Download Photovoltaic modules Session 6 -spot-heating

Photovoltaic modules
Session 6
http://pveducation.org/pvcdrom/modules/hot
-spot-heating
DAMON FYSON
Photovoltaic modules
Session 6
PV cells can be arranged in a series
configuration to form a module (panel)
Modules (panels) can then be
connected in parallel-series
configurations to form series string and
parallel arrays.
When connecting cells or modules in
series, they must have the same
voltage rating to produce an additive
voltage output, and similarly, modules
must have the same current rating when
connected in parallel to produce larger
currents.
DAMON FYSON
Photovoltaic modules
Session 6
• A number of PV
panels in series is
termed a string
• A number of strings in
parallel is termed an
array
DAMON FYSON
Photovoltaic modules
Session 6
source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf
DAMON FYSON
Photovoltaic modules
Session 6
source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf
DAMON FYSON
Photovoltaic modules
Session 6
source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf
DAMON FYSON
Photovoltaic modules
Session 6
DAMON FYSON
Photovoltaic modules
Session 6
DAMON FYSON
Photovoltaic modules
Session 6
Mismatch losses are caused
by the interconnection of
solar cells or modules which
do not have identical
properties
• Output determined by the
solar cell with the lowest
output.
• example, when one solar cell
is shaded remainder in the
module are not, the power
being generated by the
"good" solar cells can be
dissipated by the lower
performance cell rather than
powering the load.
The comparison of an ideal and a non-ideal solar cell. For mismatch,
the greatest difference is when the cell is driven into reverse voltage
bias
Source http://pveducation.org/pvcdrom/modules/mismatch-effects
DAMON FYSON
Photovoltaic modules
Session 6
Theory of I-V Characterization
PV cells can be modeled as a current source in
parallel with a diode. When there is no light
present to generate any current, the PV cell
behaves like a diode. As the intensity of
incident light increases, current is generated by
the PV cell, as illustrated in Figure 1
DAMON FYSON
Photovoltaic modules
Session 6
I-V Curves for Modules
For a module or array of PV cells, the shape of
the I-V curve does not change. However, it is
scaled based on the number of cells connected
in series and in parallel. When n is the number
of cells connected in series and m is the
number of cells connected in parallel and ISC
and VOC are values for individual cells, the I-V
curve shown in Figure 10 is produced.
DAMON FYSON
Photovoltaic modules
Session 6
source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf
DAMON FYSON
Photovoltaic modules
strings in parallel
It = I1 +I2……
Session 6
Panels in series (string)
Vt = V1+V2….
DAMON FYSON
Photovoltaic modules
Session 6
Understanding cell connection
Current (A)
• The PV module is the basic unit in a complete
PV system
4
• Understanding how the module is designed
and assembled provides key understanding to
designing a system
• Towards this end consider the following IV
characteristics of a single cell
DAMON FYSON
Voltage (V) 0.6
Photovoltaic modules
Session 6
•With three cells
connected in series the
combined characteristics
are shown
•Connecting the cells in
series maintains the same
current, only the voltage
of each cell is added
together
Current (A)
4
Voltage (V)
0.6
1.2
The combined IV characteristics of three
identical cells connected in series
DAMON FYSON
1.8
Photovoltaic modules
Session 6
Current (A)
C
• If two cells with
different
characteristics
(dissilimar) are
wired together in
series, the result is
shown in following
figures
• Series connected
dissimilar cells
produce an added
voltage output, but
series current is
equal to the lowest
value of the two
Current (A)
Voltage (V)
A B
Voltage (V)
A B
The individual IV characteristics of two dissimilar cells
Current (A)
C
D
Voltage (V)
A+B
The combined IV characteristics of the two
dissimilar
cells
connected in series
DAMON
FYSON
Photovoltaic modules
Session 6
Fill Factor
(slide ½)
source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf
DAMON FYSON
Photovoltaic modules
Session 6
source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf
DAMON FYSON
Photovoltaic modules
Session 6
Commercial Modules
• Solar module manufacture was
39MWs in 1994 increased to 1900MWs
in 1994
• PV module production capacity increased by
nearly 70% over the course of 2010, reaching
nearly 30 GW by the end of the year according
to IMS Research
source : superhydrophobic-pv-array
Some Common standards applied to PV modules
• IEC61215- Crystalline Silicon Terrestrial photovoltaic (PV )
modules
• IEC61646- Crystalline Thin-film Terrestrial photovoltaic modules
DAMON FYSON
Photovoltaic modules
Session 6
Five common solar panel defects
The following defects are common when testing solar
panels:
• Scratches on frame / glass
• Excessive or uneven glue marks / Glue marks on glass
• Gap between frame and glass due to poor sealing
• Lower output than stated in data sheet (we require
positive tolerance on each solar panel)
• Lower FF than stated in requirements
DAMON FYSON
Photovoltaic modules
Session 6
Standard PV Panel testing parameters:
With the use of the flash test, the following parameters are tested.
1. VOC (V), open-circuit voltage, The voltage output of the module is measured with the module disconnected
from any load.
2. VMP (V), voltage at maximum power point, the voltage at which the module puts out the most power
3. ISC (A), the short-circuit current, Circuit Current (Isc)” and is the amount of current that the pv module supplies
into a dead short.
4. Imp (A), Current at maximum power point (Imp)” and is the number of Amperes delivered by the module at its
maximum power point.
5. Pm (W), Maximum Power and Maximum Power Point, power is equal to Amperes times Volts (P=IE, or
Watts=Amperes X Volts). Every module has a specific point on its power curve where the product of Amps times
Volts yields the greatest Wattage. This is the Maximum Power Point, the flash test takes data over the entire range
of voltage and current. This way the wattage for each Current and Voltage data point can be calculated. By doing
this we can find the Maximum Power Point in the sea of Current versus Voltage data.
6. FF (%), Fill Factor, the Fill Factor is defined as the maximum power produced (at MPP) divided by the product of
Isc and Voc. One can see that the Fill Factor will always be less than 1.
DAMON FYSON
Photovoltaic modules
Session 6
DAMON FYSON
Photovoltaic modules
Session 6
2011 Global Top Ten Solar Cell Manufacturer
Company
Capacity (MW)
Country
Suntech
2,400
China
JA Solar
2,100
China
Trina
1,900
China
Yingli
1,700
China
Motech Solar
1,500
Taiwan
Gintech
1,500
Taiwan
Canadian Solar
1,300
China
Neo Solar Power
1,300
Taiwan
Hanwha Solar One
1,100
China
JinkoSolar
1,100
China
Source
EnergyTrend
[3]
DAMON FYSON
Photovoltaic modules
Session 6
2011 Global Top Ten Solar Module
Company
Capacity (MW)
Country
Suntech
2,400
China
LDK
2,500
China
Canadian Solar
2,000
China
Trina
1,900
China
Yingli
1,700
China
Hanwha Solarone
1,500
China
SolarWorld
1,400
Germany
Jinko
1,100
China
Sunneeg
1,000
China
Sunpower
1,000
USA
Source
EnergyTrend
[4]
DAMON FYSON
Photovoltaic modules
Session 6
Although yearly ranking is as listed above, quarterly ranking can indicate that which company can sustain particular conditions such
DAMON FYSON
Photovoltaic modules
Session 6
Example of
specification on a
typical module
188 Watt
monocrystalline panel
Source:
DAMON FYSON
Photovoltaic modules
Session 6
Continue Example of specification on a typical module
188 Watt
monocrystalline panel
Source:
DAMON FYSON
Photovoltaic modules
Session 6
String inverter with one string
grid
String inverter
The PV array is
connected as one
string and then
connected to one
inverter
DAMON FYSON
Photovoltaic modules
Session 6
grid
Central inverter
Several strings
connected in parallel
DAMON FYSON
Photovoltaic modules
Session 6
The output of a single module Vmp =
17V Imp= 4A
What will be the
array output
DAMON FYSON
Photovoltaic modules
Session 6
The output of a single module Vmp = 17V Imp= 4A
What will be the array output
DAMON FYSON
Photovoltaic modules
Session 6
source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf
DAMON FYSON
Photovoltaic modules
Session 6
Electrical Protection
•The PV module far right will not pass
current
•Because the cells in the module are
connected in series and a cell is
damaged(or some cells shaded) the
current from the whole modules is
reduced, and hence the string or array
•If one cell is damaged the rest of the array
can force current through it
•This phenomenon is known as a Hot –
spot, the cell may cause the whole array
to go open circuit
•The following slides shown how a diode
may minimize the problem
DAMON FYSON
Photovoltaic modules
Session 6
BYPASS DIODES
The module will produce less power
• One or more of the cells is defective
• One of more of the cells is shaded
• An operating module will cause a
reverse voltage to appear across the
defective or shaded cell
• The diode provides an alternative
path for a current when a reverse
voltage is present
DAMON FYSON
+
_
Photovoltaic modules
Session 6
Hot-Spot Heating and Bypass Diodes
Dissipation of power in poor cells leads to
breakdown in localized regions of the cell p-n
junction. An enormous power dissipation can
occur in a small area, leading to local
overheating, or "hot spots", which in turn
leads to destructive effects, such as cell or
glass cracking or melting of solder
http://www.southalabama.edu/engineering/ece/faculty/akhan/Courses/EE590Renewable/supporting%20meterial/PVDevices/pvcdrom/Ch06/Hotspot.Htm
DAMON FYSON
Photovoltaic modules
Session 6
source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf
DAMON FYSON
Photovoltaic modules
Session 6
DAMON FYSON
Photovoltaic modules
Session 6
source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf
DAMON FYSON
Photovoltaic modules
Session 6
source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf
DAMON FYSON
Photovoltaic modules
Session 6
DAMON FYSON
Photovoltaic modules
Session 6
source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf
DAMON FYSON
Photovoltaic modules
Session 6
Example of Non-Uniform
Soiling
DAMON FYSON
Photovoltaic modules
Session 6
source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf
DAMON FYSON
Photovoltaic modules
Session 6
The next 3
slides show
what may
happen with
blocking diodes
source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf
DAMON FYSON
Photovoltaic modules
Session 6
source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf
DAMON FYSON
Photovoltaic modules
Session 6
Bypass
diodes fit a
potential
catastrophi
c event.
source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf
DAMON FYSON
Photovoltaic modules
Session 6
Bypass diodes allow current
to pass around shaded cells
and thereby reduce the
voltage losses through the
module. When a module
becomes shaded its bypass
diode becomes “forward
biased” and begins to
conduct current through
itself. All the current greater
than the shaded cell’s new
short circuit current is
“bypassed” through the
diode, thus reducing
drastically the amount of
local heating at the shaded
area.
Source: http://www.civicsolar.com/forum/9824/what-bypass-diode
DAMON FYSON
Photovoltaic modules
Session 6
bypass diodes are
integrated into the
solar cell structure
during cell fabrication.
The main conclusion is
that the present
integral bypass diode
approach
automatically protects
against thermal
instability in both small
and large arrays
without the need for
any other protective
measures.
Source: http://wenrunopto.com/product/Diode.htm
DAMON FYSON
Photovoltaic modules
Session 6
Source: Paul Hernday so
DAMON FYSON
Photovoltaic modules
Session 6
DAMON FYSON
Photovoltaic modules
Session 6
Bypass diodes do
cause other
problems
source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf
DAMON FYSON
Photovoltaic modules
Session 6
source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf
DAMON FYSON
Photovoltaic modules
Session 6
One potential problem
arises from an opencircuit in one of the
series strings. The
current from the parallel
connected string (often
called a "block") will
then have a lower
current than the
remaining blocks in the
module. This is
electrically identical to
the case of one shaded
solar cell in series with
several good cells, and
the power from the
entire block of solar cells
is lost. The figure below
shows this effect.
Potential mismatch effects in larger PV arrays. Although all
modules may be identical and the array does not
experience any shading, mismatch and hot spot effects
may still occur
sorce: http://pvcdrom.pveducation.org/MODULE/Array.htm
DAMON FYSON
Photovoltaic modules
Session 6
The current may now flow
through the by-pass diodes
associated with each module,
but must also pass through the
one string of by-pass diodes.
These by-pass diodes then
become even hotter, further
reducing their resistance and
increasing the current flow. If
the diodes are not rated to
handle the current from the
parallel combination of
modules, they will burn out and
allows damage to the PV
modules to occur.
Bypass diodes in paralleled modules. There are
typically two bypass diodes in each 36 cell module.
Source: http://pvcdrom.pveducation.org/MODULE/Array.htm
DAMON FYSON
Photovoltaic modules
Session 6
In addition to the use of bypass diodes to prevent
mismatch losses, an additional
diode, called a blocking diode,
may be used to minimize
mismatch losses.
With parallel connected modules,
each string to be connected in
parallel should have its own
blocking diode. This not only
reduces the required current
carrying capability of the blocking
diode, but also prevents current
flowing from one parallel string into
a lower-current string and
therefore helps to minimise
mismatch losses arising in parallel
connected arrays.
Impact of blocking diodes in parallel connected
modules
DAMON FYSON
Photovoltaic modules
Session 6
If an inactive cell (e.g.
due to shading) is fed
current by the other,
active cells, it converts
this energy into heat.
The worst case scenario
is that a hot spot builds
up in the inactive cell
that can destroy the
module. To avoid this,
bypass diodes are used
that duct the current
past the cell string
containing the inactive
cell.
Junction box with integrated bypass diodes
Source: http://www.solarfassade.info/en/construction/planning_factors/bypass_diodes.php
DAMON FYSON
Source: pv_verband 2009
Photovoltaic modules
Session 6
Minimising power loss
Without a bypass diode,
a single shaded cell
would reduce power
production of the entire
series connection to a
minimum. Thanks to the
bypass diode, the total
power yield only
decreases by the lost
yield of the bypassed cell
string.
Shading with and
without bypass diode
Source:
http://www.solarfassade.info/en/construction/planning_factors/bypass_diodes.php
DAMON FYSON
Source: pv_verband 2009
Photovoltaic modules
Session 6
http://ask.metafilter.com/144073/Help-Connecting-A-Solar-Junction-Box
DAMON FYSON
Source: pv_verband 2009
Photovoltaic modules
Session 6
AS/NZS 5033:2005
1.4.4 Bypass diode
A diode that is connected in parallel with a PV
module, or a group of PV cells within a PV module,
and prevents the PV module or group of cells from
being reverse biased
(see Figures 1.1 and 1.2).
DAMON FYSON
Source: pv_verband 2009
Photovoltaic modules
Session 6
AS/NZS 5033:2005
2.2 BYPASS DIODES
Bypass diodes may be used to prevent PV modules from being reverse
biased and consequent hot spots occurring. If bypass diodes are added by
the installer, they shall comply with all the following requirements:
(a) Have a voltage rating of at least 2 × VOC MOD of the protected module.
(b) Have a current rating of at least 1.25 × ISC MOD.
(c) Be installed so no live parts are exposed.
(d) Be protected from degradation due to environmental factors.
DAMON FYSON
Source: pv_verband 2009
Photovoltaic modules
Session 6
AS/NZS 5033:2005
2.3 BLOCKING DIODES
Blocking diodes may be used but they are not a substitute for fault current
protection. One of their purposes is to prevent reverse currents from battery
systems leaking into a PV array at night, when this protection is not an
integral part of the battery charge controller.
If used, blocking diodes shall comply with all the following requirements:
(a) Have a voltage rating of at least 2 × VOC ARRAY.
(b) Have a current rating of at least 1.3 times the short circuit current at STC
of the
circuit that they are intended to protect. That is—
(i) 1.25 × ISC MOD for PV strings;
(ii) 1.25 × ISC S-ARRAY for PV sub-arrays; or
(iii) 1.25 × ISC ARRAY for PV arrays.
(c) Be installed so no live parts are exposed.
(d) Be protected from degradation due to environmental factors.
DAMON FYSON
Photovoltaic modules
Session 6
The shape of
modules are
restricted to
rectanglar
DAMON FYSON
Photovoltaic modules
Session 6
PV Panel Warranties and guarantees
Australian Standards
Accredited installer to provide proof that panels meet Australian standards.
The Clean Energy Council has a frequently updated list of all solar panel
and inverter models that meet Australian standards..
Solar PV systems must also comply with The CEC Design and Installation
Guidelines.
Warranties and guarantees
Solar PV panels generally come with a performance warranty that can
last up to 25 years and a guarantee lasting five to ten years.
Additionally, panel material warranties and workmanship guarantees
generally span 5-10 years.
DAMON FYSON
Photovoltaic modules
Session 6
Warranties and guarantees cont……………..
It is important to know who is providing the warranty – the manufacturer
or the importer. In the absence of a manufacturer, the importer is
responsible for the warranty. However, if the importer changes their
business name or sells their business, their warranty obligations towards
the customer cease.
Installer must state who is providing the warranty.
A system manual that provides operation, maintenance and safety
information should be provided by your installer. This must also include a
system energy output (kWh) estimate. It is important for you to provide
written confirmation of statements including performance claims,
guarantees and warranties.
DAMON FYSON
Source: pv_verband 2009
Photovoltaic modules
Session 6
Great source
http://www.nwsolarexpo.com/2011Presentations/NW_Solar_Expo_Hernday_4.29.
pdf
http://www.pveducation.org/pvcdrom/pnjunction/absorption-of-light
Great web site for pv understanding
http://pveducation.org/pvcdrom/modules/byp
ass-diodes
DAMON FYSON