The regulating role of dessalination in the water-energy balance: Application to the hybrid system of Milos island

The subject of this thesis is the operation of combined management of water and energy systems, which have as interface desalination units. These units serve water needs, consuming energy for water treatment and pumping. Based on the recently constructed system of the wind farm and desalination plant on the island of Milos, a simulation model of the island's water balance is developed, in combination with the utilization of the wind energy produced by the wind farm to cover the energy of the unit.

The model is runs in hourly time step. It gets as input data wind time series adapted to the data of Milos, the estimated population and the water needs of the island for the year 2020. The total length of simulation is 10 years, and concerns the operation of the system, using the above data as well as the real technical characteristics of the desalination unit, the pumping system, the water supply tank and the wind turbines. The simulation model was applied for three management cases, each one based on a different operating rationale. The first is a zero-reference scenario, according to which the desalination plant operates without using energy from the wind turbines, thus consuming energy only from the PPC network, and desalinating a fixed hourly amount of water that depends on the total daily demand. According to the second management case, the simulation is based on the utilization of the energy produced by the wind park and the corresponding maximum hourly amount of water that can be desalinated by consuming this energy. In this scenario, the water to be produced is by definition not constant, as it depends on the production of wind energy, which is randomly varying. In case of water demand deficits, it consumes additional energy from the PPC network. Finally, in the third management scenario, we consider a required hourly amount of water for desalination which is constant during the day and depends on the total daily demand. In order to cover the energy needs of the desalination unit, the available energy produced by the wind turbines is used by priority, and whenever this is not enough, additional energy of the PPC network is consumed. It should be noted that for the two scenarios that account for the operation of wind turbines, the surplus wind energy that is not consumed by the desalination plant, is available to the electricity network.

The results of the three management scenarios concern the way the system operates and its performance according to specific evaluation indices. Then, from the parametric analysis performed, general conclusions emerge regarding the effect of the technical characteristics of the system (i.e., pumping capacity, drinking water tank capacity, and number of wind turbines) both in its operation and in its performance, according to the evaluation indices. Finally, based on the most reliable solution, the system is optimized in terms of specific techno-economic evaluation metrics, such as the reliability of providing drinking water and the total cost of the system.