Impact of hybrid heat pump shares and building envelope retrofit rates on load penetration in German low-voltage grids

This paper addresses the challenges posed by the increasing deployment of low-carbon technologies—such as heat pumps, electric vehicles, photovoltaic units, and battery storage units—on the operation of existing low-voltage grids in the residential sector. The focus is on the electrification of building heating systems using air-source heat pumps that can significantly elevate electrical peak loads during cold weather periods. To mitigate the need for grid reinforcements, this research work analyzes and discusses two key strategies: building envelope retrofits to reduce thermal loads and the use of hybrid heat pumps with fossil-fuel backup heaters to reduce electrical loads. In this light, this study comprehensively investigates how increased building envelope retrofit rate and hybrid heat pump share can alleviate the need for grid reinforcements in typical suburban German low-voltage grids under various low-carbon technology penetration scenarios. The authors couple detailed building energy system simulations with electrical power flow calculations to assess the impact on key grid operation parameters for different local substation/transformer sizes. To account for uncertainties in building and technology assignments within the low-voltage grid, extensive Monte Carlo simulations are employed. The results quantify the efficacy of building envelope retrofits and hybrid heat pump systems in reducing the need for transformer replacement and further grid reinforcement. Depending on the low-carbon technology portfolio, hybrid heat pump shares and building envelope retrofit rates between 40% and 100% are sufficient to achieve the minimum required transformer size. The findings provide insights to guide future energy policy and grid planning decisions, enabling the cost-effective integration of low-carbon technologies into low-voltage grids.