Solar Strings Research Articles

Studying the Impact of Shading on the Energy Characteristics of a Solar String

The current article presents an analysis of the impact of shading on the characteristics of a solar string, with and without the presence of bypass diodes. A solar string consisting of four solar modules was used for this purpose. Experiments were sequentially conducted by connecting one, two, and four bypass diodes. The study was conducted in laboratory conditions using an artificial light source while maintaining the cell temperature mode. The obtained results were analyzed concerning the volt-ampere characteristics, power characteristics, and the coefficient of performance of the photovoltaic string. All the obtained characteristics are compared with the characteristics of the non-shaded solar string.

Solar Photovoltaic Hotspot Inspection Using Unmanned Aerial Vehicle Thermal Images at a Solar Field in South India

The sun is an abundant source of energy, and solar energy has been at the forefront of the renewable energy sector for years. A way to convert it into electricity is by the use of solar cells. Multiple solar cells, connected to each other, create solar panels, which in their turn, are connected in a solar string, and they create solar farms. These structures are extremely efficient in electricity production, but also, cells are fragile in nature and delicate to environmental conditions, which is the reason why some of them show discrepancies and are called defective. In this research, a thermal camera mounted on a drone has been used for the first time in the solar farm operating conditions of India in order to capture images of the solar field and investigate solar panels for defective cells and create an orthomosaic image of the entire area. This procedure next year will be established on an international scale as a best practice example for commercialization, providing effortless photovoltaic monitoring and maintenance planning. For this process, an open source software WebODM has been used, and the entire field was digitized so as to identify the location of defective panels in the field. This software was the base in order to provide and analyze a digital twin of the studied area and the included photovoltaic panels. The defects on solar cells were identified with the use of thermal bands, which record and point out their temperature of them, whereas anomalies in the detected temperature in defective solar cells were captured using thermal electromagnetic waves, and these areas are mentioned as hotspots. In this research, a total number of 232.934 solar panels were identified, and 2481 defective solar panels were automatically indicated. The majority of the defects were due to manufacturing failure and normal aging, but also due to persistent shadowing and soiling from aerosols and especially dust transport, as well as from extreme weather conditions, including hail. The originality of this study relies on the application of the proposed under development technology to the specific conditions of India, including high photovoltaic panels wear rates due to extreme aerosol loads (India presents one of the highest aerosol levels worldwide) and the monsoon effects. The ability to autonomously monitor solar farms in such conditions has a strong energy and economic benefit for production management and for long-term optimization purposes.

Assembly cell for the manufacturing of flexible solar modules in building integrated photovoltaics

The current use of photovoltaics is often limited to the utilization of roof surfaces or ground-mounted systems. In particular, building integrated photovoltaics (BIPV) have enormous potential to make energy production more sustainable, because the energy is generated where it is used. However, most of these modules either do not meet the aesthetic requirements of the architects as well as the building owner or are uneconomical, since visually appealing building-integrated PV modules cost several times more than standard modules. In this article, an approach for a (semi) automated assembly line that allows geometry- and material-flexible manufacturing of PV modules is presented. The challenges in automating the flexible manufacturing processes include mainly the handling of limp components and the complexity of geometry variability. Appropriate gripper systems are required to ensure safe and reliable handling of the components. A gripper developed in this article offers the ability to flexibly deposit solar strings. Preliminary tests show that 66% of all conducted trials meet the accuracy requirements.

GRID-CONNECTED PV SYSTEM EMPLOYING THREE INVERTERS REGULATED BY SYNCHRONOUS SCHEME OF PWM

The paper presents comparative analysis of three versions of the modified scheme of space-vector-based synchronous pulsewidth modulation (PWM), applied for control of three two-level inverters of transformer-based photovoltaic (PV) system, and focused on providing of the symmetry of winding voltage of power transformer during the whole adjustment range. Power supply of inverters is providing by the corresponding three solar strings consisting of a set of PV panels, and the outputs of three inverters are connected specifically with inverter-side windings of multi-winding grid-tired transformer. Results of MATLAB-simulation prove the fact of advanced spectral composition of the winding voltage of triple-inverter-based PV installation regulated by algorithms of synchronous space-vector PWM, assuring potential reduction of losses in these systems. References 10, table 1, figures 9.

Grid and PV Fed Uninterruptible Induction Motor Drive Implementation and Measurements

Motors powered directly from solar panels are becoming more and more popular in pump applications. However, solar panels can be the source of operational issues due to varying irradiance, ambient temperature, weather. This paper shows how it is worth expanding a solar induction motor drive to provide an uninterrupted flow of electricity to the motor. In addition, the main components of the uninterruptible induction motor drive are presented, including the LLC (inductor-inductor-capacitor) converter, the three-phase inverter, and the three-phase rectifier. LLC converters that can increase the voltage from 25–40 V to 330 V cannot be bought directly from manufacturers. Therefore, a custom LLC converter was made for the research. It was necessary to build a custom converter to avoid the use of solar panel strings. This way, solar panels connected in parallel can be used. A low-voltage (25–40 V) supply was implemented from the solar side, while the induction motor requires 230 V AC three-phase voltage in delta connection. For this reason, a voltage boost is required from the low voltage side. The grid feeds the universal DC link through the three-phase rectifier. This allows the motor to consume varying amounts of electricity from the grid or the solar panel. The study also presents in detail the LLC converter that performs the voltage boost. Measuring the entire motor drive, switching transients and efficiencies can be observed at different input voltages for different supplies as well as loads.

Experimental study of static and dynamic behaviours of cracked PV panels

Solar cell power performance is greatly affected by two critical factors ageing and crack. In order to mitigate their negative effects on the solar system, these cells are to be substituted by new cells, thus, replacing the panels. This study presents an active crack detection method that detects the cracked cells within a solar string by using AC parameter characterisation without a need to have a physical inspection. The mathematical module of the solar cell shows that it constitutes of series and parallel resistors in addition to a parallel capacitor and that their values change by ageing and crack. In addition to studying the effects of the crack on the solar cell, it is verified by the experiment that the solar cells behave as a capacitive circuit, and their capacitance increases when the cell gets cracked, getting higher as the crack becomes more serious. The experiment is extended to investigate the effect of series and parallel PV strings, which are affected by cracked and partially shaded cells to evaluate their criticality levels. By monitoring the AC parameter of the solar cell and the change of the capacitance, it is easy to detect the crack when it occurs.

Experimental Comparison of Two-Level Full-SiC and Three-Level Si–SiC Quasi-Z-Source Inverters for PV Applications

The paper presents a comparative study of two solar string inverters based on the Quasi-Z-Source (QZS) network. The first solution comprises a full-SiC two-level QZS inverter, while the second design was built based on a three-level neutral-point-clamped QZS inverter with Silicon based Metal–Oxide–Semiconductor Field-Effect Transistors (Si MOSFETs). Several criteria were taken into consideration: the size of passive elements, thermal design and size of heatsinks, voltage stress across semiconductors, and efficiency investigation. The Photovoltaic (PV)-string rated at 1.8 kW power was selected as a case study system. The advantages and drawbacks of both solutions are presented along with conclusions.

Implementation of new high efficient input parallel output series partial power DC-DC converter for solar photovoltaic partial shading conditions

The proposed research suggests an improvised performance which is efficient and a reliable converter as a reasonable solar photo Voltaic (PV) approach. The proposed research helps in elevating the performance levels so that power extraction is maximized from the respective PV arrays specifically during the case of limited shading. In order to track the maximum amount of power from every solar PV string, connection of DC-DC converters is done amid the solar PV strings. By doing so, maximum power output can be ensured by the operation of each string irrespective of the occurrence of variation in the solar radiation amongst diverse strings. Usually, the DC-DC converter that would be employed for this purpose would process the string’s power completely. This Full Power Processing (FPP) architecture gives rise to extreme losses of conversion. Hence, the suggested work propound a Partial Power Processing (PPP) that processed a part of the total system power, while the rest of the power is straight away delivered to the output side, thus provides high conversion efficiency when compared to the existing DC-DC FPP converters. An input parallel output series structure having a novel Non-Isolated Partial Power Processing topology (NIPPP) is recommended and the operation’s details are elucidated depending on the operating principle. For the purpose of evaluating the performance of the converter, Matlab Simulink environmental platform are carried out. The closed loop prototype experimental approach is also carried out with the improvement of efficiency compared to conventional it appears in efficient manner.

Dynamic electro-thermal modeling of solar cells and modules

An accurate model describing the electro-thermal behavior of solar modules, subject to varying irradiance conditions, is presented. The model relies on an enhanced version of the popular one-diode model, implementing the temperature dependence of the parameters by means of a thermal feedback network. The feedback network is built by exploiting a very effective analytical approach which reduces computational efforts and allows an automated solution. The cell-level discretization allows the description of the temperature distribution over solar cell surfaces in panels subject to mismatch events (e.g., partial shading, localized soiling, etc.), along with its time evolution. Experiments performed on a partially shaded solar string evidence good agreement with the model. In uniform condition the temperature error is less than 3 °C, while, under mismatch, the error on the maximum temperature of a cell subject to hot spot is limited to 5 °C.

A wireless metering and monitoring system for solar string inverters

The design and implementation studies of a real time monitoring and smart metering system are presented in this study. The proposed design is improved in terms of smart metering infrastructure based on current, voltage, and power measurements. The communication among the string inverter and host PC is performed by the designed ZigBee transceiver system. Sensing circuits are the most significant devices for measuring both current and voltage magnitudes of the systems. The measured data are processed by the microcontroller unit (MCU) and are modulated after signal processing operations for serial communication. Although the transceiver is configured to execute bi-directional communication, unidirectional data flow is performed where the smart metering system transmits data to monitoring substructure. The monitoring software is also implemented in the context of the presented study. The Visual Studio software development kit is used to design and to code the software by using C#. The performed experimental studies showed that the proposed real time monitoring and smart metering system could be exploited to monitor current, voltage and power magnitudes of the string inverters in an efficient way.

Mismatch Based Diagnosis of PV Fields Relying on Monitored String Currents

This paper presents a DC side oriented diagnostic method for photovoltaic fields which operates on string currents previously supplied by an appropriate monitoring system. The relevance of the work relies on the definition of an effective and reliable day-by-day target for the power that every string of the field should have produced. The procedure is carried out by comparing the instantaneous power produced by all solar strings having the same orientation and by attributing, as producible power for all of them, the maximum value. As figure of merit, the difference between the maximum allowed energy production (evaluated as the integral of the power during a defined time interval) and the energy actually produced by the strings is defined. Such a definition accounts for both weather and irradiance conditions, without needing additional sensors. The reliability of the approach was experimentally verified by analyzing the performance of two medium size solar fields that were monitored over a period of four years. Results allowed quantifying energy losses attributable to underperforming solar strings and precisely locating their position in the field.

Photovoltaic and Micro-Hydroelectric Proposed Plant for Stand Alone Electric Generation in a Sixty-Floor Skyscraper (P60)

Abstract: The aim of this paper is the feasibility study of a micro-hydroelectric (Pelton turbine with a rated power lower than 50 kW) and a Photovoltaic plant integrated in a sixty floor skyscraper. In this proposal, the hydraulic plant is located in the foundation and it is designed to use the greywater from each apartment; the photovoltaic system is on the top of the building, to take advantage of the height and the wind. A multi-tank configuration has been analyzed, its periodical emptying, fixes and regulate the turbine working cycles, guaranteeing a steady power generation; at the bottom of this turbine, a high efficient ultra-filtration plant has been designed. The purified water is now ready to be pumped back to the users and used again. On the roof, there are 28 solar strings, each one of 25 serial panels made, facing south and installed at a tilt angle of 35°. The total power is 165 kW p .

Efficient and Reliable Solar Panels for Small CubeSat Picosatellites

CubeSat picosatellites have a limited area of walls for solar cells assembling and the available area has to be effectively shared with other parts, such as planar antennas, optical sensors, camera lens, and access port. With standard size of solar cell strings, it is not possible to construct a reliable solar panel for CubeSat with redundant strings interconnection. Typical solar panels for CubeSat consist of two solar cell strings serially wired with no redundancy in case of solar string failure. The loss of electric energy from one solar panel can cause a serious problem for most picosatellites due to minimum margin in the blueprints of the picosatellite subsystem power budget. In this paper, we propose a new architecture of solar panels for PilsenCUBE CubeSat with a high level of redundancy in the case of solar string failure or following switched power regulator failure. Our solar panels use a high efficiency triple junction GaInP2/GaAs/Ge in the form of small triangle strings from the Spectrolab Company. A suitable technology for precise solar cell assembling is also discussed, because CubeSat picosatellites are usually developed by small teams with limited access to high-end facilities.

Performance of low series-resistance interconnections on the polycrystalline solar cells

The performance of four ribbons of lead SnAgPb (SAP) and lead-free SnAgCu (SAC) photovoltaic (PV) ribbons in patterned (pat-) and high-conductivity (con-) types soldered on silicon solar cells are investigated by electron characteristics and microstructure analyses. The electrical performances of the solar strings were characterized before and after the soldering process by a solar flasher, and strings with commercial ribbons of lead and lead-free are compared. In general, lead ribbon solar strings show lower power loss value than lead-free counterparts. And the commercial lead and lead-free ribbon strings show highest power loss around 6.66%–10.65% of all the solar strings. Furthermore, the power losses for patterned lead (pat-SAP) and lead-free (pat-SAC) solar string are 3.93% and 5.51%, respectively, implying that a patterned structure should improve the soldering process and result in lower power loss. Yet, significant low output power loss values are detected in the solar strings which are soldered with high-conductivity ribbons. It is estimated that the power loss for high-conductivity lead (con-SAP) and lead-free (con-SAC) solar strings are 3.89% and 4.43%, respectively. And a similar condition was revealed when the solder materials were practically interconnected the solar cells in PV modules. According to the microstructure analyses, the low power loss of con-SAP solar string should be due to the good electrical performance in low series resistance ( R s) and high shunt resistance ( R sh), thus resulting in a high fill factor of the solar device.

Thermal Control Schemes for a Micro-Satellite with All-Active and Selectively Active Solar String Designs

In this study, a finite element model of a micro-satellite named X-SAT was developed to perform heat transfer analysis and design a passive thermal control scheme in the form of thermal coatings, film, and paints. To start with, the modeling philosophy and computational methodology were introduced along with the suitable assumptions made. A typical thermal control scheme was proposed and implemented using SINDA/G-NEVADA software. The sensitivity of the results to the software settings was then assessed. It was observed that the limits on the ray counts for Monte Carlo simulation in RENO and VEGAS routines play a vital role in deciding reliability of the results, especially the temperature gradients within solar panels. Subsequently, two types of solar panel designs, one with all-active solar strings and other with selectively active solar strings, were examined. When the panels with all-active type of solar cell strings were adopted, heat dissipation through shunt regulators posed a challenge for thermal control. Various scenarios for the second case with high-efficiency, selectively operable solar strings were also simulated. For both case studies, a sun-tracking mode and an overhead pass-imaging operation were considered for the worst hot and cold cases. The results showed that the switchable string design was preferable in terms of operational flexibility and thermal control.