Patent ID: 7618726

Claim:
A fuel cell system, comprising: a fuel cell which generates power by supplying an oxidizing agent and a hydrogen-containing gas to an electrolyte membrane, a water supply device which supplies water to the fuel cell, and a controller functioning to: estimate a restart time when the fuel cell is restarted, estimate a shift of an outside air temperature, compute a first energy amount required when the system is protected by a first protection mode which prevents freezing of water in the system by heating water supplied to the fuel cell when the fuel cell has stopped, and a second energy amount required when the system is protected by a second protection mode which prevents freezing of water in the system by discharging water from the fuel cell when the fuel cell has stopped, respectively based on the estimated restart time and outside air temperature shift, select the first protection mode when the first energy amount is less than the second energy amount, and select the second protection mode when the first energy amount is larger than the second energy amount as a protection mode used when the fuel cell has stopped, protect the system with the selected protection mode, correct the estimated restart time when the fuel cell is not restarted although a predetermined time after the estimated restart time has elapsed, and perform the protection mode selection again based on the corrected restart time.