The Tokai Challenger completed the journey in 29 hours and 49 minutes despite a flat tire—that's an average speed of about 63mph. That's actually not the best time in history. That Dutch team we mentioned above achieved the current record back in 2005—29 hours and 11 minutes. But obviously conditions like sunlight and wind can skew these numbers on a year to year comparison basis. [Global Green Challenge via Wired via Engadget]
UPDATE: Reader Stephen gives us another reason for the recently slower times:
"A major reason why the Nuna team from 2005 holds the time record is because there were no speed limits in the Northern Territory of Australia before January 2007. Now the speed limit in the Northern Territory is 130km/h (81mph). In the race there are time penalties for breaking the speed limit. I know this because I was a member of the University of Waterloo's solar car team that raced in Australia in 2007."