Investigation of a novel hybrid photovoltaic-thermoelectric generator system

Effective thermal management of photovoltaic is essential for improving its conversion efficiency and increasing its life span. Photovoltaics can convert the ultraviolet and visible regions of the solar spectrum into electrical energy directly while thermoelectric generators utilize the infrared region to generate electrical energy. Consequently, the combination of photovoltaic (PV) and thermoelectric generators would enable the utilization of a wider solar spectrum. Therefore, this research aims to present an innovative thermal management technique for photovoltaic by the incorporation of thermoelectric generator (TEG) and heat pipe to form a hybrid photovoltaic system with improved overall efficiency, increased electricity generation and greater energy harvesting from the solar spectrum.The strength and innovation of the hybrid system studied in this thesis are as follows: (1) a low cost and high efficiency microchannel heat pipe (MCHP) is used to reduce thermal resistance of heat flow across interfaces and increase heat transfer capacity; (2) the flat plate structure of the MCHP eliminates geometry mismatch and reduces thermal losses; (3) water cooling is used for the TEG cold side thus, the hybrid system feasibility for co-generation of electricity and hot water is demonstrated; and (4) the use of flat plate MCHP results in significant reduction in TEG quantity needed thereby reducing the system cost. These structural innovations are intended to overcome some of the drawbacks and provide experimental data for the development of hybrid photovoltaic-thermoelectric (PV-TE) systems.A basic methodology of combined theoretical and experimental analysis is followed in this thesis and it involves, detailed literature review, conceptual design, mathematical analysis, computer simulation model development, experimental testing, model validation, and optimization case studies. Computer simulation models are developed to predict and optimize the performance of the systems using three- dimensional finite element models and COMSOL Multiphysics software.Experimental results show that the electrical conversion efficiencies of the PV- TE-MCHP with and without insulation and that of the photovoltaic only after 1 h are 11.98%, 12.19% and 11.94% respectively. Therefore, the hybrid system provides an enhanced performance. In addition, the highest and lowest thermal efficiencies obtained are 69.53% and 56.57% respectively under certain conditions. Steady state computer simulation results show that that at a high ambient temperature of 50 °C, the PV-TE-MCHP overall efficiency is greater than that of the PV only and PV-TE systems by 9.76% and 14.46% respectively. Therefore, the hybrid PV-TE-MCHP is recommended for sunny regions with high ambient temperature. Results also show that the asymmetrical leg geometry provides enhanced TEG only performance compared to the symmetrical leg geometry although the reverse is the case for the hybrid concentrated PV-TE system.This research shows that the hybrid PV-TE-MCHP design is feasible and provides enhanced performance compared to the PV only and PV-TE systems. In addition, the effectiveness of thermoelectric geometry optimization for performance enhancement is demonstrated in this research. Therefore, the experimental and simulation results from this research provide fundamental data for developing highly efficient hybrid photovoltaic-thermoelectric systems and thermoelectric generators

Series of detail comparison and optimization of thermoelectric element geometry considering the PV effect

This study investigates the optimum geometry for maximum efficiency of a hybrid PV-TE uni-couple using Finite Element Method. COMSOL Multiphysics is used to solve the 3-Dimensional heat transfer equations considering thermoelectric materials with temperature dependent properties. Two types of thermoelectric element geometry area ratios are considered for the range and . Nine different geometric configurations are analysed for two different PV cells. Effects of thermoelectric generator (TEG) geometric parameters, solar irradiation and concentration ratio on the hybrid system efficiency are presented. The results show that a hybrid PV-TE system will perform better with symmetrical TEG geometry () if a PV temperature coefficient of 0.004/K (Cell B) is used. This is different from the optimum geometry for a TEG only system. However, the optimum geometry of the TEG in a hybrid system will be the same as that of a TEG only system (dissymmetrical i.e. ) if a PV temperature coefficient of 0.001/K (Cell A) is used. The overall efficiency and TE temperature difference show a decreasing trend as thermoelectric element length and area increase respectively no matter the configuration or temperature coefficient value used. Results obtained from this research would influence hybrid PV-TE system design for obtaining maximum conversion efficiency

Thermoelectric generator performance enhancement by the application of pulsed heat power

Thermoelectric generator (TEG) is usually studied under steady state heating conditions however, the use of pulsed heat power could significantly enhance its performance. Therefore, this paper presents a numerical investigation of the thermal and electrical performance of a typical thermoelectric generator (TEG) under both steady state and transient pulsed heating conditions. A threedimensional finite element model is used to study the temperature, voltage, current distribution and power output of the TEG. A comparison is made between the performance of the TEG under steady state and transient pulsed heating conditions. Furthermore, a parametric study is performed to investigate the influence of thermoelectric leg length and cross-sectional area on the performance of the TEG under both heating conditions. Rectangular and triangular pulsed heat functions are used for the transient study. Results show that rectangular pulsed heating provides the best performance compared to the triangular pulsed heating and steady state heating. In addition, the power output of the TEG decreased as the leg height increased however, it increased as the leg area increased. Therefore, shorter thermoelectric legs with wider cross-sectional area are suggested to enhance the performance of the TEG. This study will provide a valuable reference for future design of thermoelectric generators to obtain optimum performance

Scale effect on electrical characteristics of CPC-PV

Recently, the flux distribution and Photovoltaic (PV) structure optimization have been paid more attention in the design of concentrating Photovoltaic (CPV) by several researchers while the scale factor is sometimes decided by the processing technology used and cost. However, the same CPV devices with the same concentration ratio under different scales may possess different electrical characteristics. Therefore, this paper presents a comparison of two different scales of compound parabolic concentrating (CPC) PV with the same concentration ratio of 4X, based on the commercial crystalline silicon solar cell. The model is verified by experiment firstly, then the electrical characteristics comparison is performed. The results show that the maximum output power of small-scale CPC-PV cells is 424.960 mW, which is significantly higher than the maximum output power of large-scale CPC-PV cells of 420.713 mW. This means that the small scale one has a better electrical performance than the large scale one in this situation thus, this study will provide a reference for future CPC-PV design

Thermoelectric Element Geometry Optimization for Maximum Hybrid Photovoltaic-Thermoelectric System Efficiency

The geometry of thermoelectric elements in a hybrid Photovoltaic-Thermoelectric (PV-TE) power generation system can influence the conversion efficiency of the hybrid system. Therefore, this study investigates the optimum geometry for maximum conversion efficiency of a hybrid PV-TE uni-couple using Finite Element Method (FEM). COMSOL Multiphysics is used to solve the 3-Dimensional heat transfer equations considering thermoelectric materials with temperature dependent properties. The thermoelectric element geometry area ratio is considered for the range 0.5≤R_A≤2. R_A is the cross-sectional area ratio of the thermoelectric element hot and cold junctions (AH/AC). Therefore, three different geometric configurations are analysed. Temperature and voltage distributions in the hybrid system for the different configurations considered are presented. Effects of thermoelectric generator (TEG) geometric parameters and load resistance on the hybrid system efficiency are presented. The results show that a hybrid PV-TE system will perform better with symmetrical TEG geometry (R_A=1) however, this is different from the optimum geometry for a TEG only system (R_A≠1). The influence of solar irradiation and concentration ratio on the hybrid system performance are also studied. Results obtained from this research would influence hybrid PV-TE system designs for obtaining maximum conversion efficiency

Building integrated thermoelectric air conditioners—a potentially fully environmentally friendly solution in building services

The refrigerants used in conventional vapor-compression air conditioning systems have detrimental effects on the global environment. Phasing-down hydrofluorocarbon (HFC) refrigerants for HVAC equipment over the next 20 years has been proposed. A thermoelectric air conditioning system that directly converts electrical energy to thermal energy using a simple solid-state semiconductor device, has the advantages of environmentally friendly, no refrigerant, very compact, high reliability, no moving parts (except for small fans), and it can be easily integrated into the building structure. However, the existing thermoelectric air conditioning systems have the problem of low Coefficient of Performance (COP), which limits its applications for domestic air conditioning. With the development of the thermoelectric technologies, the above problem is prospected to be solved. The paper presents an overview of recent advances in thermoelectric materials, thermoelectric module design and thermoelectric heating and cooling system design which would provide the potential to greatly improve the COP of the thermoelectric air conditioner. In addition, utilizing the waste heat of the thermoelectric system for domestic applications to improve the overall COP of the system would be an ideal way to promote public adoption of the TE air conditioner, which is discussed in this paper. The paper also presents an overview of the existing building integrated thermoelectric air conditioning systems and proposes a novel building integrated thermoelectric system that integrates a thermoelectric heat pump unit into a double-skin ventilated facade to provide heating and cooling, heat recovery ventilation and domestic hot water or drying services for buildings, based on the thermoelectric waste heat utilization. Several building integration methods of the proposed system are presented

Preliminary experiment on a novel photovoltaic-thermoelectric system in summer

© 2019 Elsevier Ltd Compared with the PV electricity generation, the hybrid Photovoltaic-thermoelectric (PV-TE) can generate more electricity due to its ability to utilize a wider solar spectrum than the PV. The PV-TE employing micro-channel heat pipe array is a novel PV-TE-MCHP system which is capable of providing high cost performance compared to the traditional PV-TE due to the use of the micro-channel heat pipe array. In this paper, the experimental investigation of this new system in summer in Hefei city, China is presented for the first time. The comparison between this system and PV alone is made, and the details are presented. The power output, PV temperature, and the hot and cold sides temperatures of the TE are all tested. The results show that the novel system has a higher electrical output than the PV alone. The electrical efficiencies of this system during the test are all higher than 14.0% and the PV temperatures are about 20 °C higher than the ambient temperature. Based on this experiment, the results also verify the feasibility of the new system, which will give a valuable reference for the PV-TE design

A statistical model for dew point air cooler based on the multiple polynomial regression approach

Swift assessment of evaporative cooling systems has become a necessity in practical engineering applications of this advanced technology. This paper bypasses details of the performance process and pioneers in developing a statistical model based on the multiple polynomial regression (MPR) to predict the performance of a dew point cooling (DPC) system. Thousands of numerical and experimental data are explored and the statistical model is produced. The developed statistical model correlates the performance parameters with the key operational parameters, including the flow and geometric characteristics. The selected operational parameters are, intake air conditions, including temperature, relative humidity and flow rate as well as the working air fraction over the intake air, while cooling capacity, coefficient of performance (COP), pressure drop, dew point and wet-bulb effectiveness are selected as performance parameters. The considered geometric characteristics are channel height, channel interval and number of layers in heat and mass exchanger. The model with different polynomial degrees is assessed by R2, MRE and MSE metrics. The 8th degree polynomial model is selected. The maximum relative error of the cooling capacity, coefficient of performance, pressure drop, dew point and wet-bulb effectiveness are 6.1%, 7.54%, 0.07%, 3.54% and 2.53% respectively. Finally, as examples, the model is used to predict the performance of the DPC system in random operating conditions and in a dry climate i.e. Las Vegas. Model developed in this study would enable the swift prediction of the DPC system

Optimization and performance analysis of a solar concentrated photovoltaic-thermoelectric (CPV-TE) hybrid system

This work presents, for the first time, a statistical model to forecast the electrical efficiency of concentrated photovoltaic-thermoelectric system (CPV-TE). The main objective of this work is to analyze the impact of the input factors (product of solar radiation and optical concentration, external load resistance, leg height of TE and ambient temperature) most affecting the electrical efficiency of CPV-TE system. An innovative and integrated approach based on a multi-physics numerical model coupling radiative, conductive and convective heat transfers Seebeck and photoelectrical conversion physical phenomena inside the CPV-TE collector and a response surface methodology (RSM) model was developed. COMSOL 5.4 Multiphysics software is used to perform the three-dimensional numerical study based on finite element method. Furthermore, results from the numerical model is then analysed using the statistical tool, response surface methodology. The analysis of variance (ANOVA) is conducted to develop the quadratic regression model and examine the statistical significance of each input factor. The results reveal that the obtained determination coefficient Image 1 for electrical efficiency is 0.9945. An excellent fitting is achieved between forecast values obtained from the statistical model and the numerical data provided by the three-dimensional numerical model. The influence of the parameters in order of importance on the electrical efficiency are respectively: product of solar radiation and optical concentration, the height legs of TE, external electrical resistance load, and ambient temperature. A simple polynomial statistical model is created in this work to predict and maximize the electrical efficiency from the solar CPV-TE system based on the four investigated input parameters. The maximum electrical efficiency of the proposed CPVTE (17.448%) is obtained for optimum operating parameters at 229.698 W/m2 value of product of solar radiation and optical concentration, 303.353 K value of ambient temperature, 2.681Ω value of resistance electrical load and at 3.083 mm value of height of TE module

Performance analysis and discussion on the thermoelectric element footprint for PV–TE maximum power generation

Geometrical optimisation is a valuable way to improve the efficiency of a thermoelectric element (TE). In a hybrid photovoltaic-thermoelectric (PV-TE) system, the photovoltaic (PV) and thermoelectric (TE) components have a relatively complex relationship; their individual effects mean that geometrical optimisation of the TE element alone may not be sufficient to optimize the entire PV–TE hybrid system. In this paper, we introduce a parametric optimisation of the geometry of the thermoelectric element footprint for a PV–TE system. A uni-couple TE model was built for the PV–TE using the finite element method and temperature-dependent thermoelectric material properties. Two types of PV cells were investigated in this paper and the performance of PV–TE with different lengths of TE elements and different footprint areas was analysed. The outcome showed that no matter the TE element's length and the footprint areas, the maximum power output occurs when An/Ap= 1. This finding is useful, as it provides a reference whenever PV–TE optimisation is investigated