  Energy model distortions may unknowingly appear and represent unrealistic and
non-physical effects that can mislead optimal model decisions. A prominent
misleading effect is unintended storage cycling that was observed in previous
literature by simultaneous charging and discharging of the same storage in 12
of 18 energy models. Especially for popular net-zero energy model scenarios,
unintended storage cycling can cause high distortions and, hence, urges for its
removal. Methods to remove such misleading effects exist, but are not
computational efficient and sometimes not effective such as MILP formulations.
Other techniques are successful, but only if renewable energy target
constraints exist. This paper explores how to eradicate unintended storage
cycling for models without renewable target constraints by correctly setting
variable costs of relevant system components. We find through 124 simulations
that determining appropriate levels of variable costs depends on the solver
accuracy used for the optimization. If set too loose, the solver prevents the
removal of unintended storage cycling. We further find that reliable data for
variable costs in energy modelling needs to be improved and provide a list of
recommended model inputs as well as a minimum variable cost threshold that can
significantly reduce the magnitude and likeliness of unintended storage
cycling. Finally, our results suggest that variable cost additives may remove
other known unintended energy cycling effects, such as unintended line cycling
or sector cycling.
