Patent ID: 8685223

Claim:
A method for operating a water electrolysis system including a water electrolysis apparatus which includes power feeders provided on an anode side and a cathode side of an electrolyte membrane and which generates oxygen on the anode side and generates hydrogen on the cathode side at a higher pressure than a pressure of the oxygen by electrolysis of water, a water circulation apparatus which circulates the water in the water electrolysis apparatus, a gas-liquid separation apparatus which separates a gas component discharged from the water electrolysis apparatus from the water in the water circulation apparatus, and an exhaust pipe which is connected to the gas-liquid separation apparatus and through which the gas component separated in the gas-liquid separation apparatus is exhausted, the method comprising: determining whether or not the water electrolysis apparatus is shut down; releasing pressure on the cathode side when it is determined that the water electrolysis apparatus is shut down; operating the water circulation apparatus during the releasing of pressure after stopping the electrolysis of water in the water electrolysis; and continue operating, under a condition in which a release of pressure on the cathode side is completed, the water circulation apparatus until a concentration of hydrogen remaining on the anode side is a specified value or less.