Optimal operation of energy systems including thermal energy storage and battery under different connections

Some types of storage equipment, such as thermal energy storage (TES) and batteries, have recently become increasingly important for peak-load shifting in energy systems. In addition, the sale of photovoltaic (PV) system and battery electric power has also helped minimize operating costs. However, optimizing energy systems is difficult because each machine has multiple combinations of operations, and the objective function and modeling of some practical machines contain transformed nonlinear or non-convex characteristics. Therefore, we adopted the epsilon-constrained differential evolution (ε DE), which is categorized as a metaheuristic optimization method, in order to minimize operating costs under nonlinear conditions and various energy system connections. First, we consider the case in which electric power generated from the PV system and battery is provided only to the electric demand. The second case limits the sale of this electric power to the electric grid. The third condition includes the sale of this electric power not only to the grid but also to the electric demand, heat source machinery, and some pumps. We demonstrate that the ε DE method efficiently solved this strict constraint optimization problem. Moreover, we confirm that the total-amount purchase system (the second case) is not always suitable when minimizing operating costs because it depends not only on the price of the purchased electricity but also on the price of the sold electricity.