Sustainability assessment of technology systems that address the energy-water nexus: the case of desalination in the Western Cape

[摘要] ENGLISH ABSTRACT: In recent decades, the critical interdependencies that exist between the energy and water sectors,referred to as the energy-water nexus, have been investigated. It has become apparent that a policychange or intervention in one of the sectors can have a significant impact on the other. The impacton the entire energy-water nexus, therefore, needs to be considered when implementing changes ineither sector. The Western Cape Province needs to increase its available water supply to ensure thatthe future water demand can be met. The aim of this research was to investigate theappropriateness of seawater desalination used in conjunction with renewable energy as a possiblewater supply intervention. The objectives of this research were to: select an appropriate modellingapproach; compile, verify and validate the model; simulate different scenarios with and without thetechnology; and provide policymakers with recommendations regarding the sustainability ofimplementing a desalination technology system.It was determined that the Western Cape Province's energy-water nexus is a complex system,because of the number of subsystems that exist within the system. A literature survey of theprevious efforts that had been made to model similar systems was conducted. System dynamicsmodelling was found to be the most appropriate modelling tool, given the objectives of the researchand the complexity of the problem.A systems thinking and modelling process was followed to develop a model of the Western CapeProvince's energy-water nexus. The first phase was problem formulation, and the second phase wasthe development of the conceptual model using causal loop diagrams. The construction, verificationand validation of the dynamic computer simulation model was done in the third phase.Once confidence in the dynamic model was established, the fourth phase of the modelling processwas completed. For this phase, a number of scenarios were developed and simulated to determinethe effect of different desalination technology systems on the Western Cape Province. The impact ofmulti-effect distillation (MED) and reverse osmosis (RO) were compared. The effects of combiningthese technologies with different renewable energy sources, including thermal waste heat and solarenergy, were also investigated. It was seen that the Western Cape Province's water supply would beunable to meet the future water demand if no intervention was made. The results indicated that ROwith photovoltaics would be the most sustainable and that the system's life cycle cost up until 2040is the lowest of all the simulated systems. In phase five, it was recommended to policymakers that,of all the systems that were considered, this system would be the best to implement. Additionalwater supply interventions, however, need to be investigated, as the recommended desalinationsystem would not be enough to ensure sufficient future water supply.This research provides a better understanding of the complexities involved in the installation of anew technology system, such as desalination, in the Western Cape Province's energy-water nexus.This research can be used as a platform to further explore the impacts of a desalination system or toinvestigate the sustainability of other technology systems that will affect the nexus.

[发布机构] Stellenbosch University