Later in the morning, Borschberg called the flight an extraordinary experience, saying it marked historical firsts for aviation and for renewable energy. Ground crews pushed the plane toward a hangar, where a celebratory attitude waited along with leis and hula dancers. The project, which began in 2002 and is estimated to cost more than $100 million, is meant to highlight the importance of renewable energy and the spirit of innovation. Solar-powered air travel is not yet commercially practical, however, given the slow travel time, weather and weight constraints of the aircraft. Gov.