Solar Power
Sunny
Prospects
for Concentrated Photovoltaic
Until recently, concentrated photovoltaics was still in its infancy.
Now the technology has achieved market maturity, and thanks to its
high efficiency is believed to have the very best growth prospects
on the market for renewable energies.
Text: Manuel Meyer Photos: Luis Díaz Díaz Illustration: Anna-Louise Bath
F
Record-Breaking Technology
With a coefficient of 33.9 percent, proprietary CPV module prototypes developed
by solar company Semprius hold the world record for efficiency.
System characteristics for Semprius’ technology:
Smallest cell
(1 cell = 0.35 mm2)
18 Living Energy · No. 7 | November 2012
ower cost due to
L
highest ­concentration
Highest efficiency due
to tailored absorption
(1,100×)
(cell > 40% / module > 30%)
rancisca Rubio points out of her
office window: “If investments
are made in this technology
now, what we see outside is the future
of the solar energy market.” Before
us, across the grounds of the Spanish
Institute of Concentration Photovoltaic
Systems (ISFOC), stretches a sea of
parabolic mirrors and lenses. Where
olive trees used to stand on the sunbaked earth, today high-performance
solar cells convert sunlight into electrical energy.
The concentrated photovoltaic (CPV)
test systems in Puertollano have a
power of 800 kilowatts in the main
site, plus 1,200 kilowatts in the second
site to generate electricity. The location in the southern Spanish province
of Ciudad Real is almost perfect for
the solar electricity systems, says
Francisca Rubio, the R&D Director at
ISFOC. Since 2006, the state-run research and development center has
defined CPV standards, implemented
reliability measurements for companies, and financed test installations.
Here on the border between CastileLa Mancha and Andalusia, there are
few clouds in the sky. In summer, the
temperatures regularly exceed 40° Celsius, and there is also adequate space
for CPV systems. It is here that ISFOC
tests CPV technologies from various
suppliers from Spain and E
­ urope, but
also from the USA and ­Asia − technologies that have long since ceased to be
technologies of the f­ uture, as the electrical engineer points out.
A concentrated photovoltaic system
converts light energy into electrical
energy in the same manner as conventional photovoltaic technology. The
difference, however, lies in the additional use of an optical system that
concentrates the broad spectral range
of sunlight up to 1,000-fold onto highly
efficient solar cells. Since a CPV module requires fewer cell area than a
conventional PV module, it is more
cost-efficient to use high-quality nonSi cells out of III-V semiconductors
similar to inorganic LEDs in order to
boost the performance. The efficiency
of CPV modules is significantly higher
than that of a conventional PV system.
CPV Technology Has Achieved
Market Maturity
Thanks to the technological advances
of recent years and the development
of the photovoltaic market, CPV systems are now ready for large-scale production of electricity, according to
­Rubio. Powerful, high-performance
solar cells are available, and new optical concepts and tracking systems
have been developed. “The technology has now attained market maturity,
and 2013 could be a decisive year for
the continued development,” the
­scientist explains. The only obstacle
to the success of CPV so far has been
the lack of the “volume effect” that is
necessary to reduce the price of the
systems and hence make CPV competitive.
It is precisely this “volume effect”
that is now slowly starting to take effect. The number of CPV cell manufacturers has grown significantly over
Living Energy · No. 7 | November 2012 19
Solar Power
Europe
Croatia
Bosnia and Herzegovina
Serbia
Montenegro
Bulgaria
Macedonia
Turkey
Greece
Albania
Italy
Portugal
Spain
France
Cyprus
DNI [kwh/m2]
2,500
2,000
North America
Mexico
USA
1,500
1,000
South America
Peru
Bolivia
Chile
Argentina
Uruguay
Paraguay
Brazil
500
The Sun Belt
Stretched across the earth’s “midriff” on both sides
of the equator is the Sun Belt of countries that experience high degrees of direct insolation. It is in
these countries that CPV is an especially attractive
alternative to conventional photovoltaic systems.
Is your country part of the Sun Belt?
View an interactive map of the world showing
levels of solar radiation for ­selected countries.
Living Energy at
20 Living Energy · No. 7 | November 2012
North Africa
Tunisia
Egypt
Libya
Sudan
Chad
Niger
Mali
Mauritania
Western Sahara
Morocco
Algeria
the last two years. Above all in the
USA, an increasing number of largescale CPV systems are being put into
service. While the volume of electricity
generated worldwide using CPV systems was just 25 megawatts in 2010,
including 15 megawatts generated in
Spain, it is today a
­ lready 65 megawatts. “In addition to the USA, an increasing number of CPV systems are
currently being installed primarily in
China, South Africa, France, and Italy.
We’ve gotten the ball rolling,” says
­Rubio. The commercial use of CPV has
begun and its growth potential is enormous. Rubio certainly does not want
to place CPV above other sources of
Middle East
Turkey
Syria
Iran
Kuwait
Bahrain
Iraq
Saudi Arabia
Jordan
Israel
Southern Africa
Zambia
Zimbabwe
Botswana
South Africa
Namibia
Angola
renewable energy. Nevertheless,
she believes that this technology may
have the best growth perspectives
of all renewable energy sources, because in addition to its high efficiency,
which makes CPV cost-effective, it is
the cleanest of all renewable energies.
It is true that the worldwide generation of 65 megawatts of CPV electricity
is still insignificant when compared
with the approximately 30,000 megawatts generated using normal photovoltaic systems. But Rubio is certain
that this could soon change if the prices for CPV electricity generation continue to fall and energy utilities and
governments suddenly become aware
Asia
China
India
Australia
Australia
of the many advantages of the CPV
technology compared to traditional
PV or solar thermal systems. So far,
PV systems have been more cost-effective because they operate using silicon, which is also used, for example,
in the mobile telephone and television sectors; therefore, it was cheaper
to manufacture PV systems. However,
the price difference compared to CPV
systems has decreased enormously.
More Efficient with
Reduced Loss of Quality
While conventional solar systems
are based on silicon cells or thin-film
technologies, CPV uses technologies
consisting of multiple-junction solar
cells constructed of gallium indium
phosphide, gallium indium arsenide
and germanium with stacked, varying
band-gap semiconductor materials.
This significantly reduces energy losses compared to simple solar cells, and
the solar radiation is used more efficiently. The thermal behavior of CPV
cells is better, since they are smaller
and are thus able to dissipate the heat
better. “That’s why PV systems do not
function as well as CPV systems under
intense solar radiation. It’s the same
with a computer: The warmer the PC
chip becomes, the slower the computer
runs,” explains Rubio, before men-
Living Energy · No. 7 | November 2012 21
Solar Power
Solar Power
Types of Solar Energy Systems
Solar thermal systems
(CSP – concentrated solar power):
Solar thermal power stations convert sunlight
into heat. They have the advantage of storage
capacity, but have higher operating and maintenance costs than PV and require a certain
minimum size.
Photovoltaic (PV) systems
Solar electricity systems convert sunlight directly into electrical current using
silicon solar cells.
Concentrated photovoltaic
(CPV) systems
CPV systems work on the same principle as PV,
but concentrate the sunlight up to 1,000-fold
using mirrors and lenses onto small, but highly
efficient multi-junction solar cells
Categories of CPV:
• Low concentration (LCPV)
20- to 40-fold concentration
• Medium concentration (MCPV)
40- to 350-fold concentration
• High concentration (HCPV)
350- to 1,000-fold concentration
22 Living Energy · No. 7 | November 2012
s­ upplied by CPV systems. Everything
is now dependent on politics, the decisions taken and the power of the lobby. However, as soon as CPV will be
able to achieve the price levels of normal PV systems through market volume, this technology offers many advantages, Francisca Rubio explains.
­ ther suppliers, which means that the
o
modules are better able to dissipate
heat and therefore more efficient. “At
the same time, using a relatively simple optical system, Semprius achieves
an enormously high 1,100-fold light
concentration,” says Martínez. The
­ISFOC expert was particularly surprised by the test result that showed
that all the modules displayed virtually
the same value, with a variation of
less than 1 percent. “That is quite unusual,” Martínez notes. She thinks it
is a “very promising technology,” which
uses an innovative printing technique
to produce very uniform, efficient and
at the same time cost-effective cell
modules.
Minute Solar Cells with
High ­Efficiency
While commercial PV modules on
­average achieve an efficiency of around
18 percent, CPV modules achieve an
average of 28 percent. “At the beginning of the year, our test array achieved
a world-record efficiency of 33.9 percent using Semprius CPV modules,”
says Rubio. The prototype supplied by
the US PV company, in which Siemens
Energy has been a strategic stakeholder since June 2011, has made it possible for the first time to convert more
than one-third of the solar energy
­directly into electricity. Joe Carr, the
Managing Director of Semprius, believes that the primary key to success
is the fact that his young start-up company is strongly oriented towards
­development engineering. However,
he doesn’t think that this benchmark
­result is anywhere near the achievable
maximum. In the second half of this
year, his company increasingly wants
to manufacture prototypes for the coming commercialization in its newly
constructed pilot plant in the US State
of North Carolina and is fully convinced
that by the end of the year even higher
module efficiencies can be achieved.
“I believe that by the year 2020, it will
be possible to achieve cell efficiencies
of up to 50 percent and module efficiencies of up to 40 percent,” says Joe Carr.
Indeed, it seems that the CPV modules
supplied by Semprius have considerable growth potential. María Martínez,
who is in charge of the ISFOC research
department responsible for the characterization of modules, gives Semprius top marks. The Semprius technology is quite different from that offered
by other suppliers, according to the
industrial engineer and expert in energy technologies. The substrate composition of the multiple junction is
new. Additionally, Semprius uses considerably smaller solar cells than
Access to the Market
of the Future
Photo: Angela Fernandez
Francisca Rubio, R&D director
at ISFOC, strongly believes
in the m
­ arket chances of CPV.
tioning another advantage of the CPV
technology: “We’ve seen hardly any
degradation of performance of the CPV
systems over time for the moment,
while PV systems work 3 percent less
efficiently after the first year and
­degrade by 0.7 percent in each subsequent year.”
Rubio anticipates that in the future,
CPV could account for around 50 percent of all solar energy worldwide if
investments are made in the market
now. In the meantime, the R&D director of ISFOC estimates that by 2050,
solar energy could perhaps also achieve
an overall share of 50 percent of the
worldwide energy market. In Spain,
the global pioneer in terms of solar
energy, solar energy already provides
3 percent of the total electricity production and according to Francisca
Rubio this could grow to 10 percent by
2020, whereby 2 percent could be
These were also the reasons that
­convinced Siemens to market the Semprius CPV technology, says Karsten
Heuser, CPV Business Manager at
Siemens Energy.
Although the market for CPV systems
is still in its infancy, the industry
­already anticipates an output of up
to 6 gigawatts by the year 2020. “Naturally, CPV will remain a niche market
within the field of renewable energy
sources. However, thanks to its high
efficiency and low costs, it could become a game changer in sun-intensive
regions,” Heuser prophesies. During
the last four years, sinking prices have
already strongly boosted the CPV market. “And every new percentage point
of efficiency reduces costs,” says Heuser,
who believes that the worldwide CPV
installations might reach 200 megawatts by the end of 2012.
However, due to its high dependence
on direct solar radiation, CPV can
only be used in very sun-intensive regions, while its output is poor under
conditions of diffused solar radiation
with cloudy skies. Rubio does not think
this factor will hamper the technology’s success on the solar energy market, but rather works as an advantage,
“since there are more regions in the
world with intensive solar radiation
that are suitable for large photovoltaic
arrays than otherwise.”
Thus, it is particularly in the countries of what is known as the Sun Belt
Comparing PV and CPV Systems
Worldwide solar electricity production (2011):
PV: 30,000 MW
CPV:
65 MW
Average efficiency of ­commercial and CPV systems:
PV cells:
PV modules:
18%
CPV modules:
28%
18%
CPV cells:
39%
Distribution of CPV Installed Power
USA:
35 MW
Spain:
China:
15 MW
that CPV systems are of greater interest than traditional PV systems. This
zone includes the southern parts of
the USA and Mexico, Chile, Argentina,
and parts of Brazil. China, India, Australia and South Africa are also situated in the Sun Belt. Europe’s Mediterranean countries and the Near East
also offer good prerequisites. “CPV
arrays, which are much smaller than
conventional PV systems, are ideal for
small countries such as Israel that
have a great deal of sun, but very little
space – or for countries such as Spain,
where real estate prices tend to be
high,” explains Rubio.
Large Growth Potential
in the Sun Belt
Apart from the USA, she sees the
greatest growth potential for CPV systems in North Africa. The Maghreb
states and the Sahara desert offer
practically unlimited space. Further-
4 – 5 MW
South Africa, France,
Italy, Portugal:
10 MW
more, the technology has a financial
advantage for the countries of this
­region, some of which are comparatively poor: In contrast to solar thermal systems, in order to work, CPV
systems do not require water, which
is an expensive and limited commodity in some of these countries. Conversely, normal PV systems are delivered to the countries in a completely
assembled state, whereas the tracking
systems for CPV systems have to be
installed separately, which creates jobs
for the local workforce. Thus, ­Rubio
explains, CPV energy could cover up to
50 percent of the total energy production in North Africa. The only problem is the lack of well-developed electricity grids, since CPV electricity
cannot be stored. p
Manuel Meyer is a correspondent
for the Austria Press Agency in Spain.
Living Energy · No. 7 | November 2012 23