Abstract The recent ratification of the Paris Climate Change Agreement has significant implications for Australia given its emissions intensive economy. It is likely that the electricity sector will need to decarbonize for Australia to meet medium- and long-term emissions reduction targets. This paper explored the potential role of Concentrating Solar Thermal (CST) in a 100% renewable National Electricity Market (NEM) system under different scenarios of CST configuration and subjected the results to sensitivity analysis. A Genetic algorithm (GA) was chosen as the optimization algorithm to seek the least cost combination of renewable generation technologies, transmission interconnectors and storage capacity in the NEM system at hourly temporal resolution. The main finding is that the scenario where all three CST configurations (six, nine, and 12 h of thermal storage) can be deployed achieves a lower system cost than scenarios where the size of thermal storage coupled with CST is limited to one option. The results are sensitive to assumptions of the discount rate, renewable resource availability, and the cost of CST technology. This paper found that meeting demand during winter evenings is the most challenging time period for a 100% renewable NEM power system.