With a fast growing world population, the lack of fresh water is one of the world’s biggest future concerns. Water stress can lead to conflicts, holds back economic growth and has a major impact on human health. Nowadays, more and more countries that lack fresh water sources are using the saline water from the oceans and desalinate it to produce fresh water. The most common way to do this is by the means of Reverse Osmosis (RO). However, one of the biggest negative aspects of desalination is its high energy consumption, mostly provided by fossil fuels. Therefore, a more sustainable solution using renewable energy sources to power a RO system is necessary. Delft Offshore Turbine (DOT) is currently developing a hydraulic drive train wind turbine that converts the aerodynamic power captured from the wind into hydraulic power. With a positive displacement pump, a high pressure water stream is created for centralised electricity production using a spear valve and a Pelton wheel. Using this hydraulic turbine for the purpose of fresh water production with RO can be a well fitted combination. Using wind as an energy source for desalination purposes, however, creates some major challenges, one of which is dealing with the inconsistency of wind. For varying wind speeds, a hydraulic wind turbine is controlled by regulating system pressure hence the pump torque with the spear valve. With a Seawater Reverse Osmosis (SWRO) system with ERD, it is researched how to regulate the flows and pressures for a stable operation. In this thesis, the combination of the hydraulic wind turbine with a Reverse Osmosis system with an Pressure Exchanger Energy Recovery Device (ERD) is being analysed in more detail. For this, a numerical model is used to determine the systems' behaviour and an experimental test setup is designed and constructed to validate the model results. The aim of this thesis is to compare the desalination system performance with a stand-alone system without an ERD, to determine the influence of varying ERD settings on the systems' pressure for potential system pressure and torque controllability, and to investigate how the RO system with an ERD affects the wind turbines stability. The analysis shows a large positive influence on the amount of produced permeate when using an ERD in the RO system. In addition, the power consumption of the RO process can be reduced by up to 80%. A varying input provided by the high pressure pump, for example as a results of varying wind speeds, does not seem to (negatively) affect the efficiency of permeate production. By varying the ERDs' rotational speed, the feed pressure at the membranes inlet hence the pressure at the high pressure pump can be slightly influenced. However, this limited influence is not enough to effectively affect and control the high pressure pumps' torque. On top of that, for the wind turbine to operate in a stable operating region, it seems that the use of an ERD affects the system in such a way that water production can only be realised at fairly high wind speeds. To optimally make use of the hydraulic wind turbine and operate at the highest possible aerodynamic efficiency, a combination of electricity production at low wind speeds and water production with an ERD when wind speeds are sufficient, can be interesting. For this, future research is required.

Due to climate change and growing cities, water scarcity is becoming one of the futures biggest problems. On top of that, the population and prosperity of cities around the equator are growing fast. Meaning that the need for electricity, cooling and drinking water will grow fast in the following decades. ROTEC’s vision is that these growing problems require a sustainable approach for the future. A solution to these challenges can be found in the oceans temperature difference. The top layer of the ocean is heated by the sun, while the deeper layer remains cold. This causes around the equator a temperature difference of more than 20 degrees over the ocean’s depth. This offers a lot of opportunities. It can be used as a vast source for electricity production (OTEC), large scale drinking water production (ROTEC) and for cooling (SWAC). Indonesia is one of the best locations worldwide, due to the easy access of cold deep sea water and the abundant presence of hot surface water. North-Sulawesi has a unique access to these sources. Due to the steep slope of the seabed the cold deep seawater can easily be reached. Team ROTEC conducted a research in Manado for two months and came up with several solutions that can contribute to a more sustainable and beneficial future of North Sulawesi. There was mainly focussed on performing a need assessment for the capital Manado and the touristic Bunaken Island. This pointed out that Manado can reduce their electricity usage during peak loads by implementing a new way of cooling of malls and hotels along the boulevard. Bunaken needs electricity and drinking water in a way that is more easy to maintain and operate. Data analysis and measurements showed that both Bunaken and Manado have a high theoretical potential, since cold deep seawater is close to shore and found at relative shallow depths. For Manado a new seawater district cooling system is proposed. This system uses cold deep seawater to cool the large buildings along the boulevard, instead of conventional chiller-cooling-tower units. The solution reduces their electricity usage for cooling by 96% and more electricity is left for the grid of Manado. The yearly costs for the operation of the cooling is 92% cheaper and the investment for the installation is earned back within 6 years after construction. Peak loads in the grid are decreased and emissions reduced; equivalent to 19,000 tons CO2 per year. For Bunaken an integrated drinking water and electricity solution is found. By just using the temperature difference in the ocean, to produce clean and constant electricity and drinking water from seawater. The proposed installation provides the base load (80kW) for Bunaken for the same price as current solar PV and diesel generators together. Clean drinking water for the villagers is 12 times cheaper than Aqua Danone and 1.4 times cheaper than the not drinkable water from fresh water wells on the island. Such a kind of installation can produce 24/7, is stable and that without the need of fuels.