This study presents a techno-economic feasibility study of a decentralized autonomous green methanol plant fully powered by renewable energy. Designed for deployment in remote, off-grid regions, the concept integrated solar photovoltaic generation, solid sorbent-based direct air capture of carbon dioxide, sorbent-based atmospheric water harvesting with indirect carbon dioxide hydrogenation. A multi-criteria decision analysis framework was applied for selection of subsystems based on autonomy, robustness, integration complexity, and energy efficiency. A comprehensive energy and mass balance revealed a specific energy consumption of 2119 kilojoules per mole, highlighting the energy-intensive nature of the process. Despite this, the plant remained competitive due to its modularity and site-specific optimization. Location analysis using a system modelling tool identified Duqm, Oman, as the most favourable site, offering consistent solar irradiance and low energy costs. A solar-only configuration is selected to reduce system complexity compared to hybrid solar-wind setups. A custom simulation framework incorporating model predictive control demonstrated uninterrupted operation under variable solar conditions, even with forecast uncertainty. Under these conditions, the plant achieved a levelized cost of energy of 174.30 dollars per megawatt-hour, which aligns with projected e-fuel costs for 2030. These findings confirmed the technical viability and economic competitiveness of autonomous decentralized methanol production, offering a scalable solution for sustainable fuel generation in remote and decarbonizing regions.