Nearly 500 years after Juan Sebastián Elcano completed the first circumnavigation of the globe using nothing but renewable power, Swiss engineer Raphael Domjan and French sailor Gerard D'Abouville are preparing to repeat Elcano's journey in an all-electric boat powered by the energy gathered by 470 square meters of solar panels.

Unveiled for the first time in a ceremony at a shipyard in Kiel, Germany, last week, their vessel is a catamaran made entirely out of the same kind of carbon-fiber composites that make modern airplane wings strong yet light. On its 40,000-kilometer journey, the 30-meter long and 15.2-meter wide boat, known as PlanetSolar, will have to withstand high winds, stormy seas and days without sunshine. On board, the world's largest lithium-ion battery, a 13-tonne monster capable of storing 1,300 kilowatt-hours of energy when fully charged, will allow the boat to slice through the water at an average speed of 13 kilometers per hour for three days straight in complete darkness before its charge is completely exhausted.

The ship can fully recharge its battery in the span of a little more than two days of full sunshine if it's not drawing power at the same time, such as when it's docked in a marina, according to Domjan, a paramedic turned engineer who is the visionary behind PlanetSolar as well as its co-captain. The ship is designed, however, to operate at sea indefinitely, and under normal conditions its 38,000 solar cells average enough power production to muster the 20 kilowatts of power needed to keep the boat cruising along at its average speed. The maximum electrical output of all the cells together on a sunny day is about 100 kilowatts.

On a solar boat, where the amount of energy available is much lower than on a traditional fossil-fuel–powered vessel, efficiency is of the utmost importance, says Jeff Morehouse, head of the Solar Splash intercollegiate solar boat competition and professor of mechanical engineering at University of South Carolina in Columbia. In addition to its double-hulled design, which means the boat has much less drag when it moves through the water compared with a single-hulled boat of similar size, PlanetSolar has a number of innovations to make it as efficient as possible.

One of these innovations is PlanetSolar's propeller design—both propellers sit at the water line, half in the water and half out. This kind of prop, known as a "surface-piercing" propeller, can be much more efficient than traditional propellers, because it prevents the blades of the propeller from interfering with one another as they push through the water, Morehouse says. The blades of a surface-piercing propeller also experience almost no drag during the time spent out of the water.

PlanetSolar also uses the highest efficiency mass-produced solar cells. Manufactured by SunPower Corp. for installation on the rooftops of homes and commercial buildings, these cells can convert 22 percent of the sun's energy into electricity, says Joern Juergens, director of components at SunPower. After installation on the ship, however, the cells' efficiency is reduced to 19 percent, because they must be covered in layers of plastic and transparent composites in order to make them immune to the corrosive effects of seawater and variable temperatures.

The solar cells powering PlanetSolar are at the high end of what's available for home installation, but overall, the technology being used is "very straightforward," Morehouse says. The solar power component of this project is "purely a matter of being rugged enough to withstand ocean travel," he adds.

Using standard, widely available technology is exactly the point of PlanetSolar, Domjan says. "What we want to show with this project is that today we have the technology—you could buy this technology for your home," he adds.

PlanetSolar will be tested in the water for the first time later this month, and by early 2011 its captains hope to be on their way, with stops including Hamburg, London, Paris, New York, San Francisco, Singapore and Abu Dhabi. At each stop, the focus will be education. "Our main goal is to be optimistic and to spread optimism," Domjan says, "because almost everybody on this planet knows we have to change, but they think we cannot change. What we'd like to say to the world is, 'look, it will work—we can keep our level of life and if we use technology, it can be sustainable.'"