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Selected
Publications & Articles by ASU-PTL Staff
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 Outdoor
Energy Rating of Photovoltaic Modules:
Module Temperature Prediction and Spectral Mismatch Analysis
by
Y. Tang, G. TamizhMani, L. Ji, and C. Osterwald
EuroPV Conference, June 2005
The performance of a photovoltaic
(PV) module is dictated by the module temperature, solar irradiance
and solar spectrum. The objective of this work is two fold:
(i) develop a thermal model for predicting the module temperature
based on the field acquired long-term data with diverse climates
and PV technologies, and (ii) quantify the extent of influence
of outdoor spectral variation on the performance measurements.
The first objective was achieved using a 2-year field data
of two systems installed at Mesa, Arizona and Golden, Colorado.
An analysis of the coefficients of these models indicate that
the module temperature is practically, if not exclusively,
dictated by the ambient temperature (near-unity coefficient,
0.943), irradiance (0.028oC per W/m2) and wind speed (-1.528oC
per m/s). The second objective was achieved using the data
obtained with calibrated reference cells (mono-Si and GaAs),
calibrated test devices (mono-Si, poly-Si and CdTe) and a
spectral radiometer. This study indicates that the spectral
mismatch error for the outdoor measurements at the Mesa site
is negligibly small if a matched (<0.47%) or near-matched
(<0.70%) technology is used as the reference cell. These
results demonstrate that the Mesa site spectral conditions
are normally not far from the AM1.5G reference spectral condition.
>>Read
full paper
Representative
Samples For Concentrator Photovoltaic Module Qualification Testing
by Robert McConnell, Liang Ji and
Govindasamy Tamizhmani
CPV Conference, Scottsdale, May 2005
This paper reports the developmental status of a new test
standard IEC 62108, titled “Concentrator Photovoltaic (CPV)
Receivers and Modules - Design Qualification and Type Approval.”
The IEC CPV working group, TC82/ WG7, is currently exploring the
possibility and validity of using small representative samples in
place of large/actual product for the design qualification testing.
By using appropriately designed and fabricated representative smaller
samples, the qualification tests can be conducted to considerably
reduce the testing costs and/or time to the manufacturers, while
maintaining a reasonable engineering confidence level on the results.
In the year 2000, the flat-plate PV module working group, TC82/WG2,
developed a Retest/Similarity Test Guideline. This guideline has
been accepted and adopted by the worldwide PV community including
the independent testing laboratories. Based on this guideline, after
the largest type/model from a given flat-plate module family passed
a full sequence in the qualification test program, other smaller
types/models in the same family can be fully qualified by running
a fewer tests on fewer samples. This larger-representing-smaller
approach, however, can not be directly applied to CPV, because many
CPV systems are in the range of several kilowatts, and their sizes
are much larger than available test equipment can handle, primarily
environmental chambers. The intention of TC82/WG7 is to apply the
“similarity” approach to the CPV qualification but in
the reverse order, that is, smaller-representing-larger. This paper
discusses the potential failure mechanisms under different testing
sequences, and then gives some suggestions on how to design and
fabricate appropriate smaller representative samples. This new approach
will be discussed within TC82/WG7 for a possible incorporation in
the IEC 62108 standard, and then submitted for an international
voting
Performance Test
of Amorphous Silicon Modules in Different Climates – Year
Three
Higher Minimum Operating Temperatures Lead To Higher Performance
Levels
by R. Rüther, G. Tamizh-Mani,
J. del Cueto, J. Adelstein, M.M. Dacoregio & B. von Roedern
IEEE PVSC, January 2005
This paper presents third year results of a round robin exposure
experiment designed to assess the performance of thin-film amorphous
silicon (a-Si) solar modules operating in different climatic conditions.
Three identical sets of commercially available a-Si PV modules from
five different manufacturers were simultaneously deployed outdoors
in three sites with distinct climates (Arizona – USA, Colorado
– USA and Florianopolis – Brazil). Every year all PV
module sets were sent to the National Renewable Energy Laboratory
(NREL) for Standard Testing Conditions measurements under a SPIRE
simulator. The fouryear experiment aims to determine the light-induced
degradation and stabilization characteristics of a-Si regarding
specific history of exposure, and to monitor and compare degradation
rates in different climates. We present results from the first three
years of measurements, showing that while most of the manufacturers
underrate their products by 20 to 25% to account for the light-induced
degradation, outdoor exposure temperature seems to be what will
ultimately determine the stabilized performance level of a-Si.
>>Read full paper
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 Outdoor
Energy Rating Measurements of Photovoltaic Modules
by Yingtang Tang
, Govindasamy TamizhMani, Liang Ji
NCPV conference, October 2004
Photovoltaic (PV) modules are currently rated for power (W)
under standard test conditions (STC). The overall objective of this
work is to rate the PV modules for the energy (Wh) production per
IEEE1479 and IEC61853 draft standards, and per user defined site
specific conditions. The primary difference between the previous
works and this work is the use of outdoor (natural sunlight) based
equipment rather than the indoor (solar simulator) based equipment.
This paper presents key information on this outdoor equipment including:
the design characteristics of thermal test bed (TTB) installed on
a 2-axis tracker outdoor; the capability of this TTB to control
the module temperatures between 5 oC and 60 oC; the means to change
the irradiances on the test module; and the technique to carry out
spectral mismatch measurements. The results obtained from these
measurements, on a typical PV module, are analyzed, modeled and
presented.
>>Read full paper
Fuel Cell Based
Uninterruptible Power Supply for Computers and other Applications
by James Gonzales and Govindasamy
TamizhMani
REAP-MURA conference @ ASU, August 2003
The foundation for fuel cell technology was discovered in
1839, but only recently has the fuel cell begun to find a viable
outlet in commercial industry. More recently, fuel cell stacks (FCS)
have been used to power a wide variety of applications, including
buses and cars, portable electronic devices, and even large –
and some smaller – stationary generating devices. One particular
area of interest is to use a fuel cell for an uninterruptible power
supply (UPS). Using a fuel cell to power a UPS has several benefits
over the present widely available battery-powered UPS. A fuel cell
powered UPS eliminates several problems traditionally associated
with a battery-powered UPS, and therefore offers a superior alternative
for highly critical power needs.
>>Read
full paper
Performance of
Concentrator PV Trackers
by Ovuekoghene
Irune
REAP-MURA conference @ ASU, August 2003
As an intern student from Clark Atlanta University, my research
work at the Arizona State University-Photovoltaic Testing Laboratory
(ASU-PTL) for the summer of 2003 involves reviewing the solar tracker
test standards (draft), contacting the industry to obtain performance
and design specifications of solar trackers, reviewing the tracking
systems and also to obtain scientific and trade literature on the
concentrator PV trackers. The outcome of this research will help
in providing information for the development of an International
Electrotechnical Commission (IEC) standard for these concentrator
PV trackers since there is currently no industry-wide defined standard
available.
>>Read
full paper
Performance of
A-Si Modules in Desert Climatic Conditions
by Vijay Lakshman, Todd Arends,
Govindasamy TamizhMani
REAP-MURA conference @ ASU, August 2003
This paper focuses on the methodology for long term outdoor
exposure testing and the performance of dual-junction amorphous
silicon (a-Si) modules from two different manufacturers in desert
climatic conditions. The performance of these modules appears to
stabilize after about 1000 kWh/m 2 of exposure to sunlight in desert
climatic conditions. The stabilized Pmax of these modules experience
a sinusoidal variation due to seasonal effects.
>>Read
full paper
Remote Data Acquisition
Systems:
A TINI Based System for Photovoltaic Weather Data Acquisition
by Sumanth Lokanath, Bruce Millard,
Liang Ji, Govindasamy TamizhMani
REAP-MURA conference @ ASU, August 2003
The concept of applications that operate independently
and automatically with minimal human interaction finds appeal
in various areas ranging from the home to the far frontiers of
space. One such area is the application to remote data acquisition
systems. The data can be anything from the status of a light to
the parameters of a complex system such as weather. The project
reported here has investigated a remote weather data acquisition
system, which is low cost, user configurable, and has a generic
framework to support extensibility. The solution uses the TINI,
a Java based, programmable Internet enabled device connected to
a network of environmental sensors. The TINI is used to collect
and transfer data to a remote server for storage and processing,
using either a wired or a wireless interface. This system autonomously
and periodically transfers a data file of comma separated values
containing the weather data collected at specified intervals.
The data is moved from the remote station to a server that stores
and analyzes this data. The work presented in this paper is an
extract of an Applied Project report of one of the authors
>>Read
full paper
Thermal Model
Development for Energy Rating of Photovoltaic Module
by Govindasamy TamizhMani, C. Osterwald,
Liang Ji, Yingtang Tang and Luis Petacci
REAP-MURA conference @ ASU, August 2003
The performance of all photovoltaic modules depends on many
factors, which include solar irradiance level, module temperature,
solar spectrum, soiling, and angle-of-incidence of the sunlight
to modules. In order to predict the energy production of photovoltaic
(PV) modules, it is necessary to predict the module temperature
as a function of ambient conditions, such as ambient temperature,
wind speed, wind direction, total irradiance, and relative humidity.
This paper presents a mathematical model to predict the module temperature
based on the field monitored real data of module temperature, ambient
temperature, wind speed, wind direction and relative humidity.
>>Read
full paper
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Experimental Solar
Facility Turns on ASU's Polytechnic campus
by First Solar and
Dr. Govindasamy Tamizhmani
Ariticle in INSIGHT EAST newspaper, July 2001
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