Waylaid by U.S. Customs since Thursday, the Apollo solar car made it downtown well after its competitors started taking test laps around the Shell Eco-marathon track. The car promptly gave its creators mechanical problems when freed from its wooden crate on Saturday, but the students from Milan’s polytechnic college remain the team to watch as the competition continues into today.

“We will finish very, very high,” says Paolo Magni, “if we finish, of course …”

Finishing high in this case would mean proving Apollo is efficient enough to travel 10,000 to 15,000 miles using the same amount of energy in one gallon of gas — roughly the distance of their round-trip flight to Milan. The three-wheeled tube of carbon fiber weighs 91 pounds, only accommodates drivers under 5 1/2 feet tall and coasted for a mile after being towed to 20 mph in a test. About half the size of a Collins glass, its electric motor gets its juice from a stop-sign-sized solar panel, one of several fuel classes that also include biofuels, hydrogen and regular gas.

A steady crowd gathered at the street-turned-racetrack around Discovery Green to watch them Saturday. Some of the lithe creations crept around silently while others blared past, unencumbered by mufflers that might slow down their tiny motors.

Their looks range from four-wheeled, urban-class cars that wouldn’t appear too far fetched on a city street to prototypes resembling recumbent bicycles sheathed in fiberglass. The races continued into the evening, with each team allowed to run the track as many times as they wanted in order to tweak their rides for maximum efficiency.

As of Saturday afternoon, all of the entries posted mpgs in the hundreds, although the superior efficiency of electric motors keeps the solar entrants consistently on the top the board. To qualify for the race, teams must prove their solar panels create more energy than the car uses. Then a second run measures how efficiently they use that power. Last year, Pulsar from the Purdue University team recorded the equivalent of 4,913 mpg, which they hope to beat this weekend.

“We have a lot of sophisticated telemetry and modeling,” team driver/aeronautical engineering grad student Mark Welch says. Constant refinement of systems like body materials and electrical wiring helps returning teams consistently improve their scores, and the Purdue team has raced similar solar cars since 1991.

Both Welch and Magni have no illusions about the practicality of pancake-flat vehicles lined with fickle solar panels for day-to-day use. But in the raft of innovation on display around them, the cars’ designers point out the growing potential of existing efficiency boosting technologies, whether it’s rooftop solar panels to run the air conditioning or advanced composite materials that weigh a fraction of their metal counterparts.

These days, even affordable electric cars and carbon-burning vehicles that get 100 mpg aren’t that far out of reach. Looking around the George R. Brown Convention Center filled with students tinkering on the leading edge of automotive technology this weekend, you get the sense theirs will be the generation to make them a reality.