Patent ID: 8663434

Claim:
A water electrolysis system comprising: a water electrolysis device to electrolyze water to generate oxygen and high-pressure hydrogen having a pressure higher than a pressure of the oxygen; a gas-liquid separator provided in a hydrogen pipeline through which the high-pressure hydrogen is discharged from the water electrolysis device, the gas-liquid separator being provided to separate water from the high-pressure hydrogen; a water-amount detector configured to detect an amount of water in the gas-liquid separator; a hydrogen storage device to store the high-pressure hydrogen discharged from the gas-liquid separator; a decompressing device to decompress and drain the gas-liquid separator when a water electrolysis process performed by the water electrolysis device is terminated; and a control device comprising: a residual capacity calculator configured to calculate a residual capacity of the hydrogen storage device, the residual capacity corresponding to an amount of hydrogen required to make the hydrogen storage device full from when it is detected by the water-amount detector that the amount of water in the gas-liquid separator is at an upper limit with reference to which it is determined that drainage of the water in the gas-liquid separator is necessary; a hydrogen production amount calculator configured to calculate an amount of hydrogen produced by the water electrolysis device in a drainage period in which the amount of water in the gas-liquid separator increases to the upper limit from a lower limit with reference to which the drainage is stopped; and an electrolysis termination determiner configured to terminate the water electrolysis process when the amount of hydrogen calculated by the hydrogen production amount calculator is greater than the residual capacity calculated by the residual capacity calculator.