Abstract: A method of driving a large cooling system having a compressor operating as a chiller driven by a prime mover, such as a gas turbine, reciprocating engine or steam turbine, in conjunction with an electric motor/generator coaxially arranged on a common shaft with the other units, so that as the ambient temperature rises and the power needed to produce the cooling output increases, and as there is a corresponding drop in power output if the prime mover is a gas turbine or condensing steam turbine, the required additional driving power is supplied by the motor. Conversely, as the ambient temperature drops and required cooling power lessens, the electric motor operates as a generator to convert the excess prime mover power to electrical power.