The impact of electrolyser allocation on Great Britain's electricity transmission system in 2050

Global initiatives to mitigate climate change have spurred significant interest in hydrogen electrolysers, prompting large‐scale deployment worldwide over the coming decades. In this context, this paper investigates the impact of electrolyser spatial distribution on Great Britain's electricity transmission system in the year 2050. Using a mixed-integer linear optimization model based on the Holistic Network Design framework, we conduct sensitivity analyses across six diverse electrolyzer allocation scenarios in which electrolyser capacities vary between 0 and 70 GW and are distributed differently in Great Britain's electricity system in 2050: a baseline without electrolysers connecting in 2050, a "Basic" case with 23 GW in 2050 distributed proportionally to regional demand, a scenario with 70 GW distributed across onshore GB, a case where 23 GW is connected only in Scotland, a "Mixed" onshore-offshore configuration with 60 % offshore and 40 % onshore, and a case where 23 GW is concentrated in southern England. Results demonstrate that electrolyser placement significantly impacts transmission investment needs, with total boundary reinforcements varying from 148 GW to 298 GW across scenarios, and total system costs ranging from £4,160.8 million to £6,242 million for year 2050 (discounted to 2030). Strategic placement near renewable sources can reduce system costs by up to 28 % while producing identical hydrogen volumes, as demonstrated by the "All in Scotland" and "All in South" scenarios. This research provides critical insights for policymakers and system planners by highlighting the complex interdependencies between electrolyser allocation and electricity transmission planning for Great Britain's future energy landscape. • Placing 23 GW electrolysers in Scotland vs South England reduces total system costs by 22 % (£4,161 m vs £5,325 m). • Co-locating electrolysers with Scottish renewables cuts transmission needs 11 % below baseline levels • 70 GW electrolyser deployment reduces renewable curtailment by 97 %, from £799 m to £22 m. • Boundary reinforcement requirements vary 2-fold (148 GW - 298 GW) based on electrolyser location strategy. • London boundary LE1 requires 25–35 GW reinforcement across all scenarios due to concentrated demand.