Editing IPCC:AR6/WGIII/Chapter-6 (section)

==== 6.4.3.1 Importance of Cross-sector Coupling for Cost-effective Energy System Decarbonisation ====

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Integrated whole-system approaches can reduce the costs of low-carbon energy system transitions ( ''high confidence'' ). A lack of flexibility in the electricity system may limit the cost-effective integration of technologies as part of broader net-zero energy systems. At the same time, the enormous latent flexibility hidden in heating and cooling, hydrogen, transport, gas systems, and other energy systems provides opportunities to take advantage of synergies and to coordinate operations across systems (Martin et al. 2017; [[#Zhang--2018|Zhang et al. 2018]] ; [[#Martinez%20Cesena--2019|Martinez Cesena and Mancarella 2019]] ; [[#Pavičević--2020|Pavičević et al. 2020]] ; [[#Bogdanov--2021|Bogdanov et al. 2021]] ) (Figure 6.16).

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'''Figure 6.16 | Interaction between different energy sectors.''' Source: extracted with permission from [[#Münster--2020|Münster et al. (2020)]] .

Sector coupling can significantly increase system flexibility, driven by the application of advanced technologies (Clegg and Mancarella 2016; [[#Heinen--2016|Heinen et al. 2016]] ; [[#Bogdanov--2019|Bogdanov et al. 2019]] ; [[#Solomon--2019|Solomon et al. 2019]] ; [[#Zhang--2019b|Zhang et al. 2019b]] ; [[#Zhang--2020|Zhang and Fujimori 2020]] ; [[#Zhao--2021|Zhao et al. 2021]] ). For example, district heating infrastructure can generate both heat and power. Cooling systems and electrified heating systems in buildings can provide flexibility through preheating and precooling via thermal energy storage (Z. [[#Li--2016|Li et al. 2016]] ; G. [[#Li--2017|Li et al. 2017]] ). System balancing services can be provided by electric vehicles (EVs) based on vehicle-to-grid concepts and deferred charging through smart control of EV batteries without compromising customers’ requirements for transport ( [[#Aunedi--2020|Aunedi and Strbac 2020]] ).

Hydrogen production processes (power-to-gas and vice versa) and hydrogen storage can support short-term and long-term balancing in the energy systems and enhance resilience (Stephen and Pierluigi 2016; [[#Strbac--2020|Strbac et al. 2020]] ). However, the economic benefits of flexible power-to-gas plants, energy storage, and other flexibility technological and options will depend on the locations of VRE sources, storage sites, gas, hydrogen, and electricity networks ( [[#Jentsch--2014|Jentsch et al. 2014]] ; [[#Heymann--2015|Heymann and Bessa 2015]] ; [[#Ameli--2020|Ameli et al. 2020]] ). Coordinated operation of gas and electricity systems can bring significant benefits in supplying heat demands. For example, hybrid heating can eliminate investment in electricity infrastructure reinforcement by switching to heat pumps in off-peak hours and gas boilers in peak hours ( [[#Fischer--2017|Fischer et al. 2017]] ; [[#Dengiz--2019|Dengiz et al. 2019]] ; [[#Bistline--2021|Bistline et al. 2021]] ). The heat required by direct air carbon capture and storage (DACCS) could be effectively supplied by inherent heat energy in nuclear plants, enhancing overall system efficiency ( [[#Realmonte--2019|Realmonte et al. 2019]] ).

Rather than incremental planning, strategic energy system planning can help minimise long-term mitigation costs ( ''high confidence'' ). With a whole-system perspective, integrated planning can consider both short-term operation and long-term investment decisions, covering infrastructure from local to national and international, while meeting security of supply requirements and incorporating the flexibility provided by different technologies and advanced control strategies ( [[#Zhang--2018|Zhang et al. 2018]] ; [[#O’Malley--2020|O’Malley et al. 2020]] ; [[#Strbac--2020|Strbac et al. 2020]] ). Management of conflicts and synergies between local district and national level energy system objectives, including strategic investment in local hydrogen and heat infrastructure, can drive significant whole-system cost savings ( [[#Zhang--2019b|Zhang et al. 2019b]] ; [[#Fu--2020|Fu et al. 2020]] ). For example, long-term planning of the offshore grid infrastructure to support offshore wind development, including interconnection between different countries and regions, can provide significant savings compared to a short-term incremental approach in which every offshore wind farm is individually connected to the onshore grid ( [[#E3G--2021|E3G 2021]] ).

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