Developing decarbonisation pathways in changing TIMES for Irish homes

Decarbonising and improving the energy efficiency of dwellings is a priority for climate and energy policy. However, integrated energy systems modelling, commonly used to inform decarbonisation pathways, typically does not capture the heterogeneity of the dwelling stock, particularly internal dwelling temperatures, a key determinant of the cost of switching to low-carbon heating and upgrading building fabric. Addressing this gap, this paper presents a new model of the residential sector within an energy systems optimisation model (ESOM), which is developed using an Energy Performance Certificate (EPC) database and measured energy consumption data, allowing for the heterogeneous depiction of the housing stock. The analysis is carried out for Ireland, which has committed to ambitious legally binding climate targets. The Irish residential sector, which represented 22% of energy-related CO emissions in 2020, is characterised by poor thermal efficiency and high reliance on fossil fuels. The TIMES Ireland Model (TIM) is developed within a framework demonstrating cost-optimal pathways for energy supply, transformation, and demand sectors. The model is open-source, and the methodology outlined in this study is replicable for any country with an EPC database. The results presented are indicative of the type of insights that such modelling can provide and demonstrate that to meet climate targets, a rapid reduction in residential fossil fuel heating is necessary. The results show that deeper decarbonisation pathways require more thermal retrofits and electrical heat pumps, increasing the total cost of the energy system. The results explore the effect of internal temperatures, highlighting the importance of using empirical data for accounting for the rebound effect. Exemplifying the value of an integrated system modelling approach, deeper decarbonisation pathways place further costs on the electrical system.