Modeling Gas Flow Directions as State Variables: Does it Provide More Flexibility to Power Systems?

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.