Rapidly changing electricity markets call for innovative solutions to support balancing of energy production and consumption, and utilize the increasing amount of energy from renewable sources. MIRABEL is a future energy data management system based on flexible offers (flex-offers) for energy production and consumption. One of its core functionalities is scheduling of aggregated flex-offers to minimize the costs of the balance responsible party. This paper presents a formulation of this scheduling problem in terms of decision variables, constraints and the objective function, and discusses the problem characteristics.