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The Tour de Sol in Switzerland was the first rally for solar powered vehicles. It was carried out annually from 1985 to 1993. The first event started on June 25 in Romanshorn on the Lake of Constance, and finished on June 30 in Geneva. 72 vehicles started in two classes; over 50 finished. The vehicles were powered exclusively by direct onboard solar power in addition to an initial charge of the onboard accumulators. The second class also allowed direct human power with pedals. The rally was conceived as a kind of race with the winners being those using the least time to travel the set course each day. The course was on unclosed public roads and the drivers were required to adhere all traffic rules and speed limits. The first events were very popular with thousands of spectators lining the roads and visiting the camps where the vehicles stopped each day. In later years the fastest vehicles also raced on round-circuit closed-off courses each day after arriving at the stops. From 1990 the organisers also held separate events called Tour de Sol Alpine. These included closed courses on frozen lakes and snowy roads and on unclosed mountain passes.
After a few years other organisers carried out similar rallies, e.g. the American Tour de Sol. In 1988 the Tour de Sol also held the first race for solar powered boats on July 1 at Estavayer-le-Lac.
The Tour de Sol initially stipulated direct solar power from onboard solar cells. After the first couple of events, a class was introduced which allowed charging accumulators from stationary solar panels and swapping accumulators. Later another class also allowed charging from the 230 VAC mains, provided that this amount of electricity was generated elsewhere by solar power and fed into the mains. This led to the development of the first domestic grid-feed systems.
The legal form of the Tour de Sol was a foundation. It ceased in 2002. Solar engineer Josef Jenni is credited as the inventor of the event and Urs Muntwyler developed and led it for most of its years.