Cooling multiple parallel hydrogen fuel cell stacks

A fuel cell electrical power system, comprising:

• a first fuel cell module and a second fuel cell module;
• a heat exchanger;
• a common coolant piping having an inlet end and an outlet end and being fluidically coupled to the heat exchanger to carry coolant fluid through the heat exchanger from an inlet;
• a first coolant piping branch fluidically coupling in series the outlet end of the common coolant piping, the first fuel cell module, and the inlet end of the common coolant piping;
• a second coolant piping branch fluidically coupling in series the outlet end of the common coolant piping, the second fuel cell module, and the inlet end of the common coolant piping;
• a first pump disposed on the first coolant piping branch between the outlet of the common coolant piping and the first fuel cell module, and operable to generate a controllable flow rate of coolant fluid through the first coolant piping branch;
• a second pump disposed on the second coolant piping branch between the outlet of the common coolant piping and the second fuel cell module, and operable to generate a controllable flow rate of coolant fluid through the second coolant piping branch;
• a first valve disposed on the first coolant piping branch and configured to selectively allow the flow of coolant fluid through the first coolant piping branch;
• and
• a second valve disposed on the second coolant piping branch and configured to selectively allow the flow of coolant fluid through the second coolant piping branch;
• a header tank fluidically coupled to the first coolant piping branch between the outlet end of the common coolant piping and the first pump, and fluidically coupled to the second coolant piping branch between the outlet end of the common coolant piping and the second pump;
• the fuel cell electrical power system being 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.