It’s Still Early Days for Diesel Electric Hybrids On The Inland Waterways

The concept of a diesel-electric hybrid engine is far from new. Hybrid diesel-electric vessels have been around for more than 100 years. The German submarines that terrorized the seas in two world wars were hybrids, switching from diesel engines to battery power upon submerging. Sweden built diesel-electric submarines even before World War I.

In Europe, emissions regulations are the driving force behind the move to electric and hybrid marine engines today. The Paris Agreement, signed by 196 countries in 2015, spurred signatory countries to develop plans to reduce marine emissions, among others, in an effort to combat climate change. Advances in battery technology in recent years have made the hybrid concept more attractive and led to many studies. The United States, an initial signatory of the agreement, is set to withdraw in November. In the Netherlands, inland navigation marine emissions were targeted in 2019. Dutch shipping company Port-Liner is planning to launch a zero-emissions inland container vessel powered by a flow battery, in which liquid electrolytes store energy.

Diesel-electric boats have been part of the U.S. offshore market since the 1990s. So far, the hybrid vessels operating in the United States are either smaller offshore vessels serving the oil industry, passenger ferries or other specialized boats. The up-front costs of building a hybrid vessel can be up to 20 percent greater than a conventional vessel.

On the inland waterways, the diesel-electric hybrid vessel market is in its early days.

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Frank Ruggiero, marine senior technical adviser at Cummins Inc., said he gets lots of inquiries about diesel-electric pushboats, but knows of no one actually in the process of building one.

Cummins offers a hybrid variable-speed diesel-electric system that matches Cummins engines and a generator with controllers—an AC traction motor, a power management system from BAE Systems, and batteries from Corvus Energy. The Cummins system provides three different modes of operation: battery only, diesel power only, or diesel and electric together on the same shaft.

The advantages of a diesel-electric hybrid engine depend on the type of vessel and its power requirements. It offers the greatest advantages to vessels that often operate at variable power, so that part of their power can be switched to battery, thus saving fuel costs. If a retrofitted vessel can replace one large engine with two smaller ones plus battery, that would allow a potentially greater power, fuel savings and emissions reductions. Crews on diesel-electric boats must learn new techniques of managing and maintaining the new power systems, said Ruggiero, “but those skill sets will develop.”

For larger, line-haul towboats, the advantages would come going downriver rather than upriver. Older vessels can be converted to hybrid systems, but the “sticker shock” of the initial investment has often caused hesitation, Ruggiero said. Converted vessels can make back their initial costs within several years, depending on usage and fuel savings. “It’s more a question of reconciling up-front costs versus the fuel and maintenance payoffs long-term,” he said.