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Development of an optimisation framework for integrated planning of the renewable energy and water supply

Vakilifard, Negar (2019) Development of an optimisation framework for integrated planning of the renewable energy and water supply. PhD thesis, Murdoch University.

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Urbanisation, population growth, and economic development have turned cities into largest water resources consumers. The adverse effect of climate change adds even more pressure on the existing water resources and makes it inevitable to consider drought-proof technologies such as desalination to supply the increasing urban water demand. However, the energy intensity of these technologies questions the sustainability of their long-term application and highlights the necessity of considering renewable energy sources to meet their energy demand.

In land-restricted urban areas, electricity from residential rooftop grid-connected photovoltaics (PVs) is a promising clean energy source, which can contribute to the urban energy mix. Although, the intermittency of the surplus output from PV systems is a barrier for a higher potential capacity of their installation. This surplus energy is a result of the mismatch between energy generation and demand occurring during the day in the residential sector.

This study aims to address both issues of sustainable water supply and surplus PV output intermittency in the context of the integrated water and energy management. Different water supply system components are considered as deferrable loads exhausting surplus PV output at the time of its generation. Accordingly, the optimal decisions for a desalination-based water supply system driven by grid electricity and surplus PV output (hybrid energy sources) are achieved using mathematical optimisation modelling supported by three tools: geographical information system (GIS), system advisor model (SAM), and Excel.

The linear programming model is first developed for the optimal scheduling of the integrated system and then extended as a mixed integer linear programming (MILP) model to also include the optimal strategic decisions. The model considers temporal and spatial water and energy demands, supply systems configuration, resources capacities and associated costs as well as electricity pricing tariffs. It, then, gives the optimal solution such that it leads to the greatest compatibility of the water supply system operation with available renewable energy and the least system costs over the defined planning horizon. The model is tested for current and future water supply in an urban area located in the north-western corridor of Perth, Western Australia (WA). However, it can be applied to any urban area located in arid and semi-arid regions.

The initial results for optimal operation of the system showed that considering surplus PV output as a part of water-related energy mix leads to higher PV installation capacity and significant savings in operational and maintenance (O&M) costs. Compared to fixed (yearly basis) and semi-flexible (seasonal basis) operation of the water supply system, flexible (hourly basis) mode of operation resulted in the most compatibility with available surplus PV output; and therefore, a higher share of renewable energy in water-related energy mix. It also showed higher economic benefits over other operational scenarios in terms of the total system costs. In all cases, however, the availability of surplus PV output is a detrimental factor to the economic performance of the system.

The optimal long-term planning for the water supply system operated compatibly with available renewable energy resulted in a multistage construction and expansion of water supply components for sustainable demand supply. In addition, it was shown that decentralised water supply systems operated in flexible mode, leads to less discounted total cost of the system and higher level of potential PV uptake capacities, compared to centralised water supply systems operated in fixed mode; even though the surplus PV output is considered as a part of their energy mix. In this regard, the effect of the householders’ free will for up taking PV systems and probable imposed O&M costs of the flexible mode of operation needs to be taken into account if the decentralised scenario is chosen to be implemented in practice.

It was also indicated that considering the effect of the indirect environmental impact of purchasing grid electricity for water supply affects the optimal results in terms of system components capacity as well as the timing of the construction and expansion of the water supply system. It also results in less indirect greenhouse gas emission and higher discounted total cost of the system over the planning horizon. In this respect, the generation source of purchased electricity plays a significant role.

Finally, the achieved insight into the different aspects of the desalination-based water supply system driven by hybrid energy sources led to the series of recommendations for future studies in the context of the integrated water and energy management.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): Engineering and Energy
United Nations SDGs: Goal 7: Affordable and Clean Energy
Supervisor(s): Bahri, Parisa, Anda, Martin and Ho, Goen
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