Structural Properties of Feasible Bookings in the European Entry-Exit Gas Market System

In this work, we analyze the structural properties of the set of
feasible bookings in the European entry-exit gas market system. We present
formal definitions of feasible bookings and then analyze properties that are
important if one wants to optimize over them. Thus, we study whether the sets
of feasible nominations and bookings are bounded, convex, connected, conic,
and star-shaped. The results depend on the specific model of gas flow in a
network. Here, we discuss a simple linear flow model with arc capacities as
well as nonlinear and mixed-integer nonlinear models of passive and active
networks, respectively. It turns out that the set of feasible bookings has some
unintuitive properties. For instance, we show that the set is nonconvex even
though only a simple linear flow model is used.