Solar Thermoelectric Generator System Research Articles

Mathematical analysis of the solar assisted thermoelectric generator

The direct conversion of solar energy into electrical energy is primarily dependent on the photovoltaic systems. However, in the last few decades, researchers have shown interest to work on the thermoelectric modules for direct conversion of solar thermal energy into electrical energy based on the Seebeck effect. This research paper provides a comprehensive analysis of various Solar Thermoelectric Generator (STEG) designs, focusing on their conversion efficiencies. Despite the comparatively lower efficiency of STEG in comparison to photovoltaic (PV) cells, owing to limitations in the figure of merit value and temperature differences between hot and cold sides of the thermoelectric modules, this study proposes strategies for enhancement. Approaches include the development of materials with higher figure of merit values, design optimization, solar tracking, heat storage systems, and efficient heat sink designs. Also, Mathematical analysis of the power and efficiency calculation of a STEG has been presented on the basis of some fundamental and derived mathematical equations. The overall efficiency of STEG, a product of Opto-thermal Efficiency and thermoelectric module efficiency, is explored, identifying an optimal hot side temperature for maximum efficiency. Module mismatch analyses for series and parallel connections are also derived, underscoring conditions for mitigating power loss. These findings serve as guidelines for designing more feasible and efficient STEG systems, with considerations for economic viability, sustainability and greenhouse gas reduction throughout the life cycle.

Unidirectionally Structured Magnetic Phase-Change Composite Based on Carbonized Polyimide/Kevlar Nanofiber Complex Aerogel for Boosting Solar-Thermo-Electric Energy Conversion.

To realize highly efficient solar-thermo-electric energy conversion for clean electricity power generation, we have developed a new type of unidirectionally structured magnetic phase-change composite comprising a carbonized polyimide (C-PI)/Kevlar nanofiber (KNF) complex aerogel as a 3D carbon skeleton porous supporting material, CoFe2O4 nanoparticles as a magnetic additive, polyethylene glycol (PEG) as a phase-change material, and polypyrrole as a photothermal absorption coating layer. The as-fabricated C-PI/KNF complex aerogel exhibits a unidirectional microstructure, high porosity, robust skeleton frame, ultralight weight, and high thermal conductance. Featured with such unique structure and characteristics, the complex aerogel can offer an effective heat and electron transfer method to ensure highly efficient solar-thermal conversion and photothermal energy storage of the developed composite. The developed composite exhibits a high latent heat capacity of over 150 J g-1, outstanding shape stability along with a low leakage of 0.2 wt %, good thermal cycling stability, and high photothermal conversion efficiency of 84.8%. Based on the Seebeck effect, a solar thermoelectric generation system (STEGS) was constructed with the hot side coupled with the developed composite and the cold side immersed in air and ice water. Under 2.0 kW m-2 solar irradiation, the developed STEGS in ice water obtained maximum output voltage and current of 259.7 mV and 27.1 mA, respectively, which are significantly higher than those in air. The output power of the developed STEGS in an ice water environment is 50.6% higher than that in air under 4.0 kW m-2 solar irradiation. More importantly, the developed STEGS in ice water continuously generated output voltage and current for about 810 s without solar irradiation thanks to the latent heat release by the PEG component within the developed composite. In addition, the introduction of magnetic CoFe2O4 can accelerate solar-thermal conversion through periodic electron motion by the Néel relaxation or Brownian relaxation. This resulted in an increase in the maximum output voltage and current by 13.7 and 11.5%, respectively, under an alternating magnetic field as a result of the magnetism-accelerated solar-thermo-electric conversion. This study offers an innovative approach for developing PCM-based advanced functional materials for solar energy utilization in clean and sustainable electricity generation.

Optimization of segmented thermoelectric power generators from waste heat while considering the influence of temperature on materials

Thermoelectric technology is commonly used in waste heat utilization of automotive internal combustion engines and widely combined with solar energy units to form solar thermoelectric generator systems. The structure of the Thermoelectric Generator (TEG) needs to be optimized in order to obtain better performance for wider applications. In this paper, the influence of temperature on the height of PN-type thermoelectric arms was analyzed using an improved one-dimensional heat conduction model with the calculus method. At the same time, both the calculation formula of the maximum output power and the calculation formula of various size parameters of the TEG was derived when the influence of temperature on the performance of thermoelectric materials has been considered. In addition, the relationships among different size parameters were derived to obtain the maximum efficiency. The relationships include the most commonly used classical optimization relationship, that is, when the Seebeck coefficient, thermal conductivity and resistivity are averaged, the relationship is consistent with the classical optimization relationship. By considering the impact of temperature on the performance of thermoelectric materials, an improved calculation formula of the figure of merit (Z) was also given. The new optimization formula was compared with the classical optimization method by taking the maximum output power as the optimization index. In the case study, the temperatures of the cold end and the hot end were set at 330 K and 700 K, respectively. PbTe and PbSe were used as the materials with intermediate temperature, and Bi2Te3 was used as the material with low temperature. Through theoretical analysis, it is found that the maximum output power of the new optimization formula can be higher than that of the classical optimization formula.

Parametric analysis and potential evaluation of thermoelectric generator driven by solar energy and radiative sky cooling

Solar energy and radiative cooling (RC)-driven thermoelectric generator (TEG) technology, which harnesses the extraterrestrial heat and cold sources from the sun and deep universe, is attracting increasing attention. However, existing studies on solar TEG (STEG) and RC TEG (RCTEG) only focus on either solar spectrum or infrared spectrum. To investigate the TEG performance considering full spectrum’s influence, a thermal-electrical coupled model based on thermal resistance theory is developed. Results indicate the TEG with ideal selective absorber (ISA) provides the best power generation performance, with a power generation of around 2.06 W/m2 and a temperature difference of about 3.18 K. The maximum power generation is 2.89 and 2.87 W/m2 for the ISA and ideal broadband absorber (IBA) systems when the bottom cooling temperature is 275 K, respectively. For every 100 W/m2 increase in solar irradiance, there is a temperature difference increment of about 0.31 K. The IBA and ideal selective absorber and emitter (ISAE) systems are capable of generating electricity continuously, ensuring a 24-hour power supply. Moreover, the radiative cooling capacity provided by the ISAE system is greater than that of the RCTEG system. The proposed STEG system has promising application potential for power generation in view of its carbon footprint features.

A bidirectional solar thermoelectric generator combining heat storage for daytime and nighttime power generation

A solar thermoelectric generator (STEG) is a promising technology for harvesting solar energy for standalone applications. However, the STEG cannot generate electricity during nighttime due to unavailability of solar energy. The efficiency of thermoelectric generator (TEG) is also low that limits its application areas. This low efficiency can be improved by partially utilizing the waste heat from its cold side using phase change materials (PCMs). Further, the STEG systems operating during day and nighttime are not proposed so far. Therefore, an experimental test rig of a bidirectional (operative in day and night both) STEG coupled with latent heat storage and cooling system (LHSCS) has been developed in this paper. The LHSCS acts as a sink by storing waste heat from the TEG cold side in a phase change material during the daytime and regulates its temperature effectively. During nighttime, LHSCS acts as a heat source for TEG power generation. This proposed bidirectional model aims to provide non-intermittent electricity generation for 24 h. An experimental setup was tested under laboratory conditions and adjusted using a numerical model previously developed in COMSOL Multiphysics software. Once both models are mutually adjusted and verified, the proven numerical model is used to simulate the prototype in the environmental conditions of the Atacama Desert in Chile. The transient effects of solar radiation, ambient temperature and wind speed of the selected location on the hot and cold side temperatures, voltage, power output and efficiency of STEG have been analyzed. A maximum temperature difference of 120 °C is obtained between the TEG hot and cold sides. The experimental results showed TEG efficiency of 5%. The system generated average annual electricity of 5735 Wh. The STEG generated around 0.6 % of the total electricity during the night in the Atacama Desert location. The levelized cost of energy and storage have also been calculated for the proposed system and compared with PV and STEG systems. The LCOE and LCOS of the proposed system are 8850 and 566 USD/MWh respectively. The proposed configuration may provide a reference study for design and development of an efficient and cost-effective STEG coupled LHSCS system.

Prototype of a novel hybrid concentrator photovoltaic/thermal and solar thermoelectric generator system for outdoor study

In this study, a novel prototype of a hybrid concentrator photovoltaic/thermal and solar thermoelectric generator system has been designed and constructed for combined heat and power production. In the developed hybrid system, both the solar cells and thermoelectric modules that share a common heat transfer medium are exposed to concentrated irradiance via a compound parabolic concentrator and a parabolic trough concentrator, respectively. To assess the performance of the hybrid system, a prototype of the hybrid system was built and tested under outdoor operating conditions, and the findings were compared with those of a transient numerical simulation conducted using ANSYS Fluent. The average PV temperature obtained during the test period at a flow rate of 3.8 L/min is 318.19 K which is ∼5.6% lesser compared with a conventional hybrid CPVT-TEG system. The outdoor trials show maximum electrical efficiency of 4.86% and thermal efficiency of 40% when the solar irradiance is greater than or equal to 1000 W/m2. The overall efficiency of the developed prototype is 3 times higher compared to a standalone PV system. The hybrid system helps to reduce carbon emission by 0.5 kg/h, with an associated environmental cost of 0.025 €/h.

Comparative study of various solar power generation systems integrated with nanofluid-flat heat pipe

In recent years, photovoltaic modules and solar thermoelectric generator units have been widely used as energy conversion setups in solar power generation systems. However, the output performance may vary depending on the combination forms. Furthermore, thermal management of such systems is critical to ensuring conversion efficiency and long-term stability. The flat heat pipe is a highly efficient passive cooling device with an excellent heat transfer coefficient across extended ranges and no parasitic energy consumption. A comparative analysis is performed in this work to investigate the various configurations (photovoltaic system, solar thermoelectric generator system, bifacial-photovoltaic-solar thermoelectric generator system, tandem-photovoltaic-solar thermoelectric generator system) that use flat heat pipe as a heat sink. The effects of various solar irradiance, ambient temperature, and condenser side temperature on total energy and exergy efficiency are investigated. The results demonstrate that the bifacial-photovoltaic-solar thermoelectric generator system outperforms the other systems in terms of electrical power output yet, the solar thermoelectric generator system has the largest improvement potential due to its low conversion efficiency. When the solar irradiance is 10000 W/m2, the ambient temperature is 298.15 K, and the condenser side temperature is 298.15 K, the power output for the bifacial-photovoltaic-solar thermoelectric generator system can reach up to 1.82 W, whereas the values for the photovoltaic system, solar thermoelectric generator system, and tandem-photovoltaic-solar thermoelectric generator system are 1.54 W, 0.31 W, and 1.45 W, respectively. Furthermore, the influence of utilizing a 5% volume concentration of Ag-nanofluid and pure water as the flat heat pipe working fluid is addressed. The obtained findings show the effectiveness of using nanofluid to improve energy and exergy performance.

Analysis of Energy Management and Battery Sizing in an Off‐Grid Hybrid Solar Thermoelectric Generation System

Herein, the main aim is to analyze the idea of utilizing the thermal energy generated during the operation of a solar photovoltaic panel. The rise in temperature of the solar panels and the surrounding environment results in the reduction of the generated energy and ultimately the efficiency of solar panels. This thermal energy can be utilized to generate electrical energy by installing thermoelectric generators at the backside of the solar panel. The electrical energy generated through a thermoelectric generator depends on the temperature difference at its surface, which could be formed through any cooling mechanism such as natural air or cold water circulation. The electrical energy generated from the solar panels and thermoelectric generator can be integrated as a hybrid source, resulting in an enhancement of the overall efficiency of the system. On the other hand, designing a proper energy storage mechanism can enhance the efficiency and overall sustainability of the proposed idea. The results show that in doing so, not only does the solar panel temperature decrease resulting in the increase of its efficiency but utilizing the thermal losses by the hybrid solar thermoelectric generation system can enhance the energy generation up to 31.89% at a temperature difference of 34.4 °C.

Ultrarobust Photothermal Materials via Dynamic Crosslinking for Solar Harvesting.

Highly efficient and mechanically durable photothermal materials are urgently needed for solar harvesting, but their development still remains challenging. Here, inspired by the hierarchically oriented architecture of natural spider silk, an ultrarobust liquid metals (LMs)/polymer composite is presented via dynamic crosslinking based on the unique mechanical deformable characteristic of LMs. Dynamically cross-linked core-shell structured LMs droplets can be squeezed along with the orientational crystallization of polymer chains during drawing, thus enabling LMs nanoparticles to be uniformly programmed in the rigid polyethylene nanofiber skeleton. The resultant composite exhibits an unprecedented combination of strong broad-band light absorption (96.9-99.3%), excellent photothermal conversion ability, remarkable mechanical property (tensile strength of 283.7MPa, which can lift 200000 times its own weight), and long-term structural reliability (bearing 100000 bending cycles). A powerful and durable solar thermoelectric generator system for real-environmental solar-heat-electricity conversion is further demonstrated, providing a valuable guidance for the design and fabrication of high-performance solar-harvesting materials.

High-efficiency hybrid PV-TEG system with intelligent control to harvest maximum energy under various non-static operating conditions

Recently the cleaner energy production is in high demand. Renewable energy systems such as photovoltaic (PV), thermoelectric generators (TEG), concentrated solar, geothermal, wind and hybrid PV-TEG systems achieved cost parity with nonrenewable fossil fuels. The power density of hybrid PV-TEG systems is much higher as compared to the standard photovoltaic (PV) or concentrated solar thermoelectric generator systems. However, the nonlinear nature of the composite hybrid power system makes it impossible to attain maximum available power using classical optimization techniques. The energy from the system is sensitive to stochastic operating conditions. Non-uniform temperature distribution (NUTD) further compromises efficiency for the available power. As a solution, a novel implementation of an arithmetic optimization algorithm (AOA) is utilized as an active maximum power point tracking (MPPT) controller for hybrid PV-TEG system power control. A comprehensive case study is made using five scenarios including real-world atmospheric data and experimental setup to validate the feasibility and effectiveness of the proposed AOA technique in real-world applications. Results are compared with highly effective intelligent techniques including grey wolf optimization (GWO), cuckoo search algorithm (CSA), particles swarm optimization (PSO), and optimized perturb and observe (P&O). Quantitative and statistical analyses confirm the robustness of the proposed technique. AOA achieves 8% higher energy and 99.86% power tracking efficiency. The tracking time in transitioning operating conditions is well within 100 ms with an average settling time of 280 ms. The results, comparative analysis, and statistical indices indicate a superior performance achieved by the proposed AOA optimization making PV-TEG a cleaner source of electrical power generation.

Multi-functional carbon nanotube paper for solar water evaporation combined with electricity generation and storage

Nowadays, multi-functional systems driven by solar energy have been explored to alleviate the crisis of energy and freshwater scarcity. However, it remains a great challenge to integrate multi-functions into one hybrid system with a monolithic material, which can harvest, convert and store solar energy synergistically. Here, we firstly propose a multi-functional carbon nanotube paper, which starts from a material level to solve these problems. The carbon nanotube paper is fabricated by vacuum filtration. It exhibits high efficiency of solar-thermal conversion. Secondly, three types of energy conversion/storage systems (e.g., solar-thermal evaporation system, solar-thermoelectric generation system, and supercapacitor) are constructed based on the carbon nanotube paper, which extend the research to a device level. The solar-thermal evaporation system shows an evaporation rate of 1.28 kg m-2h−1 under simulated sunlight irradiation of 1 kW m−2. The solar-thermoelectric generation system demonstrates a stable electric power generation with an output voltage of 100 mV under light irradiation of 1 kW m−2. The supercapacitors perform the energy storage function with an areal specific capacitance of 19.6 mF cm−2. These devices and systems can be used in freshwater generation (0.84 kg m-2h−1, sunlight irradiation of 1 kW m−2), water purification/desalination (inorganic ions rejection larger than 99.9%) and portable solar charging system (maximum output voltage of 5 V). Finally, a hybrid energy system is innovatively proposed from the system level to simultaneously produce freshwater, generate and store electric power. Through the synergetic coupling of solar conversion and storage technologies, the hybrid energy system can supply sustainable freshwater and electricity for remote areas in daily life, highlighting the superiority of multi-energy (thermal energy, electrical energy, and electrochemical energy) complementary.

Intelligent light-driven flexible solar thermoelectric system

Solar thermoelectric generation (STEG) is an excellent and environmentally-friendly way to convert thermal energy into electricity by utilizing Seebeck effect of thermoelectric material. However, how to overcome the rigidity and large output fluctuation of traditional STEG is the key to realize its large-scale application in self-powered devices. Herein, a smart light-driven flexible STEG system was designed and constructed through simple layered structure of VO2 flexible film and carbon nanotube (CNT) thermoelectric modules. Based on the optical control characteristics of VO2 flexible film due to the thermal crystal phase transformation, and the light capture, photo-thermal-electric conversion capabilities of CNT flexible film, the smart light-driven flexible STEG system exhibits good flexibility, light-thermal-electrical conversion and stable voltage output. In the above system, CNT, polyvinylidene fluoride (PVDF) as raw material and polyethyleneimine (PEI) as electron donor, p- and n-type flexible thermoelectric films and modules were constructed; VO2 ultrafinepowder was dispersed in polyvinylpyrrolidone(PVP), and the optical control VO2 flexible film was obtained by simple spin coating on the flexible substrate. The system is so flexible that can be folded or bended to different shapes to adapt to different application environments. Furthermore, the intelligent light-driven flexible STEG system can obtainrelatively stable voltage to prevent the damage of equipment caused by large voltage fluctuation and has great application potential in civil micro-self-powered devices.

Preliminary experiment and performance evaluation of a terrestrial solar thermoelectric generators under fluctuant solar radiation

The solar thermoelectric generator (STEG) is a promising alternative terrestrial solar power generation device due to its ability to utilize almost full solar spectrum. Many researches have been carried out to improve its efficiency. Some improved STEG has achieved remarkable efficiency in the laboratory. However, its performance in practical situations has been few studied, which limits its practical applications. In this work, the experimental investigation and performance evaluation of the terrestrial STEG system in typical days in East China are presented. Detailed changes in efficiencies and output power of the system are revealed. The results show that the performance of the system changes with the environment. The system can obtain the highest one-day electrical efficiency of 3.22% at 12:00 in the noon and thermal efficiency of 53% at 15:00 in the afternoon. The influences of solar irradiance, cooling water temperature and water cooling quality are discussed. The optimization methods of the system running in real environment are discussed and optimized to improve the average efficiency in the long run. The performances of this system and pure solar water heating system without TE modules are compared and the details are presented. The hybrid system has a higher comprehensive performance and lower thermal performance than the pure solar water heating system. This work provides a valuable reference for the design and optimization of STEG running in real environment.

Performance optimization and thermodynamic analysis of irreversibility in a contemporary solar thermoelectric generator

In this paper, a model based on the first and second laws of thermodynamics is developed in MATLAB R2020a Simulink software and is utilized in thermodynamically optimizing a bismuth telluride based solar thermoelectric generator (STEG) while estimating all system irreversibilities. This study aims at presenting a cheaper and simpler method of optimizing the performance of traditional STEGs without using segmentation or cascading. This is achieved by studying the effects of operating thermal and electric parameters such as load-resistance ratio (LRR), optical concentration ratio (OCR), thermal concentration ratio (TCR), hot junction temperature (Th), cold junction temperature, current and voltage on STEG power output, energy and exergy efficiencies, respectively. The results obtained are validated with experimental and numerical data from previous studies. Results indicate that for an OCR of 30, a STEG exergy efficiency of about 6.5% is obtained from a conventional bismuth-telluride single-stage module. Also, a means of maximising STEG performance while reducing system irreversibilities to the barest minimum is presented. The results obtained herein will provide useful information in the maximisation of conventional and complex STEG systems employing segmentation or cascading.

Numerical Study of a Phase Change Material Integrated Solar Thermoelectric Generator

The numerical modelling of a phase change material (PCM) attached to a hybrid three-dimensional truncated compound parabolic concentrator and thermoelectric module is performed under transient and non-uniform variation in solar radiation. To demonstrate the higher performance of the system, the performance parameters of a stand-alone system (without PCM), SAS, and incorporated system (with PCM), IS, are modelled and studied using the ANSYS 2020 R1 software and MATLAB R2020a Simulink software. The PCM is placed at the hot junction of the solar thermoelectric generator (STEG) in order to act as a re-concentrating lens via the phase-change lensing effect and to decrease the adverse effect of transient and non-uniform solar radiation on the STEG. The results demonstrate an increase in the light transmissivity and refractive index of the PCM after melting and the efficacy of the PCM in shielding the STEG under extremely concentrated solar radiation intensities. The optimum heat input required to maximise the STEG efficiency and power output while minimising the challenge of excess heat dissipation in STEG systems is obtained and discussed. Finally, the results obtained show that the maximum temperature gradient, power output and efficiency from the stand-alone were higher than those from the incorporated system. The results obtained from this study will provide useful information in the design of STEGs under fluctuating meteorological conditions coupled with solar concentrators, which generate varying solar radiation.

High-performance terrestrial solar thermoelectric generators without optical concentration for residential and commercial rooftops

Solar thermoelectric generator (STEG) systems are attractive because they can convert solar heat directly into electricity via solid-state thermoelectric generators. Nevertheless, its low energy conversion efficiency has prevented it from wide-scale implementation and commercialization. To date, the best experimental efficiency for STEG without concentrated is 4.6%, and only testing single thermoelectric unicouple within a specific application deployment context. In this paper, a mathematical model containing various heat losses ignored by previous studies are developed and validated to confirm the possibility of improved STEG performance. We developed a high-performance solar thermoelectric hybrid device composed of heat pipe evacuated tubular collector, solar selective absorber, and TE modules by conducting a comprehensive optimization in terms of thermoelectric material, the optical and thermal efficiency of solar selective absorber, heat management and device integration. The experimental results show that the thermoelectric conversion efficiency of proposed device was enhanced significantly, it produced a peak electrical efficiency of 5.2%. And the residual solar energy is stored for either power generation or domestic used. The peak exergy efficiency of the system reached up to 7.17%. The efficiency is higher than the previously reported best value. We experimentally demonstrated the feasible of the scale application of solar thermoelectric generators. And the results indicated that STEG system is a promising alternative solar energy thermal utilization technology in the small scale co-generation applications.

Experimental investigation of solar thermoelectric (STEG) co-generation system

Abstract The solar thermoelectric generation（STEG）cogeneration system can provide heating and electric power simultaneously. Precedent studies on the STEG system were focused on getting higher electrical efficiency of the system and creating a new record. Optimization of thermal performance and evaluation of thermal efficiency are usually completed by calculation or numerical simulation. In this paper, a novel design of STEG cogeneration system was proposed. The system can work in three modes according to seasonal demand of hot water and electric power. A series of experiments were carried out in different working modes under variable conditions to evaluate the performance of the system. The results show that the system can generate 0.2 kW·h of electrical energy and about 100L of hot water at 41 °C in 1 day when solar irradiation is 1000 W/m2. The collector efficiency and electrical efficiency are calculated to be 42.2% and 2.1%, respectively.

Titanium nitride selective absorber enhanced solar thermoelectric generator (SA-STEG)

Solar thermoelectric generator (STEG) system has been intensively studied due to its reliability and environment-friendly property. In a STEG system, a solar absorber is an important component because it not only absorbs the solar energy, but also emits photons to environment as radiation heat loss. In this study, a selective absorber enhanced STEG system (SA-STEG) is presented. A Titanium nitride (TiN) based 2D photonic crystal (PhC) selective absorber is fabricated, which possesses a high absorptivity at short wavelength range to fully absorb the solar energy, but a suppressed absorptivity at long wavelength range to avoid the radiation loss. The selective absorber also keeps a good wavelength selectivity even after a thermal annealing over 1000 K. The selective absorptivity data were imported into the SA-STEG model and an improvement was obtained: for a Lead telluride STEG system, a 28 K temperature increase was achieved, and for a Silicon germanium alloy STEG system a 32 K temperature increase was achieved. The increased temperature yields a larger open-circuit voltage output. These results were attained based on a 40 × 40 mm2 STEG system and this value is expected to be further increased if a larger thermoelectric generator is employed.

Performance Analysis and Optimization of Concentrating Solar Thermoelectric Generator

A thermodynamic model for a concentrating solar thermoelectric generator considering the Thomson effect combined with Fourier heat conduction, Peltier, and Joule heating has been developed and optimized in MATLAB environment. The temperatures at the hot and cold junctions of the thermoelectric generator were evaluated by solving the energy balance equations at both junctions. The effects of the solar concentration ratio, input electrical current, number of thermocouples, and electrical load resistance ratio on the power output and energy and exergy efficiencies of the system were studied. Optimization studies were carried out for the STEG system, and the optimum number of thermocouples, concentration ratio, and resistance ratio determined. The results showed that the optimum values of these parameters are different for conditions of maximum power output and maximum energy and exergy efficiency. The optimum values of the concentration ratio and load resistance ratio for maximum energy efficiency of 5.85% and maximum exergy efficiency of 6.29% were found to be 180 and 1.3, respectively, with corresponding power output of 4.213 W. Furthermore, at higher concentration ratio (C = 600), the optimum number of thermocouples was found to be 101 for maximum power output of 13.75 W, maximum energy efficiency of 5.73%, and maximum exergy efficiency of 6.16%. Moreover, the optimum number of thermocouple was the same for conditions of maximum power output and energy and exergy efficiency. The results of this study may provide insight for design of actual concentrated solar thermoelectric generator systems.

Proposal and assessment of a solar thermoelectric generation system characterized by Fresnel lens, cavity receiver and heat pipe

A solar thermoelectric generation system characterized by Fresnel lens, cavity receiver and heat pipe, i.e., FCH-STGS, was proposed. To analyze the performance of FCH-STGS accurately, a comprehensive theoretical model was built, where a finite element method was employed to consider the Thomson effect and temperature-dependence of thermoelectric materials. With this model, the influences of emissivity of ceramic plate and environment factors such as solar irradiation, optical concentration ratio, wind speed, wind incident angle, system tilt angle and ambient temperature were discussed. Results show that the FCH-STGS has the potential to reach the output power and efficiency of 45.73 W and 3.289%. Both output power and efficiency of FCH-STGS can be improved by decreasing the emissivity of ceramic plate or ambient temperature, or increasing the total solar irradiation (product of solar irradiation and optical concentration ratio). However, the efficiency reduces slightly when the total solar irradiation exceeds a certain value. As the wind speed increases, both output power and efficiency rise firstly and then fall. Due to the high thermal efficiency of cavity (exceeding 85%), the effects of wind incident angle and system tilt angle are approximately negligible. Compared with the previous STGSs, the FCH-STGS is excellent in the perspectives of performance, economy and practicability.