Energy consumption has become a major concern for society, and since the industrial sector is the largest consumer, companies are urged to improve energy efficiency of their production systems. This paper investigates how Reconfigurable Manufacturing Systems (RMS), and particularly their scalability feature, can be exploited in order to minimize the energy cost in production systems w.r.t. a Time-Of-Use pricing scheme. In the case of RMS, the resulting energy cost optimization problem is a Bilevel Optimization problem, as it jointly considers both the line balancing and the production planning. After introducing the problem and its features, a solving approach based on a simulated annealing algorithm and a linear program is proposed. The approach is then validated on designed instances based on classical test problems taken from the literature. Results show that considerable savings in terms of energy cost can be achieved w.r.t. dedicated lines, even when optimally designed, ultimately showing the great potential of RMS towards energy efficiency.