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### Outdoor Monitoring and High Voltage Bias Testing of Thin-Film Photovoltaic Modules

####### NREL, UCF/FSEC Account \# 2012 8071 

> **Year 2 Quarter 1 Report, FSEC-CR 1500-04**

**February 25, 2005**

######### **Introduction**

Outdoor monitoring and High Voltage Bias Testing of Thin-Film
Photovoltaic Modules has been undertaken through the project funded by
NREL for a period of three years. This is the Year 2, Quarter 1 Report,
FSEC-CR1500-04. This report is for the period October -December 2004.
However, data until February 24, 2005 has been included for the sake of
completeness. The report contains the tasks carried out to restore the
data acquisition process and installation of remaining modules.

This work consists of the study of outdoor testing and monitoring of
photovoltaic (PV) thin-film modules fabricated by First Solar
(Glass/CdTe/Glass), Shell Solar (Glass/CIS/Glass), United Solar (a-Si on
flexible substrate), Energy Photovoltaics (Glass/ a-Si/Glass), and
Global Solar (CIS on flexible stainless steel foil substrate) with 2
additional crystalline silicon modules in the hot and humid climate of
Florida.

######### **Outdoor Monitoring and High Voltage Bias Testing of Thin-Film PV Modules** 

######### 

######### **Data Acquisition** 

######### 

As mentioned in the earlier report, thin-film PV modules from the
following US PV Manufacturers have been installed on the Florida Solar
Energy Center (FSEC) high voltage test setup: (6+6+2)-First Solar
(CdTe), (24+24)-Shell Solar (CIS), (20+20)-Uni-Solar (a-Si:H), (9+9)
Energy Photovoltaics (a-Si). (1+1) Global Solar modules (CIS), (2) BP
Solar (c-Si) modules and all the remaining modules from different
companies were installed as controls.

First Solar (FS), Shell Solar (SS), Uni-Solar (USSC) and Energy
Photovoltaics (EPV) modules are connected in series so as to reach a
maximum open circuit voltage, Voc approaching +600V and --600V. The
modules are connected across a load consisting of several resistors to
provide an operational point near the maximum power point. A small
resistor (1 Ω-50 W) and a shunt (depending on the module rating) have
been connected in series with the resistive load. The voltage and
current measurements are carried out across the small resistor and the
shunt respectively. The two BP Solar modules are also connected in
series. The two Global Solar modules are connected individually across
an optimum load. Each array voltage and current output, solar
irradiance, along with ambient parameters such as ambient temperature,
back of the module temperature at two locations, relative humidity, UV
index and wind speed are being monitored on a daily basis. This report
provides the data, data restoration and modification process.

**Data Restoration and Modification**

As reported earlier, all the FS, SS, USSC and EPV modules were
reinstalled by September 30, 2004. The Global Solar modules have also
been installed recently (Fig 1.) The circuit used earlier for data
acquisition was modified. A shunt to measure the current, two fuses, a
circuit breaker and two blocks for I-V Measurements were included in the
circuit (Fig. 2).

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Fig. 1: All US PV Manufacturers' Modules Installed After Hurricane
Season

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Fig. 2: Components of the Electrical Circuit in the Junction Box

# 

# Data Collection

# 

#  During the reinstallation process the front end of the CR 10X datalogger, mother board of the CR 10X datalogger and an AM 16/32 multiplexer were burnt. Therefore, a new CR 10X datalogger and multiplexers were procured. The present data collection setup consists of two AM 16/32 Multiplexer and a CR 10X Datalogger (Fig. 4). Multiplexer 1 is used to collect all the voltages and some temperature whereas multiplexer 2 is used to collect currents and temperatures. After all the modifications, test data collection began on December 09, 2004. A new program with the capability of measuring all the new additional parameters was uploaded in the new datalogger. The program has been designed to measure some more additional parameters instantly. 

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Fig. 3: Modified Electrical circuit diagram

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#  

# Fig. 4: Data Collection Unit

#  PV Materials Lab has installed two dataloggers to measure the various parameters. An error in the time between the two dataloggers was found recently on February 10, 2005. This was corrected as soon as it was discovered. Prior to Feb 10, 2005 the second datalogger was almost 1 hour behind the first datalogger. All the voltages, currents and temperatures are behind the atmospheric ambient conditions. A program is being written and will be uploaded to correct the error in the data on the websites. The data prior to February 10, 2005, provided along with the report has been corrected for the time difference between the two dataloggers. The data after February 10, 2005 has been provided as is.

# The Uni-Solar +600 V array has shown some high inaccurate voltage and current values during night and some current values during the day. This has not occurred daily but only occasionally. All the electrical connections were checked for any loose contacts. Data is being constantly monitored. If the problem persists, the data cable will be replaced with a new one. At regular intervals of time the voltage and current readings are measured at the datalogger and in the junction box at the same instant of time. The First Solar arrays operated with a load resistor value of 550 Ω during the last year. Since the optimum load for the First Solar Arrays was around 475 Ω. Therefore, it was decided to obtain readings with the load resistor value of 475 Ω for the period between Dec 09, 2004 and Feb 12, 2005. The load resistor value for the First Solar arrays was changed to 550 Ω from 475 Ω on Feb 12, 2005. The data is being compared with the two values of load resistors. The suitable value of load resistor will be soon decided after consultation with NREL and First Solar personnel. 

After the installation of additional components in the circuit the data
was collected. The new data was compared with the data of the previous
year. Reduction in the power was noticed for some of the arrays. To
analyze this degradation, the current-voltage (I-V) characteristics of
the whole arrays of the modules of each Company were measured with a
Daystar DS100 I-V curve tracer. Since the First Solar and Shell Solar
arrays showed substantial degradation, I-V measurements of the
individual modules were carried out for those arrays. All the I-V data
was submitted to NREL. The I-V measurements have been provided with this
report. Whenever the datalogger was shut off for maintenance in the
junction box or data collection unit or for I-V measurements, no data
was collected. On the website, the data shows a value of 32767. In the
data provided herewith these values have been replaced with blanks.

**Website Modifications**

> A new website for Energy Photovoltaics modules array,
> [www.infomonitors.com/hpt/epv](http://www.infomonitors.com/hpt/epv)

has been launched. All the other company websites along with the NREL
websites have been modified. A new link for daily comments has been
added to all the web pages. The power calculation for data available is
the product of voltage and current after December 12, 2004. Before this
date the power calculation was the ratio of the square of the array
voltage to the total resistor value (V^2^/R). It is necessary to choose
the appropriate button on the web page to get the power calculations
depending on the date. Power calculations for the data after December
12, 2004 use V^2^/R in the Summary\* Report and a product of V and I
(measured across a shunt) in the Summary\*\* Report. The comparison with
the data prior to December 12, 2004 should be made using the values of
V^2^/R in the Summary\* Report of data after February 12, 2005 where the
First Solar load resistor value was changed back to 550 Ω.

**Shadowing Effect**

After the initial installation process in the year 2003, it was
discovered that the front row consisting of +600 V arrays was casting
shadow on the lowest modules of the back row -600 V arrays during the
second/third week of December towards the end of the day. All the back
arrays were adjusted i.e., the modules were moved upwards at the same
angle. For First Solar Array all modules were moved up by one module
where as the Shell Solar and Uni-Solar modules were adjusted such that
the two bottom rows of modules were moved up. This year some shadowing
effect of the fence was observed on the front row +600 V array towards
the end of the day during the second/third week of December. To avoid
this problem the height of the fence was reduced by 2 feet. A detailed
module installation layout is provided with this report. Figure shows
the last five digits of the serial number for SS and USSC modules and
full serial numbers for the rest. The modules that showed significant
degradation have been hatched in this Figure. Of these modules, the
following modules may have had a small effect due to shadowing: First
Solar, +600 V, None, -600 V, C12230195; Shell Solar +600 V, 06457 and
06458, -600 V, 06102 and 05928. It was also found that small end pieces
of the mounting channels from the front row casts a shadow on small
portions of the back during the same time frame. These are being cut.

# High Voltage (HV) Bias Testing

The study of leakage currents in high-voltage biased thin-film
photovoltaic (PV) modules fabricated by First Solar (CdTe), Shell Solar
(CIS) and Uni-Solar (a-Si:H) has also been undertaken as a part of this
project for a period of three years. FSEC high voltage test bed
consisting of two modules from each manufacturer, First Solar (CdTe),
Shell Solar (CIS) and Uni-Solar (a-Si:H) were installed at +600 V and
--600 V respectively at the FSEC high voltage test bed. Two modules from
EPV have been installed for HV bias testing.

**Data Collection**

The EPV modules have been installed for HV bias testing together with
the modules of First Solar, Shell Solar and Uni-Solar. It was not
possible to collect data individually for the high voltage biased
modules because of circuit problems. These problems have been corrected
now and data acquisition has begun.

**Planned Activities for Year 2 Quarter 1**

1)  Constantly monitor changes in the PV modules.

2)  Take I-V Measurements for all the arrays.

3)  Carry out HV bias testing data acquisition.

4)  Launch websites for the installed Global Solar and BP Solar modules.

5)  Correct data on the website with approximately one hour time lag.