Electric Grid Resilience

Doktorsavhandling, 2025

To reinforce resilience in power systems during severe power shortage conditions, the flexibility of heat pump-equipped heating systems in single-family houses is quantified. To quantify this potential, physics-based models involving a heat pump with space and water heating systems are developed.

The Swedish power system with a maximum consumption of 20-25 GW is used as a reference case. Houses built after the 1960s in southern Sweden, representing 54% of the total single-family houses, are considered. The flexibility levels found range between 2.1 and 0.5 GW, for outdoor temperatures varying between -10°C and 10°C, respectively. These estimates are independent of the degree of thermal compromise. However, the duration for which the above flexibility can be provided is dependent on the degree of thermal compromise. An example result shows that the power system could be relieved of 2.1 GW for 5 hours and 0.8 GW as long as flexibility is required, at -10°C outside temperature, with the consequence that indoor and water temperatures reduce to 15°C and 44°C, from 20°C and 55°C, respectively.

A modified Nordic-32 bus system with a high share of renewable power installations is proposed. Here, the role of flexibility in limiting the instantaneous frequency deviation during the loss of a major generation is demonstrated.

Thus, the flexibility of heating systems from a group of houses has the potential to reinforce resilience in a large-scale power grid from seconds to several hours.

The rebound effect of using flexibility has large negative cold load pick-up effects while restoring indoor temperatures to normal conditions. Hence, an adaptive heat pump controller design is proposed to limit this effect. At -5°C outdoor temperature, approximately 1.9 GW is found to maintain indoor temperatures at 20°C, in 44% of the houses. The power system could be relieved of 1.9 GW for 7 hours and 650 MW for the next 10 hours, with the consequence that the indoor temperatures drop to 15°C. During indoor temperature recovery to 20°C, over 20 hours using the proposed controller, the peak rebound power was found to be limited to 2.6 GW compared to 3.9 GW using the standard controller.