For the future combined system of the renewable and hydrogen energy, the actual voltage fluctuation from wind power was applied to a single PEM water electrolysis cell, whose durability was studied. I-V performance of the water electrolysis cell increased up to 96-hour voltage fluctuation and slightly decreased after that. One of the reasons for such initial increase was found to decrease in activation overvoltage owing to increase in electrochemical active surface area of IrO2 through redox cycles derived by voltage fluctuation. Regarding to decrease in I-V performance after 96 h, increase in concentration overvoltage derived by temporary accumulation of produced gas inside the small pores of the electrode was a main reason. Furthermore, suppression of degradation of IrO2 was found when the voltage fluctuates lower than 1.5 V, indicating a potential of the water electrolysis system directly using renewable energy in the future.