Water electrolysis system and method of stopping operation thereof

A method of stopping operation of a water electrolysis system, the water electrolysis system comprising:

• a water electrolysis device configured to generate hydrogen and oxygen by performing electrolysis on supplied water;
• a water supply passage configured to supply the water to the water electrolysis device;
• a hydrogen supply passage configured to supply the hydrogen which was generated by the water electrolysis device to a hydrogen storage device;
• a gas-liquid separator disposed in the hydrogen supply passage and configured to separate the hydrogen into a gas and a liquid;
• a water drainage passage configured to drain liquid water separated from the hydrogen and stored in the gas-liquid separator;
• and
• a water drainage valve system configured to be switched between a valve open state in which the water drainage passage is opened, and a valve closed state in which the water drainage passage is closed;
• and
• the method comprising:
• a determination step of determining whether or not operation of the water electrolysis device has been stopped;
• and
• a water drainage step of placing the water drainage valve system in the valve open state when it is determined in the determination step that operation of the water electrolysis device has been stopped, thereby draining the liquid water from the gas-liquid separator into the water drainage passage,
• wherein:
• the hydrogen generated from the hydrogen supply passage has a pressure higher than atmospheric pressure;
• the water drainage passage has a first flow path and a second flow path disposed mutually in parallel;
• and
• the water drainage valve system comprises:
• a first water drainage valve configured to be switched between a valve open state in which the first flow path is opened, and a valve closed state in which the first flow path is closed;
• and
• a second water drainage valve configured to be switched between a valve open state in which the second flow path is opened, and a valve closed state in which the second flow path is closed;
• wherein a pressure loss of the second flow path is set to be smaller than a pressure loss of the first flow path;
• and
• wherein the water drainage step comprises:
• a first water drainage step of placing the first water drainage valve in the valve open state, and placing the second water drainage valve in the valve closed state when it is determined in the determination step that operation of the water electrolysis device has been stopped, thereby draining the liquid water from the gas-liquid separator into the first flow path;
• and
• a second water drainage step of placing the second water drainage valve in the valve open state after the first water drainage step, thereby draining the liquid water from the gas-liquid separator into the second flow path.