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2.2. To Decide the Worst-case Shading Position
Cut the BT into the same size which is found on the
worst-case shading condition. Slowly moves this BT
cover from the bottom to the top of PV module (one cell
distance of each movement) and monitor the Isc of PV
module. To find the module position that possesses the
minimum Isc among the PV entire module, as shown in
Figure 2. Then reduce/add the size of BT cover in small
increments until Isc falls within the range of 0.99 Imp < Isc
< Imp. The final width and position of BT cover deter-
mines the minimum shading area that results in the
worst-case shading condition. This is thus the shaded
area to be used for hot-spot endurance test.
2.3. Other Test Procedure and Test Duration
Place the BT cover on the candidate PV module area and
short-circuit the PV module. Again, expose the PV mod-
ule to an irradiance to 800 to 1000 W/m2 for 1 hour and
control the temperature of PV module to 50℃ ± 10℃.
Meanwhile, monitor the value of Isc and keep the PV
module in the condition of maximum power dissipation.
An appropriate temperature detector is necessary used to
determine the hottest area on the shaded cells. Finally,
the visual inspection and insulation test are then used to
judge if the PV module pass/fail in hot-spot endurance
test.
3. Steady-State Solar Simulator
Solar simulator, which simulates the real solar irradiance
and spectrum, is often used to provide a controllable in-
door test field under laboratory condition and can be ei-
ther used for performance measurements of PV cells/
modules or endurance irradiance tests. In general, solar
simulator can be divided into three categories: steady-
state, flash and pulse. The steady-state solar simulator,
possessing a light source form where illumination is
continuous in time, is most often used for low intensity
testing from less than 1 sun up to several suns. The flash
solar simulator, with typical durations of several
milliseconds, includes very high intensities possibly up
to several thousand suns. This type of simulator is often
used to prevent unnecessary heat built up in the device
under test (DUT). The pulse solar simulator, with typical
durations of a few tens milliseconds to several hundred
milliseconds, uses a shutter to quickly control the
illumination of the light from a continuous source. The
advantage of the pulse type simulator consists in the neg-
ligible heat influence to the DUT, which allows DUT to
remain uniformity at ambient temperature and the meas-
uring to be easily and accurately done [3]. In Figure 3,
some experiments are implemented by steady-state solar
simulator (SSSS) in case study, the used SSSS is con-
sisted of 9 xenon lamps, xenon lamp power supply units,
4-wire I-V measuring system, reference cell, thermome-
ter, module mounting plane, etc.
As shown in Table 1, current standard IEC 60904-9
describes three aspects, spectral match, non-uniformity
irradiance and temporal instability of irradiance, to eva-
luate the performance requirement of solar simulator [4].
In general, a solar simulator with class B or better is re-
quired for PV cells/ modules performance testing. Fol-
lowing is the evaluation of SSSS used in the study:
3.1. Spectral Match
The spectral match is presented as the worst difference
between the measured simulator spectral irradiance and
referenced AM 1.5 G spectral irradiance as presented in
IEC 60904-3, respectively, which cover six specified
wavelength intervals between 400 nm and 1100 nm [5].
Figure 4 shows the measured SSSS spectral irradiance
by high-speed spectroradiometer, and the deviations from
AM 1.5 G are calculated in Table 2. It is found the spec-
tral match to all wavelength intervals is among 0.930 to
1.068, which is classified as A by using SSSS.
3.2. Non-Uniformity of Irradiance
The irradiance non-uniformity on the test plane of a
large-area solar simulator for PV cells/modules meas-
urements depends on reflection condition inside the test
apparatus. Base on IEC 60904-9 the designated test area
is divided into at least 64 equally sized test blocks, and
then taken turn to detect the irradiance on each block. In
the study, the test plane is divided into 100 equally sized
test blocks. In Figure 5, the Isc of reference cell is re-
corded to present the irradiance distribution measured on
this test plane. The maximum Isc in test plane is 128.2
mA and the minimum is 124.3 mA. By substitute maxi-
mum and minimum Isc in (1), the non-uniformity of ir-
radiance of 1.54% for used SSSS (classification = A) is
derived.
Figure 2. The procedure of searching worst-case shading position.
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