UQ eSpace

Abstract

The electrification of remote locations that lack grid-connectivity is a global challenge. In Australia, off-grid electricity accounts for 6% of total generation. At present these needs are met through the use of fossil fuels, resulting in a high electricity cost, and environmental consequences. With the present drive towards reducing greenhouse gas emissions and increasing the use of renewable energies, there is an opportunity to transition from the use of fossil fuels in remote locations to the use of renewables. In this regard, the hybridisation of renewable technologies with diesel generators has been shown to improve reliability and increase penetration. This project aims to explore the use of a hybrid renewable energy system consisting of solar photovoltaic (PV) with battery storage, concentrating solar thermal (CST) with thermal storage and diesel generators for off-grid power generation. The analysis considers two major consumer groups, viz. mining sites and communities, at three locations-Newman, Port Augusta and Halls Creek. In particular, the solar thermal system explored utilises a supercritical carbon dioxide power cycle, due to the suitability of this technology at scales appropriate for off-grid use. This is necessitated due to the fact that existing CST plants typically utilise a steam Rankine cycle, which suffers reduced efficiencies at small scales. Based on the existing literature, the proposed technologies have been found to present excellent suitability to this application. A key area of interest with regards to the CST plant is the turbine inlet temperature, due to higher temperatures presenting a higher power cycle efficiency, which offers a route to reduce energy costs. However, these higher temperatures increase the power cycle and receiver costs, due to the requirement of higher performance materials. Increases in receiver losses are also seen at higher temperatures. Similarly, the CST plant also presents increasing field losses with increasing size. In this analysis, three turbine inlet temperatures (namely 650°C, 800°C and 1000°C) are explored. A Python program was developed, encapsulating the thermodynamics and operating characteristics of each technology, to simulate the performance of the hybrid system over the course of one year, based on weather data and a synthetic load profile. This simulation was then used along with an optimisation function to identify the optimal mix of technologies in the hybrid system based on the minimum levelised cost of energy (LCOE). Using this program, results were generated for community and mining consumer groups at the three locations, and it was found that in both cases the optimal mix consists of CST as the primary source of baseload power, with 12-15 hours of thermal storage. While PV and diesel generators were both shown to be necessary, they represent a smaller fraction of the total energy production and serve as supplementary sources of power. Notably, none of the optima included battery storage, highlighting the high costs of this technology ...