Energy consumption of robotic systems is getting more and more attention. Previous work suggests that energy losses in the actuators of robots are a significant source of high energy consumption. A possible reason is that, so far, motor-gearbox selection methods have not focussed on energy efficiency. In this work, we present a model-based motor-gearbox selection procedure with the focus on key mechanisms of energy dissipation. Using an example, we evaluate the possible efficiency gains when selecting a motor-gearbox combination for energy efficiency. In this example, the losses are reduced by 56% to 40%. We conclude that selecting a motor-gearbox combination for energy efficiency can provide a significant improvement in the efficiency. However, the energy losses in the motor-gearbox combination remain significant.