Take, for example, the solar catamaran SUN21. This high-tech solar boat is about to start a transatlantic journey from Basel to New York City. The trip, like Panamericana 2006 or AmandaAcrossAmerica, is full of promotional stops highlighting alternative energies.
The catamaran's thrust comes from two electric direct current motors, 8 kW each, that are powered by waterproof 520 Ah/C5, 48 V DC lead accumulator batteries that can run for 12 hours without light. The system has a maximum speed of seven knots and will usually travel at around five knots (about 9 km/h). The operators say that this journey, the first solar-powered Atlantic crossing, will demonstrate the great potential of the solar technique for ocean navigation. I suppose they're right, but wern't oil-free ocean-going vessels once called sailboats?
[Source: Transatlantic21 via Metafilter]