A data center includes computing devices, an air handling system, a heat engine, and a generator. Air moved by the air handling system flows across heat-producing components in the computing devices in the data center. Heat from air that has flowed over the heat-producing components heats a hot section of the heat engine. The heat engine generates mechanical work based on a temperature differential between a hot section of the heat engine and a cold section of the heat engine. The generator generates electricity from the mechanical work generated by the heat engine.