Solar Shootout in the San Joaquin
May 4, 2009 - Bob Haavind - Photovoltaics World
|Photo Credit: Conergy
Side-by-side crystalline and thin-film photovoltaic
installations at a water treatment plant in California's
Central Valley should provide a clear indication of
which provides the best energy production and cost
benefit performance over varying climatic conditions
within a year.
|The data on the Fat Spaniel
Web site also allows the group to compare the
1-MW Phase One solar-tracking system with a number
of fixed installations, such as a 1-MW fixed-axis
rooftop system at a fruit packing firm in Hanford,
CA, a system that Conergy also installed.
The 1.6-MW solar array for the South San Joaquin
Irrigation District (SSJID) was installed in two phases
by Denver-based Conergy Americas in Manteca, CA. Phase
One includes 6720 Conergy 175-W crystalline modules
mounted on a single-axis solar tracking system that
can boost peak-time output by about 15% over fixed
The Phase Two tracking system, which went active
in late March, uses cadmium telluride (CdTe) modules
from First Solar, chosen because they are expected
to perform at a lower cost/watt than crystalline modules,
according to David Vincent, Western U.S. project director
for Conergy. They add 419 kW to the project, and it
is believed to be the first commercial thin-film solar
tracking system in the U.S.
Thin-film modules "can outperform monocrystalline
in areas prone to hazy, overcast conditions or in
industries that generate dust or high degrees of air
particulates," according to Vincent. They are also
superior when there is frequent fog, such as in coastal
areas. The reason, he says, is the sensitivity of
the thin-film cells to a broader span of the solar
spectrum, including infrared and ultraviolet regions.
Thin-film cells also should perform better when
dust covers the surface, he added. Another advantage
of thin-film modules is that less interconnect is
needed between cells, so that there is less rise in
resistivity and heat loss on hot days, he explained.
Early indications, Vincent says, are that the output/DC
kW of the thin-film modules is about 10% higher that
of the monocrystalline.
The project, known as the Robert O. Schultz Solar
Farm, will handle almost all of the power needs for
a water treatment plant that provides 40 million gallons/day
for 155,000 residents and businesses of four nearby
communities, as well as irrigation water for 55,000
farm acres. The main goal of the project is to stabilize
electrical costs, which can spike in summer months
because of time-of-use metering, according to Don
Battles, utility systems director for SSJID. Also,
these are times when solar output is at a maximum.
To reduce long-term maintenance requirements for
the thin-film tracking system, the number of drive
motors had to be minimized. The challenge was to effectively
drive more than 30 tons of modules and steel following
the sun's trajectory with each 2hp motor. This was
done by means of a 30-ton screw jack and engineered
Power generation data for the crystalline and thin-film
modules will be fed from equipment that Conergy installed
on inverters to Fat Spaniel Technologies, a nearby
monitoring and reporting company. The analysis is
put online so that it can be tracked by SSJID's Battles
and his team from offices located more than 20 miles
from the solar arrays.
The data on the Fat Spaniel Web site also allows
the group to compare the 1-MW Phase One solar-tracking
system with a number of fixed installations, such
as a 1-MW fixed-axis rooftop system at a fruit packing
firm in Hanford, CA, a system that Conergy also installed.
Battles indicates that the output at the water treatment
tracking facility is typically 15%-18% ahead, even
though he believes the sun is better at the Hanford
The irrigation district expects to save nearly $400,000
a year in utility costs due to the solar system, while
getting millions of dollars in state incentives.
Conergy's Vincent says that the side-by-side face-off
between monocrystalline and thin-film systems is attracting
worldwide attention, particularly in Europe where
solar has advanced much further than in the U.S.
The performance of thin-film modules under the hazy,
often foggy conditions is attracting considerable
interest in the California valley region, according
to Vincent. For example, a 188-kW thin-film fixed
solar array is being installed by Conergy in Hanford,
CA, for Verdegaal Brothers, a fertilizer, warehousing
and soil and water amendment supplier.
Vincent said that the First Solar CdTe thin-film
installation takes about 10%-15% more ground space,
but provides more energy and is expected to cost 10%-15%
less than a monocrystalline array. The facility is
expected to offset Verdegaal's utility bills by 99%,
cutting some $60,000 a year, while providing for 82%
of the company's energy needs. Over the 25-year life
of the system, which is scheduled to start up in July,
emissions are expected to be reduced by 6,145 tons
This article was originally published by Photovoltaics
World and was reprinted with permission.