Achievement of 27% efficient and 200 Wp concentrator module and the technological roadmap toward realization of more than 31% efficient modules

A 400× and 7056 cm² concentrator module was fabricated from 36 concentrator receivers, connected in series and with the same number of newly developed dome-shape Fresnel lenses. The averaged outdoor efficiency on a clear sky day was 26.8±1.5% (25C STC). This is the highest module efficiency achieved to date using a module of practical size and electrical rating. The heat was dissipated by the module wall and no heat sinks nor external cooling were used. A glass homogenizer was introduced to give uniform illumination to the square cell, and afforded a reasonable assembly tolerance, without the need for optical alignment.     

Salt recovery from agricultural drainage water using a liquid film solar-assisted concentrator – Simulation and model validation

Salt management in irrigated agriculture is critical to the economies of the San Joaquin Valley of California and many other areas around the world. Purified salts can be recovered as marketable products through fractional crystallization following concentration of final stage drainage water from integrated on-farm drainage management systems. To obtain recovered salt and use as a commercial product, new systems which can perform with higher efficiency and lower environmental impact than solar evaporation basins or solar ponds that have previously been used for the final stage are in need of development. For this purpose, a number of solar-assisted brine concentration concepts have been explored, including an open liquid film-type using a tilted evaporation surface described here. Model performance was conceptually evaluated and then experimentally verified.A transient model was developed from energy and component mass balances and employed constitutive heat and mass transfer relationships from various other sources for simulating concentration of agricultural drainage water using a liquid film solar-assisted concentrator.Measured maximum evaporation rate and productivity were between 1.3 and 1.5 kg m⁻² h⁻¹, and 80 kg m⁻² over a 7 day experimental period respectively which was about a third better performance compared with a shallow basin horizontal concentrator. Measurements were in good agreement with model predictions: within 2 °C at the peak and 4 °C at the lowest evaporation, and 0.2 kg m⁻² h⁻¹ for evaporation rates during the peak evaporation periods of the day when compared with independent data sets. Cumulative evaporation rates were from 75 to 85 kg m⁻² for the tilted concentrator model and 60 to 65 kg m⁻² for the horizontal concentrator model after 7 days. The tilted concentrator yielded productivity and efficiency that were 33% higher than the horizontal concentrator according to the experimental result for the same period and location.     

Analysis of two models of (3D) Fresnel collectors operating in the fixed-aperture mode with a tracking absorber

In this paper, we study the reflection behavior of (3D) Fresnel collectors operating in the fixed-aperture mode with a tracking absorber. The aim of the study is to investigate the possibility of the use of this type of installation for applications in medium temperature processes (200–300°C). Two models of (3D) Fresnel concentrator are developed for this purpose. One is based on the approximation of the optical behavior of a parabolic concentrator, and the other on that of a spherical one. Via a computer simulation which includes ray-tracing, we evaluate the sensitivity of the geometric concentration ratio to concentrator design parameters, and the option of using curved versus flat elementary mirrors. The numerical results show that there is no large difference between the two models of Fresnel concentrator. For the spherical model, which seems to be slightly more suitable for this type of application, we propose a simple solution for the receiver displacement, which consists of a single-sided absorber moving tangentially to a sphere centered in the concentrator’s center.     

基于三角腔体吸收器的透射式菲涅尔定焦线系统聚光特性分析

为解决线性菲涅尔太阳能集热系统单轴跟踪过程中出现的聚光焦线偏移以及降低系统跟踪能耗等问题,提出一种透射式菲涅尔定焦线太阳能聚光器.该聚光器采用极轴跟踪方式与线性菲涅尔透镜定期滑移调节方式相结合,可实现固定焦线聚光.将该聚光器与三角腔体吸收器所组成的太阳能集热系统,利用基于蒙特卡罗光线追迹法的TracePro光学软件分析...     

用于太阳能光电水泵的菲涅耳透镜聚光收集器

报道了具有第二级Ｖ形槽聚光器的玻璃直纹菲涅尔透镜与ＬＧＢＧ高效太阳电池组成的低倍聚光收集器的试验结果。宽度为３０ｍｍ、长度为１．５８ｍ的太阳电池组件，经聚光后峰值功率从７Ｗ增大到４４Ｗ，比常规太阳电池费用减少６０％，系统总费用降低４０％。     

Design and performance study of a low concentration photovoltaic‐thermal module

Compared with traditional photovoltaic‐thermal system, low concentration photovoltaic‐thermal systems install the low‐power concentrator (compound parabolic concentrator, Fresnel concentrator, miniature trough concentrator, etc) to improve system performance. In this paper, a baffle heat exchange channel was designed, which can decrease the temperature gradient of low concentration photovoltaic‐thermal module in the flow direction, based on the traditional flat‐box photovoltaic‐thermal collector. The system performance was monitored with different baffle spacing, flow rate, inlet temperature, ambient temperature, and radiation intensity by adopting simulation methodology. Furthermore, an experiment was performed to validate and evaluate the simulation results. The results indicated that, on a typical day, the maximum of thermal efficiency and electrical efficiency of the module were 55.11% and 12.50%, respectively.     

Analysis, development and testing of a fixed tilt solar collector employing reversible vee-trough reflectors and vacuum tube receivers

The Vee-Trough/Vacuum Tube Collector (VTVTC) aimed to improve the efficiency and reduce the cost of collectors assembled from evacuated tube receivers.The VTVTC was analyzed rigorously and a mathematical model was developed to calculate the optical performance of the vee-trough concentrator and the thermal performance of the evacuated tube receiver. A test bed was constructed to verify the mathematical analyses and compare reflectors made out of glass, Alzak and aluminized FEP Teflon. Tests were run at temperatures ranging from 95 to 180°C during the months of April, May, June, July and August 1977. Vee-trough collector efficiencies of 35–40 per cent were observed at an operating temperature of about 175°C. Test results compared well with the calculated values. Test data covering a complete day are presented for selected dates throughout the test season.Predicted daily useful heat collection and efficiency values are presented for a year's duration at operation temperatures ranging from 65 to 230°C. Estimated collector costs and resulting thermal energy costs are presented. Analytical and experimental results are discussed along with an economic evaluation.     

Design and analysis of a CPV/T solar receiver with volumetric absorption combined spectral splitter

Spectral beam splitting is a promising technology to achieve the maximum electrical and thermal outputs from concentrating photovoltaic/thermal (CPV/T) systems simultaneously. In this article, a novel CPV/T receiver is proposed by incorporating a fluid based filter together with a solid absorptive filter. The geometry of the receiver is developed for a designed linear flat mirror concentrator. According to the optical transmittance of both fluid based filters and solid absorptive filters, as well as their corresponding merit functions, four fluid filters and two solid filters are determined to be the candidates of the combined filter for the silicon concentrator solar cell. Then, a complete solar radiation propagation process from concentrator to the designed CPV/T receiver is simulated using ray tracing software-LightTools. The results show that the surface illumination uniformity of the PV module filtered by each combined filter under the linear flat mirror concentrator is higher than 96%. Using 5 g/L CoSO₄ solution and HB650 as the combined filter, 33.67% of the concentrated light can be directed to the PV module with the remainder collected by the filter as thermal energy and the silicon CPV cells can convert 27.06% of this energy into electrical power. This contributes to the fact that 92.43% of the light striking the PV module is within 650-1100 nm, which is the spectral response range of the cell can work efficiently. The total efficiency of 49.88% can be achieved with such a filter and the electrical efficiency is 9.1% with respect to the total incident power on the receiver.     

Degradation of toluene and acetaldehyde with Pt-loaded TiO2 catalyst and parabolic trough concentrator

Photocatalytic degradation of volatile organic compounds (VOCs) with Pt-loaded TiO₂ was analyzed at elevated temperatures in the laboratory experiments (40–190 °C) and in the field experiments (30–230 °C). The temperature of catalyst coated on the sunlight receiver was easily elevated to around 200 °C by parabolic trough concentrator (1 m × 1 m). When gaseous toluene (15 ppm) or acetaldehyde (400 ppm) was passed through the reactor, 79% of toluene or 93% of acetaldehyde was removed continuously. In the similar condition, bare TiO₂ was rapidly deactivated by the formation of byproducts. The combination of sunlight concentrator and Pt–TiO₂ catalyst exhibited the enhancement of complete degradation of VOCs, the inhibition of deactivation, and the reactivation of photocatalyst. The contributions of photocatalytic and catalytic activities of Pt–TiO₂ were analyzed by using UV lamp and electric heater. Acetaldehyde is thermocatalytically degraded by photodeposited Pt on TiO₂ at 70–190 °C without UV irradiation, however the UV irradiation is necessary for the complete oxidation of acetaldehyde into CO₂. It is inferred that the degradation of VOCs is enhanced by the combined effect of Pt thermocatalyst and Pt–TiO₂ photocatalyst.     

Near-maximum-power-point-operation (nMPPO) design of photovoltaic power generation system

The present study proposes a PV system design, called “near-maximum power-point-operation” (nMPPO) that can maintain the performance very close to PV system with MPPT (maximum-power-point tracking) but eliminate hardware of the MPPT. The concept of nMPPO is to match the design of battery bank voltage V_set with the MPP (maximum-power point) of the PV module based on an analysis using meteorological data. Three design methods are used in the present study to determine the optimal V_set. The analytical results show that nMPPO is feasible and the optimal V_set falls in the range 13.2–15.0 V for MSX60 PV module. The long-term performance simulation shows that the overall nMPPO efficiency η_nMPPO is higher than 94%. Two outdoor field tests were carried out in the present study to verify the design of nMPPO. The test results for a single PV module (60Wp) indicate that the nMPPO efficiency η_nMPPO is mostly higher than 93% at various PV temperature T_pv. Another long-term field test of 1 kWp PV array using nMPPO shows that the power generation using nMPPO is almost identical with MPPT at various weather conditions and T_pv variation from 24 °C to 70 °C.     

Design and fabrication of low concentrating second generation PRIDE concentrator

Prototype first generation Photovoltaic Facades of Reduced Costs Incorporating Devices with Optically Concentrating Elements (PRIDE) technology incorporating 3 and 9 mm wide single crystal silicon solar cells showed excellent power output compared to a similar non-concentrating system when it was characterized both indoors using a flash and continuous solar simulator. However, durability and instability of the dielectric material occurred in long-term characterisation when the concentrator was made by using casting technology. For large scale manufacturing process, durability, and to reduce the weight of the concentrator, second generation PRIDE design incorporated 6 mm wide “Saturn” solar cells at the absorber of dielectric concentrators. Injection moulding was used to manufacture 3 kWp of such PV concentrator module for building façade integration in Europe. Special design techniques and cost implications are implemented in this paper. A randomly selected PV concentrator was characterised at outdoors from twenty-four (≈3 kWp) 2nd-G PRIDE manufactured concentrators. The initial PV concentrators achieved a power ratio of 2.01 when compared to a similar non-concentrating system. The solar to electrical conversion efficiency achieved for the PV panel was 10.2% when characterised outdoors. In large scale manufacturing process, cost reduction of 40% is achievable using this concentrator manufacturing technology.     

Two-phase flow modelling of a solar concentrator applied as ammonia vapor generator in an absorption refrigerator

A detailed one-dimensional numerical model describing the heat and fluid-dynamic behavior inside a compound parabolic concentrator (CPC) used as an ammonia vapor generator has been developed. The governing equations (continuity, momentum, and energy) inside the CPC absorber tube, together with the energy equation in the tube wall and the thermal analysis in the solar concentrator were solved.The computational method developed is useful for the solar vapor generator design applied to absorption cooling systems. The effect on the outlet temperature and vapor quality of a range of CPC design parameters was analyzed. These parameters were the acceptance half-angle and CPC length, the diameter and coating of the absorber tube, and the manufacture materials of the cover, the reflector, and the absorber tube. It was found that the most important design parameters in order to obtain a higher ammonia–water vapor production are, in order of priority: the reflector material, the absorber tube diameter, the selective surface, and the acceptance half-angle.The direct ammonia–water vapor generation resulting from a 35 m long CPC was coupled to an absorption refrigeration system model in order to determine the solar fraction, cooling capacity, coefficient of performance, and overall efficiency during a typical day of operation. The results show that approximately 3.8 kW of cooling at −10 °C could be produced with solar and overall efficiencies up to 46.3% and 21.2%, respectively.     

Heat transfer enhancement of concentrated solar absorber using hollow cylindrical fins filled with phase change material

A concentrated solar absorber with finned phase change materials was experimentally studied using a Scheffler type parabolic dish concentrator. The absorber's inner surface was fixed with hollow cylindrical containers filled with phase change material (PCM) for heat transfer augmentation. The absorber's selected PCM was acetanilide (Melting point of 116 °C)—the cylindrical capsules protruding into the fluid side to create turbulence and mixing and acting as fins. The absorber surface temperature was observed to be about 130–150 °C during the outdoor tests while passing fluid through the absorber. The fluid flow rate varied from 60 to 100 kg/h during the outdoor experiments. The peak energy and exergy efficiency of parabolic dish collector (PDC) at the fluid flow rate of 80 kg/h with PCM integrated solar absorber was found to be about 67.88% and 6.96%, respectively. The integration of cylindrical PCM containers resulted in more heat transfer augmentation in the solar absorbers. The optimized solar absorber could be suitable for various applications like steam generation, biomass gasification, space heating, and hydrogen generation.     

Effects of geometrical parameters of a dish concentrator on the optical performance of a cavity receiver in a solar dish‐Stirling system

Dish‐Stirling concentrated solar power (DS‐CSP) system is a complex system for solar energy‐thermal‐electric conversion. The dish concentrator and cavity receiver are optical devices for collecting the solar energy in DS‐CSP system; to determine the geometric parameters of dish concentrator is one of the important steps for design and development of DS‐CSP system, because it directly affects the optical performance of the cavity receiver. In this paper, the effects of the geometric parameters of a dish concentrator including aperture radius, focal length, unfilled radius, and fan‐shaped unfilled angle on optical performance (ie, optical efficiency and flux distribution) of a cavity receiver were studied. Furthermore, the influence of the receiver‐window radius of the cavity receiver and solar direct normal irradiance is also investigated. The cavity receiver is a novel structure that is equipped with a reflecting cone at bottom of the cavity to increases the optical efficiency of the cavity receiver. Moreover, a 2‐dimensional ray‐tracking program is developed to simulate the sunlight transmission path in DS‐CSP system, for helping understanding the effects mechanism of above parameters on optical performance of the cavity receiver. The analysis indicates that the optical efficiency of the cavity receiver with and without the reflecting cone is 89.88% and 85.70%, respectively, and former significantly increased 4.18% for 38 kW XEM‐Dish system. The uniformity factor of the flux distribution on the absorber surface decreases with the decreases of the rim angle of the dish concentrator, but the optical efficiency of the cavity receiver increases with the decreases of the rim angle and the increase amplitude becomes smaller and smaller when the rim angle range from 30° to 75°, So the optical efficiency and uniformity factor are conflicting performance index. Moreover, the unfilled radius has small effect on the optical efficiency, while the fan‐shaped unfilled angle and direct normal irradiance both not affect the optical efficiency. In addition, reducing the receiver‐window radius can improve the optical efficiency, but the effect is limited. This work could provide reference for design and optimization of the dish concentrator and establishing the foundation for further research on optical‐to‐thermal energy conversion.     

Prediction and optimization of the performance of parabolic solar dish concentrator with sphere receiver using analytical function

Parabolic solar dish concentrator with sphere receiver is less studied. We present an analytic function to calculate the intercept factor of the system with real sun brightness distribution and Gaussian distribution, the results indicate that the intercept factor is related to the rim angle of reflector and the ratio of receiver angle to the optical error when the optical error is larger than or equal to 5 mrad, but is related to the rim angle, receiver angle and optical error in less than 5 mrad optical error. Furthermore we propose a quick process to optimize the system to provide the maximum solar energy to net heat efficiency for different optical error under typical condition. The results indicate that the parabolic solar dish concentrator with sphere receiver has rather high solar energy to net heat efficiency which is 20% more than solar trough and tower system including higher cosine factor and lower heat loss of the receiver.     

A concentrator module of spherical Si solar cell

Spherical Si solar cell, which is made up of Si spheres with a diameter of approximately 1.0 mm, is expected to be a promising candidate for low consumption of Si feedstock and simple process technology. This paper describes the formation process and the structure of a concentrator module in detail. The concentrator lens was formed by casting with ultraviolet light hardening resin. The concentration ratio was 4.4 times and the pitch between the spheres was 2.0 mm. By this module design, it was possible to realize a consumption of the Si feedstock of about 3.0 g/W. Conversion efficiencies of 11.3% from single-sphere cell, 8.5% from a 23-spheres module and 5.2% from a 105-spheres module under AM1.5, 100 mW/cm² illumination were achieved.     

Multi-junction III–V solar cells: current status and future potential

Our recent R&D activities of III–V compound multi-junction (MJ) solar cells are presented. Conversion efficiency of InGaP/InGaAs/Ge has been improved up to 31–32% (AM1.5) as a result of technologies development such as double hetero-wide band-gap tunnel junction, InGaP–Ge hetero-face structure bottom cell, and precise lattice-matching of InGaAs middle cell to Ge substrate by adding indium into the conventional GaAs layer. For concentrator applications, grid structure has been designed in order to reduce the energy loss due to series resistance, and world-record efficiency InGaP/InGaAs/Ge 3-junction concentrator solar cell with an efficiency of 37.4% (AM1.5G, 200-suns) has been fabricated. In addition, we have also demonstrated high-efficiency and large-area (7000 cm²) concentrator InGaP/InGaAs/Ge 3-junction solar cell modules of an outdoor efficiency of 27% as a result of developing high-efficiency InGaP/InGaAs/Ge 3-junction cells, low optical loss Fresnel lens and homogenizers, and designing high thermal conductivity modules.Future prospects are also presented. We have proposed concentrator III–V compound MJ solar cells as the 3rd generation solar cells in addition to 1st generation crystalline Si solar cells and 2nd generation thin-film solar cells. We are now developing low-cost and high output power concentrator MJ solar cell modules with an output power of 400 W/m² for terrestrial applications.     

Exergetic analysis of solar concentrator aided natural gas fired combined cycle power plant

This article deals with comparative energy and exergetic analysis for evaluation of natural gas fired combined cycle power plant and solar concentrator aided (feed water heating and low pressure steam generation options) natural gas fired combined cycle power plant. Heat Transfer analysis of Linear Fresnel reflecting solar concentrator (LFRSC) is used to predict the effect of focal distance and width of reflector upon the reflecting surface area. Performance analysis of LFRSC with energetic and exergetic methods and the effect, of concentration ratio and inlet temperature of the fluid is carried out to determine, overall heat loss coefficient of the circular evacuated tube absorber at different receiver temperatures. An instantaneous increase in power generation capacity of about 10% is observed by substituting solar thermal energy for feed water heater and low pressure steam generation. It is observed that the utilization of solar energy for feed water heating and low pressure steam generation is more effective based on exergetic analysis rather than energetic analysis. Furthermore, for a solar aided feed water heating and low pressure steam generation, it is found that the land area requirement is 7 ha/MW for large scale solar thermal storage system to run the plant for 24 h.     

Performance model for two-stage optical concentrators for solar thermal applications

A performance model has been developed for evaluating benefits associated with the addition of a nonimaging secondary concentrator to a conventional paraboloidal solar dish. The model uses a Monte Carlo ray-trace procedure to determine the focal plane distribution as a function of optical parameters and, by evaluating the trade-off between thermal losses and optical gain, calculates the corresponding optimized concentration and thermal efficiency as a function of temperature, both with and without the secondary. These comparative optimizations, carried out over a wide range of design parameters, show that the efficiency of a two-stage concentrator is always greater than that of a single stage if all other design parameters are the same. For example, for a reference design corresponding to a dish with a focal length to diameter ratio of 0.6 and a characteristic slope error of 5 milliradians operated at a receiver temperature of 1000°C, the optimized efficiency with a secondary is 0.70 compared to 0.59 for the primary alone. At fixed focal ratio, the relative performance advantage with a secondary increases, if either the temperature or the primary slope error or both, are increased, whereas it decreases if they are decreased. However, the advantage remains significant at temperatures above 400°C, even in the “high performance limit” of slope errors <2 milliradians.     

Non-concentrating and asymmetric compound parabolic concentrating building façade integrated photovoltaics: An experimental comparison

Concentration of solar energy increases the illuminated flux on the photovoltaic (PV) surface thus less PV material is required. A novel asymmetric compound parabolic photovoltaic concentrator has been characterised experimentally with a similar non-concentrating system. Different numbers of PV strings connected within the system have been analysed and a power ratio of 1.62 measured compared to a similar non-concentrating PV panel with the same cell area. The solar to electrical conversion efficiency of 8.6% and 6.8% was achieved for the non-concentrating panel the concentrating system, respectively. The measured average solar cell temperature of the PV in the concentrator system was only 12 °C higher than that of the similar non-concentrating system with same cell area.