Distribution of absorbed heat in luminescent solar concentrator lightguides and effect on temperatures of mounted photovoltaic cells

Polymer plates containing fluorescent dyes with photovoltaic cells attached to one or more edges have the potential to be used for solar light collection in the built environment. The heating of the polymer plates and the resulting effects this may have on the operating temperatures of the attached photovoltaic cells and the integrity of the cells are studied. The results indicate that the luminescent solar concentrator under a solar simulator will allow the edge attached photovoltaic cells to operate up to 10 °C cooler compared to cells experiencing direct solar exposure because of the avoidance of infrared light. We also demonstrate the importance of correct adhesive to avoid rupture of the attached cell.     

Optimized excitation energy transfer in a three-dye luminescent solar concentrator

The spectral range of sunlight absorbed by a luminescent solar concentrator (LSC) is increased by using multiple dyes. Absorption, fluorescence, and fluorescence excitation spectra, and relative light output are reported for LSCs made with one, two, or three BODIPY dyes in a thin polymer layer on glass. Losses caused by multiple emission and reabsorption events are minimized by optimizing resonance excitation energy transfer between dyes. Increases in the outputs from the multiple-dye LSCs are directly proportional to increases in the number of photons absorbed. The output of the three-dye LSC is 45–170% higher than those of the single-dye LSCs.     

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.     

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.     

Thin-film luminescent solar concentrators: A device study towards rational design

A study on the effect of different device parameters on the photophysical and photovoltaic behavior of thin-film luminescent solar concentrators (LSCs) is presented in this work. The concentration of the luminescent species, the thickness of the LSC film, the geometric gain of the LSC device and the composition and thickness of the white back reflector are systematically varied and their influence on LSC thin film properties and device performance is examined. It is shown that dye concentration and LSC film thickness have a major effect on the optical response of the LSC devices. The efficiency is found to decrease with increasing geometric gain, although saturation is observed for high geometric gains suggesting that LSC devices perform best for very large LSC areas. The surface roughness of the back reflector is found to play a key role in improving the efficiency of the LSC film because it induces a reduction of specular reflectivity and an increase of isotropic light scattering. The results of this study allow a greater understanding of the relationships between key LSC device parameters and the photophysical and photovoltaic behavior of planar thin-film LSC systems and provide useful guidelines for optimal design of thin-film LSC devices.     

槽式太阳聚光器的研究

提出了一种低倍聚光的抛物面槽式聚光光伏发电方式.从聚光器的聚光比入手,推导抛物面槽式聚光的能流聚光比的公式,分析了能流聚光比和各个参数的关系.依据这些关系式制成的低倍聚光装置适宜于普及,可节约光伏装置成本,增加光伏发电量.     

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.     

Study on design of molten salt solar receivers for beam-down solar concentrator

Systems using molten salt as thermal media have been proposed for solar thermal power generation and for synthetic fuel production. We have been developing molten salt solar receivers, in which molten salt is heated by concentrated solar radiation, in the Solar Hybrid Fuel Project of Japan. A cavity shaped receiver, which is suitable for a beam-down type solar concentration system, was considered. In order to design molten salt solar receivers, a numerical simulation program for the prediction of characteristics of receivers was developed. The simulation program presents temperature distributions of a receiver and molten salt with the use of heat flux distribution of solar radiation and properties of composing materials as input data. Radiation to heat conversion efficiency is calculated from input solar power and heat transferred to molten salt. The thermal resistance of molten salt and the maximum discharge pressure of molten salt pumps were taken into account as restrictions for the design of receivers. These restrictions require control of maximum receiver temperature and pressure drop in the molten salt channel. Based on the incident heat flux distribution formed with a 100 MWth class beam-down type solar concentration system, we proposed a shape of solar receiver that satisfies the requirements. The radiation to heat conversion efficiency of the designed receiver was calculated to be about 90%.     

Increasing the efficiency of fluorescent concentrator systems

This study examines concepts for increasing the efficiency of fluorescent concentrator systems. Different system sizes and configurations are investigated in detail by external quantum efficiency measurements, light-beam-induced current maps and by I-V measurements. A photonic structure that serves as a bandstop reflection filter for light emitted from dyes in the fluorescent concentrator increases the system efficiency relatively by 20%. Such photonic structures are especially beneficial for larger systems. The combination of two fluorescent concentrators made with different dyes in one stack increases the system efficiency from 5.1% with only one dye to 6.7% for the stack.     

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.     

Productivity enhancements of compound parabolic concentrator tubular solar stills

The performance of compound parabolic concentrator assisted tubular solar still (CPC-TSS) and compound parabolic concentrator-concentric tubular solar still (CPC-CTSS) (to allow cooling water) with different augmentation systems were studied. A rectangular saline water trough of dimension 2 m × 0.03 m × 0.025 m was designed and fabricated. The effective collector area of the still is 2 m × 1 m with five sets of tubular still – CPC collectors placed horizontally with north-south orientation. Hot water taken from the CPC-CTSS was integrated to a pyramid type and single slope solar still. Diurnal variations of water temperature, air temperature, cover temperature and distillate yield were recorded. The results showed that, the productivity of the un-augmented CPC-TSS and CPC-CTSS were 3710 ml/day and 4960 ml/day, respectively. With the heat extraction technique, the productivity of CPC-CTSS with a single slope solar still and CPC-CTSS with a pyramid solar still were found as 6460 ml/day and 7770 ml/day, respectively. The process integration with different systems cost was found slightly higher but the overall efficiency and the produced distilled water yield was found augmented.     

Luminescent solar concentrator employing rare earth complex with zero self-absorption loss

Luminescent solar concentrator (LSC) employing Eu(TTA)₃(TPPO)₂ (europium tris(2-thenoyl trifluoro acetonate)-di(triphenylphosphine oxide)) was fabricated in our work firstly, and then its current–voltage (I–V) performance under AM1.5G radiation with different radiation area were measured and compared with that of LSC employing dye. As there is no overlap between absorption spectrum and fluorescence spectrum of Eu(TTA)₃(TPPO)₂, it is found that the power conversion efficiency of LSC employing Eu(TTA)₃(TPPO)₂ decreases ten times slower than that of LSC employing dye reported with the increment of radiation area under AM1.5G. To accurately characterize the zero self-absorption loss of LSC employing rare earth complex more, external quantum efficiency (EQE) was also measured and simulated theoretically. When experiment data is compared with theoretical simulation, the measured EQE data at 380 nm is found to well coincide with theoretical result by taking host absorption loss into consideration. And the conclusion could be drawn that rare earth complex obviously shows zero self-absorption loss in use of LSC system and is proposed as a potential candidate for increasing the LSC efficiency.     

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.     

Dynamic model of a parabolic trough solar concentrator with a water displacement mechanism

This paper presents a three-dimensional mathematical model for determining the dynamic behavior of a parabolic trough solar concentrator of one degree of freedom, with a water displacement mechanism capable of minimize the angle of incidence (angle between the sun's rays irradiated on a surface and the line normal to this surface). This mathematical model allows the calculation of the angle of inclination of the collecting surface and the forces acting on the system. The validity of the proposed mathematical model is verified experimentally on two solar concentrators of different dimension.     

A new design of luminescent solar concentrator and its trial run

Normal luminescent solar concentrators (LSC) have a great limitation in their light transportation because the light produced by the recently reported LSCs is not a point light source. In order to enable LSCs to use optical fibers as the effective remote light transport media, a new design of LSC, which uses three color luminescent fibers for solar absorption and uses clear optical fiber bundles to transport the absorbed sunlight into a remote place, is fabricated and tested. Radiation flux ratios with a mean value of 5.7%, the luminous flux up to 114.1 lumens, and the light efficiency of 0.56% have been achieved during the trial run. The luminous efficacy as 0.643 lm W⁻¹ is higher than that of combusting candles (0.3 lm W⁻¹) but lower than that of the incandescent light bulbs (16–40 lm W⁻¹). Further, since the sun light is free, different from electrical light sources, the luminous efficacy of the new LSC does not result in any electricity consumption when it is under operation. A color analysis and spectrum test proves that the light produced by the new LSC performs a great match to the direct sun light in color. Copyright © 2010 John Wiley & Sons, Ltd.     

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.     

Potential of a parabolic trough solar concentrator for electric energy production

At present, parabolic trough technology is considered as the most low‐cost and powerful large‐scale technology to utilize solar energy for electricity generation and produce steam for different industrial usages. This article recommends the generation of electricity by using a parabolic trough solar concentrator in the central area of the Kingdom of Saudi Arabia (KSA) at Dawadmi city. Pressurized water is used as the heat‐transfer working fluid. A computer algorithm was built using the Matlab program to simulate the performance parameters of the Euro Trough collector (ETC). The input data included the properties of the working fluid (pressurized water) and the designing parameters of ETC. The output data were the outlet water temperature, the coefficient of heat transfer, the heat loss, and the thermal, solar, and global efficiencies. The obtained results indicated the ability of this type of parabolic trough in KSA to generate electric power due to the high‐performance parameters achieved. Also, the validity of using the simulation technique was measured and it showed good conformity.     

Experimental investigation on paraboloid solar concentrator with a conical secondary concentrator

Material removal through ablation caused by concentrated solar thermal power is investigated. Experiments are conducted using a mirror‐finish electroplated paraboloid along with a conical secondary concentrator in both fall and summer months in Al Ain city, UAE. Data collection for melting of aluminum shims facilitated the assessment of the feasibility of utilizing the available solar irradiance after the two‐stage concentration. A geometric concentration factor of over 2800 is achieved for the first stage of power concentration with the current installation that also has a two‐axis sun tracking system and a built‐in pyrheliometer. The results confirm the feasibility of the approach, as the available power for ablation around solar noon is order of magnitudes higher than the power needed for the task, for the aluminum shim used. The main aim of the study is to hone the process to the power and precision of continuous pulse laser material removal, notably CO₂ lasers, as challenges further reduction of the concentrated solar beams to acceptable tolerances remain to be successfully resolved. Copyright © 2014 John Wiley & Sons, Ltd.     

Reliability simulation of solar concentrator receiver

The reliability of solar concentrator is investigated using finite element (FE) modelling. An FE model of the receiver absorber is built and simulated using latin hypercube sampling. A transient thermal structural simulation is conducted, and the maximum thermal stress affecting the absorber is determined. Based on the failure criterion, the most effective parameters are determined and assigned as random variables. A stochastic simulation is performed resulting in a probability density function (PDF) of the thermal stress-life. The PDF is used to estimate the reliability of the absorber. Different designs and materials of the absorber tubes are investigated. Consequently, methods to improve the reliability of the absorber are identified.     

Extended description of tunnel junctions for distributed modeling of concentrator multi-junction solar cells

One of the key components of highly efficient multi-junction concentrator solar cells is the tunnel junction interconnection. In this paper, an improved 3D distributed model is presented that considers real operation regimes in a tunnel junction. This advanced model is able to accurately simulate the operation of the solar cell at high concentrations at which the photogenerated current surpasses the peak current of the tunnel junction. Simulations of dual-junction solar cells were carried out with the improved model to illustrate its capabilities and the results have been correlated with experimental data reported in the literature. These simulations show that, under certain circumstances, the solar cell's short circuit current may be slightly higher than the tunnel junction peak current without showing the characteristic dip in the J-V curve. This behavior is caused by the lateral current spreading toward dark regions, which occurs through the anode/p-barrier of the tunnel junction.