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Time in the Sun: The Challenge of High PV Penetration in the German Electric Grid
Abstract and Figures
Energy supply systems are facing significant changes in many countries around the globe. A good example of such a transformation is the German power system, where renewable energy sources (RESs) are now contributing 25% of the power needed to meet electricity demand, compared with 5% only 20 years ago. In particular, photovoltaic (PV) systems have been skyrocketing over the last couple of years. As of September 2012, about 1.2 million PV systems were installed, with a total installed peak capacity of more than 31 GWp. During some hours of 2012, PV already contributed about 40% of the peak power demand. It seems that Germany is well on the way to sourcing a major portion of its energy needs from solar installations. PV must therefore provide a full range of services to system operators so as to replace services provided by conventional bulk power plants.
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... Various renewable energy sources (RES) can be connected to the microgrid such as solar panels, wind turbines, etc. With the advancement of technology, the diminishing supply of conventional power sources and many environmental and socio-economic factors have raised RES penetration in the microgrid [1][2][3][4]. Increased renewable energy in the microgrid provides numerous benefits, like increased local power availability, low-cost, clean energy, increased reliability and resilience, reduced grid congestion and peak loads, etc. However, the intermittent nature of RES creates power fluctuations and large variations in the voltage profile. ...
In recent years, the penetration of renewable energy sources (RES) in microgrids and distribution system feeders has increased manifold. Moreover, the advancement of power electronics-based devices in the distribution system has significantly increased the number of sensitive loads. Variations in the voltage under intermittent RES create functional problems with sensitive loads, necessitating voltage regulators (VR) installation. In this paper, two custom power devices: dynamic voltage restorer (DVR) and static synchronous compensator (STATCOM), used for voltage regulation in a microgrid, are investigated under different operating conditions. The efficacy of DVR and STATCOM for voltage regulation in an 11-node radial microgrid with high penetration of RES is simulated under a MATLAB Simulink environment. Furthermore, the simulated microgrid voltage profile results are analyzed to evaluate the efficacy of both voltage regulators.
... The shutdowns caused by Covid-19 are likely to increase energy consumption by home office users. At high voltage levels trading mechanisms like contracts for ancillary services [157] and balancing markets [158] can predict the economically efficient supply of system flexibility services [159]. But for for medium and low-voltage levels, with real-time load prediction of the SBIPV systems, arrangements for power consumption [160], energy storage [161], and electricity price [162] could be enabled for medium and low-voltage levels. ...
The smart building-integrated photovoltaic (SBIPV) systems have become the important source of electricity in recent years. However, many sociological and engineering challenges caused by temporal and spatial changes on demand-side and supply-side remain. In this paper, the barriers and traditional data utilization of SBIPV system causing the above challenges are summarized. Data-driven SBIPV was firstly proposed, including four aspects: Data Sensing, Data Analysis, Data-driven Prediction, and Data-driven Optimization. Data sensing goes beyond the technical limitations of a single measurement and can build the bridge between demand- and supply-side. Then, the demand-side response and electricity changes in supply-side under various environmental changes will also become clear by Data Analysis. Data-driven Prediction of load and electricity supply for the SBIPV is the basis of energy management. Data-driven Optimization is the combination of demand-side trading and disturbed system optimization in the field of engineering and sociology. Furthermore, the perspective of data-driven SBIPV, technologies and models, including all four data-driven features to make automated operational decisions on demand- and supply-side are also explored. The data -driven SBIPV system requiring much greater policy ambition and more effort from both supply and demand side, especially in the areas of data integration and the mitigation of SBIPV system.
... The increased penetration of RESs and their independent control gives to the system many advantages, such as increased available power, lesser generation from conventional power sources, increased power reliability, etc.. However, the increased penetration of RESs in the feeder may give rise to some power quality issues, in which variation in voltage level due to the intermittent nature of the RES is of major concern, especially today, when many of the loads connected in the distribution system require constant power for their better operation and behave like Constant Power Loads (CPLs) [4][5][6][7]. The power consumed by a CPL remains constant regardless of the voltage at the point of common coupling. ...
Increasing installation of Renewable Energy Sources (RESs) in microgrids and distribution system feeders benefits the power system in many ways, such as increasing power availability and reliability, but they also cause various power quality issues, such as overvoltage and undervoltage, due to their intermittent nature. The sensitive loads, such as Constant Power Load (CPL), are affected by these voltage fluctuations. The approach proposed in this paper is to install a Dynamic Voltage Regulators (DVR) adjacent to the RES to suppress the voltage issue caused by it while leaving the sensitive load operation unharmed. The proposed concept is duly endorsed with analysis and simulations in MATLAB/Simulink environment.
... Standing out is the impact of high photovoltaics (PV) proliferation, but also of other grid-connected devices such as electric vehicle supply equipment (EVSE) [2]. In case of generation outdoing demand locally, bidirectional power flows on different voltage levels as well as voltage rises are the consequences [3]. If the voltage is lifted too much this can lead to voltage band violations, which consist of voltages above or below the admissible limits. ...
The electrical energy system is undergoing major changes due to the necessity for more sustainable energy generation and the following increased integration of novel grid-connected devices, such as inverters or electric vehicle supply equipment. To operate reliably in novel circumstances, as created by the decentralization of generation, power systems usually need grid supportive functions provided by these devices. These functions include control mechanisms such as reactive power dispatch used for voltage control or active power reduction depending on the voltage. As the main contribution of this work, an approach for the development of the detection of misconfigured (e.g., wrongly parameterized control curve) grid devices using solely operational data is proposed. By generating and analyzing operational data of power distribution grids, a Deep Learning-based approach is applied to the detection problem given. An end-to-end framework is used to synthesize and process the data as well as to apply machine learning techniques to it. The results offer insights into the applicability and possible ways to improve the proposed solution and how it could be employed by grid operators. The findings show that DL methods, in contrast to traditional machine learning, can be used for the problem at hand and that the framework developed offers the necessary tools to fine-tune and scale the solution for broader usage.
Modern low-voltage distribution systems necessitate solar photovoltaic (PV) penetration. One of the primary concerns with this grid-connected PV system is overloading due to reverse power flow, which degrades the life of distribution transformers. This study investigates transformer overload issues due to reverse power flow in a low-voltage network with high PV penetration. A simulation model of a real urban electricity company in Ghana is investigated against various PV penetration levels by load flows with ETAP software. The impact of reverse power flow on the radial network transformer loadings is examined for high PV penetrations. Using the least squares method, simulation results are modelled in Excel software. Transformer backflow limitations are determined by correlating operating loads with PV penetration. At high PV penetration, the models predict reverse power flow into the transformer. Interpolations from the correlation models show transformer backflow operating limits of 78.04 kVA and 24.77% at the threshold of reverse power flow. These limits correspond to a maximum PV penetration limit of 88.30%. In low-voltage networks with high PV penetration; therefore, planners should consider transformer overload limits caused by reverse power flow, which degrades transformer life. This helps select control schemes near substation transformers to limit reverse power flow.
Solar Panel Installation as Green Energy
System Project Management
According to the data collected in 2022 during 5th International Off-Grid Renewable Energy Conference organized in Abu Dhabi by the International Renewable Energy Agency, the global energy requirements show a negative impact on approximately 785 million people facing energy poverty. The long-term energy sustainability solutions should consider off-grid solutions in the planning of an energy mix and be considered as interim both in remote and already urbanized areas. These measures require integrated planning and partnering with local distribution networks. The review presents the development of photovoltaic installations in Central European countries. For more than 40 years, this area belonged to different regimes and joined the European Union at various dates. Hence, the development of energy policies and cultural and social expectations differ even when based on the Green Deal presented by the European Union in 2020. The outcomes prove that even with a variety of policy measures, the strongest boost can be given only by a set of national rules and financial incentives supporting the stakeholders. It should be noted that the advancement of PV often does not rely on climatic conditions, but more on the level of incentives undertaken by each country, as well as the general policy measures undertaken on the EU level.
The rapid development of distributed photovoltaic (PV) systems poses great challenges to the integration capability of distribution networks. Traditionally, the transfer capacity of power distribution equipment is calculated as the maximum loading that prevents overheating under the assumption of extreme weather conditions. Dynamic thermal rating (DTR), which evaluates equipment capacity based on real-time weather conditions, could enhance the transfer capacity to improve distributed PV integration. Through case studies in Texas, Switzerland and China, we show that the application of DTR on power distribution equipment could increase installed PV capacities by 15%-27% and improve net revenues by 4%-27%. We also find that the application of DTR would be positively affected by climate change and is more profitable under the PV policies with higher tariffs for the surplus generation fed into the grid. Compared to energy storage systems, DTR provides a more cost-competitive option to enhance the integration capability of distribution networks.
This work discusses the technical and economical benefits of different active and reactive power control strategies for grid-connected photovoltaic systems in Germany. The aim of these control strategies is to limit the voltage rise, caused by a high local photovoltaic power feed-in and hence allow additional photovoltaic capacity to be connected to the mains. Autonomous inverter control strategies, which do not require any kind of data communication between the inverter and its environment, as well as an on-load tap changer for distribution transformers, is investigated. The technical and economical assessment of these strategies is derived from 12-month root mean square (rms) simulations, which are based on a real low voltage grid and measured dc power generation values. The results show that the provision of reactive power is an especially effective way to increase the hosting capacity of a low voltage grid for photovoltaic systems.
This paper describes solutions for voltage control in low-voltage distribution networks with a high penetration of decentralized feed-in systems. Electric equipment such as controllable distribution transformers with on-load tap changer (OLTC), reactive-power capable PV inverters and decentralized line voltage controllers were included in the study. After a short description of the issue of voltage control in distribution networks, we will continue with a description of the proposed solutions including the electric equipment and selected system concepts, as well as their advantages and disadvantages. In conclusion, a model of an existing low-voltage network is used to compare the concepts taking into account the potential increases in hosting capacity, losses caused by limiting active power, and the required reactive power that needs to be provided.
With the increased integration of distributed energy units (DERs) on the MV/LV level, operators of distribution systems are currently facing a challenge in terms of voltage control. Distribution systems that were initially designed for distributed consumption and central generation now face decentralized feed-in. Decentralized feed-in at the MV/LV level, can lead to dynamic and local voltage violations in the distribution system, which are hard to handle via conventional voltage control strategies. This article proposes a new optimization based voltage control framework for distribution system operation. The framework utilizes a simulation of the distribution network (DN) in combination with meta-heuristics to calculate new set-ups of the network (here reactive power of distributed generation in the network), when a voltage violation occurs. The frameworks control capabilities are tested using data from a real rural distribution network in combination with a distribution state estimator. The results are very promising, as voltage control is achieved fast and accurate, preventing a majority of the voltage violations during system operation under realistic system conditions.
Technically effective and economically efficient voltage control is a major issue in distribution systems with high amounts of installed capacity from dispersed generators, such as photovoltaic. In this paper, the results of an encompassing cost–benefit analysis for different voltage control strategies are presented. The investigated voltage control strategies comprise two different reactive power control methods and one combined reactive power/active power control method, each applied by inverters of utility scale photovoltaic systems. The results are gained by performing 12‐month root‐mean‐square simulations with a 1 min resolution, using the model of a real distribution grid as well as complex generation and load models. The simulations show that local reactive power provision methods as well as temporal active power output curtailment methods are capable of reducing the necessity of a voltage‐driven grid reinforcement. However, the economic benefit of those voltage control strategies highly depends on the parameterization of the respective control algorithm. Copyright © 2013 John Wiley & Sons, Ltd.
The installed capacity of photovoltaic systems has recently increased at a much faster rate than the development of grid codes to effectively and efficiently manage high penetrations of PV within the distribution system. In a number of countries, PV penetrations in some regions are now raising growing concerns regarding integration. Management strategies vary considerably by country - some still have an approach that photovoltaic systems should behave as passive as possible while others demand an active participation in grid control. This variety of grid codes also causes challenges in learning from 'best practice'. This paper provides a review of current grid codes in some countries with high PV penetrations. In addition, the paper presents a number of country-specific case studies on different approaches for improved integration of photovoltaic systems in the distribution grid. In particular, we consider integration approaches using active and reactive power control that can reduce or defer expensive grid reinforcement while supporting higher PV penetrations.
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