3.3. Rolling Horizon In order to achieve solutions that cope with the planning of the system, usually on monthly a basis when dealing with the PSC, a Rolling Horizon method is adopted. This method, according to As’ad and Demirli (2010), consists of solving the model only for a period at a time, so that the initial data for one period is given by the obtained results of the previous period. This method provided substantial savings in computational time. The settling time of the tanks was simplified: it was considered that, regardless whether the minimum time was fulfilled or not at the end of a period, all the tanks start the next period with the minimum rest times met (as happens at the starting of the first period).