  As a common practice, the direction of natural gas flow in every pipeline is
determined ex-ante for simplification purposes, and treated as a given
parameter within the scheduling problem. However, in integrated gas and
electric power networks with a large share of intermittent renewable power
supply, it is no longer straightforward to optimally predetermine the gas flow
directions. A wrong predetermination of gas flow directions may result in
feasible but not necessarily optimal schedules. We propose a mixed-integer
linear optimization model to determine the optimal gas flow directions while
scheduling the system. This unlocks additional flexibility to power systems,
provided that a tight coordination between power and gas systems exists. The
increased flexibility, although it comes at the cost of increased computational
complexity, is quantified by comparing the total operational cost of the entire
system with bidirectional gas flows as opposed to unidirectional gas flows. We
numerically show that modeling gas flow directions as state variables may bring
added value not only in the meshed but also in the radial gas networks.
