The changing energy landscape has increased the need for energy storage and flexible electrical consumers, also in residential buildings. Thanks to the electrification of heating systems thermal energy systems can be controlled flexibly. The Thermi-Var research project investigates practical applications and end-user benefits, complementing studies on societal targets like grid stability. A simplified RC model was developed to generalize findings from demonstration cases and lab tests, as well as to create a didactic tool. This model facilitated a parameter study, varying building and installation characteristics. The smart control strategies considered are easy to implement and based on either time schedules or PV (photovoltaic) injection rates (due to production surplus). This paper focuses on PV self-consumption. The grid consumption reduction potential is demonstrated, especially for domestic hot water. However, it highlights efficiency losses in heat pump operation in scenarios such as heating curve boosts, buffer tank usage, or auxiliary electrical heater activation. The simulations show that these losses can negate savings if the system design or control settings are suboptimal. For space heating, boosting the room temperatures following a fixed time schedule, is a simple and robust strategy. If a storage vessel is used, the boost temperature should be determined with care so that the auxiliary electrical resistance will not be activated during the boost events. When using buffer tanks to enhance SH thermal storage, proper selection of the tank’s basic setpoint, boost temperature, and volume is essential. Advanced control strategies, such as matching boost profiles to PV injection rates, could further address these challenges.