The Solar Impulse plane took off from San Francisco this morning for the first leg of its journey across the US The solar-powered plane is expected to finish the 720-mile journey tonight when it lands at Phoenix Goodyear Airport The plane is equipped to fly day and night due to solar-energy stored in batteries on the aircraft Weighing over 5,000 pounds, Solar Impulse arrived in San Francisco last week, marking the completion of its Pacific Ocean crossing The trip began in March 2015 from Abu Dhabi