advances | pv progress
1950s Solar Home Still Powered by Sun
More than five decades after it was constructed, one of the oldest solar residences in the United States is still getting most of its energy from the sun.
Completed in 1957, George Löf’s home in Englewood, Colo., features a solar-energy
system Löf designed and developed. The system consists of a large glass roof panel and
a series of pipes that lead to a gravel bed in the basement. The panels heat the gravel
during the day and, at night, the gravel releases
the stored heat to warm the house. The system
was modeled on an earlier one Löf constructed in
Boulder, Colo., in 1945.
The 1957 home went on to serve as a model
for the development of modern solar home systems and was featured on the American Solar
Energy Society’s National Solar Tour.
Löf passed away Oct. 12 (see memorial in
Inside ASES, page 54), but his solar home is still performing. His son told the Wall Street
Journal the system still works perfectly and requires little maintenance, aside from the
occasional replacement of a cracked panel.
Net-Zero Library Opens in Indiana
Chrisney, Ind., population 540, lies about 15 miles from the nearest public library. When
half the town’s citizens turned out to plan a library back in 2006, the school board was persuaded to donate a patch of school property. The state offered a grant of about $450,000 to
cover construction if the community could raise $50,000. It did, plus another $30,000 for
books, computers and furnishings. That left the problem of operating costs.
Bill Brown, from the architectural firm Browning Day Mullins Dierdorf ( bdmd.com) in
Indianapolis, came up with the solution: a 2,400-square-foot passive solar, net-zero building,
with lights and a ground-source heating system driven by an 8.9-kilowatt photovoltaic array.
The library opened last April. The solar array, consisting of 48 186-watt Sanyo bifacial
modules ( solar.sanyo.com), provides shelter for an outdoor classroom. Two SMA Sunny
Boy SB5000 inverters ( sma-america.com) tie the array to the grid.
Installer Brad Morton, of Morton Solar and Wind in Evansville ( mortonsolar.com),
reports that energy production through the first summer met specification. The array generated 1,299 kilowatt-hours (k Wh) in April, peaked at 1,524 k Wh in August, and by October
had produced a $500 credit against the utility bill. Morton believes this may be the first
net-zero public library in the nation.
To monitor the Chrisney system, see tinyurl.com/y86oajg. — Seth MaSia
geoRgia tech photo: ga Ry Meek
Professor Zhong lin Wang of Georgia Tech, with a solar cell
grown on optical fibers.
Georgia Tech Grows PV
Nanotubes on Optical Fibers
A team at the Georgia Institute of Technology has built
a system of light-conducting nanostructures to boost the
conversion efficiency of inexpensive photochemical materials. The result is a three-dimensional photovoltaic (PV)
system that might be hidden from view instead of bolted
to a rooftop.
The process uses zinc oxide nanostructures grown on
optical fibers and coated with dye-sensitized solar cell materials, “We can make photovoltaic generators that are foldable, concealed and mobile,” said Zhong Lin Wang, Regents
professor in the Georgia Tech School of Materials Science
and Engineering. “Optical fiber could conduct sunlight into
a building’s walls where the nanostructures would convert
it to electricity.”
Fabrication begins with telecommunications-grade optical fiber, stripped of cladding and coated with a conductor.
Using a standard solution method, aligned zinc oxide nanowires are grown around the fiber, to make a bottle-brush
structure. The nanowires are then coated with the dye-sensitized materials that convert light to electricity. Sunlight
entering the optical fiber passes into the nanowires, where
it interacts with the dye molecules to produce electrical current. A liquid electrolyte between the nanowires collects the
electrical charges. The result is a hybrid nanowire/optical
fiber system that can be up to six times as efficient as planar
zinc oxide cells with the same surface area. Wang and his
research team have reached an efficiency of 3. 3 percent and
hope to reach 7 to 8 percent after surface modification.
Details of the research were published in the journal
Angewandte Chemie International on Oct. 22. The work was
sponsored by the Defense Advanced Research Projects
Agency, the KAUST Global Research Partnership and the
National Science Foundation.