Abstract Desalination driven by renewable energies is an interesting technology in isolated coastal areas. Its feasibility and reliability are guaranteed by innumerable designs implemented and experiences carried out, mainly focused on small capacity systems. However, only mature and efficient technologies are suitable for medium or large scale desalination. In the case of seawater desalination, wind-powered reverse osmosis is the most efficient, mature and cost-effective technology. This paper assesses the most suitable design for seawater reverse osmosis desalination driven by off-grid wind energy systems. A high innovative design based on gradual capacity with nominal production of 1000 m3/d is compared to a conventional fixed capacity desalination plant. Due to the intermittent wind resource, the gradual capacity desalination plant is able to fit the available energy and maximize the annual water production.