Conceived and erected by teams of students and faculty mentors representing universities from across the United States and abroad, the small homes were competing in the biennial Solar Decathlon organized by the U.S. Department of Energy. Decathlon rules stipulated that the total interior floor area of a house could not exceed approximately 1,000 square feet, about the size of a typical school classroom or conventional two-bedroom apartment.
Decathlon means 10 contested events. Accordingly, the 2011 Solar Decathlon set forth 10 categories of achievement for which judges awarded points. Thus, it wasn’t enough only to score points for harvesting sunlight and saving energy. Each house was also evaluated for affordability, comfort, engineering efficiency, aesthetic qualities and potential market appeal.
Despite the decathlon’s common rules and goals, the 19 homes varied greatly in form, size, materials, use of technology and climatic response. Purdue University’s traditionally styled, Midwestern bungalow would aesthetically harmonize with suburban subdivision homes anywhere in America. With its familiar, homey appearance, it was a favorite among visitors.
By contrast, the team from the Southern California Institute of Architecture and California Institute of Technology created a geometrically abstract structure covered almost entirely with a thick quilt of insulation encapsulated in white, vinyl-coated fabric. It bore little resemblance to a house.
Generally, the homes were well insulated and employed photovoltaic solar panels on roofs or walls to generate electricity. Green roofs covered some houses. Most sought to maximize the use of daylight to reduce electrical demand. Sophisticated mechanical systems with state-of-the-art controls optimized HVAC efficiency by continually monitoring and adjusting to environmental conditions while recapturing waste heat. A number of homes incorporated landscaped exterior spaces — intimate courtyards or surrounding gardens — serving as both aesthetic enhancements and environmental adjuncts.
Solar thermal energy warmed interior spaces thanks to generously sized windows and glazed doors facing south, east and west. Floors and walls with high thermal inertia absorbed solar radiation and then re-radiated heat into the interior at night. Some homes used the sun’s energy to produce hot water. And a couple of homes captured, stored and released heat by using a chemical phase-change technique: Solar radiation melts and liquifies solid paraffin, which later releases heat as the liquid paraffin solidifies.