Abstract
Numerous factors contribute to the increased demand for food, energy, and water (FEW) resources. They include growing populations, migrations, globalization, and changing climatic patterns. As a prerequisite to achieving sustainable allocation and management of the FEW resources, a change from a solitary approach in which each sector is evaluated independently is required in favour of an integrated approach known as the Food, Energy, and Water Nexus (FEW-N). This concept acknowledges that there is a connection between the resources. This thesis proposes a hybrid quantitative decision-making framework to address natural resource allocation issues in FEW-N through a sustainable approach within social, economic, and environmental contexts. The thesis presents four mathematical models to achieve the objectives mentioned above. The first model in Chapter Three is a Mixed Integer Nonlinear Programming
iv
(MINLP) model applied to solve the multi-objective optimisation problem for a food and energy Nexus system. A demand response program was integrated into the optimisation framework within the nexus system to address the sizing problem associated with a standalone hybrid renewable energy system for food production. Minimum cost and maximum system reliability are the two objectives of the proposed model. According to the findings, the appliance scheduling case results in an annualized cost of R45,938.96 and a COE of 0.5744R/kWh less than the case without a scheduling strategy. Clearly, this represents a substantial annual cost reduction of 64 percent as well as a substantial saving in energy costs of 64 percent. From these results, it is evident that the TOU-DR program reduces the total system costs in the food-energy nexus, illustrating the benefits of the model.
Model two (detailed in Chapter Four) is a Mixed Integer Nonlinear Programming (MINLP) model used to solve a multi-objective resources allocation in the Nexus. The problem is formulated and solved using the Advanced Interactive Multidimensional Modeling System (AIMMS) Software. Results were validated based on various scenarios. 80% of the energy was renewable in the optimal energy mix, and 20% was traditional. The optimal water mix consisted of 80% ground water and 20% surface water. In light of the results, the proposed framework is robust because it introduces optimality in the face of tradeoffs among multiple objectives. The results also indicate that even though natural resources are limited, food security is achieved through the effective allocation of natural resources. The third model detailed in Chapter Five presents a FEW-N system that addresses the natural resource allocation and security issues. The integrated model consists of technical and economic models and input/output models within the optimisation framework to maximise the system’s monetary benefit. The developed framework was validated by performing a scenario analysis on three cases. It has been shown that using FEW resources in the rainfed, greenhouse, and irrigated agriculture has more significant benefits than its utilisation in the energy subsector to generate electricity through technologies such as bioenergy, solar/wind HRES, and hydropower. There has been a significant improvement in resource security due to the ability of diverse technologies within each subsector to satisfy the requirements of the populations. Specifically, the framework proposed will foster sustainability and guide national policy in the areas of food, energy, and water.
v
Chapter Six incorporates an environmental impact assessment model into the FEW-N system presented in Chapter Five. It was found that the use of FEW resources for food production was a more profitable investment than energy production. Results also indicated that the subsectors' economic output and environmental impact characteristics significantly influenced the proportion of FEW resources and technology options contributing to resource security compared with results obtained in Chapter five. Summarily, this thesis presents novel approaches using FEW-N thinking to enhance understanding of the interlinkages between the FEW resources, thereby achieving resource sustainability, reliability, and security. Keywords: Energy security, Environmental impact assessment, Food, energy and water Nexus, Food security, IO model, Renewable energy, Resource allocation, Resource security, Multi-objective optimisation, Sustainable development, Techno-economic model.