Highlights
Energy Security and Resilience: Reviewing Concepts and Advancing Planning Perspectives for Transforming Integrated Energy Systems
Richard Schmitz,Franziska Flachsbarth,Leonie Sara Plaga,Martin Braun,Philipp Härtel
- Review of interrelations between energy security, resilience, and related terms
- Classification of system disturbances into shock events and slow burn processes
- Compilation of recourse options to provide strategies for an integrated energy system
- Clarification of trade-offs between resilience levels and system costs
- Policy recommendations aiming to integrate disturbances into energy system planning Energy Security and Resilience: Reviewing Concepts and Advancing Planning Perspectives for Transforming Integrated Energy Systems
Richard Schmitz [a,b] [,][∗], Franziska Flachsbarth [c], Leonie Sara Plaga [d], Martin Braun [a,b] and Philipp Härtel [a,b]
a Fraunhofer IEE, Fraunhofer Institute for Energy Economics and Energy System Technology, Joseph-Beuys-Str. 8, 34117 Kassel, Germany b University of Kassel, Department of Sustainable Electrical Energy Systems, Wilhelmshöher Allee 73, 34121 Kassel, Germany c Öko-Institut e.V., Research Division Energy & Climate, Merzhauser Str.
173, 79100 Freiburg, Germany d Ruhr University Bochum, Chair of Energy Systems and Energy Economics, Universitätsstr. 150, 44801 Bochum, Germany
AR TI CL E I NF O
Keywords : Energy system planning Energy security Resilience
Shock events
Slow burn processes Recourse options Terminology
1. Introduction
Abstract
Recent events, including the pandemic, geopolitical conflicts, supply chain disruptions, and climate change impacts, have exposed the critical need to ensure energy security and resilience in energy systems. We review existing definitions and interrelations between energy security and resilience, conceptualising these terms in the context of energy system transformations. We introduce a classification of disturbances into shock events and slow burn processes to highlight key challenges to energy system resilience. Examples illustrate their distinct impacts on technical, economic, and environmental system performance over time. We compile relevant recourse options across resilience capacity levels and system planning horizons to address these challenges, emphasising actionable strategies for an increasingly integrated energy system. Finally, we propose policy recommendations to integrate shock events and slow burn processes into future energy system planning, enabling forward-looking decision-making and system design to analyse and mitigate potential disruptions. Energy security and resilience have become central to national and international policymaking, particularly in the wake of the energy crisis in Europe following the Russia’s attack on Ukraine. While resilience is frequently discussed in engineering, environmental, or social protection contexts, the distinction between energy security, resilience, security of supply, and related terms often remains imprecise. In the past, energy security and security of supply have been evaluated primarily based on the availability and affordability of fossil resources. However, in decarbonised energy systems, where fossil fuels play a minimal role, new measures and assessments for evaluating security of supply are required. Recent reviews highlight that security of supply now encompasses dimensions beyond fossil fuel availability.
Nevertheless, most studies primarily assess existing systems and rarely account for future uncertainties and risks. Moreover, many analyses rely on energy security indices based on factors such as energy availability and pricing
∗ Corresponding author
richard.schmitz@iee.fraunhofer.de (R. Schmitz); f.flachsbarth@oeko.de (F. Flachsbarth); leonie.plaga@ruhr-uni-bochum.de (L.S. Plaga); martin.braun@uni-kassel.de (M. Braun); philipp.haertel@iee.fraunhofer.de (P. Härtel) ORCID (s): 0000-0001-8153-3180 (R. Schmitz); 0000-0002-0813-0358 (F. Flachsbarth); 0000-0001-6339-6100 (L.S. Plaga); 0000-0003-0857-6760 (M.
Braun); 0000-0002-9706-1007 (P. Härtel)
, yet these indices fail to capture the energy system’s dynamic nature and adaptive capacity. Resilience research often focuses on the electricity system and its individual components, such as power lines or power plants. However, as Jasi¯unas et al. argue, the concept of resilience must be applied to the entire integrated energy system in the future. In longterm energy system planning, optimisation models are commonly used to represent the system’s dynamic characteristics. However, the existing literature provides limited guidance on effectively assessing energy security and resilience within long-term energy system planning. While several reviews have synthesised existing definitions of energy security, resilience and security of supply, to our knowledge, no review specifically addresses these terms in the context of long-term energy system optimisation models. When examining potential threats and hazards to energy security and resilience, a distinction can be made between shock events and so-called slow burn processes (SBPs). The negative impact of such events on the energy system is often described as a deterioration in “energy system performance”, yet this term typically lacks differentiation between technical, economic, or environmental performance. Our work aims to introduce such a distinction and propose an approach to track performance trends over time. In considering how energy security and resilience concepts can be applied to planning tasks for future integrated energy systems, a key question arises: what recourse options
Schmitz, Flachsbarth, Plaga, Braun, Härtel: Preprint submitted to Elsevier Page 1 of 22 Energy Security and Resilience: Reviewing Concepts and Advancing Planning Perspectives
Glossary
EENS expected energy not served ENTSO-E European Network of Transmission System Operators for Electricity EU European Union HHI Herfindahl-Hirschman Index HILP high-impact low-probability IEA International Energy Agency KPI key performance indicator LNG liquefied natural gas are available and can be used by decision makers to respond to shock events and SBPs? For instance, energy system planners traditionally rely on historical weather patterns, yet these are becoming increasingly unreliable indicators of future conditions, undermining robust planning for resilience. We provide an overview of potential recourse options across various planning horizons. Building on the research gaps identified thus far and aiming to support policymakers in formulating strategies that balance immediate energy needs with long-term sustainability goals, this work makes the following key contributions:
- A comprehensive review of previous definitions and a mapping of interrelations between energy security and resilience terms in the energy system domain, incorporating more than 180 references;
- The introduction of shock events and slow burn processes (SBPs) as challenges to energy system resilience, including illustrative examples of their effects on technical, economic, and environmental system performance over time;
- A compilation of relevant recourse options at different resilience capacity levels and system planning horizons as responses to disturbances;
- A clarification of trade-offs between resilience levels and system costs, recognising the need for political guidelines on desired system resilience levels and acceptable additional costs;
- Policy recommendations on how shock events and
SBPs can be incorporated into the planning task of integrated energy systems to support better-informed, sustainable political decision-making. The remainder is organised as follows. Section 2 presents an overview of key definitions related to energy security and resilience, examining their interrelations within the literature. Section 3 defines shock events and SBPs as potential challenges to energy security and resilience, followed by illustrative analysis of their impact on the energy system
LOLE loss of load expectation
NIAC National Infrastructure Advisory Council of the United States
SAIDI system average interruption duration index
SBP slow burn process
VOLL value of lost load
VRE variable renewable energy
XB cross-border
over time. Section 4 explores resilience perspectives in integrated energy system planning and introduces a conceptual approach that categorises relevant recourse options of integrated energy systems with regard to different planning horizons. Section 5 outlines the implications of these findings for integrated energy system planning while also hinting at occurring trade-offs between system resilience levels and system costs. Finally, Section 6 discusses policy implications and draws relevant conclusions. 2. Literature review
This literature review aims to provide a comprehensive overview of key definitions and concepts related to energy security and resilience in energy systems. Section 2.1 presents commonly used definitions from the literature, followed by a discussion of their interrelations in Section 2.2. Additional terms that contribute to the broader context, namely efficiency, vulnerability, and robustness, are categorised and discussed in Appendix A. 2.1. Review of key terms To establish a comprehensive mapping of interrelations between energy security and resilience terms in the energy system domain, it is first necessary to review relevant terms. 2.1.1. Energy security Although no consensus on a universal definition of energy security exists, it is widely recognised as a key objective of energy policy. The concept rapidly evolves and closely intersects with energy system resilience. The definition of energy security by the International Energy Agency (IEA) as the “uninterrupted availability of energy sources at an affordable price” features prominently in the academic discourse. Another widely referenced framework is the “four A’s” of energy security, first introduced by Kruyt et al. and frequently cited in the literature. Availability pertains to physical resources, accessibility involves the geopolitical aspects of acquiring resources, affordability relates to energy costs and prices, and acceptability addresses environmental and social considerations. In addition, other dimensions of energy security are highlighted in the literature, including infrastructure, import dependency and diversity of energy sources, governance and energy efficiency, and climate protection. As noted in the introduction, traditional energy security metrics have historically focused on fossil fuel availability. More recent literature identifies indicators such as energy reserves, import exposure, and energy prices as relevant measures of energy security. Comprehensive tabular overviews of various energy security indicators are available in Ang et al.; Siksnelyte-Butkiene et al.. However, assessing energy security through a single key performance indicator (KPI) remains a challenge due to its multidimensional nature.
2.1.2. Resilience
The concept of resilience has been widely discussed in scientific literature, with early foundational work by Holling defining ecosystem resilience as the ability to absorb changes in environmental conditions and parameters. This definition has since influenced numerous fields. The term itself is derived from the Latin “resilire”, meaning “the ability to spring back or rebound”. Despite its widespread use, no single, universally accepted definition of resilience exists, as its meaning varies significantly across disciplines and contexts.
It is often described as a multidimensional concept, encompassing diverse aspects such as energy import resilience, resilient supply chains, resilient energy communities, and resilience of critical infrastructures. From a general perspective, Erker et al. define resilience as “a concept to ensure the viability of a system by reducing the vulnerability and increasing the adaptive capacity before, during or after a stressful event”. Similar definitions appear in Cho et al., Jasi¯unas et al., VDE, and Zhou. Energy system resilience is defined as “the ability of an energy system to retain, react, overcome and overpass perturbations caused by a shock in economic, social, environmental and institutional terms”. It is also important to note the definitions of relevant institutions: The EU frames resilience of a critical organisation or infrastructure as the ability to prevent, protect against, respond to, mitigate the consequences of, absorb, manage, and recover from a security incident. In turn, the European Network of Transmission System Operators for Electricity (ENTSO-E) defines power system resilience as “the ability to withstand and mitigate the extent, severity and duration of system degradation following an impactful event”. Almost identical, the International Council on Large Electric Systems (CIGRE) defines power system resilience as “the ability to limit the extent, severity and duration of system degradation following an extreme event”. Similar adaptions of these definitions can be found in Braun et al., Izadi et al., Pitto, and Stanković et al.. To characterise resilience, the National Infrastructure Advisory Council of the United States (NIAC) identifies robustness, resourcefulness, rapid recovery, and adaptability as its key features. According to the Cabinet Office of the United Kingdom, components of resilient infrastructure are resistance, redundancy, reliability, response, and recovery. Resilience is closely linked to high-impact low-probability (HILP) events that are sometimes also referred to as extreme events, disruptive events, or black swan hazards. A resilience trapezoid is commonly employed to track the (energy) system’s performance over time to visually represent the resilience of an (energy) system in case of such an HILP event. Although terminology varies across sources, the different phases of resilience assessment typically fall under the categories of defending, preventing, detecting, resisting, absorbing, adapting, and restoring. The assessment of energy system resilience often considers both the duration and severity of disruptions. Another key metric is the elapsed time from the occurrence of a disruption to full system recovery. However, relying solely on a single or aggregated energy resilience KPI may not provide a complete picture. Instead, researchers advocate for a multi-indicator framework to capture the complexity of resilience assessment. Comprehensive tabular overviews of various resilience indicators are available in Ahmadi et al., Shafiei et al., and Monie et al..
2.1.3. Energy sovereignty Energy sovereignty has gained significant attention in recent years. As Raimi and Davicino note, a universally
Schmitz, Flachsbarth, Plaga, Braun, Härtel: Preprint submitted to Elsevier Page 3 of 22 Energy Security and Resilience: Reviewing Concepts and Advancing Planning Perspectives accepted definition remains elusive. However, they characterise energy sovereignty as a framework that enables communities or nations to make informed choices regarding all components of their energy systems. LaBelle further defines energy sovereignty as a state’s capability to safeguard its energy system against multidimensional threats through control over its energy policy. Similarly, Westphal argues that energy sovereignty is achieved when a state can provide sufficient and reliable energy supplies at economic prices without compromising its own values, interests, or foreign policy objectives. The Observatori del Deute en la Globalització defines energy sovereignty as the right to make independent decisions on energy generation, distribution, and consumption while considering economic, social, and ecological factors. Thaler and Hofmann distinguish between ‘hard’ aspects, i.e. independent decisions regarding the structure and sources of energy supply, and ‘soft’ aspects of energy sovereignty, i.e. control over the operation of the energy system, energy policy, and market regulations. Several KPIs have been proposed to assess energy sovereignty, including the share of domestic energy production in total energy consumption, the ratio of domestic renewable energy production to total energy demand, or the net energy import dependency. Another KPI for energy sovereignty is the Herfindahl-Hirschman Index (HHI), which measures the concentration of energy supply or production within a particular market or region. Closely related to energy sovereignty is the concept of technology sovereignty, which focuses on the state’s ability to produce or control strategic energy technologies domestically. This can be quantified, for example, as the proportion of strategic energy technologies manufactured within a country. 2.1.4. Energy solidarity The objective of energy solidarity is to ensure the efficient operation of energy markets and the security of energy supply, while promoting energy efficiency and innovation, and enhancing the interconnection of energy networks. More broadly, solidarity is a foundational principle of the European Union (EU), implying that Member States are expected to assist one another across various domains, even at the expense of their own national interests. When applied to the energy sector, this principle is embodied in energy solidarity, which serves as a legally binding principle within the EU’s energy law. Although no universally accepted definition of energy solidarity exists, there is a general consensus that fostering a spirit of solidarity among Member States is essential for the effective functioning of the energy market. Based on EU, energy solidarity can be defined as the collaborative commitment among countries to ensure a secure, efficient, and sustainable energy market. The literature provides limited guidance on KPIs for measuring energy solidarity. However, potential metrics could include the volume of cross-border electricity and gas exchange, the share of energy imports from allied countries, or the response time for energy crisis interventions.
2.1.5. Security of supply There are various definitions of security of supply, which is sometimes considered a dimension of energy security. However, the literature frequently blurs the distinction between the terms energy security and security of supply. According to Möst et al., security of supply is achieved when the desired quantity of energy (of the required quality) is available consistently throughout the energy system at reasonable prices, which is similar to the definition of energy security. Security of supply primarily focuses on the reliability of power supply and the adequacy of generation and power grids. It is often illustrated through the assumption of overcapacities in electricity generation and transmission. According to the German Federal Network Agency, security of supply is characterised by sufficient generating capacities, electricity grid and gas networks that fulfil their transport tasks, reliable control mechanisms, and sufficient protection against third-party interference. The German Federal Ministry for Economic Affairs and Climate Action defines security of supply as maintaining electricity supply at all times despite an advancing energy transition. Schittekatte and Meeus categorise security of supply along the temporal dimension into a realtime to short-term aspect (system reliability) and a mid-term to long-term aspect (resource adequacy). Reliability is viewed as a precursor to resilience, particularly in the context of expansion planning. With regard to power systems, reliability refers to the probability of satisfying the load demand under uncertain conditions, especially in regionally restricted disruptions. The Cabinet Office of the United Kingdom explicitly emphasises the design of power system components, defining reliability as the assurance that these components are inherently capable of functioning under various conditions. Unlike resilience, which deals with HILP events, reliability addresses high-probability and low-impact events. The term adequacy, commonly referred to as “system adequacy”, is used in various contexts. A widely accepted definition by describes it as “the system’s capacity to satisfy electrical energy requirements while complying with requirements on safety and quality of service”. This definition mainly encompasses existing grid and generation capacities. The anticipated retirement or phasing out
Schmitz, Flachsbarth, Plaga, Braun, Härtel: Preprint submitted to Elsevier Page 4 of 22 Energy Security and Resilience: Reviewing Concepts and Advancing Planning Perspectives of conventional power plants and the expansion of renewable energy are expected to pose challenges for maintaining generation adequacy in the European power system. A prominent source monitoring Europe’s security of supply over a 10-year horizon is the “European resource adequacy assessment”, published by the European Union Agency for the Cooperation of Energy Regulators. Grid adequacy (or transmission adequacy) is a subset of system adequacy and refers to the ability to transport electricity from generation sites to consumers at all times, which requires sufficient transmission and distribution grid capacity. Several KPIs are commonly used to assess security of supply, including the loss of load expectation (LOLE), expected energy not served (EENS), system average interruption duration index (SAIDI), and value of lost load (VOLL). The LOLE measures the expected number of hours per year in which the demand for (electrical) energy cannot be met. The EENS quantifies the expected amount of energy that will not be provided due to supply interruptions. The SAIDI calculates the average duration of power interruptions per customer served over a given period. The VOLL estimates the economic impact of supply interruptions, reflecting society’s willingness to pay to prevent power outages. The calculation of the VOLL is influenced by several factors, including the timing and duration of the outage, as well as regional economic conditions.
2.2. Interrelations between defined terms Based on the literature review, a conceptual framework illustrating the definitions and interrelations between key terms relevant to energy security and resilience in energy systems has been developed. The overlapping arrows in the figure indicate that these interrelations do not follow a simple linear hierarchy but are instead strongly interlinked. Starting from the left side, LaBelle argues that energy sovereignty and energy solidarity contribute to the creation of energy security rather than being variables independent from energy security. Both energy sovereignty and energy solidarity play a supportive role in enhancing security of supply: the former increases security of supply, according to Kardaś, while the latter ensures the security of energy supply in the EU, according to EU and Maltby. Furthermore, Bartenstein suggests that energy solidarity also strengthens the resilience of the (European) energy system. Resilience is often regarded as a component of energy security. According to, many indicators of resilience can also be applied in the context of security of supply. Bento et al. and Azzuni and Breyer both argue that energy security is more than just security of supply because of other economic, social, and environmental aspects that also belong to the field of energy security. As discussed in Section 2.1.5, and according to Schittekatte and Meeus, reliability represents the real-time to shortterm aspects of security of supply, while adequacy pertains to the mid-term to long-term elements of security of supply. Figure 1 also categorises the different terms based on their association with either the technical or political level. Energy security and resilience appear across both technical and political levels, encompassing infrastructure, market dynamics, and policy considerations. Energy sovereignty and energy solidarity are primarily linked to the political level, given their association with policy decisions, international cooperation, and regulatory frameworks. Security of supply, along with reliability and adequacy, is primarily considered a technical concept. However, it also borders the political level, as decisions on market design, capacity mechanisms, and cross-border cooperation influence its effectiveness. 3. Shocks and SBPs challenging resilience
The interrelations between the terms discussed in Sec tion 2 demonstrate that enhancing the energy system’s resilience contributes inherently to improvements in both energy security and security of supply. Consequently, the primary focus of this work is to explore strategies for strengthening energy system resilience, recognising that such efforts will also support energy security and security of supply. For the sake of simplicity, however, the following sections will primarily refer to energy system resilience. As identified in the literature review, resilience in energy systems is particularly challenged by hazards and threats. While hazards typically refer to natural and unintentional events, threats are linked to intentional actions driven by specific actors with the capability and intent to cause harm. In the context of energy system planning and modelling, such events can be classified as either transient or disruptive. Transient events are anticipated to some extent but may not be fully accounted for in planning. Disruptive events arise from large-scale mega-trends with unpredictable magnitudes and progression speeds. Note that in a narrower context of electrical engineering, transient events are defined as temporary, short-lived phenomena. In macro-scale energy system modelling, the term is used more broadly to describe events with similar characteristics but on a different timescale. In order to optimise system design and enhance resilience, it is essential to consider hazards and threats in planning future energy systems. Hanke et al. introduce a useful distinction between “shock events” and so-called
slow burn processes (SBPs), which provides a structured approach to classifying hazards and threats as well as examining their effects on energy systems’ technical, economic, and environmental performances. Section 3.1 first characterises the two terms, followed by a discussion of their impact over time in Section 3.2. Schmitz, Flachsbarth, Plaga, Braun, Härtel: Preprint submitted to Elsevier Page 5 of 22 Energy Security and Resilience: Reviewing Concepts and Advancing Planning Perspectives
ST Energy security LT
Uninterrupted availability of energy sources at an affordable price is one aspect of is more than
Energy sovereignty LT
Right of a state to make independent decisions on energy generation, distribution, and consumption
Energy solidarity LT
Collaborative commitment among countries to ensure a secure, efficient, and sustainable energy market
create
increases
ST Resilience LT
Ability of an energy system to retain, react, overcome and overpass perturbations caused by a shock shared indicators
strengthens
ensures
ST Security of supply LT
Maintaining energy supply at all times by ensuring sufficient generation and transportation capacities
Mid-term to long-term aspect of
Adequacy LT
System’s capacity to satisfy energy requirements while complying with requirements on security and quality of service
Probability of satisfying the load demand under uncertain conditions
Short-term aspect of
ST Reliability is a precursor to
Technical level
Figure 1: Interrelations between definitions for terms relevant to energy security and resilience in energy systems and their transformation, own illustration. The white text boxes display commonly cited definitions from the literature. The labels “ST” and “LT” indicate whether terms are typically associated with a short-term or long-term context. Directed arrows represent the interrelations between terms.
3.1. Characteristics of shock events and SBPs
As discussed in Section 2.1.2, shock events are often described as HILP events. Although such events are rare, their potential for substantial and difficult-to-mitigate damage is significant. Importantly, shock events cannot be entirely avoided. Their impact is typically unevenly distributed across countries. In highly interconnected energy systems, such disruptions can propagate across neighbouring regions amplifying their effects. In contrast, slow burn processes (SBPs) refer to protracted, persistent, structural changes in the energy system. They evolve gradually and escalate in urgency over time. While unfolding, they lead to increased vulnerability and diminishing resilience, potentially resulting in a shock event in the future. A frequently used example is climate change, which will have a profound impact on the energy system due to increased extreme weather events, global warming, and changing resource requirements. Various hazards and threats that pose potential risks to the energy system have been identified in the literature. A classification of these risks into shock events and SBPs is provided in Table 1. Beyond commonly discussed shock events in the table, the literature also identifies less frequently explored risks, including individual but more pronounced droughts of solar and wind, or pandemics. Note that it is crucial to distinguish between their respective incidents and impacts. Therefore, the table focuses on event classification rather than detailing their consequences for the energy system. Schmitz, Flachsbarth, Plaga, Braun, Härtel: Preprint submitted to Elsevier Page 6 of 22 Energy Security and Resilience: Reviewing Concepts and Advancing Planning Perspectives
Table 1
Overview of potential hazards and threats to the energy system including a classification into shock events and SBPs, with references from the literature. Potential hazard Shock event or threat or SBP