Optimal sizing of stand-alone energy systems incorporating battery capacity fading

Battery energy storage systems (BESS) are one of the key elements for designing a stand-alone system based on renewable energy generation. The capacity of these equipment, however, starts to fade due to charge cycling and ageing. In this paper, a planning scheme is presented for supplying electric vehicle (EV) charging stations by a stand-alone system composed of wind and PV generation, and batteries. The approach is based on a mixed integer linear programming (MILP) formulation and a binary expansion method is utilized to tackle the nonlinearities of the problem. After quantifying the degradation behaviour of the battery by solving the optimization problem, its capacity is modified to be able to charge and discharge according to the output of the sizing program. The formulation is applied to a
LiFePO
₄
(LFP) battery technology, and the results illustrate how the battery degradation is able to impact the final capacity and planning costs for the system. For a reliability level of 99%, a 139.78kWh with a total degradation of 18.74kWh is calculated. Also, for the reliability level of 90%, the calculated capacity and total degradation are 207.23kWh and 40.86kWh respectively.