GREENH2ATLANTIC will help Europe to reach green and affordable electrolysis at GW-scale in 2030 by developing and demonstrating a first-of-a-kind 100 MW alkaline electrolyser at TRL8, leveraging scale-up, standardization and manufacturing automation. This 100 MW electrolyser will be composed of innovative, scalable and fast-cycling 8 MW modules which overcome bottlenecks related to CAPEX (480EUR/kW, -31%), efficiency (49 kWh/kg at nominal power), size (-40%), lifetime (70 000 operating hours @ degradation rate of 0.12%/1000h), current-density (>0.5 A/cm2) and flexibility (ramp-up and down between 20-100% in less than 30 sec and 5 sec, respectively). GREENH2ATLANTIC will supply multiple local off-takers and help reduce the LCOH to 2.87EUR/kg of green H2. An innovative interface system composed of advanced power electronics will allow for the direct coupling of the electrolyser with local, dedicated hybrid (solar and wind) renewable energy. Moreover, an innovative, AI-enhanced Advanced Hydrogen Management System will allow for the optimization of OPEX, load factor, real-time H2 production management, system behaviour analysis, etc. The consortium includes the full value chain including European electrolyser manufacturing, green hydrogen production, off-takers from the chemical industry and natural gas grids, power electronics developers, AI energy management system developers, renewable energy providers and electrical grid balancing. The demonstrator will reduce greenhouse gas emissions by 82.16 ktCO2-eq/year. Clear exploitation and replication plans based on rigorous analyses are presented to reach 1 GW by 2030 in Sines and beyond, creating an estimated 1147 direct and 2744 indirect jobs. Green H2 market readiness will be enhanced in promising H2 valleys across Europe, targeting at least 5 systemic H2+RE investment plans facilitated across Europe by the end of the project. Finally, the project will provide actionable input for EU harmonisation and regulations.