Japanese Mitsubishi heavy Industries’ Kobe shipyard has completed a hybrid car carrier, designed to generate zero emissions while berthed, for Mitsui OSK Lines (MOL).MOL is describing the Emerald Ace as the world’s first hybrid car carrier. Electricity is generated by a solar power generation system while the vessel is underway and stored in lithium-ion batteries, with the solar cells (photo voltaic cells) are located on top whether deck. The diesel-powered generator is completely shut down when the ship is in berth, and the batteries provide all the electricity it needs, resulting in zero emissions alongside the berth.

But what happens when the ship comes after facing a cloudy or stormy weather, when sunlight is less and batteries are not charged fully, then perhaps the diesel generators will charge the batteries and keep them full to be used in berths when gensets are stopped. 

The 300-foot-long (92.2-meter-long) Viking Lady is set to get a battery pack, which will turn the supply vessel into a hybrid ship with technology similar to the Toyota Prius and other hybrid cars.

Built in 2009, the Viking Lady already has a fuel cell as part of its propulsion system and was the first merchant ship run with a fuel cell. Now, it's undergoing an upgrade. Researchers expect the Lady's new battery, which they plan to install in 2013, will reduce its fuel consumption and carbon dioxide emissions by 20 to 30 percent. When the ship is in harbor, researchers expect it will run only on its fuel cell and battery, reducing emissions and pollution for people and environments onshore, said Bjørn-Johan Vartdal, a project manager from Det Norske Veritas, a Norwegian risk-management company that is one of three organizations working on the hybrid ship. 

A group led by the University of Tokyo has launched its own hybrid ship concept, the ‘UT Wind Challenger’, based on a combination of sail power and engines, claimed to cut fuel consumption by an average of 30%.

The project aims to substantially reduce fuel consumption by large merchant vessels, using large retractable sails, 20m wide by 50m high. The group has carried out simulations for routes such as Yokohama to Seattle; results indicate that hybrid ships with sails and engines could reduce annual fuel consumption by about 30% on average.