Green ammonia production facilities can be situated in remote areas with access to often fully off-grid renewable power supply. This article examines plant concepts and discusses the challenges and solutions for these plant architectures. Through a case study, an efficient and innovative methodology to compare options and optimise the sizing of the plant is presented. The methodology addresses the intermittency of the power production, the flexibility limits of the main process units, and the costs of investment and operation, using proprietary techno-economic dynamic simulation software, Odyssey.