POWER November 2016 - 58

RENEWABLES
3. Solar skid. GE's LV5+ transformer and inverter system incorporates silicon carbide-
based processors that allow it to extract greater efficiencies from linked solar systems. Courtesy:
GE
4. Sunburn. Rayton Solar's particle beam-based method produces extremely thin wafers
of silicon with no manufacturing waste. The approach allows the use of ultra-pure float-zone
silicon, which up to now has been too expensive for use in solar cells. Shown here is the particle
accelerator's electrostatic acceleration chamber, which energizes H+ ions to 300 kiloelectronvolts
for implantation in a silicon ingot. Courtesy: Rayton Solar/Phoenix Nuclear Laboratories
to 6-inch wafers. The Albany facility will be
set up for 6-inch wafer production (an example
is at right in Figure 2).
Particle Beams. Giant global firms like
GE aren't the only ones working on nextgeneration
methods for extracting greater efficiency
from PV.
Solar cell manufacturers have long struggled
with a dilemma surrounding the silicon
used to create PV cells: Electronics-grade
silicon offers the best performance but is expensive
to manufacture; metallurgical grade
is much less expensive, but its lower purity
degrades performance. Although some firms
such as Silicor Materials have worked to develop
solar-specific manufacturing processes
(see " Weighing the Environmental Impacts
of Wind and Solar " in the July 2016 issue),
Los Angeles-based start-up firm Rayton
Solar has gone a different route, developing
what it says is an economical method for using
float-zone silicon, the highest purity version,
for PV.
Up to now, float-zone manufacturing has
been prohibitively expensive for solar cells;
it's only used for certain high-performance
electronic applications. Conventional PV
cell wafers are mechanically sliced from
silicon ingots, and this approach limits their
minimum thickness, in addition to wasting
some of the silicon through the cutting process.
Rayton's method, in contrast, uses a
particle accelerator to implant silicon ingots
with a layer of ions and exfoliate thin strata
of silicon directly off the ingot, resulting in
no wasted material (Figure 4). Compared
to conventional wafers that are around 200
microns thick, Rayton's method produces
3-micron-thick slices that are then backed up
with a substrate.
Because so little silicon is used for each
slice, float-zone silicon is an economic material
for this method. Rayton says it has the
potential to produce PV cells with conversion
efficiencies up to 24%, a substantial jump
from the current ~19% performance, which
would lead to an approximate 25% reduction
in system costs per kilowatt-hour.
Rayton has developed a prototype of its
talline silicon. SiC-based chips can operate
at much higher temperatures and frequencies
and are far more rugged-they can operate at
twice the power density of a Si-based chip.
This makes them ideal for high-power devices
like inverters, Keith Longtin, product
breakout lab director for GE Global Research
told POWER, because they can convert power
at higher efficiencies and lower losses.
" This allows us to switch up to 10 times faster,
which gives us a much cleaner signal, " he said.
The SiC chips (Figure 2) form the core of
58
GE's LV5+ Solar Inverter, also announced at
SPI, which it estimates can deliver around
$2.5 million more revenue over the life of a
typical 100-MW solar plant (Figure 3).
GE has been working with the State University
of New York College of Nanoscale
Science and Engineering in Albany to build a
fabrication line for manufacturing SiC power
devices. To scale up the technology and reduce
fabrication costs, the company says
manufacturing must move from the current
industry standard of 4-inch wafer production
www.powermag.com
manufacturing process and is currently seeking
financing for future development, CEO
Andrew Yakub told POWER via email.
Dual-Axis Tracking Comes to Rooftops.
Dual-axis tracking has been recognized
for some time as a reliable method to
boost PV capacity factors, especially in areas
with less-than-optimal insolation. Tracking
systems also have much flatter output profiles
because they collect sunlight more efficiently
when the sun is lower in the sky at
the beginning and end of the day.
But the mechanical supports necessary to
implement dual-axis tracking have thus far
POWER | November 2016

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POWER November 2016

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