Solar village begins to bloom on National Mall
WASHINGTON--After nearly two years of preparation, teams of architecture and engineering students will soon open the doors on a cluster of 20 solar-powered homes on the National Mall.
The teams, from colleges in the U.S., Canada, Puerto Rico, and Europe, are competitors in the Solar Decathlon, a Department of Energy-sponsored contest designed to showcase the potential of solar energy in buildings. Energy Secretary Steven Chu, who took a walk through Team California's house on Wednesday afternoon, is scheduled to speak at the opening ceremony Thursday afternoon. The homes will be open to the public for four days starting on Friday.
On Wednesday, however, students were busy putting the final touches on their 800-square-foot buildings and connecting their solar electric panels to a "microgrid" set up for the event, which feeds excess electricity to the local power grid. After constructing their buildings at home, student teams transport and then reassemble their buildings on the National Mall where they operate on solar power only.
Teams are judged by architects and designers in 10 categories, including lighting design, the market viability of their projects, and architectural design. But the route student and faculty teams have taken to self-sustaining buildings is widely different. Some buildings focus on practicality by using only off-the-shelf materials while others have deliberately pushed the envelope on the technology.
At the high end of the high-tech spectrum are the teams from Ontario/B.C., Spain, and Germany which are using building-integrated photovoltaics, or solar cells attached to the siding of their houses. The clapboards made by the German team, which won the competition in 2007, also use super-insulating material on the indoor-facing side, which students say is 10 times more insulating than traditional insulation.
The team from Penn State, meanwhile, is using specially designed solar collectors that use cylindrical, thin-film cells designed to maximize sun exposure.
At the same time, there is clear movement among some schools to show how green-building technology can be accessible. While many of the homes here cost over $500,000 to build, Rice University says that its prototype Zerow House costs $140,000 to build. With smaller panels, it could be made for $80,000. Like Team Boston, the Rice team has found a buyer for their house after the completion.
From LEDs to barn siding
Electricity-generating clapboards is not the only building technology on display. Most teams are using energy-efficient appliances, LED lighting, and energy monitoring and control systems, such as touch screens which allow people to see energy consumption and control lighting and appliances.
Energy Secretary Steven Chu on Wednesday posed for a photo with the team from California during the Solar Decathlon.
(Credit: Martin LaMonica/CNET)Team California, with students from Santa Clara University and the California College of the Arts, built a building-automation system that allows the house resident to program lighting, windows and shades, and the heating and cooling system. People can program settings from a touch-screen display in the home or from a smartphone, according to students.
A number of teams are using heat pumps, considered an efficient way to heat and cool buildings. The Rice Zerow house configured its heat pump so that there are two separate heating/cooling units, which avoids energy loss in ducts.
Another technology used more this year than two years ago is microinverters, devices that convert the direct current from solar panels to household alternating current. These microinverters, which replace larger dedicated machines, are more expensive but can increase electricity output by 10 percent, according to Martin Zeumer from Team Germany.
On the design side, most of the homes seek to use daylight strategically with large south-facing windows and blinds. Daylight cuts down on the need for artificial lighting and can help increase the amount of heat available from the sun.
Another theme on the architecture side is a conscious choice of materials, such as insulation made from recycled blue jeans or locally sourced material. The University of Illinois team's house, for example, is covered in wood planks reclaimed from a barn on one of the team member's family farm.
The specific designs from the Solar Decathlon are best suited for new construction. But opening up the homes to the public is meant to give people ideas on how to incorporate solar technologies and energy efficiency in the homes.
"In my mind, this is an open-source house," said Roque Sanchez, an engineering student from Rice University. "We're really working for the public so they can see what works. I hope somebody can copy and change what we've done."
Later this week, look for another photo gallery with more details and photos of the homes.
Martin LaMonica is a senior writer for CNET's Green Tech blog. He started at CNET News in 2002, covering IT and Web development. Before that, he was executive editor at IT publication InfoWorld. E-mail Martin. 
http://www.charles868.com/
There are certain applications where DC power would have huge advantages. For example, I agree that if you recharge your EV batteries from solar PV, and if you have thick wires (which can be justified for such a project), a DC-DC charging would be most efficient rather than doing inverters and re-inverters. This is applicable also to battery banks that you recharge directly from solar PV, DC-DC would be nice. There are now efficient DC Voltage converters (step up or step down) that were developed to use whatever voltage you want from whatever input DC voltage you supply without having to use any inverters. However, for the rest of your appliances, very seldom will you get DC appliances, and this would require even bigger infrastructure restructure of a large swath of various industries. Besides, you will now have to use bigger wires, perhaps as big as that of the jumper cables that you use on your car, unless you use dangerously high voltages.
I would selectively use DC where it would matter most, and for economics, I would still generally have AC for most other applications.
Your theories on the advantage of AC vs DC due to conductor thickness are backwards. To carry the same amount of power, DC conductors can be thinner due to the skin effect that AC experiences (the impact of which is determined by a number of factors), as well as the lower peak voltage needed to carry a given wattage rating due to the lack of the RMS part of the equation (thus allowing for lowered insulator requirements). For a given conductor cross-sectional area and peak voltage, DC will actually have a smaller drop in voltage per unit distance for a given delivered amount of power because the current flow will be smaller and DC does not suffer from RF energy leaking like AC does.
AC has some advantages as well, but relative conductor losses are not one of them. The largest advantage is the ability to easily and economically step up/down voltages with a transformer...though as you mentioned even that advantage is being eroded with ever-better DC voltage steppers.
You are correct, however, in mentioning the dearth of DC appliances that are available being the main drawback of DC power to the home.
Obviously, if you are comparing a 12V DC system to a 120V (170V peak due to RMS) AC system, the AC system wins the "conductor race". But the opposite would be true...a 120V DC (and to a greater extent a 170V DC) system would perform vastly better in that respect than a 12V AC (17V peak) system.
In a comparison between a DC system to AC system at the same peak voltage (eg say the 170V peak that is common in the U.S. for the 120V RMS delivered power), the DC system wins hands-down as I previously mentioned.
Will be interesting to see how entries that have chosen to hold costs down fare against more pricey offerings from institutions that seem to regularly win or place in the top 5.
Look forward to upcoming photo gallery and home details.
Nahhhhhhh.
- by Joe Real October 8, 2009 10:31 AM PDT
- I have just seen a documentary the other night about the previous event. Team Germany won first place, followed by University of Maryland by a very close margin.
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(9 Comments)I generally liked the idea of open-source style of designs where you don't need to worry about any patent-infringements about using the various design elements of the house. The public can pick-up the combination of technologies used without the fear of being persecuted for infringement.