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

==== 6.4.5.2 Electricity Transmission ====

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Given the significant geographical variations in the efficiency of renewable resources across different regions and continents, electricity transmission could facilitate cost-effective deployment of renewable generation, enhance resilience and security of supply, and increase operational efficiency ( ''high confidence'' ). The diurnal and seasonal characteristics of different renewable energy sources such as wind, solar, and hydropower can vary significantly by location. Through enhanced electricity transmission infrastructure, more wind turbines can be deployed in areas with high wind potential and more solar panels in areas with larger solar irradiation. Increases in electricity transmission and trade can also enhance operational efficiency and reduce or defer the need for investment in peaking plants, storage, or other load management techniques needed to meet security of supply requirements associated with localised use of VRE sources. Increased interconnectivity of large-scale grids also allows the aggregation of ‘smart grid’ solutions such as flexible heating and cooling devices for flexible demand in industrial, commercial, and domestic sectors ( [[#Hakimi--2020|Hakimi et al. 2020]] ) and EVs ( [[#Muratori--2020|Muratori and Mai 2020]] ; Li et al. 2021). In general, interconnection is more cost-optimal for countries that are geographically close to each other and can benefit from the diversity of their energy mixes and usage ( [[#Schlachtberger--2017|Schlachtberger et al. 2017]] ). Such developments are not without price, however, and among other concerns, raise issues surrounding land use, public acceptance, and resource acquisition for materials necessary for renewable developments ( [[#Capellán-Pérez--2017|Capellán-Pérez et al. 2017]] ; [[#Vakulchuk--2020|Vakulchuk et al. 2020]] ).

A number of studies have demonstrated the cost benefits of interconnected grids in a range of geographical settings, including across the USA ( [[#Bloom--2020|Bloom et al. 2020]] ), Europe ( [[#Newbery--2013|Newbery et al. 2013]] ; Cluet et al. 2020), between Australia and parts of Asia ( [[#Halawa--2018|Halawa et al. 2018]] ), and broader global regions, for example between the Middle East and Europe or North Africa and Europe ( [[#Tsoutsos--2015|Tsoutsos et al. 2015]] ). While there is growing interest in interconnection among different regions or continents, a broad range of geopolitical and socio-techno-economic challenges would need to be overcome to support this level of international cooperation and large-scale network expansion ( [[#Bertsch--2017|Bertsch et al. 2017]] ; [[#Palle--2021|Palle 2021]] ).

'''Status of electricity transmission technology.''' Long-distance electricity transmission technologies are already available. High voltage alternating current (HVAC), high-voltage direct current (HVDC), and ultra HVDC (UHVDC) technologies are well-established and widely used for bulk electricity transmission ( [[#Alassi--2019|Alassi et al. 2019]] ). HVDC is used with underground cables or long-distance overhead lines (typically voltages between 100–800 kV) ( [[#Alassi--2019|Alassi et al. 2019]] ) where HVAC is infeasible or not economic. A project development agreement, worth approximately USD17 billion, was signed in January 2021 that would connect 10 GW of PVs in the north of Australia via a 4500 km 3 GW HVDC cable to Singapore, suggesting that this would be cost effective ( [[#Sun%20Cable--2021|Sun Cable 2021]] ). In September 2019, the Changji-Guquan ±1,100 kV UHVDC transmission project built by State Grid Corporation of China was officially completed and put into operation. The transmission line is able to transmit up to 12 GW over 3341 km ( [[#Pei--2020|Pei et al. 2020]] ). This is the UHVDC transmission project with the highest voltage level, the largest transmission capacity, and the longest transmission distance in the world ( [[#Liu--2015|Liu 2015]] ).

Other technologies that could expand the size of transmission corridors and/or improve the operational characteristics include low-frequency AC transmission (LFAC) (Y. [[#Tang--2021|]] [[#Tang--2021|Tang et al. 2021]] ; [[#Xiang--2021|Xiang et al. 2021]] ) and half-wave AC transmission (HWACT) ( [[#Song--2018|Song et al. 2018]] ; [[#Xu--2019|Xu et al. 2019]] ). LFAC is technically feasible, but the circumstances in which it is the best economic choice compared to HVDC or HVAC still needs to be established ( [[#Xiang--2016|Xiang et al. 2016]] ). HWACT is restricted to very long distances, and it has not been demonstrated in practice, so its feasibility is unproven. There are still a number of technological challenges for long-distance transmission networks such as protection systems for DC or hybrid AC-DC networks ( [[#Chaffey--2016|Chaffey 2016]] ; Franck C. et al. 2017), improvement in cabling technology, and including the use of superconductors and nanocomposites ( [[#Ballarino--2016|Ballarino et al. 2016]] ; [[#Doukas--2019|Doukas 2019]] ), which require advanced solutions.

'''Challenges, barriers, and recommendations.''' The main challenge to inter-regional transmission is the absence of appropriate market designs and regulatory and policy frameworks. In addition, there are commercial barriers for further enhancement of cross-border transmission. The differing impacts of cross-border interconnections on costs and revenues for generation companies in different regions could delay the development of these interconnectors. It is not yet clear how the investment cost of interconnections should be allocated and recovered, although there is growing support for allocating costs in accordance with the benefits delivered to the market participants. Increased cross-border interconnection may also require new business models which provide incentives for investment and efficient operation, manage risks and uncertainties, and facilitate coordinated planning and governance ( [[#Poudineh--2017|Poudineh and Rubino 2017]] ).

Optimising the design and operation of the interconnected transmission system, both onshore and offshore grids, also requires more integrated economic and reliability approaches ( [[#Moreno--2012|Moreno et al. 2012]] ) to ensure the optimal balance between the economics and the provision of system security while maximising the benefits of smart network technologies.

A wide range of factors, including generation profiles, demand profiles circuit losses, reliability characteristics, and maintenance, as well as the uncertainties around them will need to be considered in designing and operating long-distance transmission systems if they are to be widely deployed ( [[#Djapic--2008|Djapic et al. 2008]] ; [[#Du--2009|Du 2009]] ; [[#De%20Sa--2011|De Sa and Al Zubaidy 2011]] ; [[#E3G--2021|E3G 2021]] ). Public support for extending transmission systems will also be crucial, and studies indicate that such support is frequently low ( [[#Vince--2010|Vince 2010]] ; [[#Perlaviciute--2018|Perlaviciute et al. 2018]] ).

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