Interview
“India shines on solar power map in
investor’s frenzy”—
continued from page 27
to be left behind. The Ministry of New and
Figure 1. Process Window Index (PWI) formula
Renewable Energy (MNRE) is consider-
ing a proposal to set up a company for
generating power from renewable sources.
How do you attach thermocouples to glance at this single number, and the tech-
The government is expected to be a 100%
fragile wafers? nician knows all he or she needs to know
owner of the proposed firm and will tap so-
The manufacturer will simply slide a new about the suitability of the profile.
lar, geothermal, wind, bio-fuel and biomass
solar wafer into the fixture and clip the
sources for power generation.
spring loaded TCs in place. Should the wa- How do you calculate the PWI index?
This will be the first public sector
fer break after repeated use, it is replaced What are the variables?
undertaking (PSU) generating power from
with a new wafer in seconds. Our testing To calculate the Process Window Index:
renewable sources. So far, public sec-
indicates that the TC readings are very ac- i=1 to N (number of thermocouples); j=1
tor companies National Thermal Power
curate and repeatable, even when replacing to M (number of statistics per thermo-
Corporation (NTPC) and National Hydro
the wafers. couple); measured_value[i,j] is the [i,j]th
Power Corporation (NHPC) are primarily
statistic’s value; average_limits[i,j] is the
engaged into coal and hydro electric power
How does the SunKIC display the average of the [i,j]th statistic’s high and low
generation, respectively.
information? limits; and range[i,j] is the [i,j]th statistic’s
The SunKIC has a self-contained user high limit minus the low limit.
Global scenario
interface that allows the user to display Thus, the PWI calculation includes
Currently, the world’s largest solar energy
it based on his or her criteria. There is a all thermocouple statistics for all ther-
project, a 280-megawatt solar thermal
range of various process window dimen- mocouples. The profile PWI is the worst
plant being built in Arizona by Abengoa
sions such as peak temperature, ‘time case profile statistic (maximum, or highest
Solar, is scheduled to go into production
above’ certain temperatures and even an percentage of the process window used),
in 2011. The largest photovoltaic power
‘area under the curve’ display for those and all other values are less (Figure 1).
plant, which is in Spain, produces 60 MW,
users who find those formulas important. Fortunately, the software performs the
though a 62 MW PV installation named
Profiles can be overlaid and the viewer can calculations automatically.
Moura photovoltaic power station is under
zoom in on areas of interest. The most
construction in Portugal and a 154 MW
important element is our PWI—Process What research are you currently
PV solar power station in Victoria, Austra-
Window Index—number attached to doing?
lia, is planned.
each profile. Alternatively, the data may One of the areas of research we are in-
be exported to Excel or another external volved with is to get a better understanding
program. of the appropriate process window for each
application. Every month, the industry
Debaish Choudhury is based in New
Can you describe the PWI concept? gains improved knowledge in this area. The
Delhi and is Global Solar Technology’s
One of the most important questions material suppliers are key to this develop-
regional editor—Asia/Pacific. Debasish
for the thermal process is how well the ment, and they share much information
has four years experience liasing and
measured profile aligns with the available with their customers. The solar cell process
reporting on solar technologiy activities in
process window. This is frequently a matter is complex in that what happens upstream
the Indian subcontinent.
of subjective viewpoints. The PWI is a may impact the relevant process window
Tel: +91 120 6453260
method to mathematically calculate how further downstream in the production line.
E-mail: dchoudhury@
well the profile fits the relevant process We work with academia and cell manufac-
globalsolartechnology.com
window. The PWI characterizes this fit turers to gain additional knowledge about
with a single number: this. We also work with them to quantify
the efficiency gains experienced by optimiz-
100: The profile is on the very ing the thermal process.
edge of the process window
>100: The profile is outside the You have many OEM deals on the
process limits SMT side of your business. Are you
<100: The profile is inside the open to similar OEM deals with fur-
process window. nace manufacturers?
Absolutely! We find that many customers
Additionally, the lower the number, the rely on their furnace manufacturers or
closer the profile is to the center of the turnkey suppliers for both equipment and
process window. “PWI = Zero” signifies a expertise for their profiling and process op-
profile directly in the middle of the process timization needs. We believe that we have
window—the ultimate optimized process. something to offer solar cell manufacturers
In addition to using a precise and ob- as well as furnace and turnkey suppliers.
jective method for this calculation, the real
brilliance of this method is its simplicity. A Bjorn, many thanks for talking to us today.
www.globalsolartechnology.com Global Solar Technology – November/December 2008 – 29
issue_2.1.indd 29 2/22/09 9:40:06 PM
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