Boats: The Other Electric Vehicle
Cars may be the electric vehicle on everyone's mind, but boats already push the envelope of electric power, and are ready for even more revolutionary advances.
This is the sixth part in an eight-part series on the future of transportation. New articles published every Monday.
To naval engineers-who have been doing radical things with ship propulsion since the Egyptians first harnessed wind to sail up the Nile around 3500 B.C.-the latest innovations in automobile drivetrains are old hat. Diesel-electric hybrids? They've been standard issue on the U.S. Navy's battleships since their debut on the USS Tennessee in 1920. All-electric ships? The Duffy Electric Boat company has been building battery-powered pleasure crafts since 1970.
Unlike motor vehicles, ships are capable of carrying huge loads, and they are so good at it that even conventional waterborne shipping is more energy efficient than every other means of transit save rail. Because of its enormous load-bearing capacity, there is room in even a small or midsize boat to carry large banks of batteries, motors, and a panoply of other innovative electric drive and power systems to help power the ship. It's a good thing, too: Almost all the world's cargo ships run on the lowest grade of fuel an internal combustion engine can burn, a tarry sludge known as "bunker fuel" that has been estimated to cause upwards of 50,000 deaths a year worldwide from its effects on air quality alone (not to mention its impact on the climate).
Unfortunately, there are no charging stations in the middle of the Atlantic, so all-electric ships capable of replacing traditional cargo vessels on thousand-mile journeys are extremely rare. That's because electric power on ships is plagued by the same problems as in cars, namely that the power density of liquid fuels is so high when compared to batteries that carrying enough batteries to allow a vessel to complete a trans-oceanic journey currently isn't feasible.
One way to get around the issue of bulk of batteries and figuring out how to charge them on all-electric ships is to use something other than batteries to produce electric power. For the Norwegian shipping company Eidesvik's "Viking Lady," that something is liquefied natural gas. Rather than burning the stuff, the ship uses a 320-kilowatt molten carbonate hydrogen fuel cell, which is sort of like a giant, ultra-hot battery that combines hydrogen stripped from the natural gas with oxygen from the atmosphere to yield electricity and water. Its primary advantage over a traditional internal combustion engine is that it is potentially much more efficient-extracting as much as twice the energy from its fuel source. DNV Marine, the builder of the ship, estimates that if all the world's ships used hydrogen- fuel-cell technology, it would reduce CO2 emissions by 500 million metric tons per year by 2030.
More commonly, ships use a hybrid-electric propulsion system that is more versatile and efficient than similar systems in average hybrid cars; these electric motors can efficiently operate across a wide range of speeds, unlike internal combustion engines, which are most efficient only at a much more narrow range of speeds.
The world's largest cruise ship, Queen Mary 2, is driven by electric motors that draw power from diesel- and natural-gas-burning plants that are big enough to light up a small town. This allows the fossil-fuel-burning power plants to run constantly, at their most efficient speed, while the electric motors vary the amount of electricity they transform into forward motion. While fuel savings from diesel-electric power trains vary, they are compelling enough that they now represent 100 percent of the worldwide orders for new cruise ships, icebreakers, and drilling vessels. Even the U.S. Navy-which, as part of the U.S. military, contributes to the world's single largest consumer of liquid fuels-has ordered a dozen diesel-electric ships.
Some shipbuilders do away with the need for storage capacity all together by going solar. In 2007, Sun21, a 45-foot-long catamaran with a sheet of solar panels spanning its two hulls, became the first solar-powered vessel to cross the Atlantic. Sun21 averaged between five and six knots on its journey (a knot is one mile per hour), which is comparable to speeds achieved by traditional sailboats. In Germany, Rivendell Holding AG is funding the construction of what it hopes will be the first solar-powered ship to circumnavigate the globe. Ninety-eight feet long and shaped like an arrowhead, Planet Solar will be studded with 5,059 square feet of solar cells. Magellan's Basque navigator may have completed the same journey in 1519 using only sails, but the real goal of Planet Solar is to demonstrate that solar-powered shipping is possible. The group's double-hulled craft will complete the journey in 120 days, at an average speed of 10 knots-more than twice as fast as the sailing ships of yore, but only half as fast as a modern container ship.
Illustrations by Jennifer Daniel.