Experimental analysis and exergy efficiency of a conventional solar still with Fresnel lens and energy storage material

This study focuses on the experimental investigation and exergy analysis of a modified solar still (MSS) with convex lenses on glass cover to collect the solar radiation at the focus on surface water. A comparative analysis of the performance and yield of the MSS with convex lenses and the conventional single slope SS were carried out for the same climatic condition of Tanta (Egypt). Similarly, the effect of modification in the SS using convex lenses, with or without black stones, on the freshwater yield is experimentally investigated. The results indicated that the lenses focus the solar radiation to the water placed in the basin and increase the water‐glass temperature difference (T _w – T _g). The yield of freshwater from the MSS with the convex lenses is comparatively higher than that of the conventional SS (26.64%). In addition to convex lenses in the inner cover surface, freshwater yield improved by 35.55% by adding blue stones as energy material inside the basin under constant water mass of 30 kg. The maximum exergy efficiency of the SS with lenses and blue stones was 11.7%, while the SS with lenses alone was 4%. The quality of freshwater produced after desalination was well within the World Health Organization standards. The total dissolved solids and pH after desalination were 22 mg/L and 8.08, respectively.     

NiAl coatings on carbon steel by self-propagating high-temperature synthesis assisted with concentrated solar energy: mass influence on adherence and porosity

NiAl have been produced by a self-propagating high-temperature synthesis (SHS). The power source that ignite the SHS reaction is concentrated solar energy. NiAl coatings are obtained in few seconds and the processes are economic and environment friendly. Three different NiAl mass are tested: 0.3; 0.6 y 1.7 g. Coating porosity and adherence to substrate depends on the NiAl mass. Pores are large in samples with 1.7 g while the other specimens have small pores. Coating adherence is better when the amount of reactive powder is larger.     

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.     

An experimental implementation and testing of a concentrated hybrid photovoltaic/thermal system with monocrystalline solar cells using linear Fresnel reflected mirrors

Integration of solar concentrators with photovoltaic (PV) systems reduces the required number of PV panels, which often account for the major costs of PV systems. The linear Fresnel reflector mirror is considered more effective because of its simplicity and effortless fabrication. An experimental test rig of a concentrated PV/thermal system that employs a linear configuration and horizontal absorber was built for evaluating its electrical and thermal performances. The considered concentrator consists of various widths of flat glass mirrors, which positioned with different angles, and with sun light focusing on the PV cells that fixed over an active cooling system. The experimental investigation of the proposed concentrated PV/thermal system shows that higher electrical and thermal efficiencies can be achieved at comparatively high temperature levels than that typically utilized in a nonconcentrated PV/thermal system. The characteristics of PV cells also indicate that the electrical efficiency values in case of no concentration and with concentration ratio of 6.0 are 9.6%, and 11%, respectively. The measured values for the inlet and outlet cooling water temperatures of the receiver showed that the maximum outlet temperature reached was 75°C with a flow rate of 0.025 L/min, and the product thermal efficiency was 62.3%. These obtained results illustrate an adequate and good thermal and electrical performance under the meteorological weather conditions of the province of Al‐Karak in Jordan.     

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.     

Performance of a concentrated photovoltaic energy system with static linear Fresnel lenses

A new type of greenhouse with linear Fresnel lenses in the cover performing as a concentrated photovoltaic (CPV) system is presented. The CPV system retains all direct solar radiation, while diffuse solar radiation passes through and enters into the greenhouse cultivation system. The removal of all direct radiation will block up to 77% of the solar energy from entering the greenhouse in summer, reducing the required cooling capacity by about a factor 4. This drastically reduce the need for cooling in the summer and reduce the use of screens or lime coating to reflect or block radiation.All of the direct radiation is concentrated by a factor of 25 on a photovoltaic/thermal (PV/T) module and converted to electrical and thermal (hot water) energy. The PV/T module is kept in position by a tracking system based on two electric motors and steel cables. The energy consumption of the tracking system, ca. 0.51 W m⁻², is less than 2% of the generated electric power yield. A peak power of 38 W m⁻² electrical output was measured at 792 W m⁻² incoming radiation and a peak power of 170 W m⁻² thermal output was measured at 630 W m⁻² incoming radiation of. Incoming direct radiation resulted in a thermal yield of 56% and an electric yield of 11%: a combined efficiency of 67%. The annual electrical energy production of the prototype system is estimated to be 29 kW h m⁻² and the thermal yield at 518 MJ m⁻². The collected thermal energy can be stored and used for winter heating. The generated electrical energy can be supplied to the grid, extra cooling with a pad and fan system and/or a desalination system. The obtained results show a promising system for the lighting and temperature control of a greenhouse system and building roofs, providing simultaneous electricity and heat. It is shown that the energy contribution is sufficient for the heating demand of well-isolated greenhouses located in north European countries.     

Concept and design of modular Fresnel lenses for concentration solar PV system

In this paper, we propose a new configuration of solar concentration optics utilizing modularly faceted Fresnel lenses to achieve a uniform intensity on the absorber plane with a moderate concentration ratio. The uniform illumination is obtained by the superposition of flux distributions resulted from modularly faceted Fresnel lenses. Based on the concept of modularly faceted Fresnel lenses, the cost effective 3-D concentration solar PV system is designed for future applications. Mathematical treatments for deriving the flux distribution and the concentration efficiency at the absorber plane are introduced. As an example, the distribution of the solar flux, at the cell position, is simulated using ray-trace technique for 9, 25, 49, 81, and 121 suns concentration systems. The irradiance distributions at the cell plane are estimated to be uniform within 20%, with a transmission efficiency larger than 70% for low and medium concentration ratios (less than 50 suns).     

Optical performance analysis of an innovative linear focus secondary trough solar concentrating system

The parabolic trough solar concentrating system has been well developed and widely used in commercial solar thermal power plants. However, the conventional system has its drawbacks when connecting receiver tube parts and enhancing the concentration ratio. To overcome those inherent disadvantages, in this paper, an innovative concept of linear focus secondary trough concentrating system was proposed, which consists of a fixed parabolic trough concentrator, one or more heliostats, and a fixed tube receiver. The proposed system not only avoids the end loss and connection problem on the receiver during the tracking process but also opens up the possibility to increase the concentration ratio by enlarging aperture. The design scheme of the proposed system was elaborated in detail in this paper. Besides, the optical performance of the semi and the whole secondary solar trough concentrator was evaluated by using the ray tracing method. This innovative solar concentrating system shows a high application value as a solar energy experimental device.     

Heat loss of a trapezoidal cavity absorber for a linear Fresnel reflecting solar concentrator

The present paper studies the heat loss of a linear absorber with a trapezoidal cavity and a set of pipes used for a linear Fresnel reflecting solar concentrator. The study includes the measurements on a 1.4 m long prototype installed in a laboratory, and its thermal simulation in steady-state using EnergyPlus software. Results of the measured vertical temperature variation inside the cavity, the surface interior and exterior wall and window temperatures, the global heat loss at steady-state and the heat loss coefficients, are presented for six different temperatures of the pipes. Measurements revealed a stable thermal gradient in the upper portion of the cavity and a convective zone below it. Around 91% of the heat transferred to outdoors occurs at the bottom transparent window, for a pipe temperature of 200 °C. The heat loss coefficient per area of absorbing pipes ranged from 3.39 W/m²K to 6.35 W/m²K (for 110 °C < T_pipe < 285 °C), and it increased with the increase of T_pipe. Simpler and less time-consuming available free software originally designed for heat transfer in buildings was tested to be a possible replacement of the highly complex CFD software commonly used to simulate the steady-state heat loss of the absorber. The experimental and predicted data sets were found to be in good agreement.     

Thermal performance of linear Fresnel reflecting solar concentrator with trapezoidal cavity absorbers

Thermal performance of the four identical trapezoidal cavity absorbers for linear Fresnel reflecting solar device were studied and compared. The absorbers were designed for operating in conjunction with a prototype Fresnel solar reflector. Rectangular and round pipe sections were used as absorber by placing in the trapezoidal cavity. The absorber pipes were coated with ordinary dull black board paint and black nickel selective surface. The bottom of the cavity was provided with plane glass to allow the solar radiation to be reflected from the Fresnel reflector. The other three sides of the cavity absorber were insulated to reduce heat loss. Thermal performance of the Fresnel reflecting concentrator with each trapezoidal cavity absorber was studied experimentally at different concentration ratio of the reflector. The study revealed that the thermal efficiency was influenced by the concentration ratio and selective surface coating on the absorber. The thermal efficiency decreased with the increase in the concentration ratio of the Fresnel reflecting collector. The selective surface coated absorber had a significant advantage in terms of superior thermal performance as compared to ordinary black painted absorber. The round pipe (multi-tube) receiver had higher surface area to absorb solar energy as compared to rectangular pipe receiver. Thermal efficiency of the solar device with round pipe absorber was found higher (up to 8%) as compared to rectangular pipe absorber.     

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.     

太阳能电站中涡轮机的设计

太阳能电站设备中,涡轮机是利用集热棚内气流动能的主要设备,对提高整个太阳能电站的效率有着极为重要的作用。针对塔囱电站中不同叶片数的涡轮进行计算,对每种情况计算的多种结果进行比较分析,最终选出每种叶片数对应的最佳情况,再综合比较不同叶片数之间的优劣,选出对应于100 kW太阳能塔囱电站最实用的涡轮机,从而提出一套计算太阳能涡轮的计算方法,解决太阳能电站中涡轮机的设计问题。通过对太阳能热气流电站的涡轮机进行优化研究,提高这种太阳能电站的整体效率,使其具有更强的竞争力。     

The study of the performance and efficiency of flat linear Fresnel lens collector with sun tracking system in Iraq

Two flat linear Fresnel lenses and two absorbers connected in series. Tracking system is constructed so that it tracks the sun in two directions. Thermal and optical losses are introduced. The thermal efficiency of the first lens is higher than the second lens and reaches 0.65. The FLFL all-day collector efficiency reaches 0.58 and it varies depending on weather condition.     

Emissive power of semitransparent spherical particle with nonuniform temperature

The ray tracing method and the zonal method is extended to study the emissive power of semitransparent spherical particle with nonuniform temperature. The particle emissive power is calculated by the radiative transfer coefficients. The effects of the related parameters on the particle emissive power and the errors resulted from omitting the nonuniformity of particle temperature are analyzed and discussed. The results show that omitting the nonuniformity of particle temperature will result in large errors of particle emissive power, and the errors increase with the nonuniformity of particle temperature. The particle emissive power based on the average temperature may deviate from its real value, and the size parameter and absorption index strongly affects the ratio of particle emissive power based on the average temperature and its real value.     

Development of thermodynamic cycles for concentrated solar power plants

Solar thermal power is a promising ‘green’ technology that could contribute significantly – in countries where it may be applicable due to available resources – towards meeting the 2020 and 2050 targets for the free energy production of emissions [Viebahn, P., Lechon, Y., and Trieb, F., 2011. The potential role of concentrated solar power (CSP) in Africa and Europe – a dynamic assessment of technology development, cost development and life cycle inventories until 2050. Energy Policy, 39 (8), 4420–4430]. Especially for the regions where solar radiation is significant, the technology of concentrated solar power (CSP) plants seems to have a great potential, once cost-related issues are resolved. The thermodynamic process, on which the component design of the plant is based, plays a significant role in the optimisation of the efficiency of the derived configuration. This paper aims to present a route for the design of thermodynamic cycles for a CSP, starting from the simplest processes and heading towards more complicated ones. For a reference output capacity, the obtained efficiencies are presented, illustrating the technical benefits of shifting to more advanced thermodynamic processes.     

Integration of direct carbon fuel cells with concentrated solar power

In this paper, we will report on a study on the thermodynamic feasibility of a concept that realizes the cracking of methane with a concentrated solar power (CSP) reactor and electricity production with a direct carbon fuel cell (DCFC) and its possible contribution to a clean energy supply for Europe in the long-term future. The natural gas (methane) is decomposed in an endothermic reaction into hydrogen and carbon. The separated carbon is fed to a direct carbon fuel cell (DCFC) and converted with high efficiency to electric power. A model of the proposed concept is carried out in the flow sheet program Cycle-Tempo and the results of the simulations and the corresponding analysis are presented in this paper. Finally the location factors influencing the implementation of this concept in the north of Africa are evaluated.     

A new calorimetric facility to investigate radiative‐convective heat exchangers for concentrated solar power applications

A new calorimetric facility for the aerothermal assessment of radiative‐convective heat exchangers in concentrating solar power applications has been developed and is described in this paper. The configuration of volumetric solar receivers enables concentrated sunlight to be absorbed and conducted within their solid volume, from where it is gradually transferred by forced convection to a heat transfer fluid flowing through their structure. Current design trends towards higher thermal conversion efficiencies have led to the use of complex intricate geometries to maximise temperatures deep inside the structure. The work presented aims to aid these objectives by commissioning a new experimental facility for the fully integrated evaluation of such components. The facility is composed of a high‐flux solar simulator that provides 1.2 kW of radiative power, a radiation homogeniser, inlet and outlet collector modules, and a working section that can accommodate volumetric receivers up to 80 mm × 80 mm in aperture. Irradiance levels and flow field nondimensional governing parameters are highly representative of on‐sun experiments at larger scales. Results from experiments with a siliconised silicon carbide monolithic honeycomb are presented, conducted at realistic conditions of incident radiative power per unit mass flow rate to validate its design point operation. Measurements conducted include absorber solid temperature distributions, air inlet and outlet temperatures, pressure drop, incident heat flux, and overall thermal efficiency. The relative influence of different sources of thermal loss is analysed and discussed.     

In-situ synthesis of Pd nanocrystals with exposed surface-active facets on g-C3N4 for photocatalytic hydrogen generation

Engineering surface-active facets of metal cocatalysts is one of the most widely explored strategies to develop advanced photocatalysts and promote photocatalytic solar energy conversion. Here, the surface-active facets of Pd nanocrystals in Pd/g-C₃N₄ photocatalyst was related to the injection flow rate of PdCl₂. When PdCl₂ was injected at a low flow rate of 7.5 mL/h (7.5-Pd/g-C₃N₄), the Pd nanocrystals were uniformly dispersed onto the g-C₃N₄ with exposed low-index {100} and {111} surface-active facets. However, increasing the injection flow rate to 150 mL/h (150-Pd/g-C₃N₄) formed Pd nanocrystals where only the {100} surface-active facet was exposed. Under visible light irradiation, the 7.5-Pd/g-C₃N₄ nanocomposite exhibited excellent water splitting activity for hydrogen production (7.61 mmol g⁻¹ h⁻¹), which was significantly better than with the 150-Pd/g-C₃N₄ nanocomposite (3.3 mmol g⁻¹ h⁻¹). Theoretical calculations and experimental results confirm the importance of the {111} surface-active facets in the 7.5-Pd/g-C₃N₄ nanocomposite for promoting photocatalytic activity.     

A novel integrated simulation approach couples MCRT and Gebhart methods to simulate solar radiation transfer in a solar power tower system with a cavity receiver

An integrated simulation approach, which couples Monte Carlo ray tracing (MCRT) and Gebhart methods, is proposed to simulate solar radiation transfer in a solar power tower system with a cavity receiver. The MCRT method is used to simulate the solar radiation transfer process from the heliostat field to interior surfaces of the cavity receiver, and the Gebhart method is used to simulate the multiple reflections process of solar radiation within the cavity. This integrated simulation method not only reveals the cavity effect on receiver performance but also provides real-time simulation results. Based on this method, the reflection loss of the cavity receiver and solar flux distributions are discussed in detail. The results indicate that the cavity effect can significantly reduce the reflection loss and homogenize the concentrated solar energy distributed on interior surfaces to some extent. Moreover, the surface absorptivity has less effect on the reflection loss when cavity effect is considered. The cavity effect on homogenizing solar flux distributions is greater with lower surface absorptivity. In addition, although the concentrated solar energy is distributed on the cavity aperture with similar shapes at different times, the shape of the solar flux distribution on interior surfaces varies greatly with time.     

菲涅尔透镜聚光光伏光热耦合系统性能模拟研究

建立带有嵌入式流道结构的低倍菲涅尔透镜聚光的光伏光热耦合系统数学模型,分别从聚光比、换热流体质量流量、几何和环境参数角度研究了耦合系统的光热光电性能。结果表明:随着聚光比增加,系统的热性能提升而电性能降低,且低Re数下聚光比对系统性能影响显著;系统各性能参数在小流量阶段变化剧烈,但变化速率逐渐减缓,直至趋于稳定;流道宽度w_1的不同造成系统性能随流道深度h变化特征的差异,根据Re数与换热面积所占比重可分为4个不同阶段;当太阳电池覆盖率Pa相同时,随着风速的增加,系统热性能参数缓慢降低,而电性能几乎不变。