It’s fair to say that each of the 20 contestants in the Department of Energy’s Solar Decathlon enhances its prestige just for being accepted into the competition and building its solar-powered house on the National Mall in Washington, D.C., for the 10-day showcase.

As we’ve noted before, though, the level of competition and the value of what can be learned from participating tend to go up, not down, with each Decathlon. The 2009 edition – the fourth since the inaugural Decathlon, in 2002, and the first featuring a net-metering challenge as one of the 10 competition categories – ended on Sunday.

A shift among the frontrunners

By midday Thursday, when points in 8 of the 10 competition categories had been tallied up, Team Illinois (representing the University of Illinois at Urbana Champaign) and Team Germany (representing Technische Universität Darmstadt) occupied the first and second spots, respectively, on the list of 20 competing teams, with judging still to be done in the engineering and net metering categories. Team California (Santa Clara University and the California College of the Arts) was in third place. (This was the first Decathlon during which each of the solar-powered houses entered in the contest was hooked up to the grid rather than a battery station.)

By the end of the day Friday, however, judging in all categories had been completed and Team Germany, with 908.297 points (out of a possible 1,000), had taken first place overall while Team Illinois had second, with 897.300 points. Team California remained in third, with 863.089.

It’s worth noting that the houses in the two top spots share a feature that likely had critical bearing on their performance during the Decathlon: both were designed to meet the Passivhaus standard.

Passivhaus + solar power

On its website, Team Germany notes that the interior design for what eventually became a 800-sq.-ft. two-story cube, called the surPLUShome, was originally engineered as if it were a single room to maximize its capacity to store heat. The team says it used 5 cm. vacuum-insulated panels on the exterior walls to reduce thermal bridging, and adjusted the size and placement of the building’s triple-glazed windows (equipped with automated louvers) to control solar gain and heat loss.

Team Germany adds that surPLUShome – which was covered with 40 single-crystal silicon panels on its roof and about 250 thin-film copper indium gallium diselenide panels on its walls – met the Passivhaus standard in performance tests. The combination of passive energy efficiency and the PV skin proved unbeatable in the net metering competition, where the team earned 150 points – the maximum score.

The next-highest score in the net metering competition, 137.236, went to Team Illinois (which also landed the only other perfect score during the 2009 Decathlon: 100 points in the hot water competition). This house, called Gable Home, featured 100-year-old barn wood siding and a traditional Midwest-rural look. But its walls, roof, and floor were packed with 12 inches of high-performance insulation (click here for a rendering of the exterior-wall construction). Gable Home used a high-efficiency HVAC system custom designed for small interiors, and a hot-water system heat exchanger that supported the building’s HVAC. The home’s solar power system was designed to generate as much as 9.1 kW of direct current.

One of the graduate students who worked on the project, Tim Moran, whose focus is engineering and architecture, told Washington City Paper that as Team Illinois worked on bringing Gable Home’s performance to the Passivhaus standard, it also collaborated with modular-home builder Homeway Homes on ways the company can incorporate Gable Home’s design into the Homeway lineup.

The big takeaway from the team’s push toward the Passivhaus standard? As Moran told City Paper paper: “Solar power is expensive, insulation is cheap.”