Optimal Energy Management of A Hydrogen and Battery-Based Energy Storage System (ESS) for Future DC Microgrids

In most electricity markets, energy storage systems (ESSs) are used for critical scenarios of power requirement; therefore, their trigger point is placed above a certain moving limit of surplus power. This makes them stay idle most of the time and causes resource underutilization. However, the energy management system (EMS) proposed in this paper (with a Hybrid ESS or HESS) will not only interact with the grid and take advantage of both storages to make a profit, but it will also consider the degradation as well as operational costs of the system. The proposed system combines Renewable Energy Sources (RES), a Battery ESS (or BESS), and a Hydrogen ESS (or HSS). The proposed EMS carefully manages the surplus energy provided by the penetration of RES between the battery and HSS to meet the demand. The proposed system not only schedules the distributed energy resources and exchange power with the main grid, but it will also consider selling back to the grid to minimize the daily cost and maintain reliable operation. The formulation of the objective function minimizes the system's daily operation and limits the battery's charging rate to prioritize HSS during high-RES penetration and increases the BESS lifespan. A benchmark case is established by implementing a system that is equipped with HSS under high and low RES generation and the ability to sell back to the grid. The case study results show that the HESS significantly reduces the system’s operational cost by 44%. The hybrid EMS problem is solved using Mixed Integer Linear programming (MILP) in CVX-MATLAB, with Gurobi being the call solver.