  Decarbonizing the building stock in cold countries by replacing fossil fuel
boilers with heat pumps is expected to drastically increase electricity demand.
While heating flexibility could reduce the impact of additional demand from
heat pumps on the power system, characterizing the national spatial
distribution of heating flexibility capacity to incorporate into sophisticated
power system models is challenging. This paper introduces a novel method for
quantifying at large scale and high spatial resolution the energy capacity and
duration of heating flexibility in existing building stock based on historical
heating consumption and temperature data. This method can reflect the
geographic diversity of the national building stock in sophisticated power
system models. The proposed heating consumption-based method was tested in
Britain using national residential gas data. The results demonstrate the
potential of this approach to characterize the heterogeneous distribution of
heating flexibility capacity at the national scale. Assuming a 3$^\circ$C
temperature flexibility window, a total thermal energy storage capacity of 500
GWh$_{th}$ is identified in the British housing stock. For an illustrative cold
weather COP value of 2.5, this thermal energy storage capacity is equivalent to
200 GWh of electricity storage. Regarding heating flexibility duration,
gas-heated homes have a median of 5.9 heat-free hours for 20th percentile
regional daily winter temperatures from 2010 to 2022. However, extreme cold
days nearly halve flexibility duration to a median of 3.6 heat-free hours.
These high spatial resolution energy capacity and self-discharge parameters can
account for geographic diversity at the national scale and provide a new
data-based layer of information for sophisticated power system models to
support energy transition.
