria of several key parameters are provided.

Section snippets

Model description

As shown in Fig. 1, the novel concentrated solar spectrum hybrid system principally consisting of a condenser lens [24], a spectrum splitter [25], a PV cell, and a TPV cell, where PPV and PTPV are the power outputs of two cells, εgPV and εgTPV are the bandgap energies of the materials in the PV and TPV cells, ε is the photon energy, qi (i = 1, 2, in, Cr, Ar, …) represents different types of heat flows indicated by the color arrows, and T0, TA, TPV, TE and TTPV are, respectively, the

Parameter optimization and performance evaluation of the PV-TPV system

As depicted in Eqs. (17), (18), the performance of the overall system is highly dependent on the material properties and design parameters of the device. It can be found from Eqs. (17), (18) that for a given value of Acon, the efficiency η of the system is proportional to the power output P. It means that for the given values of C, the efficiency η is proportional to the POD P[=P/(APV+AA)], i.e. η=P/(qinC). Thus, when C is given, it is only necessary to discuss the efficiency or the POD.

Conclusions

A novel concentrated solar spectrum PV–TPV hybrid system has been established. The influences of the voltage outputs of two cells, the area ratio of the absorber to the PV cell, bandgap energy of the material in the PV cell, and solar concentrating factor on the systemic performance are discussed in detail. The MEs and corresponding PODs of the system are calculated within the rational range of the solar concentration factor. The optimal values of the main parameters that affect the performance

CRediT authorship contribution statement

Tao Liang: Conceptualization, Methodology, Software, writing, Investigation, Validation, Writing – original draft, Writing – review & editing. Tong Fu: Investigation, Formal analysis. Cong Hu: Investigation, Formal analysis. Xiaohang Chen: Conceptualization, Methodology, Investigation, Validation, Supervision, Writing – original draft, Writing – review & editing. Shanhe Su: Investigation, Formal analysis. Jincan Chen: Conceptualization, Methodology, Software, Investigation, Validation,

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work is supported by the National Natural Science Foundation (12075197), People’s Republic of China.

References (50)

  • T. Liao et al.

    Parametric characteristics of a solar thermophotovoltaic system at the maximum efficiency

    Energy Convers. Manag.

    (2016)
  • A. Datas et al.

    Thermophotovoltaic energy in space applications: review and future potential

    Sol. Energy Mater. Sol. Cells

    (2017)
  • Q. Dong et al.

    Performance characteristics and parametric choices of a solar thermophotovoltaic cell at the maximum efficiency

    Energy Convers. Manag.

    (2017)
  • D.L. Chubb et al.

    A combined thermophotovoltaic-thermoelectric energy converter

    Sol. Energy

    (2018)
  • Z. Yang et al.

    An efficient method exploiting the waste heat from a direct carbon fuel cell by means of a thermophotovoltaic cell

    Energy Convers. Manag.

    (2017)
  • J.E. Parrott

    Radiative recombination and photon recycling in photovoltaic solar cells

    Sol. Energy Mater. Sol. Cells

    (1993)
  • M. Elzouka et al.

    Towards a near-field concentrated solar thermophotovoltaic microsystem: Part I-Modeling

    Sol. Energy

    (2017)
  • H. Wang et al.

    Performance analysis of solar thermophotovoltaic conversion enhanced by selective metamaterial absorbers and emitters

    Int. J. Heat Mass Tran.

    (2016)
  • M. Lim et al.

    Optimization of a near-field thermophotovoltaic system operating at low temperature and large vacuum gap

    J. Quant. Spectrosc. Radiat. Transf.

    (2018)
  • P. Sabbaghi et al.

    Near-field thermophotovoltaic energy conversion by excitation of magnetic polariton inside nanometric vacuum gaps with nanostructured drude emitter and Backside Reflector

    J. Quant. Spectrosc. Radiat. Transf.

    (2019)
  • Z. Utlu et al.

    Investigation of the potential of thermophotovoltaic heat recovery for the Turkish industrial sector

    Energy Convers. Manag.

    (2013)
  • T. Liao et al.

    Efficiently exploiting the waste heat in solid oxide fuel cell by means of thermophotovoltaic cell

    J. Power Sources

    (2016)
  • Z. Yang et al.

    Maximum power output and parametric choice criteria of a thermophotovoltaic cell driven by automobile exhaust

    Renew. Energy

    (2018)
  • A. Datas et al.

    Detailed balance analysis of solar thermophotovoltaic systems made up of single junction photovoltaic cells and broadband thermal emitters

    Sol. Energy Mater. Sol. Cells

    (2010)
  • Q. Lu et al.

    Low bandgap GaInAsSb thermophotovoltaic cells on GaAs substrate with advanced metamorphic buffer layer

    Sol. Energy Mater. Sol. Cells

    (2019)
  • Cited by (27)

    View all citing articles on Scopus
    View full text