Flexibility in Distribution grids with a large share of distributed energy resources – with a special focus on microgrids

Abstract

Recent changes in the global political landscape, impacting energy and food security, have made the integration of Distributed Energy Resources (DER), especially rooftop Photovoltaic (PV) systems, imperative. These systems occupy land already in use and are located near the point of consumption, thus decreasing grid losses. The increase in distributed power generation, primarily through rooftop photovoltaic systems, pushes power grids to the limits of voltage stability, which is associated with power oscillations and even power outages. All this indicates that the large-scale implementation of renewable and distributed generation poses considerable technical challenges, while their flexibility leaves much to be desired. The JRC’s 2024 DSO survey found 81% of EU DSOs report frequent voltage violations (over- or under-voltage) in their networks . This report outlines current experiences with using flexibilities in operating distribution systems, based on a survey. It also provides an overview of innovative solutions, such as Microgrids, self-consumption versus Transmission and Distribution (T&D), and LINK, to address existing challenges. The report focuses on the technical aspect by highlighting the control strategies that enable flexibility in practice, and only mentions others, such as regulatory, in passing. The report neither addresses any economic aspects, increased cybersecurity risks with more active systems, nor issues such as resilience and telecommunications dependencies for command and control, under any circumstances. Therefore, a cost-benefit analysis and an end-to-end technical assessment encompassing all dependencies should be performed before deciding to implement any technical solution. Distribution System Operators (DSO) experience is collected from a global survey conducted among utility companies in 2024, focusing on DER integration. The Working Group developed and refined the study with the CIRED committee, gathering responses from 24 utilities across 19 National Committees. Key insights include the widespread presence of DERs, particularly rooftop solar panels, and the expected significant increase in DER installations over the next decade. DSOs employ countermeasures to maintain network stability, including On-Load-Tap-Changer (OLTC) and reactive power control. Under others, several DSOs reported that the transformers' local controls (OLTCs, tap-changing transformers) were reaching their end settings. The survey also highlights challenges at the Transmission System Operator (TSO)-DSO interface and the effectiveness of energy market rules. Additionally, the impact of large-scale rooftop PV in Australia is discussed, emphasising the need for reforms to ensure system security and dynamic resilience. The survey results underscore the importance of national regulations and policies in shaping DER integration practices. This report presents a comprehensive analysis of Microgrids, focusing on their architecture, classification, control strategies, and operational roles in modern power systems. Once conceived primarily as isolated systems for backup or emergency use, microgrids have evolved into smart, grid-interactive assets that actively support energy management, grid reliability, and DER integration. This transition—from grid independence to grid integration—has been driven by advances in control technologies, the rise of renewables, and growing demands for system flexibility and resilience. The report examines how microgrids are categorised by control strategy, energy source, topology, application, and operating mode. It highlights their flexibility to operate in both island- and grid-connected modes, dynamically switching between them based on system conditions. Additionally, microgrids can mitigate voltage and thermal constraints, manage local generation and demand, and enhance real-time balancing through storage and demand response. With these integrated capabilities, microgrids are critical in modernising distribution networks and transitioning toward a more decentralised energy system, providing that the benefits of implementing microgrids outweigh their cost, encompassing TOTEX in an end-to-end perspective, including obsolescence and renewal. Nevertheless, despite the long duration of research (over 20 years), a detailed definition of microgrids is still being debated in expert forums. Microgrids’ intertwined controlling structure with primary, secondary, and tertiary controls to consider also the “main system” leads to extremely complex and multifaceted technical solutions that are difficult to implement on a large scale. Self-Consumption vs. T&D discusses the individual and collective Self-Consumption schemes. Nevertheless, it can be underlined that there is a lack of research to assess how the proposed schemes could increase the DER hosting capacity; what would be the technical challenges, which incentives must be set, and what would be the required evolutions in the national regulations? LINK paradigm and the corresponding holistic architecture, built on the fractal geometry of the grid, redefine its technical and market structures. It considers all grid voltage levels, including customer plants and electrical appliances, i.e., electricity producers and storage, regardless of size (ranging, e.g., from MW to kW) and technology (e.g., waterpower plants, photovoltaics, etc.). LINK architecture postulates a coordinated chain network of controls (comprising secondary, primary, and local controls) on the primary quantities of power systems, namely frequency and active power, as well as voltage and reactive power, thereby enabling large-scale grid flexibility through power modulation and resilience. It facilitates describing all power system operation processes such as load-generation balance, voltage assessment, dynamic security processes, price- and emergency-driven demand response, etc. The chosen distributed LINK-based architecture overcomes data privacy and cybersecurity challenges. Its key principle is to prohibit access to all resources by default, allowing access only to a minimum of data. LINK is characterised by clear guidelines regarding ownership and operating conditions, as well as standardised and modular structures. LINK enables Sector Coupling and Energy Communities and can thus effectively counteract the growing trend toward negative prices across Europe. However, it is essential to refine the holistic architecture on-site by implementing it in its entirety. This step will highlight its strengths and help to formulate concrete steps for the large-scale implementation.