The present disclosure provides a fuel cell electrical power system, a first fuel cell module, a second fuel cell module, a heat exchanger, a common coolant, a first coolant piping branch, and a second coolant piping branch. A first pump and a first valve are disposed on the first coolant branch, and a second pump and a second valve are disposed on the second coolant branch. The fuel cell electrical power system is capable of functioning in a condition in which the second fuel cell module and the second pump are not operating to cause substantially all of the flow rate of coolant fluid produced by the first pump to circulate through the common coolant piping and to circulate substantially none of the flow rate of the coolant fluid produced by the first pump through the second fuel cell module.