The effect of the hysteresis band on power management strategies in a stand-alone power system

A stand-alone power system that consists of a photovoltaic array and wind generators for the exploitation of renewable energy sources (RES), and that is capable of storing excessive energy in the form of hydrogen via water electrolysis for subsequent use in a polymer electrolyte membrane (PEM) fuel cell is currently being installed at Neo Olvio of Xanthi in Greece. The performance of two power management strategies (PMSs) that utilize a hysteresis band in the operation of the integrated system over a typical 4-month period is assessed. The state-of-charge (SOC) level of the accumulator is the main parameter that governs the operation of the electrolyzer and the fuel cell. The introduction of a hysteresis band in the boundary limits of the SOC of the accumulator provides larger flexibility in the operation of the electrolyzer, the fuel cell, and the accumulator. In this way, the units can be protected from heavy and unnecessary utilization or irregular operation (reduction of frequent start-ups and shutdowns). The simulated results for the implemented PMSs revealed important information about the reliability of the load satisfaction, the total operation time that each subsystem undergoes, as well as about the hydrogen inventory in the integrated system. The study also identified the effect of variation of hysteresis band size on the system performance as an important feature for the development of an integrated control strategy. (C) 2008 Elsevier Ltd. All rights reserved.