Sunswift a student-lead solar racing team, has broken the Guiness World Land-Speed record for a solar-powered vehicle. The record was set at 88km/h on January 7. The previous record was set by General Motors Sunraycer, which travelled 78km/h on roughly 1500 W.
That day the team set the record, conditions were mostly cloudy. The record breaking run was at 10:30 a.m. when they got lucky with enough of a break in the clouds. Solar-noon was at 13:06 that day. The car used about 1050 W to travel at the speed it did for the record run. The batteries were removed, so as to compete on the grounds of energy efficiency alone - i.e. not how big your batteries are.
This means that Sunswift IV, with ~25% less power than the previous record holder, went 13% faster. They've come a long way since 1988. The maximum power Sunswift ever saw from the solar array was 1340 W. The clouds never stayed away for long enough to complete any faster runs.