hard to read but looks like some efficient solar cellsCompound...

hard to read but looks like some efficient solar cells






Compound Semiconductor June 2008 compoundsemiconductor.net 21
Te c h n o l o g y C o n f e r e n c e R e p o r t
III-V solar states its performance case
Looking out of the window on the train from Madrid to Seville, you might catch sight of a phalanx of
solar panels in a key test plant for compound semiconductor-based energy production. With sites like
this becoming increasingly common, the concentrating photovoltaic industry gathered in Madrid to
report their systems’ latest results at the CPV Today summit, and Andy Extance joined them.
If we were to look for a birthplace for the current
resurgence of compound semiconductor solar technology,
Madrid could make a strong claim. This
year the Institute for Concentrator Photovoltaic Systems
(ISFOC) has begun an authoritative study into
the effectiveness of III-V-based systems. Although
the tests are spread across Spain, this initiative was
developed by the Universidad Politécnica de Madrid
(UPM). Madrid also recently held the inaugural
Concentrated Photovoltaics (CPV) Today summit.
Antonio Luque, director of the Solar Energy Institute
at UPM, underscored the importance of the
meeting as he gave the first presentation, calling it
“the starting gun in the race for CPV”.
Despite clearly being taken aback by the buzzing
350-strong audience, Luque and his colleague
Gabriel Sala opened proceedings by welcoming the
broad interest as crucial for the industry. The obvious
presence of investment bankers and analysts in
the throng prompted conference chair Sala to call for
improved understanding of the difference between
concentrating and conventional silicon photovoltaics
among the financial community.
The difference that Luque went on to detail predominantly
revolves around the use of compound
semiconductor cells at the heart of CPV solar arrays.
These cells monolithically integrate GaInP and
GaAs layers on top of a germanium substrate, with
each layer absorbing a different portion of the spectrum.
These triple-junction cells comfortably hold
the record for conversion efficiency of solar energy,
delivering 40% compared with silicon’s 27%.
The bad news is that this benefit comes with the
additional expense common to compound semiconductor/
silicon comparisons. However, Luque made
the point that whereas silicon is now approaching its
theoretical efficiency limit, he believes that monolithic
III-V cells could reach at least 50% efficiency.
For this to happen, a number of potential design
advances could be exploited, for example by using
quantum dots as an extra junction in the cells.
Until this happens, the refinement of current
approaches still has much to offer. Geoff Kinsey,
the technical lead in CPV products at US cell
maker Spectrolab, explained what to expect from
the company’s latest generation of triple-junction
technology. Due to hit the market in the third quarter
of 2008, the C2MJ line is aiming to push the
efficiency record to 42%. This 2% efficiency boost
should translate to the company’s day-to-day production
averages, bringing these to more than 38%
efficiency. By 2009 Spectrolab hopes to make as yet
unspecified modifications of the materials used in
their cells, to deliver a 43% hero-cell.
Azur Space, the European III-V cell manufacturer,
cut its teeth in powering satellites, like Spectrolab
Concentrated Photovoltaics
(CPV) Today 2008 was held at
the Mirasierra Suites Hotel in
Madrid, Spain, on April 1–2.
The conference boasted more
than 350 attendees, 24
speakers and 6 exhibitors,
after initially being planned for
an audience of only 150. “We
had to open up into a second
room to take the full capacity,”
said the organizers.
Concentrix sola r GMBH
compoundsemiconductor.net June 2008 22 Compound Semiconductor
Te c h n o l o g y C o n f e r e n c e R e p o r t
and Emcore. As such, the majority of its financing
still comes from the space industry, with very little
from CPV. In that sliver of CPV business, the company
supplies system makers like Concentrix Solar
and Sol3G with cells that attain 35% conversion
efficiency at 500× concentration. However, according
to the company’s director of business development,
Gerhard Strobl, more interest is needed to
push his company’s research for CPV further.
Power networking
Although there is room to improve cell efficiency,
without an economic driver these possibilities
would remain academic. A key point that CPV
Today underlined is that, across the world, increased
backing from the energy industry is providing this
driver. So, with power companies forming a notable
subset of attendees alongside the financiers, the
leading system makers sought to show the promise
of CPV in general and their products in particular.
Ironically, for a conference held amid the hotbed
of Spanish CPV, the most definitive data on system
performance came from German and Australian
companies. One of the first three participants
in ISFOC, German company Concentrix Solar,
installed the first 100 kW of its 300 kW project allocation
in February. Given the early stage of that
work, Concentrix instead showed results of a typical
September day in 2007 at a 5.75 kW plant in Llorca,
Spain. Clear data showed module efficiency of more
than 20% from before 10 a.m. until after 6 p.m. with
output power peaking at more than 5 kW at 2 p.m.
According to CEO Hansjörg Lerchenmüller,
the
efficiency benefits that this offers over competing
silicon systems, which can offer only 14% module
efficiency, readily convert to cost savings.
Lerchenmüller is undaunted that these early stage
data come in at less than the 25% efficient modules
that he says his company’s technology is capable of.
According to him, that performance level will help
Concentrix beat the euro-per-watt cost of silicon by
2010. This will also be aided by the state-of-the-art
production plant with annual module manufacturing
capacity of 25 MW that the company is due to
bring online in August.
Concentrix boasts the backing of energy companies
Abengoa Solar and Good Energy, as well as an
order backlog that will keep it busy for the whole
of 2008. Having also spun out of the highly reputed
Fraunhofer Institute for Solar Energy, Concentrix
presented its results analysis with the assurance of
a company set to be a key force in CPV.
Australian company Solar Systems could be considered
one of the pioneers of the current wave of
CPV technologies. It has existed since 1990 and has
operated commercial systems for 10 years. It is also
a convert from silicon to compound semiconductor
cells and confirms a 46% efficiency difference
between the two with its own data.
Solar Systems’ existing systems are typically
dish concentrators, in comparison to the planar
heliostat arrays common elsewhere in the world.
John Lasich, the company’s CTO, was able to present
data on a 130 kW peak output dish power plant,
where the best dishes delivered 23.7% efficiency. At
another facility, two years of data showed a single
33 kW receiver producing 196 kWh per day, under
7 kWh/m2 of solar radiation on average. This corresponded
to 21.2% system DC efficiency, which
dropped to 19.6% when converted to the AC that is
compatible with the electricity grid.
Solar Systems can claim its own energy company
backer in the shape of TruEnergy, a subsidiary of
China Light and Power, as well as strong support
from the Australian government. These partners
will help the company convert to heliostats for
deployment in a 154 MW power plant due for full
commissioning in 2013. On this massive scale – and
using Spectrolab cells – Solar Systems will once
more be forging a path for modern-day CPV.
For other system makers, proving manufacturing
ability was of more importance than showing
results. Amongst these was Concentración Solar la
Mancha – now part of the Renovalia Energy group,
which claims to be the major installer of photovoltaic
parks in Spain. Its CEO, Miguel Trinidad, is
an automobile industry veteran, who is seeking to
exploit his manufacturing experience. The kind of
discipline demanded by that industry, Trinidad reasons,
is key to getting the costs of CPV down.
Strategic concerns
Emcore brought the biggest delegation from a single
company, representing its broader focus compared
with its rival Spectrolab. Instead of its GaAs-based
cell development, the company used its presentation
to promote its CPV systems. Earl Fuller, the
vice-president leading this business unit, promoted
his systems by citing Emcore’s prior experience
as
a provider of capital equipment in manufacturing
compound semiconductor reactors. Fuller talked
about system deals that include participating in
ISFOC, and an 850 kW deployment in Spain, but
could claim little in the way of installed capacity.
This system focus unsettled some at the conference,
who could otherwise be Emcore’s cell customers.
They feared that Emcore could vertically
integrate all of its cell production, tipping their
preference in favor of Spectrolab’s record-holding,
albeit costlier, cells. However, the presence of
newer, alternative III-V cell manufacturers at CPV
Today, like Solar Junction and Taiwan-
based LED
manufacturer Arima, might have reassured these
worries. Furthermore, rumors suggested that the
likes of Sharp and Samsung might soon further
broaden CPV cell supply.
Emcore’s system focus also meant that there was
no mention of its major terrestrial III-V cell customer,
Green and Gold Energy, which itself generated
some comment. Internet speculation about the
relationship between the companies wiped a third
off Emcore’s stock price in a day, just two weeks
Solar Systems demonstrated
the effects of highly
concentrated sunlight by using
one of its concentrators to
burn a hole in a piece of 6 mm
thick copper.
The first 100 kW of
Concentrix’s ISFOC installation
in Puertollano was completed
in February.
Concentrix sola r Gmbh Sola r syst ems
Compound Semiconductor June 2008 compoundsemiconductor.net 23
Te c h n o l o g y C o n f e r e n c e R e p o r t
prior to CPV Today. Some attendees speculated that
Emcore might be trying to disown Green and Gold,
but David Danzilio, head of Emcore’s photovoltaics
division, denied this. Instead he pointed out that for
his colleague Fuller, Green and Gold is a competitor
and hence should not be mentioned in talks focused
on Emcore’s power-generating systems.
The controversy surrounding Emcore and Green
and Gold served as a focus for a concern expressed
by many at the conference. They felt that the presence
of investment analysts and bankers could be a
mixed blessing. With some attendees citing experience
in the telecoms industry, whispered anxieties
of the solar industry being pumped up into an
economic bubble by unscrupulous financial types
underlay the otherwise positive tone.
For Green and Gold’s part, CEO Greg Watson
made a confident show of his company’s technology,
developed using AUS$500,000 ($472,000) investments
from Watson and private investors. Now,
Green and Gold is close to making its SunCube
systems commercially, further funded by $6 million
earned licensing manufacturing rights outside
the company’s native Australia. Watson claimed a
“real world” peak efficiency of around 30% for his
modules on the roof of the Green and Gold facility
in March 2007. He also presented standard test
data but questioned the usefulness of the recent
IEC 62108 standard for safety and reliability of the
CPV module. The lack of an accredited test for output
power meant that no direct comparison could be
made with silicon photovoltaics.
This fact, Watson
felt, bore the signs of undue influence from silicon
industry participants in defining the standard.
The final talk came from the mayor of the Spanish
town of Puertollano, where two ISFOC installations
are sited. During the conference, descriptions
of Puertollano approached a kind of CPV El Dorado.
Take the train from Madrid to Seville, Lerchenmüller
said, look out of the window and there you’ll see our
installation. Indeed as well as ISFOC, Puertollano
will soon host a separate
research center belonging
to system maker SolFocus.
Puertollano, which has christened itself the
“International City of Energy”, is historically
a
coal-mining town. As well as retaining a strong
petrochemical industry, it boasts the first monosilicon
wafer plant in Spain. BP Solar is also investing
7100 million ($155 million) here to build one of the
largest
solar module plants in Europe.
The presence of these power incumbents so close
to the ISFOC pilots is a good reminder of the reality
of CPV technology, which is clearly beginning
to happen and is starting to grow. Yet there is still
much work to be done to find a place out of the
shadow of CPV’s larger power-generating rivals. l
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