A transport refrigeration system including: a transportation refrigeration unit configured to provide conditioned air to a refrigerated cargo space; an energy storage device configured to store DC electrical energy to power the transportation refrigeration unit; and a DC-to-AC variable invertor electrically connecting the energy storage device to the transportation refrigeration unit, the DC-to-AC variable invertor being configured to convert the DC electrical energy from the energy storage device to AC electrical energy in a variable continuous energy output to power the transportation refrigeration unit.