POWER December 2014 - 23

TOP PLANTS
are configured based on the rating of the inverter.
The Series 3 thin-film panels are each
rated from 77 watts to 82.5 watts, and 20,459
panels are connected into each 1.26-MW array
block.
A power conversion station consists of a
single PV array and two SMA Sunny Central
630CP inverters, more than 500 of which
are used on the project. This model inverter
was selected because it is designed to be used
in large open-field projects in locations with
ambient temperatures up to 122F. The inverters
use new fault ride-through technology in
order to improve the reliability and predictability
of the electricity supplied to the grid.
Agua Caliente is the first PV plant in the
U.S. to adopt this dynamic voltage regulation
technology.
Agua Caliente also features First Solar's
grid integration and plant control system
design, which improves plant reliability and
stability. The system gives the plant the ability
to regulate voltage, frequency, and power
factor much like a typical fossil fuel-fired
plant, thereby minimizing the impact of
changing cloud cover. The system also provides
control of active and reactive power
and ramp rates, and can curtail power should
the need arise. More importantly, the system
allows the plant to ride through grid system
faults and disturbances.
First Solar was the engineering, procurement,
and construction contractor for Agua
Caliente, bringing its " latest advances in system
layout and design, optimized balance-ofplant
components, and integrated work-flow
engineering " capabilities to the project. First
Solar is also responsible for the operation and
maintenance of the commercial plant as well
as supplying the thin-film PV modules.
Phased Construction
The project was constructed in two phases.
The first, 100-MW phase began construction
in the fall of 2010, with the first solar
modules beginning installation in June
2011, two months before the DOE loan
guarantee was finalized and NRG Energy
acquired the project. Seven months later, in
January 2012, the project was generating 39
MW for the grid. The plant reached the 100MW
plateau in April 2012 and was producing
200 MW that July.
Construction of the 190-MW second phase
was completed in April 2014, enabling the
plant to produce the 290-MW design output.
In fact, the plant has been producing up to
250 MW since September 2012. The plant is
predicted to produce an average of about 626
GWh each year, which is an approximately
24.6% capacity factor from a solar resource
rated at 2,405 kWh/m2/yr (Figure 1). The
plant's actual capacity factor in 2013-its
December 2014 | POWER
1. Desert dweller. The 290-MW Agua Caliente Solar Project in southwestern Arizona entered
commercial service in April of this year. The plant features approximately five million solar
panels spread over a 2,400-acre site. First Solar originally developed the project, which was later
sold to NRG Energy; MidAmerican Renewables later bought a 49% share. First Solar served as
the engineer/procure/construct contractor and is responsible for the plant's operation and maintenance.
Power produced by the plant is sold to Pacific Gas & Electric. Courtesy: NRG Energy
first full year of operation-was 26.6%,
according to data from the U.S. Energy Information
Administration
(EIA). Electric
production for 2014 (through July, the latest
data available from the EIA) is running over
17% higher than 2013.
Construction was delayed during the
second half of 2012, though not for reasons
you might expect. The delay resulted because
First Solar had not only met all of its
contractual milestones for constructing the
plant but had also exceeded its installation
efficiency targets. As a result, First Solar
had to readjust the pace of the construction
work to come more in line with future contractual
milestone completion dates. This
adjustment allowed First Solar " increased
flexibility to allocate its solar module supply
to better serve increased demand in the
second half of 2012 across its portfolio of
projects. " In other words, installation of PV
modules was proceeding faster than expected,
and Agua Caliente was consuming more
than its fair share of PV panels coming off
the assembly line.
" Large-scale utility accomplishments,
like our Agua Caliente project, raise the bar
in terms of our clean-energy technology and
production, " said Tom Doyle, president, NRG
Renew. " Proving that we can build both the
world's largest solar thermal and now one of
the world's largest solar photovoltaic facilities
advances NRG's mission to reshape the
energy landscape that is incredibly beneficial
to both the economy and in how we produce
and consume energy. Whether it's partnering,
developing or investing, NRG will lead the
way in providing a diverse set of solutions
and technologies to get the U.S. to the ultiwww.powermag.com
mate
goal of providing affordable, reliable
clean energy for everyone. "
The future of large-scale PV generation
in the Southwest is difficult to estimate. The
Arizona desert is large, but the best locations
near existing high-voltage transmission lines
are already spoken for. The challenge of financing
these very capital-intensive projects
remains. Finally, the utility appetite for more
renewable generation is questionable.
California, where the power produced
by Agua Caliente will be used, is " on track
to meet its interim requirement of 25% renewables
by 2016, and is well positioned
to meet 33% by 2020, " according to the
CPUC. In fact, the project status report on
the California Energy Commission website
shows only three new utility-scale
solar projects under construction in 2014
with a 2015 or 2016 completion date, and
no plants with a completion date beyond
2016. The remaining applications are noted
as either cancelled, on hold, or listed
with a " TBD " start date.
What we are likely observing is a spike
in utility-scale PV installations in the Southwest
that appears to abate around 2016. If
California is able to meet its 33% by 2020
renewable energy goal without additional
PV mega-plant construction, then it's likely
that future PV projects will be local distributed
generation rather than remote central
stations. This observation does not in any
way detract from the accomplishment that
Agua Caliente represents but rather celebrates
what is likely to become a unique
feature of the plant. ■
-Dr. Robert Peltier, PE is POWER's
consulting editor.
23

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POWER December 2014

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