Thermal energy storage for renewable integration: a techno-economic analysis in the Chilean energy context
Chile has set ambitious targets to reach 100% renewable generation in the electric system and supply 80% of its heating with sustainable sources by 2050. The fulfilment of these goals brings new challenges for balancing supply and demand and creates the need for providing the energy networks with operational flexibility from new sources. Thermal energy storage arises as an option that can provide part of this flexibility, decoupling supply and demand by time-shifting power delivery at a competitive cost and with fewer geographical limitations compared to other storage technologies. Although Chilean energy policy has recently turned its attention on these issues, there is still a lack of technical input for assessing the potential of thermal energy storage to support the deployment of renewables in the electric grid and for cleaning heating supply. This thesis aims to bridge that gap and focuses on assessing how different thermal energy storage technologies can help to increase the share of intermittent renewables in the Chilean electric grid and in its residential heating sector. This is performed through techno-economic optimisation of the design and operation of specific thermal energy storage systems configurations. In the case of the electric grid, a linear optimisation model of the Chilean network is developed. The long-term impact of pumped thermal energy storage on the total system’s cost is assessed. Among the main findings, it is concluded that the integration of on-grid 8h capacity storage increases the solar photovoltaic fraction, which leads to reductions in operation and investment costs by 2050. For the residential heating sector, a solar district heating network supported by borehole seasonal thermal storage is proposed as a clean alternative for heating in southern Chile. A simulation-based multi-objective optimisation of the system’s design is performed, focusing on minimising cost and emissions. The results show that this system can be cost-competitive with some conventional heating technologies under specific circumstances. The presence of seasonal thermal storage helps drive down the total emissions by reducing the use of the auxiliary gas heater in winter. Finally, the solar district heating network is combined with a heat pump, and the effect of the power-to-heat scheme supported by short and long-term storage is assessed. It is found that despite the positive impact on cost and emission of the heat pump integration under the proposed configuration, fast charging thermal storage technologies may be better suited to integrate the heat supplied by the heat pump than the slower charging borehole storage. Additionally, by combining the previously developed models, it is established that the flexibility of the electric demand of a heat pump collocated with thermal storage decreases the strain on the electricity system expansion compared with inflexible demand. The findings reported in this thesis set the ground for further research, potentially using more detailed models and assessing other thermal storage technologies to highlight their value and encourage the use of thermal energy storage to assist the Chilean energy transition. Furthermore, these tools and analyses could be applied to other countries and areas following similar energy transition pathways.