Renewable Energy in Stand-Alone Systems

Abstract

To ensure that future generations have a clean and livable planet, we, as the current temporary custodians, have a profound responsibility: to accelerate the transition to cleaner energy systems and limit global warming. Renewable energy deployments are the cornerstone of the fight against climate change. Decarbonisation of the electricity grid is already underway in many parts of the world and should be accelerated. However, there remain applications where grid connection is not feasible. In such contexts, stand-alone systems play a crucial role in ensuring reliable energy distribution. To displace fossil-fuel generators, stand-alone applications also require a rapid transition to renewable energy. This thesis investigates how renewable energy systems can be implemented in stand-alone applications. Beginning with a global review of recent literature, it analyses points of agreement and controversy, and identifies gaps in the social, economic, and environmental impacts of renewable energy deployment. Driven by the need to decarbonise activities taking place on Australia's Great Barrier Reef, the thesis then presents an assessment of the availability and feasibility of renewable energy on the Reef. Our assessments indicate that solar photovoltaics would be the best solution for rapid, near-term implementation of marine cloud brightening. Solar photovoltaic would have minimal impact on birds, is a mature technology, is available in abundance and could easily be deployed throughout the whole Reef. The thesis then focuses on incorporating green hydrogen into stand-alone energy systems. It investigates the impact of neglecting variable efficiency of electrolysers in green hydrogen production modelling. Findings indicate that using a fixed efficiency in electrolyser modelling, as commonly done in the literature, can lead to an overestimation of green hydrogen production by up to 24% and an underestimation of the optimal size of the hydrogen plant. A similar approach was used, and the impact of neglecting variability in fuel cell was investigated in a fully renewable energy system for the Great Barrier Reef. Results from this investigation indicate that ignoring the efficiency variability of fuel cells can lead to underestimations of 1.4% to 4.7%, equivalent to 30-107 kg of green hydrogen. Together, our studies on the overlooked variability in electrolyser and fuel cell efficiency highlight the need for more accurate modelling approaches, particularly when aiming to inform stakeholders and guide evidence-based policymaking. Finally, the thesis examines the load and cost conditions under which integrating green hydrogen into battery-only systems can improve the levelised cost of energy. Our results indicate that incorporating green hydrogen can help prevent significant oversizing of the battery and become economically beneficial during prolonged, infrequent, or poorly aligned loads. Our investigation into the impact of cost uncertainties, using estimates for 2025-2050, indicates that hydrogen integration becomes economically viable only when several component costs decline simultaneously. The fuel cell-to-battery power capital cost ratio was found to be the most influential factor in driving improvements in the levelised cost of energy. Our results highlight the strong sensitivity of hydrogen system viability to both load profile characteristics and cost interdependencies. These reinforce the need for targeted cost reduction strategies, particularly for fuel cells, to justify the added complexity of hydrogen integration. Altogether, the contributions from this thesis offer meaningful insights that support the broader pursuit of decarbonisation and a more sustainable future for generations to come. Show more