String Of Photovoltaic Modules Research Articles

Mono-axis vs Bi-axis Tracking for a String of Photovoltaic Modules

This paper presents a comparative study of motion laws applied to a mono-axis string of photovoltaic modules and to a bi-axis system. This study will reveal which system is more efficient (inclusive economically) in the geographical area of Braşov and under which conditions. There are two types of tracking systems: mono-axis and bi-axis, the last being split into other three types of tracking systems according to their rotation axis. First the solar angles and direct solar radiation are computed and graphically modeled. Further the optimum elevation and daily angles are determined. For each interval both tracking efficiencies are calculated and then compared. Also, the yearly tracking efficiencies of mono-axis and bi-axis systems are compared. Taking into account the technical and economical aspects, beside the energy gain of the dual-axis tracking system, it was concluded that a mono-axis system is preferred for the studied geographical area.

Innovative bi-axial tracking mechanism for PV modules

The paper deals with an innovative bi-axial tracking mechanism for a group of photovoltaic (PV) modules, which combines the features of the classical platform and string configurations. For the daily movement (corresponding to the primary axis), the sun tracking is performed as in the case of a PV platform, while the elevation movement (around the secondary axis, which is referenced to the primary one) is transmitted similar to the case of a string of PV modules. The sun tracking is conducted by an open-loop control strategy, based on a predefined step-by-step algorithm, which was designed so that to capture as much as possible incident solar radiation with a minimum energy consumption for achieving the orientation. The modeling, simulation and optimization of the solar tracker is performed by using the virtual prototyping package ADAMS.

Power dissipation analysis of PV module under partial shading

Photovoltaic (PV) generation has been growing dramatically over the last years and it ranges from small, rooftop-mounted or building integrated systems, to large utility scale power stations. Especially for rooftop-mounted PV system, PV modules are serially connected to match with PV inverter input voltage specification. For serially connected PV system, shading is a problem since the shaded PV module reduces the output whole string of PV modules. The excess power from the unshaded PV module is dissipated in the shaded PV module. In this paper, power dissipation of PV module under partial shading is analyzed with circuit analysis for series connected PV modules. The specific current and voltage operating point of the shaded PV module are analyzed under shading. PSIM simulation tool is used to verify the power dissipation analysis. When there is no bypass diode and three solar modules are connected in series, upto 39.1% of the total maximum PV power is dissipated in the shaded PV module. On the other hand, when the bypass is attached, 0.3% of the total maximum power is generated as a loss in the shaded PV module. The proposed analysis technique of shaded PV module could be used in PV system performance analysis, especially for maximum power point tracking (MPPT) performance.

Signal Propagation Through Piecewise Transmission Lines for Interpretation of Reflectometry in Photovoltaic Systems

We present a framework for analyzing electromagnetic signal propagation through piecewise-defined transmission lines with arbitrary, series-connected impedances. While the formulation is general and scalable, we apply it here to propagation through a photovoltaic module with cables on either side acting, with a home run cable, as a section of an inhomogeneous transmission line. Understanding propagation through this unit of a series-connected string of photovoltaic modules is necessary to enable the use of time-domain reflectometry techniques for monitoring the status of individual components in series-connected strings within large photovoltaic arrays.

Are Nano-Composite Coatings the Key for Photovoltaic Panel Self-Maintenance: An Experimental Evaluation

This article shows the influence of an anti-fouling nano-coating on the electrical energy produced by a string of photovoltaic modules. The coating effect was evaluated comparing the energy produced by two strings of the same PV power plant: one of them was cleaned and the other was cleaned and treated with the coating before the monitoring campaign. The PV plant is located in Modena, north of Italy. A first monitoring campaign of nine days after the treatment shows that the treatment increases the energy production on the PV arrays by about 1.82%. Results indicate that the increase is higher during sunny days with respect to cloudy days. A second monitoring campaign of the same length, but five months later, shows that the energy gain decreases from 1.82% to 0.69% due to the aging of the coating, which is guaranteed for one year by the manufacturer. A technical-economical analysis demonstrates that at the moment the yearly economic gain is 0.43 € per square meter of panel and the cost of the treatment is about 1 € per square meter. However, large scale diffusion can reduce the production cost and thus increase the affordability of the coating.

Investigation and modeling of long-term mismatch loss of photovoltaic array

Abstract Many studies have been conducted to analyze and reduce mismatch loss (MML) in photovoltaic array. They have concluded that MML is typically less than 1% at installation and the economic loss is insignificant. In this study, long-term MML effect on photovoltaic array is explored quantitatively. An outdoor test has been conducted to verify that MML is increasing over time for a string of photovoltaic modules. The electrical parameters of the modules in the string are measured at the standard test condition (STC) before installation and after the exposure of 5.5 years. MML is estimated and compared for the data by two approaches; using a stochastic model and string simulating by a SPICE program. It is confirmed from the two methods that MML increases over time. Long-term MML model is developed based on the test data and several results from previous studies. The model expected that the MML keeps increasing over time and is substantial to the output of a solar power plant. The study reveals that MML could be a detrimental factor to the long-term maintenance of solar power plant.

An Integrated Control Algorithm for a Single-Stage PV Pumping System Using an Open-End Winding Induction Motor

In this paper, a single-stage solution for solar photovoltaic (PV) pumping system using a dual-inverter fed open-end winding induction motor drive is presented. The three-level dual-inverter requires a low PV bus voltage compared with its conventional three-level counterpart. This could avoid large string of PV modules and helps in reducing the voltage rating of the capacitors and semiconductor devices used in the system. This may further help in reduction of cost of the system. The proposed single-stage system is operated using an integrated control algorithm, which includes the maximum power point tracking (MPPT), the $V/f$ control, and the sample-averaged zero-sequence elimination (SAZE) pulsewidth modulation (PWM) technique. While the MPPT algorithm ensures the extraction of maximum power from the PV source, the $V/f$ control improves the motor pump performance. Furthermore, the zero-sequence current is avoided by the SAZE PWM algorithm. Thus, the integrated control algorithm improves the overall performance of the system. Furthermore, this paper also presents the details of system design and analysis of its dynamic behavior during transient environmental conditions. The performance of the system is verified using MATLAB simulation and hardware prototype.

Implementation of a High Efficiency Grid-Tied Multi-Level Photovoltaic Power Conditioning System Using Phase Shifted H-Bridge Modules

This paper proposes a high efficiency three-phase cascaded phase shifted H-bridge multi-level inverter without DC/DC converters for grid-tied multi string photovoltaic (PV) applications. The cascaded H-bridge topology is suitable for PV applications since each PV module can act as a separate DC source for each cascaded H-bridge module. The proposed phase shifted H-bridge multi-level topology offers advantages such as operation at a lower switching frequency and a lower current ripple when compared to conventional two level topologies. It is also shown that low ripple sinusoidal current waveforms are generated with a unity power factor. The control algorithm permits the independent control of each DC link voltage with a maximum power point for each string of PV modules. The use of the controller area network (CAN) communication protocol for H-bridge multi-level inverters, along with localized PWM generation and PV voltage regulation are implemented. It is also shown that the expansion and modularization capabilities of the H-bridge modules are improved since the individual inverter modules operate more independently. The proposed topology is implemented for a three phase 240kW multi-level PV power conditioning system (PCS) which has 40kW H-bridge modules. The experimental results show that the proposed topology has good performance.

Designing the Tracking System for a String of Photovoltaic Modules

This paper presents the virtual prototype of the mono-axis tracking system used for improving the efficiency of a string of photovoltaic modules. The solar tracker simultaneously changes the daily position of the modules, using a linear actuator that drives a rack-pinion mechanism. The key in optimizing the tracking system is to maximize the received solar radiation and to minimize the energy consumption for tracking. The virtual prototype is developed using a digital platform which integrates the following software solutions: CATIA - for the solid modeling of the components, ADAMS - for developing the mechanical model in MBS (Multi-Body Systems) concept, and MATLAB/Simulink - for the control system design.

Control of a Single-Phase Cascaded H-Bridge Multilevel Inverter for Grid-Connected Photovoltaic Systems

This paper presents a single-phase cascaded H-bridge converter for a grid-connected photovoltaic (PV) application. The multilevel topology consists of several H-bridge cells connected in series, each one connected to a string of PV modules. The adopted control scheme permits the independent control of each dc-link voltage, enabling, in this way, the tracking of the maximum power point for each string of PV panels. Additionally, low-ripple sinusoidal-current waveforms are generated with almost unity power factor. The topology offers other advantages such as the operation at lower switching frequency or lower current ripple compared to standard two-level topologies. Simulation and experimental results are presented for different operating conditions.