Energy and water nexus : off-grid desalination. A critical review and a multi-criteria approach to alternatives selection

Access to clean water has risen for importance at the top of policy makers agenda, due to the growth of world population and the climate changes. Several populated regions facing water scarcity are located in coastal regions with access to seawater, or in arid inland areas with access to brackish groundwater. Desalination would be a logical solution for these regions, but it is an energy-intensive process that usually relies on fossil fuels. Conventional desalination systems powered by fossil fuels produce environmental pollution and emission of greenhouse gases and they strongly depend on the unpredictable fluctuations of the oil and gas market prices. Certain developing countries experience energy scarcity as well as water scarcity, in particular in rural areas: hence, the challenge is to develop innovative and sustainable water-energy solutions, capable to provide with freshwater rural areas with no access to the electric grid. The present study starts relying on a critical literature review on desalination solution strictly focused on technologies appropriate for small-scale off-grid desalination. From the critical review emerges that there is no best method of desalination: the selection of a solution depends on a careful study of the context, since local circumstances may play a significant role in determining the most appropriate process for a rural area. Hence, a multi-criteria decision method based on the Analytic Hierarchy Process, able to support non-technical decision-makers, is defined through the definition of the hierarchy of the problem and of a set of indicators capable to evaluate the full sustainability of the technical solution. The model is then tested on a case study. Once the most appropriate technology is identified, it is necessary to proceed with the detailed design of the desalination system. The present study eventually shows the challenges of this phase, describing the pre-feasibility study and the design of a renewable energy system (RES) intended to power a desalination laboratory at the American University in Cairo (AUC, Egypt). The pre-feasibility study includes the detailed analysis of the energy requirements of the laboratory together with an accurate assessment of the renewable energy potential of the AUC campus. Several scenarios based on this assessment study are then developed, in order to identify the most appropriate RES and to proceed with the detail design of the system.