• Energy Research

Concentrator solar cells need to be designed optimally depending on the concentrating photovoltaic (CPV) system, application and operating conditions to ensure the best system performance. The important factors while designing include concentration ratio, cell material properties, expected operating temperature, cell shape, bus bar configuration, number of fingers their size and spacing. The irradiation incident on the solar cell while being concentrated experiences several losses caused by the different physical phenomena's occurring in the system. A particular issue for CPV technology is the non-uniformity of the incident flux on the solar cell which tends to cause hot spots, current mismatch and reduce the overall efficiency of the system. Understanding of this effect and designing the cell while considering these issues, would help in improving the overall performance of the system. This study focuses on modelling a low concentrating photovoltaic system used for building integration, optimising the cell metallisation and analysing the effects of temperature on the overall output of the system. The optical analysis of the concentrator is carried out using ray tracing and finite element methods to determine electrical and thermal performance under operating conditions. Furthermore, an analysis is made to understand the effects of non-uniformity on the output of the device. About 0.5% absolute drop in solar cell efficiency was observed due to non-uniformity at 5o incident angle. A relative drop of 1.85% was observed in the fill factor due to non-uniformity of the flux distribution. A maximum cell temperature of 349.5 K was observed across the cell in both uniform and non-uniform conditions under an incident solar radiation of 1000 W/m2 which further reduced the performance of the solar cell. The solar cell design was also analysed by varying the number of fingers and the optimum grid design reported. A small prototype concentrator based on the design proposed was made using polyurethane and tested experimentally with the optimized solar cell design. On comparing the results obtained using the experimental data a good agreement in the system output could be seen. The difference in the overall system output was seen to be of the order of 11% which could be due to several losses occurring in the prototype which were not accounted in the model. © 2013 Published by Elsevier B.V. All rights reserved.

Abstract The low concentrating photovoltaic system can be a promising choice for building integration by eliminating tracking and active cooling. This paper reports the performance analysis of a low concentrating dielectric compound parabolic concentrator designed for building facades integration in northern latitudes (>55°). The range of the acceptance angles for the designed dielectric concentrator is 0–55°, having a concentration ratio (CR) of 2.8. The concentrator is manufactured in clear polyurethane using a casting process. The average AM1.5G spectrum weighted transmittance, within spectral range 300–1100 nm, of the 16.4 mm thick polyurethane concentrator is found to be 81.9%. The performance of the designed concentrator is analysed using small prototype modules with 8 solar cells in series (1.89 W p ), under a solar simulator for different incidence angles. The optical losses that occur within the concentrator-encapsulation interface and cover glass have been reduced for better performance. The indoor characterisation of the concentrating photovoltaic (CPV) module results in a maximum power ratio of 2.27 when compared to a similar non-concentrating counterpart, for 1000 W/m 2 light energy incident at 20°. The maximum experimental optical efficiency of the CPV system is found to be 80.5%; this result gives the electrical conversion efficiency of the CPV module to be an average of 9.43% with a maximum 12.1% within the range of acceptance angle of the designed concentrator. It is observed that that the power ratio decreases near the acceptance half-angles of the designed concentrator due to the optical losses caused by scattering and escaping of light from the edge of the receiver. Investigation of the optical losses from the parabolic sides of the concentrator shows that, the imperfect parabolic surface caused by machining error results in scattering with a fraction of light escaping from the parabolic side instead of reflecting back to the receiver for all angles of incidence. Cost analysis shows that the designed CPV modules can result in a 20% reduction in the cost per unit power output of the system in the current market scenario.

Concentrating photovoltaic (CPV) is a solution that is gaining attention worldwide as a potential global player in the future energy market. Despite the impressive development in terms of CPV cell efficiency recorded in the last few years, a lack of information on the module's manufacturing is still registered among the documents available in literature. This work describes the challenges faced to fabricate a densely packed cell assembly for 500× CPV applications. The reasons behind the choice of components, materials, and processes are highlighted, and all the solutions applied to overtake the problems experienced after the prototype's production are reported. This article explains all the stages required to achieve a successful fabrication, proven by the results of quality tests and experimental investigations conducted on the prototype. The reliability of the components and the interconnectors is successfully assessed through standard mechanical destructive tests, and an indoor characterization is conducted to investigate the electrical performance. The fabricated cell assembly shows a fill factor as high as 84%, which proves the low series resistance and the lack of mismatches. The outputs are compared with those of commercial assemblies. A cost breakdown is reported and commented: a cost of $0.79/Wp has been required to fabricate each of the cell assembly described in this paper. This value has been found to be positively affected by the economy of scale: a larger number of assemblies produced would have reduced it by 17%.

The low concentrating photovoltaic (PV) system such as a 2× V-trough system can be a promising choice for enhancing the power output from conventional PV panels with the inclusion of thermal management. This system is more attractive when the reflectors are retrofitted to the stationary PV panels installed in a high aspect ratio in the north-south direction and are tracked 12 times a year manually according to preset angles, thus eliminating the need of diurnal expensive tracking. In the present analysis, a V-trough system facing exactly the south direction is considered, where the tilt angle of the PV panels' row is kept constant at 18.34°. The system is installed on the terrace of CSIR-Central Salt and Marine Chemicals Research Institute in Bhavnagar, Gujarat, India (21.47 N, 71.15 E). The dimension of the entire PV system is 9.64 m×0.55 m. The V-troughs made of anodized aluminum reflectors (70% specular reflectivity) had the same dimensions. An in-house developed; experimentally validated Monte Carlo ray-trace model was used to study the effect of the angular variation of the reflectors throughout a year for the present assembly. Results of the ray trace for the optimized angles showed the maximum simulated optical efficiency to be 85.9%. The spatial distribution of solar intensity over the 0.55 m dimension of the PV panel due to the V-trough reflectors was also studied for the optimized days in periods that included solstices and equinoxes. The measured solar intensity profiles with and without the V-trough system were used to calculate the actual optical efficiencies for several sunny days in the year, and results were validated with the simulated efficiencies within an average error limit of 10%.

Soiling significantly impacts PV systems’ performance, but this can be mitigated through optimized frequency and timing of cleaning. This experimental study focused on the conditions leading to soiling. It utilized a novel method to evaluate the effectiveness of different cleaning frequencies. The transmittance of horizontally mounted glass coupons exposed outdoors in a warm and humid location was measured weekly and these measurements were used (i) to evaluate the variability of soiling and its seasonal correlations with environmental factors using linear regression models and (ii) to assess the effectiveness of the different cleaning cycles using statistical (F- and t-test) analysis. The minimum transmittance loss occurred during the season with the most frequent rainfall, which acted as the dominant natural cleaning agent. The experimental campaign showed that rainfalls do not completely clean soiling; a minimum intensity threshold has to be achieved to have a cleaning effect. The threshold rainfall was the highest for the weekly cleaned glass coupon and lowest for a coupon that was never cleaned. Based on the statistical analysis, it is suggested that weekly cleanings during winter and post-monsoon seasons and monthly cleanings during pre-monsoon and southwest monsoon seasons are optimal for areas in the Köppen–Geiger Cwa climate classification category. The correlation between soiling and environmental parameters was found to be highly dependent on the season. It may therefore not be possible to develop a simple, universal predictive relationship for soiling losses. The presented methodology is applicable to additional locations, even outside of the study area of India, to contribute to the understanding and mitigation of soiling.

The present work aimed to design, develop, and validate a soiling chamber to reproduce the deterioration of PV module efficiency due to dust deposition. Two locations with different soiling accumulation characteristics are chosen to validate the chamber under various atmospheric conditions and assess its accuracy. Specifically, the chamber results are compared with the performance of PV modules mounted in two outdoor conditions for one year. In addition, dust samples from the two locations were analysed using a scanning electron microscope (SEM) to ascertain the elemental compositions to comprehend the behaviour of dust deposition or variations in deposition patterns at the two locations. The newly constructed soiling chamber emulates soiling in a controlled environment based on historical data of rainfall, temperature, humidity, wind speed, and particulate concentration, considering also the changing seasons and conditions. The deposition density emulated in the soiling chamber is similar to that on the outside exposed samples, with a maximum variation in dust deposition of only 0.08 g/m2. Furthermore, an emulated module’s mean dust density is 2.367 g/m2, with a standard deviation of just 0.002 g/m2. This controlled indoor soiling chamber can emulate a long-term outdoor soil cycle in a few hours for any geographical location.

AbstractA novel densely packed receiver for concentrating photovoltaics has been designed to fit a 125× primary and a 4× secondary reflective optics. It can allocate 161cm2-sized high concentrating solar cells and is expected to work at about 300 Wp, with a short-circuit current of 6.6 A and an open circuit voltage of 50.72V. In the light of a preliminary thermal simulation, an aluminum-based insulated metal substrate has been use as baseplate. The original outline of the conductive copper layer has been developed to minimize the Joule losses, by reducing the number of interconnections between the cells in series. Slightly oversized Schottky diodes have been applied for bypassing purposes and the whole design fits the IPC-2221 requirements. A full- scale thermal simulation has been implemented to prove the reliability of an insulated metal substrate in CPV application, even if compared to the widely-used direct bonded copper board. The Joule heating phenomenon has been analytically calculated first, to understand the effect on the electrical power output, and then simulate, to predict the consequences on the thermal management of the board. The outcomes of the present research will be used to optimize the design of a novel actively cooled 144-cell receiver for high concentrating photovoltaic applications.