POWER SYSTEM

A power system includes: a storage battery; a water electrolyzer; a fuel cell that generates electricity using hydrogen supplied from a hydrogen reservoir that stores hydrogen generated by the water electrolyzer; a detector that detects whether there is a person in a building; and a controller that performs at least one of first control and second control. The first control determines a priority between the storage battery and the water electrolyzer, to which electric power is supplied from a power generation device using renewable energy, based on information detected by the detector. The second control determines a priority between the storage battery and the fuel cell, from which electric power is supplied to a power load provided in the building, based on the information detected by the detector.