Performance testing of a linear fresnel reflector

Results of optical and thermal performance evaluation tests conducted on a prototype linear Fresnel reflector system fabricated using locally available material are presented in this paper.     

Performance characteristics of spray-pyrolysed selective cobalt-oxide coated tubular absorber operated with a linear solar concentrator

Spray-pyrolysed selective cobalt-oxide (CoO_x) coatings were prepared on the surface of a bright nickel-plated copper tubular absorber (α = 0.89–0.91 and ?_100°C = 0.18) for operation in conjunction with a prototype linear Fresnel reflector solar concentrator (LFRSC). Some preliminary tests were conducted to study the optical and thermal performance characteristics of the selective cobalt-oxide coated absorber in the concentrated solar flux. The tests conducted included determination of the overall heat loss coefficient U_L of the absorber at temperatures from 50 to ～ 120°C, and the optical efficiency η_o of the concentrator-absorber system, and measurement of the stagnation temperature of the absorber with the prototype solar concentrator. Based on the results of U_L and η_o measurements, the thermal efficiency η of the concentrator-absorber system at a working temperature of 115°C has been determined for a typical beam radiation I_b of 600 W/m². Further, comparison of the results of this study with those obtained using a dimensionally identical black-painted absorber indicates that the performance of the selective cobalt-oxide coated absorber is considerably superior to that of an ordinary black-painted absorber.     

A new design of nontracking seasonally adjusted plane mirror linear trough solar concentrator with a flat horizontal absorber

This paper presents an optical design based on a single-reflection criterion, and performance characteristics of an east-west aligned nontracking seasonally adjusted linear trough solar concentrator with a flat horizontal absorber, using plane mirror elements. The design procedure allows the use of any desired number of mirror elements to reflect solar energy onto the base absorber in one reflection. The angle of inclination of each mirror element with respect to the absorber surface, and the width of the mirror element, are determined so that a ray incident on the extreme upper edge of the mirror element at a specified angle to the normal to the concentrator aperture (acceptance half-angle), after reflection, strikes the extreme edge of the absorber on the opposite side of the mirror element. Other rays making angles less than the design acceptance half-angle are also reflected onto the base absorber in one reflection. Concentrator designs resulting from this approach appear to have the important characteristic of relatively smaller heights, and hence appear highly cost-effective in terms of the amount of material required for fabrication. Some numerical calculations have been carried out to illustrate the performance of concentrators for different acceptance half-angles. Results obtained are presented in graphic and tabular forms, and are discussed.     

Some geometrical design aspects of a linear fresnel reflector concentrator

A somewhat new approach to the design of solar concentrators of Fresnel reflector geometry is outlined. the constituent mirror elements of the concentrator surface are characterised by three parameters, shift, tilt and width. the evaluation of these parameters and the concentration characteristics are investigated on the basis of a simple ray optical model.     

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.     

Optimal geometries of a seasonally adjusted discrete-mirror solar concentrator employing a tubular absorber

The geometrical profile of a seasonally adjusted solar concentrator composed of plane mirror elements and employing a tubular absorber has been optimized. The procedure maximizes concentration for any specified number of mirror elements, and for acceptance angle, with the height of the concentrator or the reflector area as a constraint. The geometrical characteristics of the optimal concentrators have been analysed in detail. The results for a tubular absorber are compared with those for a flat horizontal absorber. Detailed results for a wide range of number of mirror elements, reflector heights, and reflector areas are provided as a design aid. Designs using a glazed tubular absorber are also considered.     

A new trough solar concentrator and its performance analysis

The operation principle and design method of a new trough solar concentrator is presented in this paper. Some important design parameters about the concentrator are analyzed and optimized. Their magnitude ranges are given. Some characteristic parameters about the concentrator are compared with that of the conventional parabolic trough solar concentrator. The factors having influence on the performance of the unit are discussed. It is indicated through the analysis that the new trough solar concentrator can actualize reflection focusing for the sun light using multiple curved surface compound method. It also has the advantages of improving the work performance and environment of high-temperature solar absorber and enhancing the configuration intensity of the reflection surface.     

Static solar concentrator with vertical flat plate photovoltaic cells and switchable white/transparent bottom plate

A new type of static solar concentrator is proposed to match the aesthetic features of towns. The concentrator consists of vertical plate solar cells and white/transparent switchable bottom plate, which is operated with external power. The bottom is switched to be a diffuse reflection white surface when the cell generates electric power, and switched to be a light transmissible transparent surface when the cell does not deliver power. The light collection of this concentrator was analyzed by using multiple total internal reflection model and ray tracing simulation. For the same ratio of the area of the solar cells to that of the collector surface, the collection efficiency for the proposed concentrator is about half of that of the conventional concentrator for flat plate cell, and nearly equal to that of the concentrator for the embedded spherical silicon solar cells.     

Simulation and model validation of a horizontal shallow basin solar concentrator

Salt removal from drainage water is becoming increasingly important for sustainable irrigated arid land agriculture, where inadequate drainage infrastructure exists. Solar evaporation and concentration systems are currently in development in California for this purpose. The thermal behavior and evaporation rates of a horizontal shallow basin solar concentrator were modeled for design purposes and investigated experimentally in order to validate the model. Three different evaporation rate models were evaluated and compared. Measured and predicted peak brine temperatures differed by as much as 5 °C when using prescribed literature coefficients without calibration. Model prediction was improved by calibration so that peak brine temperature deviated less than 3 °C when tested against independent data sets.Minimum root mean square error was used to calibrate the mass transfer coefficient and absorptance of the collector surface for solar radiation, which are the main factors affecting the heat transfer associated with the solar concentrator. Calibrated collector surface absorptance for solar radiation declined while mass transfer coefficients were increased from reported literature values. Under calibration, the absorptance of the collector surface was adjusted from 0.8 to 0.61, and mass transfer coefficients estimated by Newell et al. [Newell, T.A., Smith, M.K., Cowie, R.G., Upper, J.M., Cler, C.L., 1994. Characteristics of a solar pond brine reconcentration system. Journal of Solar Energy Engineering 116 (2), 69–73] from 1.36 × 10⁻⁶(1.9 + 1.065V) to 1.70 × 10⁻⁶(1.84 + 1.0V) kg m⁻² s⁻¹ mm Hg⁻¹, by Manganaro and Schwartz [Manganaro, J.L., Schwartz, J.C., 1985. Simulation of an evaporative solar salt pond. Industrial & Engineering Chemistry Process Design and Development 24, 1245–1251] from 0.0208(1 + 0.224V) to 0.0233(1 + 0.214V) kg m⁻² h⁻¹ mm Hg⁻¹, and by Alagao et al. [Alagao, F.B., Akbarzadeh, A., Johnson, P.W., 1994. The design, construction, and initial operation of a closed-cycle, salt-gradient solar pond. Solar Energy 53 (4), 343–351] from 2.8 + 3.0V to 3.0 + 3.33V W m⁻² °C⁻¹. The calibrated models were tested using an independent data set. Maximum deviation between measured and predicted brine temperatures differed by less than 3 °C. The measured and predicted peak evaporation rates were between 1.2 and 1.4 kg m⁻² h⁻¹.The calibrated Newell model was used to predict the monthly productivity and daily maximum evaporation rates at Five Points, California for the year 2004. The productivity from April to September and from March to October was 80.7% and 94.3% of the total annual productivity, respectively.     

Thermal performance of a linear Fresnel reflector solar concentrator using a black liquid

Results of some simple experiments conducted on a Linear Fresnel reflector solar concentrator using a tubular transparent corning glass absorber through which a highly absorbent black liquid is passed are presented in this short communication.     

Electrical and thermal performance of silicon concentrator solar cells immersed in dielectric liquids

Direct liquid-immersion cooling of concentrator solar cells was proposed as a solution for receiver thermal management of concentrating photovoltaic (CPV) and hybrid concentrating photovoltaic thermal (CPV-T) systems. De-ionized (DI) water, isopropyl alcohol (IPA), ethyl acetate, and dimethyl silicon oil were selected as potential immersion liquids based on optical transmittance measurement results. Improvements to the electrical performance of silicon CPV cells were observed under a range of concentrations in the candidate dielectric liquids, arising from improved light collection and reduced cell surface recombination losses from surface adsorption of polar molecules. Three-dimensional numerical simulations with the four candidate liquids as the working fluids, exploring the thermal performance of a silicon CPV cell array in a liquid immersion prototype receiver, have been performed. Simulation results show that the direct-immersion cooling approach can maintain low and uniform cell temperature in the designed liquid immersion receiver. The fluid inlet velocity and flow mode, along with the fluid thermal properties, all have a significant influence on the cell array temperature.     

The effect of a scattering layer on the edge output of a luminescent solar concentrator

The effect of adding white scattering layers to the bottom side of luminescent solar concentrator waveguides is evaluated. It is determined that adding a rear scatterer separated from the waveguide by an air gap results in a large increase of energy output from the waveguides, and this enhancement persists over long (>30 cm) distances, although the magnitude of the enhancement decreases with distance. An attached scatterer resulted in the greatest improvement of light output for short (∼6 cm) distances, but actually reduced edge emissions over longer distances. We provide estimates for the relative contribution of dye-emitted light and scattered light to the total waveguide emission, as well as distinguishing between the contributions of direct and indirect scattering of light to the total output as a function of dye content of the waveguides.     

Improving the optical efficiency and concentration of a single-plate quantum dot solar concentrator using near infra-red emitting quantum dots

Low luminescent quantum yields and large overlap between quantum dot (QD) emission and absorption spectra of present commercially-available visible-emitting QDs have led to low optical efficiencies for single-plate quantum dot solar concentrators (QDSCs). It is shown that using near infra-red (NIR) emitting QDs, re-absorption of QD emitted photons can be reduced greatly, thereby diminishing escape cone losses thus improving optical efficiencies and concentration ratios. Using Monte-Carlo ray-trace modelling, escape cone losses are quantified for different types of QD. A minimum 25% escape cone loss would be expected for a plate with refractive index of 1.5 containing QDs with no spectral overlap. It is shown that escape cone losses account for ∼57% of incident photons absorbed in QDSCs containing commercially-available visible-emitting QDs.     

Experimental analysis and evaluation of a vacuum enclosed concentrated solar thermoelectric generator coupled with a spectrally selective absorber coating

Significant research in the past decade has been focused on quantitatively and qualitatively validating potential of solar thermoelectric modules to harness electricity. In the present study, we have experimentally analysed steady-state temperature variation of a spectrally selective solar absorber coating (α?=?0.954, ε?=?0.13) with variation in solar irradiation flux (concentration ratios?=?39, 50 and 65) using Fresnel lens and vacuum enclosure pressure (200?mbar to 900?mbar in steps of 100?mbar). It is observed that the experimental results so obtained go hand in hand with a COMSOL simulation model of the set-up. Further, we have carried out performance analysis of a solar thermoelectric generator (STEG) set-up enclosed in vacuum conditions equipped with Fresnel lens and absorber set-up coupled to Bi₂Te₃ thermoelectric module array electrically connected in series. The results depict a maximum power output of 0.91?W and a peak efficiency of 2.21% at a hot-side temperature of 642?K.     

Impact of heliostat curvature on optical performance of Linear Fresnel solar concentrators

The present paper gives a numerical investigation of the effect of mirror curvature on optical performance of a Linear Fresnel Reflector solar field installed recently in Morocco. The objective is to highlight and discuss the effect of mirror curvature on the flux density distribution over the receiver and the system optical efficiency. For this purpose, a Monte Carlo-ray tracing simulation tool is developed and used to optimize the optical design taking into account the curvature degree of the heliostat field. In order to assess the accuracy of the numerical code developed and the validity of simulation results, a set of verification tests were developed and detailed within this article. Then, the optical performance of the system is evaluated as a function of mirror curvature and receiver height. The major challenge of this study is to find a trade-off between heliostat curvature and receiver height since lower and smaller receivers may reduce the system cost. It has been found that the flux distribution over the receiver and the optical efficiency of the system are relatively sensitive to the mirror curvature. We have demonstrated quantitatively how the use of curved mirrors can enhance the optical performance and reduce the required receiver size.     

槽式聚光热电联供系统抛物反射面的性能参数分析

分析了跟踪方式和太阳张角对理想槽式抛物面反射镜的影响,给出了几何聚光比、相对口径、能流分布、边界角之间的函数关系式。在理想情况下,边界角δ为44.87°时,槽式聚光器的最大聚光比为212.59,此时相对口径为1.652 m。讨论了北京、上海、昆明等地单轴跟踪在全年不同时刻入射角余弦值的变化规律。采取东-西水平轴跟踪时,入射角余弦值与各地纬度无关;采取南-北水平轴跟踪时,春冬两季每天不同时刻入射角的变化范围较大,夏秋两季的变化范围较小。文章针对不同宽度太阳电池和聚光比对抛物镜面参数进行了设计分析。     

Application of optical film with micro-lens array on a solar concentrator

A plastic solar concentrating optical film with horizontal cylinder micro-lens array (HCMA) is presented in this study. The solar concentrator (SC) is in the form of optical film with HCMA and it is attached on the surface of a solar cell. This film is a polymethylmethacrylate (PMMA)-based optical layer. Compared with a plain solar collecting optical film without HCMA, the solar collecting optical film with HCMA can reduce the opportunity of reflection as light arrives at the surface and therefore can increase the refraction coefficient. As a result, the gain of photovoltaic power can be improved with the SC. Light is efficiently refracted by the HCMA and absorbed by the solar cell without the need of a solar tracking mechanism. Optimization of geometrical parameters of HCMA such as contact angle and gap (interspace) between each horizontal cylinder micro-lens is designed by simulation. The procedures of fabrication include reflow process, nickel-cobalt (Ni-Co) electroplating, and molding process. The measurement equipment of NEWPORT Oriel 91160+MODEL 6285 is utilized to measure the parameters such as open-circuit voltage V_oc, short-circuit current I_sc, and fill factor F.F., relating to the efficiency of the complete system. The experimental results show that a gain of photovoltaic power of about 3.30% is obtained with a contact angle of 62° and a gap of 15 μm.     

The effect of plane booster reflectors on the performance of a solar air heater with solar cells suitable for a solar dryer

We present a theoretical study of a solar photovoltaic-thermal (hybrid) system consisting of a flat-plate solar air heater mounted with solar cells and a plane booster. A conventional flat-plate collector is converted into a hybrid system by mounting solar cells directly on the absorber plate. A hybrid system is self-sufficient in the sense that the electrical energy required by the pump is supplied by the panel. Such systems are well suited to applications such as solar drying. The combined system is analysed for the case when the radiative and absorptive properties of the cell surface and the absorber plate are nearly the same. The solar cell efficiency is a linearly-decreasing function of the absorber plate temperature. The performance of the system has been evaluated for various combinations of boosters. The minimum area of the solar cells required to run the pump at a given flow rate has been calculated as a function of time, with and without boosters. The minimum cell area required decreases with the use of boosters. High cost cells may be replaced by low cost reflectors. The solar air heaters presently available on the market are not suitable for direct conversion to hybrid systems.     

Stand alone triple basin solar desalination system with cover cooling and parabolic dish concentrator

A stand-alone triple basin solar desalination system is experimentally tested and the results are discussed in this paper. This system mainly consists of a triple basin glass solar still (TBSS), cover cooling (CC) arrangement, parabolic dish concentrator (PDC) and photovoltaic (PV) panel. Four triangular hollow fins are attached at the bottom of the upper and middle basin in order to increase the heat transfer rate and place the energy storing materials. The performance of the system is studied by, conventional TBSS system, integrating the TBSS with CC, TBSS with PDC, and TBSS with CC and PDC. Also, each configuration is tested further by using fins without energy storing material, fins filled with river sand, and fins filled with charcoal. The results of the test reveal that, TBSS with charcoal and TBSS with river sand enhance the distillate by 34.2 and 25.6% higher than conventional TBSS distillates. TBSS with cover cooling reduces the glass temperature to about 8 °C compared to the conventional TBSS. The presence of concentrator increases the lower basin water temperature upto 85 °C. The maximum distillate yield of 16.94 kg/m².day is obtained for TBSS with concentrator, cover cooling and charcoal in fins.     

Design and investigation of a novel concentrator used in solar fiber lamp

A novel concentrator used in solar fiber lamp has been designed and made. The method of the design has been introduced. The lamp has been tested under the real solar condition and the experiment curves have been given. The light transmission will be influenced by the structure of the lamp and the diameter of the fiber, which has been studied in this paper. The experimental results show that the brightness of this solar fiber lamp is about the brightness of a 6-W ordinary electrical energy-saving lamp. The computer simulation for the lamp has been presented and the improvement schemes are proposed.