Small-scale Photovoltaic Systems Research Articles

A Day-Ahead Irradiance Forecasting Strategy for the Integration of Photovoltaic Systems in Virtual Power Plants

Encouraged by the considerable cost reduction, small-scale solar power deployment has become a reality during the last decade. However, grid integration of small-scale photovoltaic (PV) solar systems still remains unresolved. High penetration of Renewable Energy Sources (RESs) results in technical challenges for grid operators. To address this, Virtual Power Plants (VPPs) have been defined and developed to manage distributed energy resources with the aim of facilitating the integration of RESs. This paper introduces a hybrid irradiance forecasting approach aimed at facilitating the integration of PV systems into a VPP, especially when a historical irradiance dataset is exiguous or non-existent. This approach is based on Artificial Neural Networks (ANNs) and a novel similar hour-based selection algorithm, has been tested for a real PV installation, and has been validated also considering irradiance measurements from an aggregation of ground-based meteorological stations, which emulate the nodes of a VPP. Under a reduced historical dataset, the results show that the proposed similar hour-based method produces the best forecasts with regard to those obtained by the ANN-based approach. This is particularly true for one-month and two-month datasets minimizing the mean error by 16.32% and 9.07% respectively. Finally, to demonstrate the potential of the proposed approach, a comparative analysis has been carried out between the hybrid method and the most used benchmarks in the literature, namely, the persistence method and the method based on similar days. It has been demonstrated conclusively that the proposed model yields promising results regardless the length of the historical dataset.

ROCOF for detecting Islanding of Photovoltaic system

Power industry has been emphasizing more importance on a distributed generation because there is new technology like Photovoltaic (PV), fuel cell, wind turbine, and power electronic use for advancement of the power system has been evolved so much which cannot be possible without distributed generation. The majority of small scale PV systems are domestic roof-top type installations and are generally single-phase systems. Rebates and concession schemes that were introduced by the government for installing small scale PV systems along with price reductions in PV panels are the main reasons for the increased number of grid-connected small scale PV systems in the power distribution grid. Hence Distributed Generation (DG) has become an inseparable part in power system and gained so much importance because of economic and environmental purpose. Islanding is a situation where a part of the distributed generation system containing a distributed generator gets electrically isolated from the remainder of the power system continues to energize the network where the situation has occurred. Thus it has become important that the portion where islanding has occurred must detect this situation immediately for safety purpose. If tripping doesn’t occur in time, there can be a various and critical problem. Currently, in industry practice, we disconnect all distributed generators after islanding has occurred. Generally, a distributed generator should be disconnected within 0.1s to 0.3s after the loss of grid/main supply. This paper gives a simulation model to achieve this, each distributed generator must be supplied with an anti-islanding device which detects islanding like UOF and ROCOF relays.

The Technical Challenges Facing the Integration of Small-Scale and Large-scale PV Systems into the Grid: A Critical Review

Decarbonisation, energy security and expanding energy access are the main driving forces behind the worldwide increasing attention in renewable energy. This paper focuses on the solar photovoltaic (PV) technology because, currently, it has the most attention in the energy sector due to the sharp drop in the solar PV system cost, which was one of the main barriers of PV large-scale deployment. Firstly, this paper extensively reviews the technical challenges, potential technical solutions and the research carried out in integrating high shares of small-scale PV systems into the distribution network of the grid in order to give a clearer picture of the impact since most of the PV systems installations were at small scales and connected into the distribution network. The paper reviews the localised technical challenges, grid stability challenges and technical solutions on integrating large-scale PV systems into the transmission network of the grid. In addition, the current practices for managing the variability of large-scale PV systems by the grid operators are discussed. Finally, this paper concludes by summarising the critical technical aspects facing the integration of the PV system depending on their size into the grid, in which it provides a strong point of reference and a useful framework for the researchers planning to exploit this field further on.

An Improved Group Decision-Making Model for the Investment Options of Small-Scale Photovoltaic Systems Based on Cumulative Prospect Theory and Choquet Integral

With the development of photovoltaic (PV) industry, installing small-scale PV systems which are integrated into the buildings becomes popular. Therefore, it is important to make optimal investment decisions for investors and consumers. This paper proposes an improved group decision-making method which integrates the cumulative prospect theory and Choquet integral for the investment options of small-scale PV systems. From the perspective of sustainability, the alternatives are evaluated by four criteria, including economic benefits, solar energy condition, carbon emissions and social benefits. Since the performances of criteria are given by decision makers as linguistic variables, the proposed method measures the criteria values by intuitionistic trapezoidal fuzzy numbers. Then the alternatives are evaluated and ranked to determine the optimal option. Finally, the proposed method is implemented in a case study to illustrate its feasibility and effectiveness.

An Improved Technique to Estimate the Total Generated Power by Neighboring Photovoltaic Systems Using Single-Point Irradiance Measurement and Correlational Models

A major operational challenge of photovoltaic (PV) systems is the variability in their output power, which is mainly caused by the movements of clouds. This variability can be reduced through building several smaller PV systems, distributed within an area, rather than a single, large PV system, often referred to as the geographic smoothing. This smoothing can be expressed mathematically by the variability reduction index (VRI), which denotes the reduced level of variations in the output power of a group of neighboring PV systems. VRI considers the size of the PV systems, the distances between them, as well as the mathematical correlation model that reflects the timescale, along with the speed, direction, and density of the clouds passing over the PV systems. The VRI and solar irradiance, measured at one location, can be used to estimate the power generated by a group of neighboring PV systems. This article initially compares and assesses various VRI models through their application on a group of 16 small-scale neighboring rooftop PV systems, distributed over a square kilometer area in Brisbane, Australia. Then, a technique is proposed to improve the estimation accuracy of the overall generated power by a group of neighboring small-scale rooftop PV systems. This new technique is validated by comparing the estimated power with the measured power, generated by the investigated PV systems.

Evaluation of the Success of a Small-Scale Photovoltaic Energy System

Solar photovoltaic energy generation is growing in Brazil and in the world. Considered a new investment alternative, many investors lack knowledge and difficulty in evaluating the success it will have with photovoltaic systems. This study aims to evaluate the percentage of investor success in a small scale photovoltaic power generation project in Brazil. A measurement modeling was developed through the methodology MCDM (AHP) and Key Performance Indicators (KPI). The case study was in a system of a supermarket of the state of Rio Grande do Sul, of 75kW of installed power. For the analysis of the importance of KPIs, 29 photovoltaic entrepreneurs in Brazil participated in the research. Analysis of the importance levels of the 33 KPI by the investor and the experts resulted in a 73.25% success rate of the project, classifying it as Potential Success.. Systematic analysis of a high initial capital investment is important in assisting the investor in decision making. The 33 KPI is relevant to an assessment of investor success.

Addressing the soft cost challenge in U.S. small-scale solar PV system pricing

Solar photovoltaic (PV) prices have fallen significantly over the past two decades. These price reductions have relied primarily on falling system hardware costs. Future reductions in PV prices—which are needed to ensure that enough PV will be deployed to meet global clean energy objectives—will require reductions in non-hardware or “soft” costs, particularly in markets with relatively high soft costs such as the United States. In this article, we draw insights from the literature on which factors affect soft costs for small-scale PV systems in the United States. The literature shows that soft costs tend to be lower for systems that are larger, installed during new construction, installed by more experienced installers, installed in more concentrated markets and in more competitive markets, installed in markets where customers receive more quotes, or installed in markets with less onerous permitting requirements. We identify three marketplace design strategies that policymakers could pursue to address the soft cost challenge in the United States and similar markets: encourage the expansion of quote platforms; encourage or require that PV system installation be integrated into the new construction and roof replacement process; and encourage the expansion of customer aggregation models such as Solarize campaigns and community solar.

Coordination of Distributed Reactive Power Sources for Voltage Support of Transmission Networks

The provision of voltage support from distribution systems to transmission networks requires new cost-effective coordination schemes to drive thousands of non-centrally monitored distributed energy resources (DERs). In this paper, we demonstrate how small-scale photovoltaic systems in distribution systems can provide reactive power services to other networks. This is achieved by means of their local controllers that change their logic to respond to external requests. These controllers operate with local information and without direct knowledge of the full system performance. This facilitates scalability as new DERs can be added to participate in a plug-and-play fashion. The paper focuses on the voltage support concept for the Swiss transmission system. The coordination defines when DERs must participate in voltage support, which task to perform and how to fulfill it. It is demonstrated that dispersed units can engage in system objectives, and still be able to support local voltages when required. The proposed approach is tested in different systems with high penetration of PV systems.

Design and operation of an OCC‐based scheme for a stand‐alone PV system powering DC loads

Distributed energy resources such as stand-alone photovoltaic (PV) systems have been widely used in electric systems in the last decades due to the increase in global energy demand, and the concern about the environmental problems caused by fossil fuels power generation. Owing to the fast growing of direct current (DC) microgrids and electronic devices, such as their current compatibility nature in relation to primary sources, a small-scale stand-alone PV system with battery storage for DC applications is proposed in this work. The system consists of three DC-DC converters which operate according to the PV panel power and the main bus load demand. The control of these converters considers the quality in power supply ensuring safety to the loads and batteries of the system. Thus, this study proposes the implementation of the control units through the use of one-cycle control (OCC) which allows fast response to transient conditions, great accuracy of convergence and has low-cost analogue implementation. In this study, one-cycle controllers' waveforms are analysed in steady-state conditions and its duty cycles are compared with the expected in relation to the system operation. Simulations of transition conditions were performed through real situations such as cloud-edge effects, slow passing clouds and absence of sunlight.

Optimal Photovoltaic/Battery Energy Storage/Electric Vehicle Charging Station Design Based on Multi-Agent Particle Swarm Optimization Algorithm

In order to effectively improve the utilization rate of solar energy resources and to develop sustainable urban efficiency, an integrated system of electric vehicle charging station (EVCS), small-scale photovoltaic (PV) system, and battery energy storage system (BESS) has been proposed and implemented in many cities around the world. This paper proposes an optimization model for grid-connected photovoltaic/battery energy storage/electric vehicle charging station (PBES) to size PV, BESS, and determine the charging/discharging pattern of BESS. The multi-agent particle swarm optimization (MAPSO) algorithm solves this model is solved, which combines multi-agent system (MAS) and the mechanism of particle swarm optimization (PSO). In this model, a load simulation model is presented to simulate EV charging patterns and to calculate the EV charging demand at each time interval. Finally, a case in Shanghai, China is conducted and three scenarios are analyzed to prove the effectiveness of the proposed model. A comparative analysis is also performed to show the superiority of MAPSO algorithm.

Sizing and Improved Grid Integration of Residential PV Systems With Heat Pumps and Battery Storage Systems

In the future, the remuneration of photovoltaic (PV) grid feed-in might significantly drop in Germany and questions arise if small-scale PV systems remain economically attractive. However, battery storage systems (BSSs) and sector coupling with heat pumps (HPs) provide promising opportunities to increase PV self-consumption and the value of local energy generation, but change the dynamics of PV grid integration. Thus, an optimization model is proposed to enable all involved stakeholders to analyze interdependencies between different flexibility options for PV systems, incentive, and grid integration. A case study-based approach allows an efficient evaluation of future PV systems with BSSs and HPs, the impact of such decentralized power-heat-storage systems on grid integration as well as proper incentive setting for sector coupling. The analysis shows that such shifting technologies are required to avoid undersizing of PV systems. BSSs only provide a benefit for the adoption of inflexible HPs, which is not preferable from a grid integration point of view. Operational incentives, such as peak charges and PV feed-in limits, offer a chance to foster PV grid integration and use new flexibilities in a grid-supporting way. The adoption of market-oriented operation leads to small benefit for such systems, which heavily rely on PV self-consumption.

Impact of Performance Degradation and Capital Subsidy on the Revenue of Rooftop Solar PV System

The capital subsidy is one of the recognized techniques to promote solar Photovoltaic (PV) systems to the investors. Most of the nations have offered subsidies to investors, who are willing to invest on developing small-scale photovoltaic system to large-scale multi-megawatt system. This paper tries to analyze whether the given subsidy will have any influence on the revenue generated from a PV plant considering two studies, one is without capital subsidy, and second is with 15 % capital subsidy. The revenue generated in each case is analyzed considering the approved grid feed-in tariff rates set by the electricity regulatory commissions separately for each case depending on the plant capacity. Another known fact is that there exists performance degradation in the PV plant throughout its lifetime or age. Hence during the evaluation of revenue, the energy degradation over the PV plant lifetime i.e. 25 years is considered. Focused results for analyzing the system includes energy yields for the first year, energy yields considering degradation, yield factors, capacity factors, revenue generation, and payback periods. With the analysis on the above-mentioned parameters revenue benefits of PV systems with and without capital subsidy are discussed.

Developing a small photovoltaic power supply system with adaptive technologies for rural Africa: Design, cost and efficiency analyses

The objective of this study was to design a small-scale photovoltaic system to support electricity supply to a rural village in the Republic of Congo. A simple impedance-matching system and an innovative panel-tilting system were implemented as adaptive technologies to increase the power output of the system and reduce its capital and running costs. The experimentally obtained results showed that the daily energy output of a four-panel, 400 W photovoltaic system could be increased by 15% through a series parallel impedance match configuration, and by 36% from 3.3 kWh per day to approximately 4.5 kWh per day through implementing an automated panel tilting system with always normal incidence of solar irradiation on the panels in an equatorial environment. Implementing these technologies accordingly reduced the cost of energy supplied by the same percentages, with an eventual electricity cost of about ZAR 3.60 per kWhr, as calculated over an operation time of ten years, and an initial capital outlay of ZAR 37 per watt. These costs are much lower than for installing power grid lines to the village, and the technology also ensures complete autonomy of power supply to the community. The study also identified the potential to generate many new business and job opportunities locally in this community, as well as in the rest of Africa.

Dynamic Voltage Support by TL-PV Systems to Mitigate Short-Term Voltage Instability in Residential DN

Recently, transformerless (TL) inverters are being extensively used in small-scale photovoltaic (PV) systems due to their compact-size, lighter-weight, lower-cost and higher-efficiency compared to their counterpart with transformer. However, the growing penetration of these small-scale based PV systems and low-inertia induction motor (IM) loads in low-voltage distribution networks (DNs) make the grid more vulnerable to short-term voltage stability (STVS). Hence, this paper thoroughly examines the STVS of DN with high-penetration of TL-PV units, and provides countermeasures by TL-PV systems to mitigate any short-term voltage instability. The detailed dynamic model of the TL inverter is developed first. Next, three control strategies: (1) constant peak current (CPC), (2) constant active current (CAC), and (3) constant active power (CAP) with low voltage ride through (LVRT) and dynamic voltage support (DVS) capabilities are proposed to improve STVS. The impacts of different level of PV penetrations and LVRT capability of TL-PV inverters on the STVS are explored. Moreover, countermeasures, such as LVRT with CAC and CAP controls and DVS by the TL-PV systems are designed and implemented. Several case studies are carried out on an IEEE 4 bus system first, and later extended to IEEE 13 node test feeder. The results show that DVS can further improve STVS in residential DNs. In addition, CAP and CAC control strategies can speed-up the postdisturbance voltage recovery compared with the conventional CPC control.

Data-driven estimation of expected photovoltaic generation

Photovoltaic (PV) systems’ monitoring and performance assessment are relevant tools to ensure its correct operation. The standard methodology consists in determining irradiance in the plane of the array and convert it into PV power, considering system efficiency. This work proposes an effective data-driven approach based on past PV generation of the system being assessed and local measurements of solar radiation. Using local global horizontal irradiance (GHI) measurements, model performance degrades with the difference in tilt between the PV module and the pyranometer; when radiation is measured in the plane of the array (in this case for a horizontal module) the data driven method is more accurate than the standard approach. The method was also tested for a small-scale residential PV system context, replacing the local irradiation measurements by satellite GHI estimates. Although errors increase significantly, the data-driven method outperforms the standard approach for all tilts.

Developing a small photovoltaic power supply system with adaptive technologies for rural Africa: Design, cost and efficiency analyses

The objective of this study was to design a small-scale photovoltaic system to support electricity supply to a rural village in the Republic of Congo. A simple impedance-matching system and an innovative panel-tilting system were implemented as adaptive technologies to increase the power output of the system and reduce its capital and running costs. The experimentally obtained results showed that the daily energy output of a four-panel, 400 W photovoltaic system could be increased by 15% through a series parallel impedance match configuration, and by 36% from 3.3 kWh per day to approximately 4.5 kWh per day through implementing an automated panel tilting system with always normal incidence of solar irradiation on the panels in an equatorial environment. Implementing these technologies accordingly reduced the cost of energy supplied by the same percentages, with an eventual electricity cost of about ZAR 3.60 per kWhr, as calculated over an operation time of ten years, and an initial capital outlay of ZAR 37 per watt. These costs are much lower than for installing power grid lines to the village, and the technology also ensures complete autonomy of power supply to the community. The study also identified the potential to generate many new business and job opportunities locally in this community, as well as in the rest of Africa.

An offline penetration-free protection scheme for PV-dominated distribution systems

The rapid growth of small-scale photovoltaic (PV) units in distribution grids brings new challenges in the protection coordination of overcurrent relays. So far, various adaptive techniques have been addressed to solve DG units’ mis-coordination problem, however, the un-predictable penetration of installed PV units highlights the importance of a penetration-free methodology. This study presents a novel offline, quick, applicable and cheap solution which guarantees protection coordination for any penetration and location of PV units. To do so, first, under different PV penetration levels and locations, the conventional protection performance is studied to discover the worst mis-coordination cases. Next, according to relays standards, the characteristic curve of the back-up relay is modified such that it can maintain coordination in all worst cases. The proposed methodology is applied to a practical power distribution network equipped with numerous small-scale PV systems. The results successfully prove the effectiveness of the proposed method. Since this technique only applies some changes in characteristic curves of the back-up relays, lack of programmable relay or adaptive protection requirements cannot decrease its performance. This fact makes this method an attractive option for distribution systems with PV units.

A Project-Based Cooperative Approach to Teaching Sustainable Energy Systems

Engineering education is undergoing a restructuring driven by the needs of an increasingly multidisciplinary engineering profession. At the same time, power systems are transitioning toward future smart grids that will require power engineers with skills outside of the core power engineering domain. Since including new topics in the existing curriculum while maintaining the existing requirements is difficult, this paper proposes a project-based cooperative learning approach to promote soft skills in an engineering course. This paper then shows how to construct a realistic open-ended multidisciplinary problem whose solution requires a wide range of skills, which is not a trivial task. The design and technoeconomic viability assessment of a small-scale photovoltaic battery system is used as a case study. The effectiveness of the approach and students’ satisfaction were assessed over two years. Survey results after the first year revealed that the students did not feel sufficiently prepared for multidisciplinary work. After appropriate adjustments in the second year, the survey results improved noticeably. Statistical analysis reveals that the project teaches skills that are complementary to the core domain skills, which confirms the validity of the approach.

Application of Typical Meteorological Years for Sizing Building Integrated PV Systems under Zero Load Rejections

Abstract Autonomous photovoltaic systems have already been proved as one of the most reliable ways to handle the electrification requirements of remote consumers in isolated areas. The technology improvement in the field of building integrated photovoltaic systems, along with the governmental financial incentives for boosting the corresponding energy sector, have increased the interest of installing small scale photovoltaic systems not only in remote dwellings but also in grid-connected households. The penetration of photovoltaic systems in densely populated areas has made people even more familiar with them and therefore people with environmental consciousness are more likely to adopt the specific technology. In this context, the present work aims in highlighting the capabilities of building integrated photovoltaic systems along with battery storage devices in covering the electrical needs of a typical dwelling using real electricity demand and meteorological data based on Typical Meteorological Year time series. The system is simulated on an hourly basis by using an integrated numerical code that has been developed by the Soft Energy Applications & Environmental Protection Laboratory of the Mechanical Engineering Dept. of Piraeus University of Applied Sciences in Greece. The proposed solution guarantees zero load rejections under different solar potential schemes investigating also the possibilities of minimizing the storage system capacity.

Techno-economic analysis and life-cycle environmental impacts of small-scale building-integrated PV systems in Greece

Photovoltaic (PV) power system is a technology for producing electricity from renewable resources that is rapidly expanding thanks to its capability to save conventional fossil fuels and to decrease the emissions of greenhouse gases. However, as more attention is being focused globally on the development of building-integrated PV systems, the technical, the economic as well as the environmental assessment of these systems is crucial to ascertain their viability. The purpose of this paper is to present an economic and environmental analysis of relatively small rooftop PV-grid-interconnected energy systems of 2–10kWp rated power, located in Athens, Greece. The techno-economic feasibility of the PV systems is conducted employing the computerized renewable energy technologies assessment tool ‘RETScreen’. The energy and environmental assessment of the systems is carried out employing SimaPro 7.1 software, which is a standard Life Cycle Assessment tool. The results of the economic analysis indicate that with the current prices, investment in PV-grid-interconnected systems with power capacity higher than 5kWp is in general viable. However, an increase in energy sale prices and/or cost reductions in the production of PV systems are crucial for the successful development of small-scale residential size PV systems in the country. The environmental analysis reveals that the PV systems with higher rated power perform worse as far as the environmental impact is concerned. The critical phase of the life cycle of PV systems is the module manufacturing process, which is characterized by high electricity consumption, representing most of the environmental impact. Nevertheless, it is further shown that the application of PV technology presents important environmental benefits compared to conventional energy production systems.