The rapid growth in world population and increasing demands have led to the lack of fresh water, taking a toll on several of earths reserves, mainly the fresh water supply reserves. Water stress deters economic growth, leads to conflicts and has a direct impact on the health of humans. Studies show the trends in the increase of water consumption per capita due to increase in higher standards of living over the last years, resulting in the decrease of usable high purity water. 97% of the world’s water supply is locked in the salted, often unusable oceans. In recent times, water stressed countries are using the saline water from the oceans and desalinating it to produce fresh water for domestic, industrial or agricultural use. The state-of-the art method for desalinating saltwater is by Reverse Osmosis (RO). The biggest drawback of this technology is its high energy consumption mostly provided by conventional sources like fossil fuels. Therefore, for a sustainable future, a renewable energy source must be integrated to power the RO system. Delft Offshore Turbine (DOT) is currently developing and testing a new hydraulic drive train solution for fluid power transmission in offshore wind turbines using seawater as the medium. A hydraulic positive displacement pump is driven by the DOT wind turbine creating a flow of sea water under high pressure. This high-pressure flow can be either directed to a RO unit to desalinate seawater or converted into electricity using a spear valve and pelton turbine generator. A major challenge while using wind as an energy source is its intermittency. Reverse osmosis plants are designed to operate at a fixed flow and pressure while due to the uncontrolled, varying nature of the wind, the pump output experiences fluctuations in both pressures and flows. The aim of this thesis is to analyze the steady-state behavior of the integrated system for wind speeds up to the turbine rated wind speed under different operating conditions. This is achieved by simulating the behavior of the DOT500 hydraulic drive train wind turbine coupled to a RO system with pressure exchanger energy recovery device and a nozzle with a pelton turbine generator. The main objective of this research is to build a numerical model in Python using algorithms to solve the system of steady-state equations and optimize the integrated system for maximum water and maximum electricity production at specified locations. The numerical model is simulated for all combinations of wind speeds and nozzle positions and the behavior of the high-pressure pump, RO system, pelton turbine and various system parameters are shown. A sensitivity study is performed for important desalination parameters and their effect on system performance is analyzed. This research has yielded three main conclusions / deliverables: 1. Behavior of the wind powered integrated system to produce freshwater and electricity at different operating conditions. 2. Steady state control of DOT500 turbine and behavior of the pelton turbine to produce either maximum electricity or maximum water. 3. Sensitivity of important desalination system parameters on overall system behavior for future optimization of RO membranes.

The rapid increase in global population and rising demands have resulted in a shortage of clean water, depleting several of the Earth's reservoirs, especially those that reserve fresh water. Just 0.007% of the water on Earth is used to hydrate and feed billions of people, as determined by the water balance of the planet. Water-stressed nations are now desalinating salty ocean water to produce fresh water for use in their homes, industries, and fields. Among the processes used to produce freshwater, reverse osmosis (RO) is the most reliable technique for seawater desalination due to the high energy efficiency of the membranes and low desalination-associated costs. The major disadvantage of this technology is its high energy consumption, which is mostly derived from conventional sources like fossil fuels. Therefore, with a view to a sustainable future, renewable energy sources must be integrated to power the reverse osmosis systems. All conventional wind systems convert mechanical energy into electricity, which is used to power the desalination units. Delft Offshore Turbine (DOT) aims to replace the conventional drivetrain with a hydraulic transmission system that uses seawater as a hydraulic transfer medium. The examined DOT500 PRO system consists of a wind turbine connected to a hydraulic positive displacement pump, which induces seawater flow under high pressure. A reverse osmosis unit can be used to desalinate saltwater using this high-pressure flow and a Pelton turbine generator can be used to produce electricity. The long-term objective of the DOT project is to lower complexity, mass, maintenance, and capital expense to make offshore wind a competitive source of electricity. To further reinforce the concept's techno-economic components, the future strategy calls for the centralized production of electricity. This study aims to develop an operating strategy for the DOT500 PRO system for freshwater production at an offshore location. The viability of using such a system in a place with offshore wind conditions and predetermined freshwater demand was investigated using a constant operating scheme of a single spear valve. A numerical model is developed in Python to deliver the appropriate desalination unit size under offshore wind conditions in order to cover the water requirements of a given location. The model is applied to a case study of Agios Efstratios in Greece and can be used as a tool to investigate possible applications using the associated datasets. This research has yielded the following results: 1. A simple and robust system operating strategy for maximum water production that will ensure stable turbine function, while active control is used to maintain the system at constant operation when its limits are reached. 2. The direct influence of the spear valve position and reverse osmosis unit size on the system’s rated conditions and a reduced rated wind speed by 21.3% from the one utilized conventionally on the reference wind turbine. 3. The minimum required number of RO pressure vessels and membranes according to site-specific offshore wind profile and freshwater demand, as well as options for reducing the RO unit size.