wref offers aia, leeD credits 12 ePa rules 12 community solar 14
SolarCity
launches Home
Energy loans
solarcity in March unveiled a home-loan program designed to reduce or eliminate the up-front costs
of energy-efficiency upgrades nationwide. the company offers a comprehensive home-energy evaluation
to diagnose the cause of high utility bills and energy
loss, and a range of upgrades to reduce energy costs
and improve indoor air quality.
solarcity introduced energy-efficiency services in
2010 and has launched more than 5,000 efficiency
projects in arizona, california, colorado, oregon
and texas (out of 33,000 energy projects across the
country). the energy-efficiency service now moves to
connecticut, Maryland, Massachusetts, New jersey,
New york and washington, D.c.
a proprietary software package performs billions of
calculations during each home evaluation to produce
a comprehensive overview of upgrade options, including air infiltration, insulation, heating/cooling and
duct leakage. the loan program is underwritten by
admirals bank of boston. Packages include a one-year
“save Now, Pay later” option, or a three- or 10-year
“Pay as you Go” option.
Ampulse Corp., working with the oak ridge national laboratory (ornl) and the national renewable Energy laboratory (nrEl), has
developed a chemical vapor deposition process to
grow silicon on inexpensive foil, creating cells just
thick enough — 10 microns or less — to convert
most of the solar energy into electricity. the process
eliminates the waste involved in sawing wafers from
massive silicon boules. the company has built a pilot
production line in the Process development integration laboratory (Pdil) at nrEl.
A team of nrEl scientists, including Howard Branz
and Chaz teplin, in 2005 developed a way to thicken
silicon wafers with a perfect crystal coating. A hot
tungsten filament decomposes the silane gas at about
700°C (1,292°F), allowing silicon layers to deposit
directly onto the substrate.
then in 2007, visiting investors from Battelle Ven-
tures asked Branz and teplin whether they could use
a breakthrough at ornl called rABitS (rolling-assisted
biaxially textured substrates). if metal foil is to work as
a substrate, it must be able to act as a seed crystal so
the silicon can grow on it with the correct structure.
the rABitS process forms crystals in the foil that are
correctly oriented to receive the silicon atoms and lock
them into just the right positions.
using the correct intermediate buffer layers to coat
the foil substrates, the researchers were able to rep-
licate the desired foil crystal structure in the silicon
layer grown epitaxially over metal foil.
Battelle Ventures and innovation Valley Partners
then formed Ampulse, and established a $500,000
cooperative research and development agreement
(CrAdA) with nrEl and a similar agreement with
ornl. the company now has 13 employees and
six full-time consultants and is currently working with
22 sponsored researchers from two national labs.
“We have the potential to produce a 15 percent
efficient solar cell at less than 50 cents per watt with
a fraction of the capital investment of other venture-
funded [photovoltaics] companies,” said Ampulse CEo
Steven Hane. “And that’s due
to our r&d collaborations
with the national labs.”
the production line at Pdil
consists of half a dozen vacu-
um chambers where foils are
overcoated with buffer and
silicon layers. it was built to
Ampulse’s specifications by
roth & rau Microsystems of
Germany. Quartz lamps heat
metal foils to 850°C (1,562°F)
and the foils are coated with
the necessary buffer layers. After transfer to a specially
designed chamber, the key silicon layers are grown.
the silicon is then exposed to atomic hydrogen to
improve its electronic properties. Finally, solar cell
junction and electrical contacts are developed.
“the main thing is that we can grow high-quali-
ty silicon layers very fast and without putting much
energy into the process. that means the solar cells can
turn out much cheaper than the wafer-based cells,”
said Branz.
“our process goes directly from gas to the epitaxial
silicon phase, bypassing the growth and sawing phase,”
said Mike Colby, Ampulse’s director of planning and
logistics. “the goal is to achieve the crystal silicon perfor-
mance that until now focused on thicker wafers — and
without having to use a 1,400°C [ 2,552°F] furnace.”
Growing Silicon Crystals directly on Foil by BILL SCANLON
De NNis schroeDer
Ampulse pilot production
line at NREL grows high-quality silicon wafers
directly from silane gas,
bypassing the wasteful
sawing process.
Bill scanlon is a writer in the Public affairs Office at NreL.
