Transcript PV modules characteristics

PV Modules Characteristics
Diala Haddad
MSc Energy and Sustainability with Electrical Power
Engineering-University of Southampton/UK
BSc Electrical Engineering-Jordan University of Sience and
Technology
‫المــــركــز الوطنــــــي لبحــــــوث الطـــاقــــــة‬
National Energy Research Center
E-mail: [email protected]
What is a PV
module?
Silicon PV cells
The silicon PV cell is the basic photovoltaic device that is the building
block for PV modules.
Assembling PV cells
Cells are attached together with a thin ribbons of wire, top to bottom (in
series).
Module Materials
Crystalline based module
structure
Front surface: mainly glass cover.
1. High transmission
2. Low reflection capability
Low iron glass is commonly used because of its low cost, strong, stable, highly
transparent
Encapsulant: is used to provide a strong bond between the solar cells in the module:
1. Should be stable at different operating temperatures
2.Should be transparent with low thermal resistance.
EVA (ethyl vinyl acetate) is commonly used with a very thin layer at the front and back
surface of the assembled cells
PV cells: is the part which is responsible for producing power.
Back surface: It must have low thermal resistance it can be made from Tedlar (thin
polymer sheet) or glass.
Frame
-
lightweight
supports easy assembling
4 seasons suitability, weather
resistance
frame
junction box
cable
connectors
Junction box
frame
junction box
cable
connectors
Cable
-
Flexible
Resistant against abrasion, chemicals,
extreme heat, cold and UV
Connectors
MC3 or MC4
solar cell | PVF film | EVA foil | glass | frame | junction box | bypass diode | cable and connectors
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• Quality Check
 IEC61215: Crystalline silicon terrestrial photovoltaic (PV) modules –
Design qualification and type approval.
 IEC 61646: Thin film silicon terrestrial photovoltaic (PV) modules –
Design qualification and type approval.
Module Circuit
Design
Solar Cells in Series
• Simplest thing to consider is when we have two identical solar cells
connected in series
• Since the cells are in series, the currents will be matched (not a
problem as they are identical), voltages will add.
• Useful for when we want a specific voltage, typical voltages for a
single solar cell will be < 0.6 V.
Final Combination
+
-
Solar Cells in Series
• Recall the solar cell’s IV-curve
Solar Cells in Series
Peak Power of one cell
(1.36 W)
Peak Power of two cells in
series (1.36*2 =2.72 W)
Characteristics of PV modules:
The Maximum Power Point
•
The I-V and P-V of a module, if the irradiance and cell temperature
are held constant.
• Locating the MPP (Maximum Power Point)
Characteristics of PV modules: Fill
Factor
Fill Factor
• The fill factor (FF) of a PV module is an important performance
indicator.
• Why is the fill factor important? The Fill Factor (FF) is essentially a
measure of quality of the PV module. If the I-V curves of two
individual PV modules have the same values of Isc and Voc, the
module with the higher fill factor (squarer I-V curve) will produce
more power
Fill Factor
Curve of high FF panel
Curve of low FF panel
Protection Diodes - Introduction
• IV curve
extension:
• What a solar cell
does depends on
its bias condition
Protection Diodes - Introduction
• Diodes are semiconductor devices that allow current to flow in only
one direction.
• The two uses of diodes in a PV module electrical
design:
– Bypass diodes
– Blocking diodes
+
-
Bypass Diodes
• Used to pass current around,
rather than through a group of
cells.
• Normally reverse-biased (OFF)
• Permit the power produced by other
parts of the array to pass around
groups of cells that develop an
open-circuit or high resistance
condition.
Bypass Diodes
•
•
•
•
•
Most 36-cell crystalline modules have 2 bypass diodes.
Most 60-cell and 72-cell modules have 3 bypass diodes.
Size for 1.5 times the module Isc rating.
Size for greater than 1.5 times the Voc of cells bypassed.
In the junction box
Protection Diodes
Mismatch for Cells
Connected in series
Shading Effect- Partial Shading
• Normal running
• Partially shading one Cell
In series connected solar cells the current for the chain is set by the current
of the worst performing cell.
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•
Partial shading:
Shift of graph origin
New operating
point of the
module
X
0 current,0 Voltage
What a solar cell does depends on it’s bias
Shading Effect- Full Shading
Full shading:
Shift of graph origin
0 current,
0 Voltage
New operating
point of the
module
X
• This is called hot spot heating
• Can severely damage the
module
• Which diode is
ON?
Particulate build up ”Soiling”
• These particulates block the amount of light reaching the module
and therefore reduce the power produced by the module
• The reduction in power from particulate build up can range from
5%-30% in dry areas.
Snow
• Snow does not usually collect on the modules, because they are
angled to catch the sun.
• If snow does collect, it quickly melts. Mechanically, modules are
designed to withstand golf ball size hail.
Electrical
Characteristics of Solar
Panels (PV Modules)
STC Conditions
• Each solar panel, or module, is rated
to produce a certain wattage, voltage
and amperage under specific
conditions, called the STANDARD
TEST CONDITIONS (STC)
according to EN 60904-3.
STC includes three factors:
Normal Operating cell
temperature-NOCT
Normal Operating cell temperature-NOCT condition is the case when
the PV module operates under the following standard operating
condition- SOC
1.Global solar irradiation as 800 W/m²
2.Ambient temperature 20oC
3.Tilt angle 45°
4.Wind speed of (1 m/s)
With the back side of the solar panel open to that breeze, together with
the solar spectrum of corresponding AM1.5.
STC versus NOCT
PV module technologies
Polycrystalline module
• Efficiency: 14% to 17 %.
• Form: Square to maximize
energy yield.
• Thickness: 0.24mm to 0.3mm.
• Color: blue, silver, grey,
brown, gold and green.
Polycrystalline Comparisons
Monocrystalline module
• Efficiency: 16% to 21.5%.
• Form: round, semi round or
square shape.
• Thickness: 0.2mm to
0.3mm.
• Color: dark blue to black
(with ARC), grey (Without
ARC).
Thin film Technology
• Despite the relatively low efficiency per unit area, thin film
technology has many advantages:
– Better utilization of diffuse and low light intensity.
– Less sensitive to higher operating temperature
– Less sensitive to shading because of long narrow strip design, while a
shaded cell on crystalline module will affect the whole module.
– Energy yield at certain condition is higher than crystalline technology.
13% efficiency
Nameplate Ratings versus RealWorld Performance (or STC v. PTC)
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