Designed by Christoph Behling in London and developed by subsidiary Kopf Solardesign, Neckar Sonne is silent in operation and aimed at tourist service on the Neckar at Heidelberg and possibly also on the Rhine. It is available for special events and hopes are it will carry 50,000 visitors a year.

The boat is driven by two 25kW electric motors fed by 77 flexible solar panels. Speed under solar power is just 5kms/hour - which can be upped to 12-23kms/hour using the onboard batteries. The boat has a range of 80km and is easy to maintain and overhaul.

The Kopf Shipyard built the ship in 10 weeks. A smaller 10.2m, 20-passenger boat in the yard's ECOSOL series has since also been delivered to Leipzig.

MD Friedrich Kopf said talks were underway about further orders. Reports said the yard was now developing a solar-driven vessel for 350 passengers.

Germany's first stainless steel solar catamaran went into service in Ulm in 1996 and was built for just 12 passengers. Kopf has in the meantime built more than 30 vessels of different types and sizes for 4-100 passengers.

They are in service in Germany, the U.S. , England and Switzerland.