Solar Impulse 2, a solar-powered plane that will attempt a global flight in 2015, takes to the skies above Switzerland for the first time.
"It's a great day for all the team of Solar Impulse," Mr Piccard told BBC News.
"An aeroplane like this is absolutely unique. And for the first time in history, we have an aeroplane that is flying with no fuel day and night, showing the incredible potential of the clean technologies - all these technologies that the world can also use in order to reduce the dependency to fossil fuel and to be cleaner and solve a lot of problems of pollution."
The carbon-fibre aircraft has a huge wingspan, which at 72m is wider than a Boeing 747 jet. And yet, the vehicle weighs only 2.3 tonnes.
The tops of the wings are covered by 17,000 solar cells, which drive four brushless electric motors at speeds of up to 140km/h (90mph).
During the day, the solar cells will recharge lithium batteries, which can then be used to keep the plane’s propellers turning through the night.