The Princess Benedikte is not in service right now, but when retrofits are completed, it will be the world’s largest hybrid diesel electric ferry.
The Princess Benedikte is already diesel electric, as most ships are these days. Powerful diesel engines turn generators, the power of which is then fed to electric motors on the propellers. On the short eleven miles between Rødbyhavn, Denmark and Puttgarden, Germany, the ferry carries up to 300 vehicles and 900 passengers, which the diesel engines running the whole time in order to turn the generators.
The current retrofit is adding 2.7MWh of lithium-polymer rechargeable battery packs and a controller. In the harbor, the hybrid ferry will be able to operate on battery power alone for up to 30 minutes. This might seem insignificant, but keep in mind the Princess Benedikte also weighs 16,500 tons. Recharging is done by the onboard generators or can be charged by connecting on shore. The battery packs will reduce reliance on the diesel engines, reducing fuel consumption and extending their lifespan. The company expects the battery packs will pay for themselves in about four years.