Greentech Media

As the competition continues, more and more international teams are becoming involved. This year, the Technische Universität Darmstadt (TUD) came the farthest -- all the way from Germany with its house and rather large team.

Similar to Carnegie Mellon's plan, TUD employed a flat-roof strategy. But the 40 SunPower SPR-210 panels on the roof were only a portion of the total PV technology it used. Twenty of the panels were oriented south, and the other 20 faced north on a three-degree slope. Eight-percent efficiency was lost due to the unconventional orientation.

The overall design of the house was a square covered in bi-fold, louvered doors that could be opened to an interior core. These doors essentially created a frame around the house and a promenade of sorts between them and the exterior walls of the building. Each louver had an array of Schott amorphous-silicon photovoltaic cells. The louvers themselves could be positioned for optimum capture of sunlight. To further capture energy from the sun, the south-facing promenade had a roof of semi-transparent solar panels. These panels absorbed energy while letting a minimal amount of daylight through to light the passage. The panels were custom-built by Scheuten Solar.

When the louvered doors were fully opened, a lot of daylight was able to get into the building, enough, in fact, to win them second place in the lighting contest. With one wall of windows facing south, it seemed as though it could become very hot inside -- almost like a fishbowl -- but the team used quadruple-glazed glass to help insulate and control the interior temperature.

One particularly interesting material used was the gypsum board. This particular board was made of gypsum and phase-changing wax in plastic microcapsules. This product is called Micronal PCM and manufactured by BASF. When the temperature increases, the wax begins to melt and can store heat. As the temperature drops, the wax hardens again and releases the stored heat into the room. While the board is only 1/2" thick, it has the heat capacity of 4" concrete. The technology is used in astronauts' space suits.

The design itself was quite impressive. Unless specifically told that the house was solar-powered and eco-friendly, one would have never known. As the market for low- and zero-energy homes continues to grow, integrating these homes into already-established communities is an important element. "Our concept was [to build a] calm house," said Leon Schmidt, a student at TUD. "We wanted it to be clean and natural and part of its surroundings. The solar panels shouldn't determine the architecture."

Their idea of integration into the natural landscape was a guiding design principle. By opening and closing the louvers and windows, the building's facade changes with the weather, the seasons and the user; Schmidt said the house is built on "a layer principle." And inside the house, the room layout was very modular. The bed/sleeping area is recessed into the floor. When the user needs more space or wants to hide the private sleeping corners, the bed can be covered over with retractable floor panels.

Germany has the Passivhaus (Passive House) standard, a voluntary standard for energy use in buildings. The first Passvihaus was built in Darmstadt, from where the German team hails. The Passivhaus-Institut also is in Darmstadt. The heating-energy standard says the house must not use more than 15kWh per square meter per year. Schmidt said this standard is an important part of the future of low-energy building in Germany and that their competition house conforms with the rigorous standards of Passivhaus.