P2ATES investigates the summer recovery, via a heat pump (HP), of low-enthalpy heat and low-carbon electricity, for winter use on a district heating system (DH), with seasonal phase shifting by aquifer thermal storage (ATES). A numerical simulation study of the DH - HP - ATES system was used to determine: i) the summer excess heat, linked to continuous heat pump production (as opposed to production modulated by demand); ii) the thermal response of the ATES storage, as a function of its hydrogeological characteristics; iii) the responses of the system according to the size of the heating network, the production mix, the temperature levels of the DH, and the discharge mode; as well as iv) the CO₂ content of the heat produced/recovered, taking into account the seasonal dynamics of the CO₂ content of Swiss electricity (including imports/exports). The parametric analysis of the system allowed to characterise the energy and the environmental performance of the various systems, to establish sizing rules and to propose recommendations for actors in the sector based on a charge/discharge model developed during this project. We were able to demonstrate that in order to maximise the operation of the storage, it is necessary to guarantee: i) a certain flow balance at the DH/aquifer interface; and ii) manage the injection temperature in the hot well, which has proved incompatible with the current legal requirement which imposes a temperature difference of less than 3 K at 100 m from the injection well. In cases where these constraints are met, it has been shown that the use of ATES enables, in most cases, better summer electricity recovery than a power-to-gas system. In addition, the use of heat pumps to charge the aquifer has been shown to be effective, reducing CO₂ emissions from heating networks by up to 50%. However, this system seems not suitable for high-temperature DH networks, for which the storage of high-temperature thermal waste is sufficient to decarbonise the system.