Performance analysis of a hybrid solar thermoelectric generator

In this paper, a theoretical model is developed to investigate the performance of the hybrid solar thermoelectric generator (HSTEG) system, which is designed without (B-HSTEG) and with an evacuated glass tube (V-HSTEG). The heat loss, power output, thermal efficiency, and electrical efficiency of the B-HSTEG/V-HSTEG system are evaluated by analyzing the design parameters such as geometric solar concentration ratio, thermoelectric figure of merit, and cold-side inlet fluid temperature. The performance of the B-HSTEG is compared with the V-HSTEG system using two heat transfer fluids: water and Therminol VP-1. The maximum electrical efficiency of the B-HSTEG and V-HSTEG is estimated to be 12.2 and 15.6% (ZT = 3) with a corresponding thermal efficiency of about 61.9 and 60.3%, respectively. Overall, this paper provides a systematic performance analysis of HSTEG systems.     

Experimental investigation of a novel heat pipe thermoelectric generator for waste heat recovery and electricity generation

Waste heat recovery helps reduce energy consumption, decreases carbon emissions, and enhances sustainable energy development. In China, energy-intensive industries dominate the industrial sector and have significant potential for waste heat recovery. We propose a novel waste heat recovery system assisted by a heat pipe and thermoelectric generator (TEG) namely, heat pipe TEG (HPTEG)，to simultaneously recover waste heat and achieve electricity generation. Moreover, the HPTEG provides a good approach to bridging the mismatch between energy supply and demand. Based on the technical reserve on high-temperature heat pipe manufacturing and TEG device integration, a laboratory-scale HPTEG prototype was established to investigate the coupling performances of the heat pipes and TEGs. Static energy conversion and passive thermal transport were achieved with the assistance of skutterudite TEGs and potassium heat pipes. Based on the HPTEG prototype, the heat transfer and the thermoelectric conversion performances were investigated. Potassium heat pipes exhibited excellent heat transfer performance with 95% thermal efficiency. The isothermality of such a heat pipe was excellent, and the heat pipe temperature gradient was within 15°C. The TEG's thermoelectric conversion efficiency of 7.5% and HPTEG's prototype system thermoelectric conversion efficiency of 6.2% were achieved. When the TEG hot surface temperature reached 625°C, the maximum electrical output power of the TEG peaked at 183.2 W, and the open-circuit voltage reached 42.2 V. The high performances of the HPTEG prototype demonstrated the potential of the HPTEG for use in engineering applications.     

Theoretical and experimental study of efficiency factor,heat transfer and thermal heat loss coefficients in solar air collectors with selective and nonselective absorbers

The thermal heat performance of a solar air collector depends strongly on the thermal heat loss and the efficiency factor. In order to increase these performances, it is necessary to use a solar air collector which is well insulated and where the fluid flow is fully developed turbulent flow. It needs a high heat transfer between the absorber plate and the fluid to decrease the absorber‐plate temperature and hence the heat loss by radiation from the absorber to the ambient. This increases the efficiency factor. In the present paper, the heat loss and efficiency factor are treated for solar air collectors with selective and nonselective absorber plate. It is shown that the selectivity of the absorber plate cannot play an important role in a well‐insulated solar collector with a fanned system which permits a fully developed turbulent flow and, in consequence, high heat transfer. Copyright © 1999 John Wiley & Sons, Ltd.     

Experimental investigation of a box-type solar cooker with a finned absorber plate

This article provides the results and finding of an experimental work undertaken in the desert of Algeria. That aimed to compare experimental performance of a box-type solar cooker equipped with a finned absorber plate to a similar box-type cooker which absorber plate without fins. Tests have been carried out on the experimental platform of the Renewable Energies Research Unit in Saharan Environment of Algeria at Adrar. Adrar is located at a latitude 27° 53′ North and a longitude 0° 17′ West. Fins that have been used in solar air collectors enhanced heat transfer from absorber plate to air. Experimental tests have been undertaken as part of this project where was applied this phenomenon to a box-type solar cooker. The results of the experimental investigation have been rigorously analysed and showed that the stagnation temperature for box-type solar cooker equipped with a finned absorber plate was about 7% more than box-type solar cooker equipped with an ordinary absorber plate. The time required for heating water up to boiling temperature in both box-type solar cookers was reduced with about 12% when a finned absorber plate was used.     

Parametrical analysis of the design and performance of a solar heat pipe thermoelectric generator unit

This paper describes a solar heat pipe thermoelectric generator (SHP-TEG) unit comprising an evacuated double-skin glass tube, a finned heat pipe and a TEG module. The system takes the advantage of heat pipe to convert the absorbed solar irradiation to a high heat flux to meet the TEG operating requirement. An analytical model of the SHP-TEG unit is presented for the condition of constant solar irradiation, which may lead to different performance characteristics and optimal design parameters compared with the condition of constant temperature difference usually dealt with in other studies. The analytical model presents the complex influence of basic parameters such as solar irradiation, cooling water temperature, thermoelement length and cross-section area and number of thermoelements, etc. on the maximum power output and conversion efficiency of the SHP-TEG. Simulation based on the analytical model has been carried out to study the performance and design optimization of the SHP-TEG.     

Defining indispensability of storage for raised renewable penetration in conventional and thermoelectric coupled microgrid: Modeling,analysis and validation

The inflation of clean, efficient, sustainable, effective, secure, and reliable electricity demand have been triggered much interest for Microgrid (MG) at a miraculous and quickened pace. The necessity of reliability enhancement, diversity of fuel, cutback of greenhouse gases, severe weather fluctuation etc. has stimulated the inclusion of MG concept not only in utility level but also in customer and community level. Incorporation of solar photovoltaic (SPV) and thermoelectric (TE), termed as Solar photovoltaic-thermoelectric (SPV-TE) hybrid system is found be a very promising technique to broadening the utilization of solar spectrum and enhancing the power output effectively-cum-efficiently. This hybrid architecture caters electrical energy with additional thermal energy that signifies upon harnessing of solar insolation in an exceptional way. But in order to retain the voltage profile in the permissible level, MG needs storage mechanism for smoothening of renewable based power inconstancy, catering high active power significantly and dodging the long term reactive power rising. This paper illustrates the comparative analysis of three systems such as Conventional MG;TE coupled Conventional MG, and only TE coupled solar PV based MG defining the necessity of employment of energy storage system (ESS). The superiority of third system has been outlined in terms of lesser complexity in source integration, mitigating the detriment of Wind energy system (WES) and Fuel Cell Systems (FCT) integration in real life application, delivery of higher active power, and lesser reactive power absorbance over the two other systems. The studied system is modeled in MATLAB/Simulink environment and the results are presented to support, verify, and validate the analysis.     

Geometrical designs and performance analysis of a linear fresnel reflector solar concentrator with a flat horizontal absorber

Two different approaches for designing a linear Fresnel reflector solar concentrator (LFRSC) with a flat horizontal absorber are described. The performance characteristics of both the designs are studied in detail. The distribution of local concentration ratio on the surface of the absorber, for each design, is investigated using the ray trace technique. Results of some typical numerical calculations are presented graphically and discussed.     

Investigation of solar hybrid system with concentrating Fresnel lens,photovoltaic and thermoelectric generators

An experimental model of a solar hybrid system including photovoltaic (PV) module, concentrating Fresnel lens, thermoelectric generator (TEG), and running water heat extracting unit was created and studied. The PV module used was of c‐Si and TEG of Bi₂Te₃; the Fresnel lens (solar concentrator) and TEG share an optical train, whereas PV module was illuminated separately with non‐concentrated light. Heat extracting unit operated in thermo siphon mode. In climatic conditions of Mexico (Queretaro, 20^o of North latitude, summer time), the Fresnel lens accepted 120 W of solar radiation power, and the system generated 7.0 W of electric power and 30 W of thermal one. The discussion is made of the possible characteristics of a hypothetical hybrid system where all its elements share the same optical train. Copyright © 2016 John Wiley & Sons, Ltd.     

Analysis of the top heat loss factor of flat plate solar collectors with single and double glazing

The dependence of the top heat loss factor of flat plate solar collectors with single and double glazing on the basic parameters was studied. An improved technique for calculation of the top heat loss factor of flat plate collectors with single glazing has recently been proposed by the authors. The present work, covering the flat plate collectors with single as well as double glazing, carefully examines the impact of the glass cover temperature(s) estimated by simple empirical relation(s) on the individual heat transfer coefficients and hence on the top heat loss factor. An analysis of the capability of the new method to accurately compute the top heat loss factor over an extensive number of combinations of the basic parameters has been carried out.     

Performance analysis and experimental validation of a vee-corrugated absorber integrated collector storage solar water heater

This paper focuses on enhancing the energy collection efficiency of an integrated collector storage solar water heater (ICS SWH) by vee-corrugating the absorber and optimizing the design for the vee-included angle through simulation and experimental study. This paper presents an efficient algorithm for analyzing a vee-corrugated absorber ICS SWH using Engineering Equation Solver Software. For validating this algorithm, two models of ICS SWH systems have been fabricated: one with a flat absorber and the other with a 60° vee-included angle corrugated absorber with eight corrugations. The basic purpose of the fabrication of the flat absorber ICS SWH system was to approximate the absorptivity of the absorber. A typical value of 0.68 was estimated for the absorptivity of the aluminum absorber coated with nonselective black paint. After the experimental investigation of the 60° vee-included angle ICS SWH system, it was found that the real-time readings were in close agreement with the numerical model readings. For comparison with the previous work, a five-corrugation system with an approximate 90° vee-included angle with the same projected dimensions was modeled and the efficiencies of both the models for the time from 7 a.m. to 3 p.m. were calculated. The efficiency of the eight-corrugation model was 42.56%, which was better than the previous work of the five-corrugation model, with a 38.86% efficiency for the same ambient conditions. Also, it was theoretically deduced that we had an optimized system at 18 corrugations and a vee-included angle of 28.78°.     

Experimental performance analysis and optimisation of medium temperature solar thermal collectors with silicon oil as a heat transfer fluid

Heat transfer fluids (HTFs) play an essential role in solar water heating systems by transferring collected energy from the collector, perhaps via a heat exchanger to the store. If the store is at a much higher temperature than the fluid, the store acts as a heat source, whereas the fluid acts as a coolant, thus reversing the collection process. This action must be avoided through good controls. Experimental performance analysis and comparison of three different types of solar collectors; a non‐concentrating evacuated tube heat pipe and two concentrating single‐sided and double‐sided coated evacuated tube heat pipes collectors are installed and tested using Dow‐corning 550® silicon oil as an HTF under the same operating in‐door control conditions, and results are presented in this paper. The performance of these solar collectors was determined from the overall increase in inlet and outlet fluid temperatures, overall fluid temperature differential, energy collection rate, optical efficiencies, and thermal performances. Temperature differential, energy, and collection efficiency diagrams plotted against time were used to represent and compare the solar collectors. Finally, a comparative analysis of these solar collectors using either pressurised water or Dow‐corning 550 silicon oil as HTF is presented. Copyright © 2011 John Wiley & Sons, Ltd.     

Power generation characteristics of a sandwich‐type self‐heating thermoelectric generator with spatially varying embedded heat source

Power generation characteristics of a sandwich‐type thermoelectric generator in which the heat source is embedded into thermoelectric elements are investigated. Our previous work on a similar concept only considered a uniform heat source distribution inside thermoelectric elements. In this work, the effect of the spatial distribution of a heat source is examined. In particular, the effect of the concentration of heat source near the one end, that is, the hot end, is intensively studied as a potential means of improving the efficiency of the device. Although the effects of heat source concentration in impractical cases without heat transfer limitations on the cold side remain ambiguous, it become clear that heat source concentration indeed has positive effects in more realistic cases with finite heat transfer coefficients imposed on the cold side. Because of the relatively low efficiency of typical thermoelectric generation, a significant amount of heat must be dissipated from the cold end of the thermoelectric element. Greater heat source concentration near the hot end leads to more effective utilization of available heat source, reduces the amount of heat rejected at the cold end, and lowers the hot end temperature of the thermoelectric element. Overall, it is suggested that heat source concentration can be used as a method to achieve more efficient operation and better structural integrity of the system. Copyright © 2015 John Wiley & Sons, Ltd.     

Study on design and thermal characteristics of vacuum tube solar collector intubated with heat storage tube

In this work, a heat storage vacuum tube solar collector intubated with heat storage tube is designed, which consists of solar vacuum tube, phase change material insert tube, and heat holding cover. The internal energy conversion, transmission, and storage theory are established based on the structure of the heat storage vacuum tube. The parallel and series‐parallel solar air collector system prototype consisting of nine heat storage solar vacuum tube solar collectors is designed and tested. The test results showed that the daily average conversion efficiency of the parallel and series‐parallel prototype reached 56.9% and 48.46%, respectively. Compared with nonheat storage prototype, the heat storage parallel and series‐parallel prototype had higher conversion efficiency by, respectively, 10.9% and 7.8%, longer effective heating time, and better heating stability and practicability. At the same time, the heat storage solar collector has compact structure, which is convenient to use.     

Comparison between predicted and actually observed in-service degradation of a nickel pigmented anodized aluminium absorber coating for solar DHW systems

The actual service degradation in optical performance of a nickel pigmented anodized aluminium absorber coating has been investigated in order to better validate predicted service life data from accelerated life testing. Samples from the coating taken from collectors used in solar DHW systems for time periods of 10 years or more were analysed for that purpose. The study, which was performed by the IEA Working Group: Materials in Solar Thermal Collectors, utilized results from a comprehensive joint case study on accelerated life testing previously performed in Task X of the IEA Solar Heating and Cooling Programme. It could be concluded from the present study that the agreement between degradation data determined for the absorber samples from the DHW systems and that from accelerated life testing from the Task X study was astonishingly good both from a quantitative and a qualitative point of view. For the anodized aluminium coating the results of the present study strongly point to the fact that the design of the solar collector with respect to airtightness is the most crucial factor in determining service life. The service life was defined as the period during which the optical performance is not less than 95% of its original value. The estimated service life is of the order of 30–40 years for the coating in an airtight solar collector with controlled ventilation of air, whereas in a non-airtight collector with essential uncontrolled ventilation of air, the corresponding life is around 5–10 years. The general conclusion from the study is that the accelerated life testing method as developed by the Task X group is an efficient tool in predicting expected service life of absorber coatings and is therefore to be recommended for qualification of durability of new kinds of absorber coatings.     

Experimental and economic analysis of energy storage-based single-slope solar still with hollow-finned absorber basin

The paucity of drinking water is an alarming glitch across the globe. The conversion of available seawater into drinking water by utilizing renewable energy is the best way to surmount this challenge. Desalination through solar still is one of the notable, monetary, and viable processes among various desalination approaches. The current research aims to augment the potable water yield of single-slope solar still by using a hollow-finned absorber basin inserted into paraffin wax—phase change material (PCM). The effect of hollow-finned absorber basin on the yield of solar still is investigated separately, with and without PCM, and compared with the results of conventional solar still (CSS). In the first set of experiments, the CSS and solar still with a hollow-finned absorber basin without PCM (SSHF) are investigated. In the second set of experiments, the CSS and solar still with a hollow-finned absorber basin inserted into PCM (SSHFP) are investigated. The experimental results reported that the CSS is having almost the same yield on the 2 days of testing. The yield of SSHF and SSHFP is increased by 15.7% and 52.4%, respectively, when compared with CSS. The results of the economic analysis proved that the payback period and cost per liter of freshwater produced from SSHFP are comparatively better than SSHF and CSS.     

Development and performance analysis of a two‐axis solar tracker for concentrated photovoltaics

This study presents a two‐axis solar tracking system equipped with a small concentrator module for electricity generation through a multijunction solar cell. The system can accurately track the sun without the need of calibration for an extended period and operate as a stand‐alone system. High‐precision solar tracking was achieved by a combination of open‐loop and closed‐loop controls. A camera tracking sensor was introduced as a feedback device in closed‐loop control. Two different types of solar concentrator modules were designed and fabricated. Their concentration ratios were analyzed against solar tracking errors by means of ray tracing software. One is made up of a paraboloidal primary concentrator and a paraboloidal secondary reflector, whereas the other has a paraboloidal primary concentrator and a hyperboloidal secondary reflector. Both modules showed an almost identical concentration ratio of 610 provided that the solar tracker is pointing perfectly at the sun. However, their performance differs considerably when tracking error is present. The maximum power output was obtained near solar noon with multijunction cells, whose average solar conversion efficiency was 21%, much higher than that of conventional photovoltaic systems. Copyright © 2015 John Wiley & Sons, Ltd.     

Development and multi-criteria optimization of a solar thermal power plant integrated with PEM electrolyzer and thermoelectric generator

This study investigates a novel solar-driven energy system for co-generating power, hydrogen, oxygen, and hot water. In the proposed system, parabolic trough collectors (PTCs) are used as the heat source of cascaded power cycles, i.e., steam and organic Rankine cycles (SRC and ORC). While the electricity produced by the SRC is supplied to the grid, the energy output of the ORC is used to drive an electrolyzer for hydrogen production. In addition, the use of a thermoelectric generator (TEG) using heat rejected from the ORC condenser for supplying additional electricity to the electrolyzer is investigated. A multi-objective optimization based on the genetic algorithm approach is carried out to estimate the optimal results for the proposed system. The specific cost of the system product and exergy efficiency are the chosen objective parameters to be minimized and maximized, respectively. The results show that, for the optimal system with the TEG, the specific cost of the system product and the exergy efficiency are 30.2$/GJ and 21.9%, respectively, and the produced hydrogen rate is 2.906 kg/h. The results also show that using a TEG increases efficiency and reduces the specific cost of system product. For having the most realistic interpretation of the investigations, the performance of the proposed system is investigated for four cities in Khuzestan province in Iran.     

一种可蓄热太阳能睡床结构及性能分析

介绍了一种兼具蓄热与散热两种状态的太阳能供暖用睡床。该睡床的下部为蓄热水箱，可从太阳能集热板获取热量供给睡床。研究了基于该睡床的供暖系统在北京地区的应用情况，并分析了不同状态下床板上表面的散热量与被褥内的温度。结果表明：在全天散热状态下，典型年供暖季集热器效率为37.7 %，复合型睡床的有效供热量为4 390.2 MJ，太阳能保证率为80.7 %；在白天保温−夜间散热下，集热器效率为33.1 %，复合型睡床的有效供热量为4 441.1 MJ，太阳能保证率为81.8 %。     

Investigation of performance and emission characteristics of a biogas fuelled electric generator integrated with solar concentrated photovoltaic system

Integration of renewable energy systems with the appropriate technology plays a pivotal role in resolving the problem of sustainable energy supply. This paper is aimed to describe the concept of integration of biomass and solar concentrated photovoltaic (CPV) energy system. The present study focused particularly on the investigation of performance and emission from a 1.4 kVA Spark Ignition, constant speed generator using raw biogas integrated in hybrid energy system. The experiments are conducted at different fuel flow rates under varying electric loading conditions. Comparing with LPG as fuel, the power deterioration is observed to be 32% on raw biogas, due to its low calorific value. The maximum power output and brake thermal efficiency using biogas is witnessed to be 812 W and 19.50% respectively. The exhaust emission analysis of generator using biogas displays considerably reduced carbon monoxide and hydrocarbons whereas there is no significant difference in nitrogen oxides concentration levels while comparing with LPG, ascertaining it to be an eco-friendly fuel. The biogas fuelled electric generator integration with CPV system can attain sustainable rural energy supply.     

Numerical evaluation of the thermal performance of a solar air heater equipped with two different types of baffles

In the present study, the effect of utilizing two different types of baffles in the channel of the solar air heater is investigated numerically. The studied baffles include angled rectangular baffles and angled V‐shaped baffles, which are mounted on the bottom and top walls of the duct, respectively. Both considered baffles were evaluated separately which the studied parameter in each section was the angular position of baffles. Finally, the best‐obtained results of both sections were compared to each other. The results indicated that in the rectangular model by comparison between 90° model and no baffle, it was found that the pressure drop and average Nusselt number increase 316.67% and 148.15%, respectively at Reynolds number (Re) = 2000. Also, in V‐shaped angled baffles, the thermal efficiency of β = 90°, 60°, 45°, and 30° are 27%, 18%, 13% higher than no baffle channel at Re = 2000, respectively. Furthermore, at low Re (about Re below 300), utilizing baffles into the channel had no effect on the thermal efficiency of the system compared to the no baffle channel. However, at high Re, it was found that the highest thermal efficiency occurred in the model of rectangular baffles with an angle of 90°.