Performance Of Solar Thermoelectric Generator Research Articles

Effect of nonuniform solar radiation on the performance of solar thermoelectric generators

Solar radiation must be concentrated before irradiating hot sides in solar thermoelectric generators (STEGs) to increase the temperature difference between hot and cold sides and thus enhance output performance. However, concentrated solar radiation is often nonuniform. This condition affects the output performance of STEGs. Herein, a thermal–electric coupled model of STEGs was constructed to investigate the thermoelectric performance of STEGs under nonuniform solar radiation. Results demonstrate that when the concentration ratio is low, increasing nonuniformity facilitates the increase in the output power of STEGs. When the concentration ratio is 60, output power increases by a maximum of 3.05 %, whereas the average temperature difference decreases by 4.44 K. When the concentration ratio is high, STEG output power peaks under a specific nonuniformity, and some thermoelectric legs at the edges of STEGs turn into load, affecting the overall STEG output performance. When the cold-side cooling performance is poor, the solar radiation input to STEGs should be made as uniform as possible to ensure the output performance and safe operation of STEGs. The results of this study provide guidance for the design of efficient STEGs.

Solar thermoelectric generator and thermoelectric cooler performance: analysis and comparison using a different shape geometry

Abstract Thermoelectric devices are one of the technologies used either to generate electricity by applying a temperature difference using thermal energy or as a heating/cooling system by applying an electrical voltage. The number of materials required to produce a product is an important factor in determining its price. Production costs associated with these materials, as well as their availability and quality, play a crucial role in price determination by manufacturers. In this context, a method that employs a uniform volume distribution was implemented. This approach enabled the analysis to focus on other variables, thereby promoting a more precise and relevant evaluation of overall performance. Based on the finite element method, this study investigated the influence of geometric shape, including Rect-leg, Y-leg, Pin-leg and X-leg designs, on the performance of solar thermoelectric generators and thermoelectric coolers. The study was conducted considering the same hot alumina junction surface that receives solar radiation; however, the effective surface, which corresponded to the heat flow area and had a similar area near the exposed surface, varied depending on the chosen leg geometry, thus impacting the heat flux due to the variation in thermal resistance. In the case of a solar thermoelectric generator, the Rect-leg model, having the same effective surface area, presented the lowest heat loss value resulting from convection and radiation in the heat spreader and the hot alumina plate. Under the same conditions, the Y-leg showed the highest value. The Rect-leg design generated, by using thermal and optical concentration, the highest output power of 0.028 and 0.054 W, and efficiency of 3.47% and 4.7%, respectively, whereas the Y-leg generated lower values of 0.006523 and 0.018744 W for power, and 2.83% and 2.71% for efficiency, respectively. In the case of the thermoelectric coolers, the Y-leg generated the highest temperature difference between the hot and cold sides of 67.28 K at an electric current value of 1.8 A, whereas the Rect-leg, Pin-leg and X-leg generated ~66.25, ~67.02 and ~67.19 K at 6.1, 2.7 and 2.6 A.

Structural optimization of solar thermoelectric generators considering thermal stress conditions

The optimization of the thermoelectric leg (TEL) structure is an effective means which can improve the thermoelectric performance of solar thermoelectric generator (STEG), however, the optimized dimensions may not satisfy the allowed stress and thus prevent the STEG from normal operation properly. To address this issue, we constructed a coupled thermal-electrical-stress multi-physical field model of STEG, and optimized the STEG structure under the condition of allowed stress. The results show that when the allowed stress is not considered, the optimal ratio of cross-sectional ratio (f) to height (h) is 0.03 mm−1 to maximize the thermoelectric conversion efficiency, but then the maximum thermal stress of the STEG far exceeds the allowed stress of the material. When the allowed stress conditions are considered, the critical cross-sectional ratio of the module is much higher than the optimal cross-sectional ratio. The critical output power that can be obtained from the module is 38.5% less than the maximum output power without considering the allowed stress, and the influence of thermal stress on the optimal structural parameters is significant at a high concentration ratio. The critical output power gradually increases with the increase in the concentration ratio, and a greater output performance can be obtained at larger heights, while a greater output power density can be obtained at smaller heights. The outcomes presented by this study have certain guide to the construction of high-efficiency STEG.

Effect of non-uniform heat flux on solar thermoelectric generator

Solar thermoelectric generators (TEGs) need concentrators to increase the irradiation intensity, thus achieving increased generation performance. However, the irradiation intensity on the surface of the TEG is not uniform, which in turn affects the thermoelectric performance of solar thermoelectric generators. In this study, a numerical model of the TEG is constructed to study the effect of non-uniform heat flux on the performance. The results show that at a total input heat of 150 W, the temperature of the center of the module gradually increases with the increase of the unevenness of the heat flux at the hot end of the TEG. The maximum temperature difference is up to 46.2 K, while the output power is reduced by 3.8%. The effect of non-uniformity of heat flux should be considered in concentrated solar thermoelectric generation systems.

Electrical and mechanical analysis of a segmented solar thermoelectric generator under non-uniform heat flux

Optimization of segmented solar thermoelectric generator for power output enhancement has been well researched however, the mechanical reliability study of such devices is usually neglected. In addition, assumed heat flux distribution or uniform flux distribution from solar concentrators is usually used for solar thermoelectric generator however, this is not accurate. Therefore, this study presents a detailed three-dimensional numerical investigation on the effect of non-uniform and uniform heat flux on the electrical and mechanical performance of segmented and non-segmented solar thermoelectric generator. Flux distribution from a compound parabolic concentrator is obtained by ray tracing using Lighttools software and COMSOL 5.4 Multiphysics software is used to perform the numerical study based on finite element method. Thermal stress analysis in a full-scale solar thermoelectric generator is presented and the effects of load resistance, solar radiation and cold side temperature on performance of solar thermoelectric generator is analysed. Results show that the power output of the segmented solar thermoelectric generators in Case 3, Case 4 and Case 5 increased by 44.07%, 59.12% and 37.9% respectively compared to that of Case 1 (bismuth telluride non-segmented solar TEG) at 13000W/m2. Results from this study will provide valuable guidance for segmented and non-segmented solar thermoelectric generator design.

Transient and non-uniform heat flux effect on solar thermoelectric generator with phase change material

Transient and non-uniform heat flux from solar concentrators can affect the performance of solar thermoelectric generators, which generate electricity from concentrated solar radiation. Therefore, this paper presents a detailed three-dimensional study on the effect of transient and non-uniform heat flux on the performance of a solar thermoelectric generator (STEG). COMSOL 5.4 Multiphysics software is utilized for the numerical study while the non-uniform heat flux from a compound parabolic concentrator is obtained through ray tracing simulation using Lighttools software. Varying solar radiation under typical partly cloudy weather condition is utilized. Furthermore, phase change material (PCM) is used to reduce the effect of transient and non-uniform heat flux therefore; it is positioned at the top surface of the solar thermoelectric generator. A comparison between the performance of the STEG with and without PCM is presented, and a parametric study on the effect of PCM fins and PCM height on the STEG performance is carried out. Results show that the place of PCM on the top surface of the solar thermoelectric generator is an effective approach to provide a stable electrical performance form the STEG under varying weather conditions. Furthermore, results reveal the effectiveness of the phase change material in protecting the solar thermoelectric generator under highly concentrated solar radiation. This study will provide valuable design guidance for solar thermoelectric generators under varying weather conditions and with solar concentrators, which produce non-uniform heat flux.

Cylindrical thermoelectric generator with water heating system for high solar energy conversion efficiency

Thermoelectric generator (TEG) with water heating system, which utilizes solar energy with a high total energy conversion efficiency, is promising environmental technology for eco-housing and factories to reduce their carbon footprints. In this study, a newly developed cylindrical TEG consisting of ring-disk thermoelectric material is proposed showing that the total energy conversion efficiency is higher than that of a conventional pillar-type TEG. The cylindrical TEG is implemented using high-performance CoSb3-based filled skutterudite thermoelectric materials and a unique 45Ni-55Fe electrode as the hot-side junction. The solar TEG performance is demonstrated under the real sunlight, which is concentrated by a Fresnel lens. The maximum thermoelectric efficiency of the presented solar TEG is 1.8%, with a water heating efficiency of 59% when the temperature difference across the TEG is 428 °C. Further improvement should be achieved by lowering the internal resistance of the TEG and increasing the average dimensionless figure of merit of the thermoelectric materials.

Effect of non-uniform illumination on performance of solar thermoelectric generators

Solar thermoelectric generators (STEGs) are heat engines which can generate electricity from concentrated sunlight. The non-uniform illumination caused by the optical concentrator may affect the performance of solar thermoelectric generators. In this paper, a three-dimensional finite element model of solar thermoelectric generators is established. The two-dimensional Gaussian distribution is employed to modify the illumination profiles incident on the thermoelectric generator. Six non-uniformities of solar illumination are investigated while keeping the total energy constant. The influences of non-uniform illumination on the temperature distribution, the voltage distribution, and the maximum output power are respectively discussed. Three thermoelectric generators with 32, 18 and 8 pairs of thermocouples are compared to investigate their capability under non-uniform solar radiation. The result shows that the non-uniformity of the solar illumination has a great effect on the temperature distribution and the voltage distribution. Central thermoelectric legs can achieve a larger temperature difference and generate a larger voltage than peripheral ones. The non-uniform solar illumination will weaken the capability of the TE generator, and the maximum output power decrease by 1.4% among the range of non-uniformity studied in this paper. Reducing the number of the thermoelectric legs for non-uniform solar illumination can greatly increase the performance of the thermoelectric generator.

The real-time study of solar thermoelectric generator

Due to the energy and environment crisis, the solar thermoelectric generation technology has got more attention for its high reliability, compact size and light weight. At present, the researches of solar thermoelectric generator are focused on mathematical models building and experimental devices development. To simplify the research and predict the daily performance of a practical flat-panel solar thermoelectric generator under real condition, this paper proposes a real-time simulation model. A way to optimize the simulation model is provided as well. An experiment is designed to validate and modify the real-time simulation model. Then, the experimental validated and modified real-time simulation model is performed to study the performance of solar thermoelectric generator. To optimize the daily performance of solar thermoelectric generator under real meteorological conditions, the daily power generation and daily power generation efficiency are discussed, and approaches obtaining the optimal daily performance are proposed. Meanwhile sensitivity analysis of operating conditions was conducted in this study. For the solar thermoelectric generator studied in this paper, results showed that the daily power generation varied in a range of [−69.2%, 0.6%] over the electrical load. And the electrical loads for achieving the maximum daily power generation (i.e. 6.588kWh/day) and maximum daily power generation efficiency (i.e. 2.657%) were both equal to 5.8Ω.

Thermal design and management for performance optimization of solar thermoelectric generator

We established a three-dimensional finite element model of thermoelectric module based on low-temperature thermoelectric material bismuth telluride and medium-temperature thermoelectric material filled-skutterudite. The material properties of the thermoelectric materials such as the Seebeck coefficient, thermal conductivity, and electrical conductivity are temperature dependent. Based on the formal model, multi-stage models consist of low- and medium-temperature thermoelectric modules are proposed. The effect of input energy on performance of solar thermoelectric generator is considered according to the real operating condition. Results show that, reasonable thermal design of solar thermoelectric generator can take full advantage of the characteristics of thermoelectric materials and effectively improve the performance of power generation.