Grid-connected Photovoltaic Power Plants Research Articles

High-Penetration Grid-Tied Photovoltaics: Analysis of Power Quality and Feeder Voltage Profile

More People are Turning to Photovoltaic (PV) technology to supply energy needs as concerns rise about greenhouse gases. Thus, installed PV capacity across the smart grid distribution systems has been rising. However, the high penetration of PVs could affect the operation and planning of distribution networks. To evaluate the impact of PVs connected to the grid, a case study on power quality and voltage profile was conducted using a 1.1-MW ac gridconnected PV power plant in Miami, Florida. As part of the power quality analysis, total harmonic distortion (THD) was explored, and high-power and high-energy ramp rate analyses were made.

Voltage Sag Detection in Grid-Connected Photovoltaic Power Plant for Low Voltage Ride-Through Control

Background: Due to the high level of photovoltaic power plants (PVPPs) penetration into power grids, disconnections of these plants during faults are no longer possible as it may cause problems concerning stability, quality, and operation of the power system. Therefore, new grid codes have been established with low voltage ride-through (LVRT) capability standard requirements for grid-connected PVPPs that should be met. Therefore, for an efficient LVRT control, the fast and precise sag detection strategy is essential for the system to switch from normal operation to LVRT mode of operation. Methods: For this purpose, this paper presents a two automatic fault detection methods which are RMS-based (d-q) components of grid voltage and positive sequence voltage. These methods were utilized to determine the beginning and end of a voltage sag and to determine the sag depth to regulate the required reactive current that should be injected according to the LVRT standard requirements. The operating method depends on calculating present grid voltage under faults to the nominal voltage that identifies the sags’ depth and therefore inject the required amount of reactive power accordingly. Also, a comparison between the two proposed methods regarding response speed and accuracy was made. The effectiveness of these detection strategies is that it can be integrated into the voltage source inverter (VSI) without utilizing additional external hardware or software programming. Results: The simulation results demonstrated a good precision and how straightforward the proposed methods’ usage is, proving that the RMS method is faster and more accurate than positive sequence method. Conclusion: In conclusion, it was found that RMS detection algorithm is preferred for a more accurate and efficient LVRT control.

Technical challenges for the optimum penetration of grid-connected photovoltaic systems: Spain as a case study

This research reviews the technical requirements of grid-connected photovoltaic power plants to increase their competitiveness and efficiently integrate into the grid to satisfy future demand requirements and grid management challenges, focusing on Spain as a case study. The integration of distributed resources into the electric network, in particular photovoltaic energy, requires an accurate control of the system. The integration of photovoltaic energy has resulted in significant changes to the regulatory framework to ensure proper integration of distributed generation units in the grid. In this study, the requirements of the system operator for the management and smart control are first analysed and then the technical specifications established by the network operator in reference to the components of the facility are evaluated. This analysis identifies the shortcomings of the current legislation and concludes with a summary of the main technical recommendations and future regulatory challenges that need to be undertaken in the future. It is presented as a reference case that can be adapted worldwide.

Performance and Economic Assessment of a Grid-Connected Photovoltaic Power Plant with a Storage System: A Comparison between the North and the South of Italy

Grid-connected low voltage photovoltaic power plants cover most of the power capacity installed in Italy. They offer an important contribution to the power demand of the utilities connected but, due to the nature of the solar resource, the night-time consumption can be satisfied only withdrawing the energy by the national grid, at the price of the energy distributor. Thanks to the improvement of storage technologies, the installation of a system of battery looks like a promising solution by giving the possibility to increase auto-consumption dramatically. In this paper, a model-based approach to analyze and discuss the performance and the economic feasibility of grid-connected domestic photovoltaic power plants with a storage system is presented. Using as input to the model the historical series (2008–2017) of the main ambient variables, the proposed model, based on Stochastic Hybrid Fault Tree Automaton, allowed us to simulate and compare two alternative technical solutions characterized by different environmental conditions, in the north and in the south of Italy. The performances of these systems were compared and an economic analysis, addressing the convenience of the storage systems was carried out, considering the characteristic useful-life time, 20 years, of a photovoltaic power plant. To this end the Net Present Value and the payback time were evaluated, considering the main characteristics of the Italian market scenario.

Performance evaluation of 830 kWp grid-connected photovoltaic power plant at Kamuzu International Airport-Malawi

The paper presents performance evaluation for 830 kWp grid-connected PV power plant at Kamuzu International Airport in Malawi. The study used both measured and simulated data for the period September 2013 to August 2017. The PV array comprises 3540 solar modules of Heterojunction with Intrinsic Thin-layer (HIT) technology; each module was rated 235 Wp and tilted at 30°. The annual four-year average array, inverter and overall system efficiencies were 15.3%, 95.2% and 14.6%, respectively. An average annual capacity factor of 17.7% was obtained and the annual four-year average performance ratio was 79.5%. The results from this study are compared with those of representative PV power plants reported elsewhere.

A Multi-Mode Flexible Power Point Tracking Algorithm for Photovoltaic Power Plants

Flexible power point tracking (FPPT) is the control of active power generated by grid-connected photovoltaic power plants (GCPVPPs) to provide grid-support functionality. An FPPT algorithm for the reduction of the extracted power from photovoltaic (PV) strings during voltage sags was previously proposed by the authors. An advantage of this algorithm, compared to conventional FPPT algorithms, was its fast dynamics facilitated by use of a simple PI controller that dynamically modifies the PV voltage reference. The previously proposed scheme could only be employed for the short duration in which the power system experiences a voltage sag. A novel modification to this algorithm with multi-mode operation is introduced in this letter, which provides FPPT capability for continuous operation of GCPVPPs. Unlike the previous algorithm, which was able to only move the operation point to the right-hand side of MPP, the proposed algorithm in this letter is able to move the operation point to both right- and left-hand sides of the MPP that provides the flexibility to operate in the optimum operation region for both single- and two-stage GCPVPPs. Experimental results are provided to demonstrate the performance of the proposed algorithm under dynamic irradiance conditions.

Sensitivity analysis, adaptability improvement and control of grid-connected photovoltaic power plants under grid frequency variations

Photovoltaic power plants are obliged to maintain power quality standards when interconnected to the grid based on the grid codes (GCs). Variations in grid frequency can be one of the main sources of harmonic distortions in a generated currents of a grid-connected photovoltaic power plant (GCPPP) as long as it is incorporated with frequency-dependant controllers such as resonant controllers in the current control loops. In fact, either the controller itself or the reference currents can contribute to the harmonic components of the generated currents. Current references in turn may become distorted due to outer voltage controller or inaccurate phase angle detection by phase-locked-loop (PLL) technique. In this paper, a comprehensive analysis of a 3-phase GCPPP under grid frequency variations is performed with the focus on associated frequency-dependant controllers i.e. current controller and filtered-sequence PLL (FSPLL). The resonant controllers are selected in this study which have the capability to attenuate generated odd-order harmonics but their performance under frequency variations need to be investigated for both ideal and non-ideal controller types. FSPLL is an effective PLL, however its performance is highly dependent to the grid frequency which requires more research regarding frequency sensitivity. Afterwards, FSPLL is developed further to detect the instantaneous grid frequency to enhance the GCPPP performance. Finally, the GCPPP is equipped with an active power controller to contribute to the frequency control of the power system. Presented results within MATLAB/Simulink environment verify the enhanced capability of the GCPPP with frequency detector/controller satisfying GCs.

Development and sizing of a grid-connected solar PV power plant for Canaanland community

Development and sizing of a grid-connected solar PV power plant for Canaanland community

Development and sizing of a grid-connected solar PV power plant for Canaanland community

High costs of installation and maintenance as a result of storage units discourage the use of solar Photovoltaic system for power generation. To reduce these costs, Solar PV systems can be installed without storage units alongside conventional power generation systems. Such that the Solar systems cater for the daytime loads while the conventional generation system caters for loads at other times. This research paper explored the potential of installing Stand-Alone solar PV systems without storage to satisfy the daytime load demand of the Canaanland community. The load profile analysis of the Canaanland community was carried out from load consumption data and the solar power plants were designed based on this analysis. Simulation was carried out using the PV Syst 6.43 software and the result from the design was analyzed. The study revealed that the solar power plant will serve the daytime load of the community during the period of 10:30am-4:30pm daily satisfying the peak and base loads (5.16MW and 0.78MW) of the Canaanland community respectively.

An Adaptive Control Scheme for Flexible Power Point Tracking in Photovoltaic Systems

One of the major concerns associated with the increasing penetration of grid-connected photovoltaic (PV) power plants is the operational challenges (e.g., overloading and overvoltage), imposed due to the variability of PV power generation. A flexible power point tracking (FPPT), which can limit the PV output power to a specific value, has thus been defined in grid-connection regulations to tackle some of the integration challenging issues. However, the conventional FPPT algorithm based on the perturb and observe method suffers from slow dynamics. In this paper, an adaptive FPPT algorithm is thus proposed, which features fast dynamics under rapidly changing environmental conditions (e.g., due to passing clouds), while maintaining low power oscillations in steady state. The proposed algorithm employs an extra measured sampling at each perturbation to observe the change in the operating condition (e.g., solar irradiance). Afterwards, the voltage-step is adaptively calculated following the observed condition (e.g., transient or steady state) in a way to improve the tracking performance. Experimental results on a 3-kVA grid-connected single-phase PV system validate the effectiveness of the proposed algorithm in terms of fast dynamics and high accuracy under various operational conditions.

Economic and Environmental Feasibility of Constructing a Grid-Connected Sun-Tracking PV Power Plant in Iraq

Feasibility assessment of constructing a 10 MW sun-tracking PV power plant in Iraq from an economic and environmental perspective has been analysed. A type of PV panel having desirable specific properties according to the international standards has been selected and used. Three PV-panel installation systems, namely: fixed-tilt, single-axis, and dual-axis tracking systems have been tested. Al-Anbar city (33.26°N, 40.31°E) west of Iraq has been selected for constructing the proposed power plant. The study mainly concerns the assessment of the annual and cumulative revenues rising from the proposed PV power plant. Evaluation of other economic parameters including the levelized cost of energy (LCOE), cash flow over the power plant lifecycle, and net present value (NPV) also have been achieved and revealed. The analysis demonstrates that the selected region is very promising for solar PV investment in electric power production. Moreover, incorporation of a dual-axis tracking system substantially enhances the economic feasibility of the project. The environmental benefits relating to the reduction of greenhouse gas (GHG) emissions have been confirmed in all the PV-panel installation modes considered in this study.

Economic assessment of renewable power generation based on wind speed and solar radiation in urban regions

Economic evaluation of 12 MW grid-connected wind farms and PV power plants in two regions in Northern Cyprus for electricity generation was investigated. The wind speed, sunshine duration, and solar global radiation characteristics were analyzed using monthly data collected over 17 years (2000-2016) for Girne and nine years (2008-2016) for Lefkosa, which were measured at various heights. The result showed that during 2000-2016, the mean wind speed at Girne was 2.505 m/s and during 2008-2016, the mean wind speed at Lefkosa was 2.536 m/s. The result showed that both regions had annual mean wind speed greater than 2 m/s at 10 m height. Moreover, the annual mean sunshine duration and global solar radiation were higher than seven h/day and 15 MJ./m2/day at a height of 2 m for all studied regions, respectively. In this study, eight distribution functions were used to analyze the wind speeds and global solar radiation data in each region. The results indicated that Weibull and Logistic were the best distributions for analyzing the wind speeds and global solar radiation data of the studied regions, respectively. Furthermore, the capacity factors of the selected regions ranged between 1.92% and 48.53%. Based on the renewable energy cost results, it is found that the generation costs of the wind farm were between 0.023 and 0.04 Euro/kWh, while the PV plant was between 0.08 and 0.098 Euro/kWh.

Flexible Control of Photovoltaic Grid-Connected Cascaded H-Bridge Converters During Unbalanced Voltage Sags

Multilevel cascade H-bridge (CHB) converters are one of the promising solutions for medium- and large-scale grid-connected photovoltaic power plants. However, there is a lack of a complete study about their operation during voltage sags. This paper proposes a flexible control strategy for the operation of photovoltaic grid-connected CHB inverters during unbalanced voltage sags. The key novelty is that the proposed strategy is able to inject both active and reactive powers to the grid with either balanced or unbalanced currents, while ensuring that all dc-link capacitor voltages remain balanced. The simulation and experimental evaluations of a 9-kVA grid-connected seven-level CHB illustrate and validate the performance of the proposed strategy for the operation of the grid-connected CHB converter during different unbalanced voltage sags.

Control and energy management of a large scale grid-connected PV system for power quality improvement

Power quality is highlighted as an important parameter in modern power systems. Moreover, grid-connected photovoltaic power plants are increasing significantly in size and capacity. Elsewhere, due to the progressive integration of nonlinear loads in the grid, the principal role of a Solar Energy Conversion System (SECS) is not only to capture the maximum power from solar but, also to ensure some ancillary services and improve the quality of power. This paper presents a novel strategy dedicated to improve the management of active power generation, reactive power compensation and power quality of a SECS, while guaranteeing the possibility of exploiting the full capacity of the Power Conditioning System (PCS) and the PhotoVoltaic System (PVS). The proposed control algorithm is applied to a large scale PVS connected to the grid through a cascade of a DC-DC converter and a PWM inverter. This control strategy manages the SECS function’s priorities, between main active power generation, reactive power compensation and active filtering in such a way to guarantee a smooth and stable DC voltage and ensure a sinusoidal grid current. Top priority is given to the active power production over power quality improvement. Then, priority is given to reactive power compensation over mitigation of current harmonics absorbed by the non-linear load connected to the Point of Common Coupling (PCC). Moreover, the whole system upper limits of active and reactive powers have been determined in the (PQ) power plane on the basis of PVS available power, converters rated power and DC bus voltage smoothness and stability. Finally, a control procedure dedicated to the calculation of the inverter current commands is proposed in order to exploit the full capacity of the SECS and respect the determined power limits. Simulation results confirm the effectiveness and the performance of this control strategy and prove that the SECS can operate at its full power whilst the power quality can be improved by reactive power compensation and active filtering.

Influence of Insulation Level on Electric Power Quality and Transformation Efficiency of Grid-Connected Photovoltaic Power Plants

The paper considers the influence of the insolation level on the electric power quality indicators and efficiency of a grid-tie inverter operating as part of a grid-connected photovoltaic power plant. Over the course of a year, data were recorded for Moscow on incoming solar radiation and the grid-tie inverter input and output capacity provided by a 1 kW grid-connected photovoltaic power plant. The insolation threshold values for a Solar River 1100 TL inverter are experimentally established, corresponding to both the beginning and end of stable inverter operation, as well as the required phase angle value for the electric energy supplied to the grid.

Analysis and design of a robust controller for a grid-connected photovoltaic power plant

ABSTRACTApplication of renewable energy systems has a drastic impact on the present power system. In particular, solar photovoltaic power generation is expanding exponentially. Hence, in this article analysis and design of a 1 Mega Watt (1 MW) solar power plant has been modelled. The obtained power is given as an input to the voltage source converter, which contently regulates the active and reactive power by controlling the pulse width modulation signals. In this article, robust control schemes were discussed to support the required active and reactive power. Further, a detailed analysis has been presented at various fault conditions and the results are explored.

Impact of tropical desert maritime climate on the performance of a PV grid-connected power plant

Abstract This paper provides experimental results on the performance of a grid-connected PV power plant operating under dusty, desert maritime climate conditions using data from the first installation of its kind in Djibouti. The first 4 years of operation were evaluated in terms of IEC 61724 measures, and the impact of climate factors was estimated using a novel combination of analysis techniques. The monthly average daily array yield and final yield were 5.1 kWh/kWp and 4.7 kWh/kWp, respectively. The average performance ratio for respective PV arrays and the global grid-connected system were 90% and 84%, corresponding to monthly average daily PV module and system efficiencies of 12.68% and 11.75%. The seasonal variation in PV module efficiency was found to follow a funnel-shape with a sharp minimum centred on July. The impact of ambient temperature and soiling-induced losses were evaluated, revealing a reduction in the performance ratio by 0.7% for each 1 °C rise in daily ambient temperature. Losses due to soiling varied from 0.03% following rainfall events, to 14.23% during dry dusty periods. Finally, to maintain the modules performances losses less than 5%, a cleaning schedule is recommended every two weeks.

Grid-connected photovoltaic power plants: A review of the recent integration requirements in modern grid codes

The high integration of photovoltaic power plants (PVPPs) has started to affect the operation, stability, and security of utility grids. Thus, many countries have established new requirements for grid integration of solar photovoltaics to address the issues in stability and security of the power grid. In this paper, a comprehensive study of the recent international grid codes requirement concerning the penetration of PVPPs into electrical grids is provided. Firstly, the paper discusses the trends of PVPPs worldwide and the significance of improving grid codes' requirements. In addition, the comparison of common requirements covered in the majority of international grid codes considers high‐ and low‐voltage ride‐through capabilities, voltage and frequency regulation, and active and reactive power support requirements. Finally, a broad discussion on the compliance technology challenges and global harmonization of international grid codes that the PVPPs have to address is presented. The study summarizes the most recent international regulation regarding photovoltaic integration and research findings on the compliance of these regulations and proposed recommendations for future research. It also can assist power system operators to compare their existing requirements with other universal operators or establish their own regulations for the first time. Additionally, this research assists photovoltaic manufacturers and developers to get more accurate understanding from the recent global requirements enforced by the modern grid codes.

Influence of meteorological parameters on the operation of a grid - connected PV solar plant

Elementary description and information on a grid-connected photovoltaic solar power plant (PV plant) of 2 kWp installed in Niš and the influence of meteorological parameters on its operation are given in this paper. Besides, experimental results of the calculation of the energy efficiency, electrical energy generated and output power of this PV plant operating in the real climate conditions in 2017 are presented. The results regarding climate parameters and characteristic performance parameter of 2 kWp PV plant in Niš in 2017 are discussed and it was found that in 2017 annual energy efficiency of this PV plant was 10.63% and it decreased with the ambient temperature increasing.

Performance assessment of domestic photovoltaic power plant with a storage system

Grid-connected low voltage photovoltaic power plants cover the majority of the power capacity installed in Italy. They offer an important contribution to the power demand of the utilities connected but, due to the nature of the solar resource, the night time consumption can be satisfied only withdrawing the energy by the national grid, at the price of the energy distributor. Thanks to the improvement of storage technologies and the decreasing of costs, the installation of a system of battery looks a promising solution. In this paper, a model-based approach to analyze and discuss the performance of a domestic photovoltaic power plant with a storage system is presented.