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Introduction: The Need for Sector Coupling and the Energy Transition Goals

Marialaura Di Somma1, Christina Papadimitriou2, Giorgio Graditi1, and Koen Kok2

1Italian National Agency for New Technologies, Energy and Sustainable Economic Development, Department of Energy Technologies and Renewable Sources, Lungotevere Thaon di Revel, 76, 00196, Rome, Italy

2Eindhoven University of Technology, Electrical Engineering Department, Groene Loper 3, 5612 AE, Eindhoven, the Netherlands

1.1 Introduction

1.1.1 The Needs and Challenges of the Current Energy System

The present energy system faces several pressing needs. With a growing demand for energy driven by population growth, industrialization, and improved living standards, there is an urgency to meet it in a sustainable manner. Simultaneously, addressing climate change requires a transition to low-carbon or carbon-neutral energy sources. However, integrating renewable energy sources (RESs) poses challenges due to their converter-based, intermittent, and variable nature. To ensure a reliable and resilient power system, aging infrastructure needs to be upgraded and modernized. Grid resilience must also be enhanced to withstand extreme weather events, cyberattacks, and other disruptions. Furthermore, supporting the electrification of different sectors, e.g. heating, cooling, and transportation, necessitates infrastructure development and adequate grid capacity that is now lacking. To this end, advancements in energy storage technologies are also crucial. Lastly, improving energy efficiency across sectors is vital to reduce overall energy demand and greenhouse gas (GHG) emissions, which requires a combination of technological advancements and policy measures.

Addressing the aforementioned needs is not trivial and numerous challenges are present. Balancing energy supply with the ever-increasing demand is a hard task as it does not only presuppose upgrades in related infrastructure and equipment but also changes on how the operators schedule and manage the grid. Transitioning to low-carbon energy sources while ensuring a reliable and uninterrupted power supply poses a complex task that requires careful planning and investment. Integrating RES into the grid requires addressing the intermittency and variability associated with them, by necessitating innovative solutions for effective integration. Moreover, upgrading and maintaining aging infrastructure presents financial and logistical challenges. Safeguarding the power grid against risks such as extreme weather events and cyberattacks requires robust strategies and investments in cybersecurity measures but also affects the "business as usual" in the operational planning of the operators. Advancing energy storage technologies is crucial for both dealing with the excess renewable energy and providing flexibility for balancing supply and demand. The electrification of various sectors presents several challenges that impact the power system overall. First, to satisfy all types of energy demands resulting from electrification, a significant amount of additional power network capacity is required. This includes accommodating the increased electricity consumption from transportation, buildings, and industry. Second, contingencies in the power system can have far-reaching consequences. Any disruption or failure can lead to power outages, affecting not only the resilience of the power system and of the electrified sectors but also the overall functioning of society. Grid stability and management become crucial factors in ensuring a reliable and resilient power supply in this case. As electrification changes the energy landscape, operators face new challenges in planning and scheduling. They must consider the increased complexity of managing diverse energy sources, grid capacity, and demand patterns to optimize system performance and ensure uninterrupted power supply.

As such, the distribution operators' planning and scheduling processes need to adapt to the evolving requirements of an electrified system to maintain efficient operations. Promoting energy-efficient practices and technologies across sectors requires changes in consumer behavior as well as supportive policies and incentives.

Finally, creating and implementing effective policies and regulations to facilitate the transition to a sustainable and resilient power system necessitates balancing the interests of different stakeholders and ensuring fair market competition.

Addressing these needs and challenges requires collaborative efforts from governments, energy providers, technology developers, researchers, and consumers to create a sustainable, secure, and affordable energy power system for the future.

1.1.2 What Is Sector Coupling?

Sector coupling originally referred to the electrification of end-use sectors such as heating, cooling, and transport, aiming at increasing the RES share in these sectors, based on the assumption that the electricity supply can be mostly renewable. More recently, the concept has been widened by also including supply-side sector coupling, integrating, for instance, power and gas sectors through power-to-gas (P2G) technologies. It must be highlighted that sector coupling is very similar to that of integrated energy systems, introduced by ETIP SNET Vision 2050 [1-3], defined as a system of systems. Namely, an integrated energy system is an integrated infrastructure for all energy carriers with the electrical system as a backbone, characterized by a high level of integration between all networks of energy carriers, coupling electrical networks with gas networks, heating, and cooling, supported by energy storage and conversion processes. The creation of these systems is based on the coordination of the planning and operation key processes. Within these processes, different types of energy systems across multiple geographical scales are considered to foster reliability and efficiency in energy services while also minimizing negative environmental impacts [4]. The different sectors that can be involved under the concept of sector coupling are represented in Figure 1.1.

Figure 1.1 Representation of sector coupling concept.

Source: Adapted from Van Nuffel et al. [4].

Two different strategies are considered under the concept of sector coupling, namely [5]:

• "End-user" sector coupling aiming at the electrification of end-use sectors and consisting of energy conversion technologies for electrification of final users' energy demand, thus enabling flexibility at the final users/prosumers level. An example of these technologies is well represented by electric vehicles (EVs) allowing for the electrification of the transport sector.
• "Cross-vector" sector coupling aiming at integrating multiple energy carriers mainly linking electricity and gas sectors through P2G technologies that can be used to produce hydrogen or synthetic methane when excess renewable electricity is available. The produced gas can be then stored for later re-conversion into electricity when renewable electricity supply is insufficient (and hence high electricity prices), by using the so-called power-to-gas-to-power process. On the other hand, electricity can be produced by hydrogen through fuel cells. Another alternative is that the hydrogen produced can be processed into methane or liquid fuel like methanol by making it reacts with CO or CO2, the so-called power-to-liquid route. These fuels can be used in transport sectors such as shipping.

The combination of these two strategies allows increasing the flexibility of the energy system, while also supporting RES integration through optimal use strategies. A good example was already provided above, but there is another key example represented by Power-to-Heat technology such as heat pumps. These latter, especially when combined with thermal storage, allow for thermal energy production in periods with excess renewable electricity which can be then stored and re-used in periods with insufficient renewable electricity, thereby representing a cost-effective and efficient solution.

1.2 Opportunities for Sector Coupling to Contribute to Decarbonization

1.2.1 Electrification and Sector Coupling

Electrification in power systems refers to the process of transitioning from traditional, fossil fuel-based energy sources to electrical power for various applications. It involves replacing the direct use of fossil fuels, such as gasoline and natural gas, with electricity as the primary source of energy.

The concept of electrification has gained significant attention in recent years due to its potential to reduce GHG emissions and combat climate change. So, electrification is one of the main drivers of energy transition as it is perceived nowadays and a reliable solution for effective decarbonization at the end user's side.

Therefore, the electrification scenario can be applied in different sectors. Some examples that can foster electrification are given below:

• Transportation: Electrification of transportation involves transitioning from conventional internal combustion engines (ICEs) to EVs. This shift reduces reliance on fossil fuels, decreases air pollution, and offers opportunities for smart charging and integration...