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The Paris Agreement on climate change entered into force in 2016 and has been ratified by 193 of the 197 Parties to-date, followed by country targets to cut greenhouse gas emissions, not least through an increasing penetration of renewable energy sources. In its 2021 annual World Energy Outlook, the IEA envisages a Net-Zero Emissions by 2050 scenario (NZE) in which renewables as a percentage of total energy supply increase from around 10% in 2020 to over 65% in 2050 and is reflected by a similar change in the percentage of variable renewables in total generation, thereby increasing the need for system flexibility.

Thermal grids are a significant supplier of heat to buildings in Europe, Russia and China, providing 45 % of heat in some European countries. One of the advantages of district heating is its ability to consume multiple fuel sources, including electricity. Technologies for converting heat back to electricity mean that, in theory, district heating can adjust both the consumption of electricity, and potentially supply electricity, to provide short-term flexibility and ancillary services to the power grid, and thus may help to meet future system flexibility needs.

This thesis describes the results of literature reviews and a techno-economic study to determine and quantify the potential for thermal grids to address future system flexibility needs, through possible contributions to the electricity balancing market or provision of ancillary services. These studies focus on the potential use of heat-to-power technologies in thermal grids; on identifying and quantifying short term heat storage options that can be used for increased flexibility in thermal grids; and whether the use of this flexibility could contribute to reduced curtailment of renewable electricity sources, leading to avoided emissions. 

The results show that most thermal grids have multiple options for the storage of heat, with storage capacity already available that could potentially be used to provide additional flexibility. Stored heat may be converted to electricity with commercially available heat-to-power technologies, although economic feasibility may still be limited. It is shown that if storage flexibility is used to reduce the curtailment of renewable energy sources at a country scale through power-to-heat technology, this storage flexibility can lead to megatonnes of avoided CO₂eq emissions.