The Incredible, Affordable Solar Decathlon 2011

March 01, 2012
March/April 2012
A version of this article appears in the March/April 2012 issue of Home Energy Magazine.
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Last September, 19 college teams with more than 4,000 students from around the world arrived on the National Mall's West Potomac Park. Their mission: Build a self-powered solar house for less than $250,000 to compete in architecture, energy efficiency, market appeal, and seven other contests for DOE’s Solar Decathlon 2011. The result—the average house cost dropped from $485,000 in 2009 to $325,000. Seven of the houses—after ten days of mostly cloudy weather—met more than 100% of their own power, lighting, and thermal-comfort needs.

Perpetual bridesmaid University of Maryland (runner-up in 2007 and high finisher in 2002 and 2005) finally won the 2011 Solar Decathlon. Maryland’s WaterShed House earned more than 951 out of 1,000 possible points from judges scoring criteria such as architectural merit, engineering, and affordability of construction. Maryland used some of the same thermal innovations it had used previously, but improved on them. (For more on Maryland’s 2007 house, see “Keeping Cool at the Third Solar Decathlon,” HE Jan/Feb ’08, p. 10.) Maryland was in first or second place through the entire 2011 competition and was competitive in every category.

Team AlbertaTeam Alberta, Canada, one of the least traditional houses. (Richard King)
Team CaliforniaTeam California, one of the least traditional houses. (Richard King)
Team ChinaTeam China, one of the least traditional houses. (Richard King)

Why Affordability?

“By initiating the Affordability contest this year, we wanted to emphasize that many of the energy-efficient features in these amazing houses are within reach of most Americans,” says Richard King, the DOE official who conceived of the Solar Decathlon and is now its director. “The energy-efficient designs and products on display this week are affordable, and they can help anyone save money at home.” Some visitors I talked to at the 2011 site also were happy with the Affordability contest, saying that the contest was going back to its roots and away from the high-end home show it had threatened to become.

“I was a little worried at first that the Affordability contest would reduce the amount of innovation, but the teams responded with cost-effective houses that were full of inspiration,” says King. And pointing to California’s Compact Hyper Insulated Prototype (CHIP), Alberta Canada's Technological Residence, Traditional Living, or TRTL, and China’s Y-container, he adds, “As you can see, we had houses that really pushed the boundaries of architecture.” (See photos above.)

I worried that since affordability wasn’t an excellence measure and it just wasn’t a very sexy contest, Affordability winners would not get the recognition they deserved. My worries seemed justified when the Solar Decathlon press office didn’t even send out a separate press release for the Affordability contest announcement. But Affordability is one of the most important contests, if houses like this are to be widely commercialized.

Scoring ‘Curve’ for Affordablility Content
Figure 1. Solar Decathlon Director Richard King and his technical support team developed a two-phase scoring system that reduced points only slightly for houses nearest the $250,000 target.
Comparison of Costs of Solar Decathlon Homes in 2009 and 2011
Figure 2. Most of the 2009 houses cost more than the most expensive 2011 house.

Affordability Requirements

Each house must be under 1,000 square feet. Most of the houses were close to the limit. But the smallest was California’s CHIP house at 713 square feet.

A professional estimator determined the construction cost of each house. Teams earned 100 points for achieving a target construction cost of $250,000 or less. King and his technical support team from the National Renewable Energy Laboratory (NREL) developed a two-phase scoring system that reduced points only slightly for houses nearest the $250,000 target (see Figure 1).

Houses with estimated construction costs between $250,001 and $600,000 lost points—with the reduced points scaled linearly. Houses that cost between $250,000 and $350,000 are only very slightly penalized. The four houses that cost more than $350,000 are penalized far more severely. Still, in 2011 the lowest Affordability score was 47 points.

Affordability Contest Results

When the new Affordability contest was announced after the 2009 Solar Decathlon, it was clear that it would have a huge impact on the design of the competition houses. Only one house in the 2009 contest cost less than $250,000, and the average house in that contest cost $485,000. By comparison, the average house in the 2011 contest cost about $325,000. This held true even for the three teams (Ohio, Illinois, and Alberta, Canada) that competed in both years. Most of the 2009 houses cost more than the most expensive 2011 house. These costs are summarized in Figure 2.

Calling it “a tangible sign that the cost of clean energy home upgrades has come down,” DOE noted in its press release on the results of the 2011 Affordability contest that two teams had tied for first place with houses that cost less than $250,000. The second-place house scored 99.2 points with an estimated cost of $257,854. And the third-place house earned 98.8 points with an estimated cost of $262,495. The house that came in last in Affordability at $471,000 still managed to score 47 affordability points and came in eighth overall.

The Impact of Affordability Score

It appears that getting close to the target price was a necessary but not sufficient condition to have a shot at a top-three ranking overall. Almost everyone did get close—15 of the 19 competitors scored more than 90 out of 100 points in this category. The top three overall—as well as the three teams who competed in 2009—were in the group of 15 that scored more than 90 points.

Experience definitely helped the 2011 overall winner, Maryland, which had competed in 2002, 2005, 2007, and 2011. I guessed that the three teams that also competed in 2009 might have an advantage in 2011. That appeared to be the case with the Ohio State University team, which would have scored well in the 2011 Affordability contest with its 2009 House. The experience of building two affordable houses may have helped Ohio move from tenth place overall in 2009 to fifth place in 2011 with its enCORE house. The 2011 enCORE further optimized its solar-thermal hot-air space-heating system to maximize comfort and minimize energy consumption.

But the Alberta, Canada, team, which cut its house cost by a whopping 84%, and Illinois, which cut its house cost by 41% from 2009 to 2011, did not fare so well in the Solar Decathlon overall. Alberta fell from sixth to tenth place, and Illinois from second to seventh. While both the Illinois and the Alberta team completely changed their approach from 2009 to 2011, their respective stories are very different.

Three-time participant Illinois decided to aim at the postdisaster market with a standardized modular approach. Their Re_home, “a rapid-response solution for rebuilding after a natural disaster,” can be ordered and built in a matter of days to provide a solution that does not depend upon the infrastructure for a family left without a home. I tried to joke with the Illinois team that if Washington, D.C., had had a bigger earthquake (than the 5.8 temblor that struck on August 23, 2011), the juries might have valued Re_home more highly. Team Illinois was not amused. As it was, Re_home lost points for having a small market potential and for using too many tried-and-true design approaches.

Southern Alberta’s aboriginal people inspired Canada’s daringly designed Technological Residence, Traditional Living, or TRTL, house. But the TRTL lost points due to its dark and nonuniformly lit interior. The Canada team wanted the interior to evoke a tipi, but this resulted in poor color rendition inside the house. The TRTL’s east-facing entrance and south-facing windows were intended to acknowledge the power and importance of the sun, but this layout made the energy from the sun difficult to control. The Canada house was also judged difficult for the typical contractor to construct. Despite this, it was judged to have excellent appeal for the intended market of the First Nation peoples of Western Canada.

Solar Decathlon Visitors TourVisitors tour the U.S. Department of Energy Solar Decathlon 2011 in Washington, with Arlington, Virginia, left, and the Lincoln Memorial, right, in the background. (Stefano Paltera/U.S. Department of Energy)
Secretary of Energy Steven ChuSecretary of Energy Steven Chu inspects the evacuated-tube solar water heater outside of the University of Maryland’s house, followed by students Scott Tjaden, left, and Jeff Rappaport, second from left. (Stefano Paltera/U.S. Department of Energy)

How They Did It

Here’s how the four most affordable houses—each with a radically different approach—kept up-front costs low.

Affordability Contest First Place. This year, two contestants tied for first place in Affordability. Parsons the New School for Design and Stevens University (which includes the Milano School of International Affairs, Management, and Urban Policy at The New School) built Empowerhouse for $229,890. “Parsons NS Stevens… house is based on the affordability needs of the team’s target market in an urban context: low initial costs, low maintenance costs, and low utility costs,” says Affordability Juror Matt Hansen, founder of Takeoffs Construction Estimating and partner at Licata Hansen Associates Architecture. At the time, its winning the Affordability contest allowed Parsons NS Stevens to jump from 8th to 4th place overall, but there were many more contests to go, and Parsons NS Stevens finished 13th in the Solar Decathlon overall.

Team Belgium (Ghent University) tied for first place with Parsons NS Stevens by constructing a house estimated to cost $249,568. They started with a cube—the cheapest structure to build per square foot—and filled it with the least-expensive components. Unfortunately, their E-Cube was mistakenly denied first place in DOE’s initial press release. The Affordability jury later praised Belgium in the corrected press release, saying “ingenuity, the use of known materials, and limited use of heavy equipment added to the affordability of the house.” Belgium lost points with the Architecture jury because the E-Cube lacked curb appeal, and Belgium finished 16th out of 19 in the Solar Decathlon overall.

Affordability Contest Second Place. Purdue’s INhome took second place in the Affordability contest. Purdue lowered costs by creating a house that builders were used to building. The jury commented that “Purdue’s use of a traditional design and construction approach demonstrated high-tech energy and control systems for a sophisticated yet conventional market,” adding that “the general public would not perceive it as a solar home.” Purdue’s INhome scored 99.2 points, which was enough to put them in the lead for a time. In the end, Purdue finished second overall.

Affordability Contest Third Place. The Southern California Institute of Architecture and California Institute of Technology team’s CHIP (Compact Hyper Insulated Prototype), valued at $262,495, scored 98.8 points to take third place in the Affordability contest. One way the California team saved money was by eliminating all interior walls, and using different floor levels to achieve a sense of privacy. This house also scored second in Engineering for its unique thermal envelope (‘Outsulation’) design, which uses commercially available materials such as recycled denim. This house had a fun vibe with furniture that stacked into the walls and HVAC and lighting controlled by a video game controller.

Real-World Implications and What It All Means

The real test, of course, is whether anyone will buy these and similar houses. Second-place New Zealand and winner Maryland had both found buyers as of this writing. At the time of the competition, however, only 4 of the 19 houses were for sale.

learn more

To find out more about the 2011 Solar Decathlon (and the decathlons in 2002, 2005, 2007, and 2009), including lots more great photos and information about the teams and their houses, go to the contest home page at

After going to these Solar Decathlons since 2002, I’m beginning to sound like a sports announcer—reciting statistics on the contestants’ previous records and future chances. But talking to the students made me realize that the Decathlon is about more than winning and placing. I chatted up the friendly University of Tennessee student handing out brochures during the tour. I asked her about the fancy glazed walls in the Tennessee house that folded away completely–noting that they cost 5 to 10 times more per square foot than conventional sliding glass doors. “I know,” she said, “but they are so much more welcoming—they show our y’all come spirit.” I asked the Middlebury team about their splurge on locally sourced slate flooring and countertops. “I know it’s not good for our Affordability score,” said one Middlebury student, “but this is about more than scoring points—it’s about designing buildings that support our local economy and jobs. If we don’t do that, it’s not very sustainable, is it?”

I couldn’t have said it better myself. —See you in 2013, when the contest will take place in sunny Irvine, California.

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