Energy storage systems are an important asset inthe future power grid, ensuring the safety and reliability inface of growing power consumption and intermittent supply.Occupying a vital role, the reliability of the storage system itselfhas to be guaranteed and taken into account for, especially inthe design procedure. This study utilizes reliability methods toanalyze the storage’s system reliability and optimize the systemsize to an appropriate level. A residential building with a 3.3kWphotovoltaic system serves as a case study to analyze differentenergy storage types and their resulting optimum systemstructure. The paper also includes an economic evaluation tomeasure the storage’s suitability for the particular case with thephotovoltaic system.