Solar Decathlon 2007: Recap, Analysis and Results

[pagebreak:SolarDecathlon2007RecapAnalysisandResults]

This brief report provides a recap of the event, complete with analysis and results, including details about which technologies were used and why, and if performance expectations were met. Technology suppliers highlighted in this report include:

• Apricus
• BP
• Centria
• Concorde Battery Company
• EPV Solar
• Ernst Schweizer AG
• GE
• HunterDouglas
• Isofotón
• NanaWall
• OutBack Power Systems
• Sanyo
• Scheuten Solar
• Schott Solar
• Stiebel Eltron
• Sunda Solar
• SunPower
• TekMar
• Xantrex

The Solar Decathlon is a competition to design, build and operate a solar-powered house, using the latest technologies at the disposal of the competitors. Twenty teams competed to see whose innovations were the most advanced. This event is held every two years on the National Mall in Washington, D.C., in the "Solar Village."

The goal is to create "the most attractive, effective and energy-efficient solar-powered house." All the solar houses must be entirely solar-powered. This power must be able to handle all of a family's day-to-day activities. The house must be 800 sq. ft. and have a maximum height of 18 feet.

Each team is responsible for raising its own funding from outside sources on top of the $100,000 each team receives from the Department of Energy for being accepted into the competition. These outside sources range from small businesses that make green products and contractors to large companies such as Ford and BP. Through this project, competitors focus on environmental responsibility, construction management and implementation as well as gain valuable fund-raising skills as potential future entrepreneurs, not to mention they learn how to build a house! While each team has faculty advisors, the students have all of the primary responsibilities associated with this unique project. Teams strive to build the best house and, in turn, come up with some very unique and innovative solutions.

In addition to the money awarded by the DOE, each team is given an electric car that it must use during the competition. This year, the teams were given a GEM (Global Electric Motorcars) e2 NEV.

The 2007 Solar Decathlon was the third competition, with past Decathlons occurring in the fall of 2005 and 2002. During each of the past Solar Decathlons, more than 100,000 visitors congregated on the National Mall in Washington, D.C., to visit the "solar village." This year, however, the attendance is estimated to have broken all previous records, although exact numbers have yet to be published.

The inaugural event was held in 2002 with 14 teams from across the country. The second decathlon was held three years later, in 2005. That year, 18 teams participated, including international teams from Canada, Puerto Rico and Spain. The presence of international teams showed the worldwide awareness and interest in this important issue. This year, the Decathlon returned for its third time, with 20 teams, including two more international additions, Technische Universität Darmstadt from Germany and Team Montreal.

Primarily sponsored by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy and managed by the National Renewable Energy Laboratory, the event also was sponsored by many other groups. The event's title sponsors were: The American Institute of Architects, The National Association of Home Builders, The American Society of Heating, Refrigerating and Air-Conditioning Engineers, The US Green Building Council, BP and Sprint. (For a complete list of sponsors, please visit the Solar Decathlon Web site.)

The U.S. Secretary of Energy, Samuel Bodman, has been very involved with the Solar Decathlon since his appointment in 2005. During his closing-ceremony speech, he said "[the Solar Decathlon] is one of the best parts of my job." He also noted that because of such high attendance and the overwhelmingly positive response, the competition "is now a permanent part of America."

The technical and design levels have dramatically increased since the competition's inception. Every year, teams learn from each other and from their own experiences. Secretary Bodman said, "The technology we see here works and I don't think I can pay it any higher complement than that." And he is absolutely right. This is a tangible showcase for the world of the future feasibility of energy-efficient and zero-energy buildings.

[pagebreak:The Teams]

Solar Decathlon 2007: The Teams

Of the 20 teams that competed last week, many were Solar Decathlon veterans, while others were competing for the first time. If you couldn't make it to D.C. last week, you can keep tabs on all the teams by visiting their individual Web sites. Having a Web site is an integral part of the communications portion of the competition.

[pagebreak:The Winners]

Solar Decathlon 2007: The Winners

Technische Universität Darmstadt

University of Maryland

Santa Clara University

As it is a true decathlon, the competition consists of 10 contests in which each team must participate. A tally of the total points gained from all the competitions determines final ranking.

Detailed contest results can be found on the Solar Decathlon Web site.

[pagebreak:Competitor Profiles]

Solar Decathlon 2007: Competitor Profiles

The following sections are profiles of key competitors. They are ordered by final ranking.

Note: Not all teams were profiled.

• Technische Universität Darmstadt - 1st Place
• University of Maryland - 2nd Place
• Universidad Politécnica de Madrid - 4th Place
• Georgia Institute of Technology - 6th Place
• University of Colorado at Boulder - 7th Place
• University of Texas at Austin - 10th Place
• New York Institute of Technology - 10th Place
• Massachusetts Institute of Technology - 13th Place
• Carnegie Mellon University - 14th Place
• Cornell University - 19th Place

[pagebreak:Darmstadt]

Technische Universität Darmstadt — 1st Overall

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.

Mark Hampel holds the Technische Universitat Darmstädt team's first-place trophy.

Source: Kaye Evans-Lutterodt, Solar Decathlon

BIPV panels attached to individual louvers add to the power generated.

Source: Oka Tai-Lee

Oak louvers on the Technishe Universitat Darmstadt's solar powered home provide shading and privacy.

Source: Oka Tai-Lee

A bed "cavity" can be hidden away when more space is needed.

Source: TUD Website

[pagebreak:UofMD]

University of Maryland "Leaf House" — 2nd Overall

As competition veterans, the University of Maryland made an impact on the jury. The lines to view the house were astoundingly long.

A unique feature of the Maryland house was the liquid-desiccant wall. What appeared to be a waterfall inside the entertainment center was actually a de-humidifying system filled with liquid desiccants. The material is similar to the little sugarlike packets found in new pairs of shoes, but in liquid form. Through a series of fans, humid air is sucked into the wall and expelled as comfortable dry air. The conditions in the Chesapeake Bay area are very humid, and this feature was designed around that concept. "This wall is a very cool feature," said Evan Merkel, a structural-engineering student at UMD. "If you know Maryland, you know how humid it can get in the summers. Right now, this is a prototype and we don't know of anyone else doing it."

Maryland's truly innovative element was SHAC, the Smart House Adaptive Control System. The team's engineers built the system from the ground up. The Web-based system allows occupants to track and control all the systems running in the house. By having the system Web-based, a user can access it from anywhere they can get to the Internet. Also, as the system is used, it begins to learn the natural climate of the area and the user's preferences. The adaptive system helps to control energy usage.

Thirty-four Sanyo HIP-205BA3 panels, each generating 205 watts of electricity for a total of 6.9 kW, were installed on the roof.

A solar-thermal system by Apricus heated domestic hot water as well as radiant flooring. A back-up instant hot-water heater, Stiebel Eltron Tempra 20, was installed, because Maryland's peak amount of sun usable for hot water is lower than places such as California or Florida. This system uses energy generated from the PV panels on the roof when it is in use.

The team already has designed 1,600- and 2,000-square-foot versions of the "Leafhouse" to show its flexibility in expanding. The local American Institute of Architects chapter already has purchased the house to serve as its office.

The front view of the Leaf House.

Source: Jim Tetro, Solar Decathlon

The innovative liquid desiccant wall inside the UMD house.

Source: Oka Tai-Lee

Translucent panels and wood beams create the ceiling.

Source: Oka Tai-Lee

[pagebreak:madrid]

Universidad Politécnica de Madrid "Casa Solar" — 4th Overall

In 2005, Universidad Politécnica de Madrid was the first European team to compete in the Solar Decathlon and, in 2010, Spain will be home to the first European Solar Decathlon.

Entering into the third Solar Decathlon, Mario Toledano, a student in the Center for Integral Domotics (home automation), said the team has learned "how to plan ahead for weather and how to manage the competitions [better]." He seemed to be happy with their performance this time around.

The team used solar panels by Isofoton, a Spanish solar company. Toledano said the 54 panels were performing quite well. And, of course, competing during an incredibly sunny week didn't hurt anyone either. The battery system was comprised of 24 batteries that have a 90 kW storage capacity.

It had a domotic walkway, which monitored the energy systems in search of an optimal balance between generation and consumption.

An interesting innovation the Madrid team used was an adsorption machine. This system produced cold air to help cool the house and was run from the solar-thermal system. This system also was optimized because, as well as putting collectors on the roof, collectors were incorporated into the south facade of the house. In this way, energy could be harnessed at a variety of times during the day. Because of the location on the facade, the collectors were physically closer to the tanks and had less heat loss in the transfer between the two.

Two water tanks in the mechanical area provided domestic hot water and temperature control. Most teams that use the dual-tank system have equally sized tanks around 60 gallons each. This team, however, used a 20-gallon instant hot-water heater for domestic hot water and a 50-gallon tank that would be used for heating and cooling purposes.

The exterior green wall not only provided an aesthetic appeal, it helped insulate the structure.

South view of "Casa Solar"

Source: Jim Tetro, Solar Deacthlon

[pagebreak:GIT] Georgia Institute of Technology "Icarus" — 6th Overall

Georgia Tech was a first-time competitor, and the team came in with a rather impressive placing.

By far, the most interesting feature of the house was the rooftop retractable reflectors. These reflectors come out from underneath the solar panels and help reflect extra sunlight into the panels on a cloudy day. Ultimately, these would be completely automated, but for competition and demonstration purposes they were manually operated. Not only were these a unique feature of the house, but this also is a new technology entirely designed by the students at Georgia Tech.

Along with the 6.5 kW array on the roof was a 2 kW array on the south facade. "Those panels can generate about 20 percent of the energy [needed] for afternoon activities," said Jonathan Cook, an architecture student. Adding panels that are oriented vertically allowed late-afternoon sunlight to be harnessed.

Rainwater was captured in 20" PVC pipes underneath the exterior deck. The gray water in these tanks is not for potable use. Instead, the water was used to cool mechanical systems. While the concept is green, the use of PVC pipes is very controversial as they are very environmentally unfriendly.

A series of light shelves ran along the south and east facades of the structure. These shelves bounced harsh sunlight away from the house to keep the interior cooler. Because the exterior wall was made of translucent panels, only filtered indirect light reached inside.

In the back of the house it appeared that there was an art piece. Upon further inspection, it was a creative way to house a solar-thermal system. The tubes were set upright inside a Zen rock gardenlike area. Form and function.

The computer software that controlled the variety of technologies in the house continuously monitored energy use. It even had the ability to warn the homeowner when energy supplies were low.

While Georgia Tech does not have a sustainable-design program in place, the interest is definitely growing. Cook told Greentech Media that there "are a lot of new professors who are really into it." Taking sixth place in its first competition will no doubt show the school that not only is there interest, there is talent.

The south facade of Icarus.

Source: Jim Tetro, Solar Decathlon

A view of the eastern facade showing the light shelves that help to reduce direct sunlight into the house.

Source: Oka Tai-Lee

The retractable reflective panels are extended as clouds roll over the mall.

Source: Oka Tai-Lee

SMA Sunny Island PV inverters change the current from the panels for use in the house.

Source: Oka Tai-Lee

Georgia Tech uses a Zen garden concept to incorporate the evacuated tubes into the landscape.

Source: Oka Tai-Lee

[pagebreak:Colordao]

University of Colorado at Boulder — 7th Overall

As returning two-time champions, University of Colorado may have been a little disappointed with their seventh-place finish.

One of the most visible innovations was the bright orange shipping container. Once a shipping container is used, it frequently is left behind. The team decided to use an abandoned container to build the core of the house. Within the core was housed the main living space, the kitchen, bathroom and mechanical systems. The idea was that bedrooms are additional pieces that can be added onto the central "spine" as needed.

The team already has designed a 1,400-square-foot add-on to the existing structure, explained Sam Mason, a student team member. This addition will be added once the home returns to Colorado. The team's home and addition were purchased by Xcel Energy.

Colorado used a different solar strategy than most of the teams this year: a BIPV roof system. "SolRif is a Swiss framing system that allows the solar-panel array to be a watertight shell over the roof -- so you don't need shingles," said Jon Previtali, a team member. "The way it works is that the frames that come standard with the solar panels are removed by A.G. Schweizer, the maker of SolRif, and new SolRif frames are glued on the PV laminates (the glass part of the panel). The SolRif frames hook to each other in the horizontal direction and the frames allow the panels to lay over each other like shingles in the vertical direction." The system can be powder-coated with whatever color suits the design. Colorado used an 8.8 kW array of SunPower panels with the SolRif system.

Below the panels, a water-tube network was installed. Water flowing through these tubes helps to cool the PV panels. The tubes absorb the heat generated by the panels and then transfer that heat/hot water into the holding tanks for use as temperature control.

A water-to-water heat pump strategy was used for the HVAC system. The tanks and mechanics themselves were hidden in the mechanical closet, however the copper piping, used to radiate heat into the living space, was visible. The team used an artistic array of copper piping as a divider between the kitchen and living space. One tank was for hot water and the other was used for cold. They were heated as needed by heat exchangers on the backs of the PV systems.

The west facade of the University of Colorado at Boulder house.

Source: Oka Tai-Lee

Decorative, yet functional copper radiant heating pipes.

Source: Oka Tai-Lee

Colorado created an external battery shed to maximize the interior space of the house.

Source: Oka Tai-Lee

[pagebreak:UT Austin]

University of Texas at Austin "BLOOM House" — 10th Overall

UT Austin has one of the best sustainable-design graduate programs in the country and this was its third time competing. This year, the team placed second in engineering.

BP held a design competition in the design phase of the competition. The winners of the competition won solar panels for use in the decathlon. UT Austin was the winner -- so it installed forty 190-watt panels for a total of 7.6 kW, in what Matthew Brugman, an architectural engineer for the team, called "the ideal orientation."

A salient point of the team's engineering strategy was to use the panels in the most optimal setting. Brugman said it is "irresponsible to install panels in any other way [besides the optimum configuration]."

Because of their optimum installation, the panels were performing at their expected efficiency, explained Brugman.

A TekMar control system equipped with sensors and digital controls monitored the house from an exterior trailer. This year, teams were allowed to house their batteries in a separate shed-like unit. The addition of the unit made way for more interior space for several of the teams that chose to use the shed.

Brugman explained that the team's idea was to reconceptualize the mobile home. This is evident in the trailer-like design. All the interior products were products that are readily available to the public. The goal of this was to make sustainable living seem accessible to the general public. The HVAC was a standard Mitsubishi model. Any HVAC technician could service it, even having little or no experience with PV technologies.

Apricus solar-thermal tubes were very popular on the Mall this year. The energy produced by the evacuated tubes was used to heat two large water tanks that stored water for domestic use and for a radiant flooring system.

"If anything goes wrong, it is usually blamed on the engineer, so [the professors] drill life safety into us," Brugman explained about the positioning of the evacuated tubes. He noted that many of the other teams had installed the panels on the sides of their homes, which he thought was very dangerous. "A little kid could easily run into those while playing ... And that's a trip to the hospital, almost definitely the burn ward."

The house will find a new home after its vacation to D.C. It will exist on the UT Austin campus as part of a research village.

The front view of the BLOOM House.

Source: Jim Tetro, Solar Decathlon

The two large hot water tanks are stored in the west side of the house behind to barn doors.

Source: Oka Tai-Lee

[pagebreak:NYIT]

New York Institute of Technology "OPEN House" — 12th Overall

While the house was named "OPEN House," one might have found it hard to enter if no one was around because of the keyless fingerprint-ID system the New York Institute of Technology installed. But that was not a problem this week as the house was open for visitors to the Solar Decathlon.

The fingerprint identification was tied into the home's building-management -- or "smart house" -- system. When a user enters the house using their fingerprint, all their customized settings are turned on. These can be anything from temperature to lighting conditions. The "control system not only lies in the ability to operate and monitor the home but in the addition of a platform that can be used to educate those not immediately comfortable with becoming independent power producers," according to the NYIT Solar Decathlon Web site.

Employing a 7.5 kW SunPower array, the team seemed happy with its performance. The panels were able to get about 6 kW on a sunny day.

Some unusual features atop NYIT's roof were the pond and waterfall. The pond served as a thermal reservoir and was tied to a geothermal heat pump within the house. NYIT added the pond as a simulation of the use of geothermal energy. Obviously, the team couldn't just drill into the Mall, but still wanted to show that geothermal was a very viable option for sustainable living. The waterfall dissipated any excess heat through evaporation -- as was necessary during the unseasonably warm week of the competition.

Matt Vecchione, student project manager, explained that a shading device or overhang was added to control the amount of heat from the summer sun that was entering into the house. According to simulations and testing, the annual cooling load was reduced 11 percent by this overhang. In addition to reducing the cooling load, the overhang was equipped with building-integrated photovoltaic panels (BIPVs), by EPV, that were able to produce 400 W of additional energy.

Coupled with the BIPV overhang was a NanaWall system. NanaWall manufactures Energy Star-rated folding glass-door systems. These systems allow for natural ventilation when opened, but also serve as aesthetically pleasing insulation.

Jason Selss, the media manager for the team, said, "We see this [commercially] as a beach house. It would work well in Old Westbury [Long Island, NY]."

Long Island Power Authority is a top-tier sponsor and has been very enthusiastic about the whole project. "The students on NYIT's 2007 Solar Decathlon team are happy to see OPEN House return to the college's Old Westbury, N.Y., campus," Vecchione said, "and hope to see it one day become a solar-research center within the Center for Metropolitan Sustainability, NYIT's new interdisciplinary graduate center."

Source: Jim Tetro, Solar Decathlon [pagebreak:MIT]

Massachusetts Institute of Technology "Solar 7" — 13th Overall

MIT has a long history of building solar houses, but this was its debut in the Solar Decathlon. The school has built six houses previously, with the most recent one in the '80s.

A 9 kW-rated array by SunPower sat atop its house. These panels are the most efficient by area and seem to "perform unusually well in cloudy [conditions]," said Randall Pope, an architecture student.

A unique feature of the MIT house was the south-facing Trombe wall. This wall was made of plastic blocks layered with aerogel (an insulation technology developed by NASA) and sandwiching water. The water within the blocks absorbs heat and radiates it into the house when it is cold outside. The system also keeps heat inside the home. Disadvantageously, these blocks will make the inside of the house extremely hot during high-sun summer months. A shade blocks sun from warming the blocks. These blocks are produced by Hunter Douglas and not yet commercially available. Pope maintained that the blocks had an R-value of 8.

Unlike many of the houses, MIT used two sets of solar-thermal collectors made by Apricus. Despite having extra collectors, the team only took eighth place in the hot-water contest.

It used a plywood and foam SIP to create the walls of the house. These SIPs provide all the insulation the house will need without the use of traditional and unsustainable materials such as fiberglass.

MIT also received 100 points for having a zero-energy balance at the end of the week. It also scored sixth in the Getting Around contest, meaning the team was able to produce enough excess power to charge its car and drive it around Washington, D.C.

The front facade of Solar 7.

Source: Jim Tetro, Solar Decathlon

A sample of the blocks that make up the Trombe wall on the south side of the house.

Source: Oka Tai-Lee

The hot water tank is housed in the mechanical closet.

Source: Oka Tai-Lee

[pagebreak:CMU]

Carnegie Mellon University "TriPOD" — 14th Overall

Carnegie Mellon is a three-time competitor comprised of students from many disciplines and programs throughout the university as well as the Art Institute of Pittsburgh and the University of Pittsburgh.

Their concept this year was based on modular housing that can be customized to suite the needs of different families. There is a central core that holds all the mechanical systems, as well as the kitchen and bathroom. Individual "pods" can be added in a variety of configurations and easily "plugged in" to the core's mechanical systems. This concept allows for a high level of flexibility and individual customization.

"The idea of plug and play is to allow scalability of the house so it can be marketed as a product to allow a family to add to the house or subtract from it [as needed]," said Ben Saks, a senior architecture student and the project manager for the team. Team Tripod envisions the individual "pods" being sold and traded on eBay as consumers' lifestyles change.

Because of the modularity of the house, it only took four hours to assemble on-site.

While CMU finished 14th overall, the team was very happy with their project. "It was more important to have a house that we were proud of than to win the competition," said Robin Fok, one of the team members.

One of the big technological innovations was the Centria structural insulated panels (SIPs). These panels are 4" thick and provided all the insulation for the house. They covered the whole shell. Because the panels do all of the insulation work, the house can be covered with any building material (CMU chose cypress siding and corrugated stainless steel) -- another aspect of its customizability. These panels are also fully recyclable at the end of their usage life.

Because of the flat-roof strategy, CMU chose SunPower 215 solar panels, which have the highest efficiency available on the market. The roof holds a 7 kW array. As part of their system they are beta-testing Xantrex's hybrid inverter chargers and battery system. Flat-roof panel installation is not the optimum configuration for solar panels. However, on cloudy days, the panels are able to catch more energy than a traditional 45° angle installation. Clouds cause the UV rays to bounce and spread over the sky, which is a domed surface. A traditional array will only be able to use the ones directly in front of it, and when it's cloudy, those numbers are minimal. With a flat configuration, the panels are able to absorb energy from a much wider area of the sky, thus allowing for higher efficiency on a gray day.

Also employed with the rooftop solar panels were solar-thermal evacuated tubes made by Apricus. These tubes are the conventional evacuated tubes used for solar-thermal heating. A 50-gallon water tank in the house stores hot water for everyday use.

At the end of the competition, the house will be disassembled and trucked back to Pennsylvania, where it will be permanently installed (with all working plumbing and water-filtration systems) at the Powder Mill Nature Reserve in Westmoreland County, Penn. The nature reserve is the biological research center of the Carnegie Museum of Natural History.

A view of "TriPOD" from the south side.

Source: Jim Tetro, Solar Decathlon

Carnegie Mellon's kitchen features generously sized appliances. A backlit translucent panel behind the kitchen counter casts a warm glow.

Source: Kaye Evans-Lutterodt/Solar Decathlon

Solar-thermal tubes double as a skylight in the house.

Source: Stephen Lee, CMU

The west side of the house served as the battery storage area.

Source: Stephen Lee, CMU

The SunPower system nestled into the mechanical room.

Source: Stephen Lee, CMU

[pagebreak:Cornell]

Cornell University "Light Canopy" — 9th Overall

Cornell University's "light canopy" served as support for solar electric panels, solar thermal tubes and vegetated screens to shade the school's 2007 Solar Decathlon entry on the National Mall in Washington, D.C.

Source: Kaye Evans-Lutterodt, Solar Decathlon

Cornell returned in 2007 having had one previous Decathlon under its belt. In 2005, it placed second overall.

The team at Cornell came up with the concept of the "Light Canopy" for this year's competition. Knowing that not everyone who wants a solar house can afford one, the team took an add-on approach. Its canopy is a steel frame made of off-the-shelf steel that can be customized to fit over any house, regardless of its current roof shape or orientation to the sun. Most houses on the National Mall cost well over $250,000 to build, but the Cornell house could be mass-produced for around $16,000 dollars -- with the biggest expense being the panels themselves.

"We hope that our strategy can be employed in places like developing nations or disaster zones ... areas where the grid doesn't exist or has been destroyed," said Bryan Wolin, a senior science communications major. The canopy itself would take only one day to install over a pre-existing building. The short installation time makes it a viable solution for the areas that are off the grid.

The canopy had 69 solar panels, each 110W, made by GE-- for a total of 7.59 kW. Wolin said that the whole system is rated at 11 percent efficiency, but the actual is closer to 8 percent. The panels were coupled with Concorde Battery Corporation PVX-9150T lead-acid batteries. The energy generated was controlled by OutBack Power Systems FLEXware system components.

Also on the canopy were evacuated tubes, by Sunda Seido, that were large enough to heat two hot-water tanks. One of these tanks was used for domestic hot water and the other was used to run hot water through coils in the duct system. These coils served as the heating system for the house.

In New York State, the minimum R-value for a home is R-25. By using SIPs, with an R-value of 40, the team was able to decrease energy usage by 75 percent.

Cornell's' house already has been bought for $150,000 and will be permanently installed in Connecticut as a guest home.

South view of "Light Canopy".

Source: Jim Tetro, Solar Deacthlon