Electric propulsion

Electric propulsion is a fuel-efficient propulsion solution when the hotel load is a significant fraction of the propulsion power requirement and the operating profile is diverse, because the generator power can be used for both propulsion, through the electric motors, and auxiliary systems. To achieve this, a power management system (PMS) matches the amount of running engines with the required combined propulsion and hotel load power. This control strategy ensures engines do not run inefficiently in part load and is often referred to as the power station concept. Secondly, the NOx emissions of electric propulsion are likely to be less than those of mechanical propulsion, because the propulsion power at full ship speed is, in most cases, split over more engines, which due to their lower individual power run at a higher speed.

Figure 61. Typical electrical propulsion system layout

Moreover, due to the power station concept of electrical propulsion, the diesel generators run closer to their design point, at which they typically produce less NOx emissions or need less fuel-consumption increasing NOx abatement measures [5].