Browsing by Author "Burger, JDV"
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- ItemTechno-economic evaluation of long-term energy storage options for variable renewable energies in South Africa(Stellenbosch : Stellenbosch University, 2022-11) Burger, JDV; Harms, TM; Van der Spuy, SJ; Sebitosi, B; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: Energy generated by renewable technologies like solar photovoltaics (PV), concentrated solar power (CSP) and wind power, is intermittent (i.e., not dispatchable) and is therefore known as variable renewable energy (VRE). Since the value of electricity is dependent on when it is generated, a dispatchable energy power plant that can deliver electricity when it is needed, is more valuable. With the inclusion of energy storage systems (ESSs), VRE plants can produce dispatchable electricity. This can increase their share of the national energy mix and facilitate the transition away from traditional, greenhouse gas emitting, hence climate change inducing, electricity generation based on fossil fuels like coal or natural gas. The motivation for this study was to identify the most cost-effective ESS technologies for VREs, based on selected applications. This study sets out to conduct a literature survey of the state-of-the-art ESS, develop a method of comparing their technical and financial performance and based on the results, draw conclusions pertaining to the deployment of such systems. An appropriate solution is proposed for the development of the South African energy mix going forward. The special case of CSP is considered since it includes built-in low-cost thermal energy storage (TES) and electricity generating inertia, which other VREs do not have. Based on findings in the literature, two energy storage applications are selected, namely peaker replacement and long-term seasonal energy storage, for evaluation in this study. State-of-the-art ESSs are investigated, and five technologies are selected for comparison: pumped storage hydroelectricity, compressed air energy storage, lithium-ion battery energy storage, vanadium-redox flow batteries and hydrogen power-to-gas energy storage. A metric like LCOE, levelised cost of energy storage (LCOS), is identified as a suitable method for comparing ESS technologies. A probabilistic model, in the form of Monte Carlo analysis, is developed to account for the uncertainty associated with some of the input variables of the LCOS model. The model is verified and its sensitivity to some of the input variables is determined. The techno-economic model is used to compare the five ESSs in the peaker replacement and long-term seasonal storage applications. The sensitivity of the LCOS to variance of the discount rate and discharge duration is investigated. A method is developed to compare the cost-competitiveness of CSP (with built-in TES) to PV and wind-powered plants coupled with the five ESSs considered in this study. It was found that the investment cost had the greatest influence on LCOS, while that of replacement and operational costs were far less. This sensitivity was found to be even more significant for long-term seasonal storage applications. It was also found that the LCOS is more sensitive to changes in the annual cycle frequency than the discharge duration. While it was found that pumped hydroelectricity and compressed air energy storage proved cost competitive with South African CSP plants (commissioned between 2018-2019), a comparison with the Aurora CSP plant in Australia showed that CSP has a value proposition at storage capacities of 4-8 h. As such, an argument is presented for CSP to be re-introduced in South Africa’s integrated resource plan, particularly whenever dispatchable generation is called for.