  Energy system models for long-term planning are widely used to explore the
future electricity system. Typically, to represent the future electricity
demand in these models, historical demand profiles are used directly or scaled
up linearly. Although the volume change for the electricity demand is
considered, the potential change of the demand pattern is ignored. Meanwhile,
the future electricity demand pattern is highly uncertain due to various
factors, including climate change, e-mobility, electric heating, and electric
cooling. We use a techno-economic cost optimization model to investigate a
stylized case and assess the effects on system cost and electricity supply mix
of assuming different demand patterns for the models. Our results show that
differences in diurnal demand patterns affect the system cost by less than 3%.
Similarly, demand profiles with a flat seasonal variation or a winter peak
result in only minor changes in system cost, as compared to the present demand
profile. Demand profiles with a summer peak may display a system cost increase
of up to 8%, whereas the electricity supply mix may differ by a factor of two.
A more detailed case study is conducted for Europe and the results are
consistent with the findings from the stylized case.
