solar PV

DEFINITION OF PHOTOVOLTAIC
Photovoltaic (PV) cells convert light energy into electricity. The term
‘photo’ is derived from the Greek word ‘phos’, which means ‘light’.
‘Volt’ is named for the scientist Alessandro Volta (1745-1827) who
pioneered the study of electricity. Literally, photovoltaic means light-
electricity. PV cells are also commonly known as ‘solar cells’.

PHOTON TO ELECTRICITY
PV cells consist of a junction between two thin layers of dissimilar
semiconductor materials known as ‘p’ (positive) type and ‘n’ (negative) type
semiconductors.
n-type semiconductors are made by doping pure silicon with phosphorus. n-
type material is negatively charged as it possess surplus electrons that are
relatively free to wander off or be donated.
Similarly, silicon is doped with small amount of other impurity for example
boron to create positively charged p-type material. Owing to its relative
deficiency of electron, it is a sort of acceptor (of electrons) semiconductor.
In a PV cell, wafer thin (0.2 to 0.3 mm thick) layers of both these materials are
brought together to form a P-N junction that creates an electric field.
When sunlight (consisting of a stream of tiny particles of energy called photons)
strike the p-n material, it transfers the energy of photons to some of electrons in
the material, so prompting them to higher energy levels. Consequently , an
electron attains too much energy to remain in its place, and escapes to become
a free electrons leaving behind positively charged hole. This electron is
attracted by a neighboring positively charged hole. Similarly, the positive ‘hole’
can also be said to wander by virtue of the fact that another electron, freed from
a neighboring structure, can fall into it leaving a new hole further away.
Electricity is thus produced as a result of the flow of electrons triggered by
Photons.

HISTORY OF SOLAR PHOTVOLTAIC
The photoelectric effect was first noted by a French physicist, Edmund Bequerel, in 1839,
who found that certain materials would produce small amounts of electric current when
exposed to light.
In 1905, Albert Einstein described the nature of light and the photoelectric effect on which
photovoltaic technology is based, for which he later won a Nobel prize in physics.
The first photovoltaic module was built by Bell Laboratories in 1954 and an efficiency of
6% was achieved.
In the 1960s, the space industry began to make the first serious use of the technology to
provide power aboard spacecraft. Through the space programs, the technology
advanced, its reliability was established, and the cost began to decline.
During the energy crisis in the 1970s, photovoltaic technology gained recognition as a
source of power for non-space applications.

TYPOLOGY OF SOLAR PV
http://www.sbc.slb.com/SBCInstitute/Publications/SolarPhotovoltaic.aspx

OVERVIEW OF SOALR PV TYPES
Current stage of
Development
Module Efficiency
(%)
Cell Efficiency (%)
Construction
Type
Industrial production
13-17
24
Uniform crystalline
structure-single crystal
Monocrystalline
silicon
11-15
18
Multi-crystalline structure-
different crystals visible
Ploycrystalline silicon
4-7
11-12
Particles irregularly –
arranged – thin film
Amorphous silicon
25
Crystalline
Gallium-arsenide
Up to over 40%
Tandem (multi-junction),
different layers sensitive
to different light
wavelengths
Gallium-arsenide,
Gallium-antimony etc
10-12
18
Thin-film
Copper-indium-
diselenide
Ready for industrial
production
9-10
17
Thin-film
Cadmium-telluride
R&D
5-8
Electrochemical principle
based
Organic

MONO-CRYSTALLINE PV
Monocrystalline PV is made from
highly pure moncrystalline silicon.
It is made from a single large crystal,
cut from ingots and has ordered
crystal structure, with each atom
ideally lying in a pre-ordained position
and exhibits predictable and uniform
behavior.
It has higher efficiency compared to
other mainstream PV types but is also
most expensive in terms of production
cost, energy and time.

POLY-CRYSTALLINE PV
Polycrystalline or multicrystalline
cells are produced from numerous
grains of monocrystalline silicon.
Polycrystalline PV is cheaper
compared to monocrystalline PV
due to simpler manufacutruing
process and is also slightly less
efficient than the latter.

AMORPHOUS PV
• They are made by depositing a thin film of photosensitive
materials onto a sheet of another material such as glass, steel
and plastic. The panel is formed as one piece and the
individual cells are not as visible as in other types.
• The efficiency of amorphous solar cells is lower than
crystalline solar cells.
•
Thin film manufacturing processes result in lower production
costs compared to the crystalline technology.

AMORPHOUS PV
• The price advantage is however counterbalanced by lower
efficiency rates (from 4% to 8%). More panels are needed for
the same power output and therefore more space is taken up.
• The main types of thin film cells include: Amorphous silicon
(a-Si), Cadmium telluride (CdTe) , Copper Indium/gallium
Diselenide/disulphide (CIS, CIGS) and Multi junction cells (a-
Si/m-Si).
• Thin-film crystalline solar cell consists of layers about 10μm
thick compared with 200-300μm layers for crystalline silicon
cells
• They are much more resistant to the effect of shade and high
temperatures.

CONCENTRATED PHOTOVOLTAICS
• In concentrated PV (CPV), cells are built into
concentrating collectors that use mirrors or lenses
to focus the sunlight onto the cells.
• CPV use multi-layer crystalline cells that capture
energy from a wider bandwidth of solar spectrum.
• The main objective of these cells is to use very little
of the expensive semiconducting PV material while
collecting as much sunlight as possible.
• Efficiencies of these cells are in the range of 20 to
30% though an efficiency of over 42% has also
been achieved.

CONCENTRATED PHOTOVOLTAICS
• A CPV require sun tracking system
(sensors, motors and controls) to allow cells
to receive optimum solar radiation.
• It needs a cooling mechanism to cool cells in
order to avoid overheating.
• It uses only direct beam.
• A CPV is more complex than flat-plate
systems because of moving parts

Conversion Efficiencies vs. Time
(NREL)

There has been steady progress in the improvement of conversion efficiencies for a
number of PV technologies over the last few decades.

COMPARISON OF COMMON PV MODULES
Type Efficiency
(%)
Life time
(years)
Warranty
(years)
Appearance Area per kWp
(m2)
Monocrystalline
silicon
13-17 15-30 10-25 Uniform dark
blue cells
7
Ploycrystalline
silicon
11-15 10-30 10-20 Blue with
reflection
pattern cells
8
Amorphous
silicon
4-7 5-20 5-10 Brown colored
cells
16

CELL, MODULE AND ARRAY - I
A solar cell is the basic semiconductor device that
converts light energy into electric energy. Solar cells are
connected electrically in series and/or parallel circuits to
produce higher voltages, currents and power levels.
Photovoltaic module or solar panel consists of PV cell
circuits sealed in an environmentally protective laminate
and are the fundamental solar PV units available to
customers.
Panel is a group of modules (containing usually 2-3
modules) that can be packaged and pre-wired off-site.
A photovoltaic array is the complete power-generating
unit, consisting of any number of PV modules and panels.

CELL, MODULE AND ARRAY - II
Individual solar PV cells are too small to do much work. A typical single
crystalline silicon solar cell (10cm x 10cm) produces a voltage of
around 0.5V at a current of approximately 3A thus delivering a peak
power of 1.5W.
Usually in a module 36 cells are connected together in series to
generate enough voltage to charge 12 volt batteries. Owing to losses in
the electric circuit, the output voltage from a 36 cell-module is less than
18 V. 12-volt batteries typically need about 14 volts for a charge, so the
36 cell module has become the standard of the solar battery charger
industry.

Lecture Overview
Topic:
Solar PV
Objective:
To develop understanding of design principles of Solar PV
systems

PROS AND CONS OF PV SYSTEMS
Advantages
Low running costs
Low user/overall maintenance
Long service life
Easily upgradable
Minimum risk of electric shock
Quiet operation
No toxic fumes
Disadvantages
High capital cost
Weather dependent performance
Batteries are the weakest link and need
rigorous maintenance and periodic
replacement
User training is important for optimum
performance/operation
Cannot support heavy loads
Requires careful manual/automatic
monitoring
Liable to theft/vandalism

BASIC PRINCIPLES
The system should be designed so that it provides enough
energy for all seasons and loads.
There usually has to be some form of energy storage.
The system needs to be able to supply the peak power
requirements of the loads.

FUNDAMENTAL MEASUREMENTS - I
Hour (h) – unit of time
Volt (V) – unit of voltage
Ampere (A) – unit of electricity
Ampere-hour (Ah) – unit for capacity of battery – Ah = A x h
Watt (W) – unit of power
Watt-hour (Wh) – unit of energy
Power = voltage x current
W = A x V
Energy = power x time
Wh = W x h

FUNDAMENTAL MEASUREMENTS - II
Example
Power of a 20 V laptop using 1.5 A current:
If laptop functions for 5 hours, the energy consumed:
An 8W lamp powered with 12V consumes a current:
A lamp that consumes 30Wh in 3 hours has a power:
After 2 hours the energy consumption of 10W lamp:
Example
Power of a 20 V laptop using 1.5 A current:
If laptop functions for 5 hours, the energy consumed:
An 8W lamp powered with 12V consumes a current:
A lamp that consumes 30Wh in 3 hours has a power:
After 2 hours the energy consumption of 10W lamp:
Solution
P = 20V x 1.5 A = 30W
E = 30W x 5h =150Wh
I = 8W/12V=0.666A
P = 30Wh/3h = 10W
E = 2h x 10W = 20Wh

STANDARD APPLICATION CONDITIONS
The maximum power or output of a module is indicated as Watt peak
(Wp).
Optimum weather conditions
Solar irradiance – 1000W/m2
Temperature – 25ºC
Air mass – 1.5
A 60Wp module can produce a maximum of 60W under the above
conditions.
Owing to losses a PV module will always produce a bit less than its
peak power.

IMPACT OF TEMPERATURE ON THE
PERFORMANCE OF PV
A PV module will always produce a bit less than its peak power, especially in hot
climates.
In summer the module temperature can reach up to 70 °C. For this reason modules
should be kept as cool as possible. At temperatures greater than 25°C (temperature of
the cell itself), power output from will decrease by 0.5% for each degree rise in
temperature of the crystalline PV module. Amorphous cells may be preferable because
they experience an efficiency loss of 0.2% for each °C rise in temperature.
Example:
Determine the loss in output from a 60Wp PV module operating at a temperature of
50°C.
Solution:

CELL EFFICIENCY AS A FUNCTION OF
TEMPERATURE

PRINCIPAL CHARACTERISTICS
Peak Power
The maximum power a PV system is likely to produce is called its peak
power (Wp). It is usually expressed as 10, 40, 60 to 160Wp
Short circuit current (Isc)
Current measured when the two poles of a PV module are connected
to a multi-meter or an ammeter i.e. 3.65 A for 60Wp module
Open circuit voltage (Voc)
Voltage of a system (for example, a battery, a PV module) when it is
disconnected from all electrical circuits i.e. 20V for 60Wp module

V-I CURVE
Voc does not experience much variation with a change in the
irradiance level (W/m2). Voc varies between 0.5 et 0.7 V for
each cell (for example, a module with 36 cells has an open
circuit voltage Voc of 36 x 0.6 = 21.6 V)
Isc is directly proportional to the surface area of the cells (for
example, a module with 36 cells each 10 cm x 10 cm, will have
an Isc twice as large as a module composed of the same
number of cells each 10 cm x 5 cm).
Isc and power output are almost directly proportional to the
irradiance received on a module.
Irradiance (W/m2) Voc (V) Isc (A) Power output
(W)
100(grey clouds at noon) 15 0.36 6
500(white clouds at non) 19 1.8 30
1000 (clear sky at noon) 20 3.65 60
Example of a typical behavior of 60W module

http://en.wikipedia.org/wiki/Solar_cell

COMMON CLASSIFICATION OF PV
SYSTEMS BY APPLICATION
Stand alone system
Grid connected system

A TYPICAL STAND ALONE PV SYSTEM
PV module
10-400W
Regulator/CC
3-30A
Earthing
Battery
12V-24V
30-400Ah Inverter
AC
DC
DC
DC

SERIES AND PARALLEL CONNETIONS
PV modules can be connected in
series or parallel depending
upon the battery/load
requirements.
For example, 24V modules
should be connected in parallel if
the battery voltage is also 24V.
If the battery voltage is 48V,
these panels are to be arranged
in series to deliver 48V power to
the batter.
24V 10A
240W
Shading diode
48V 5A
240W
+
24V
5A
_
+
24V
5A
_
+
24V
5A
_
+
24V
5A
_

SIZING PV ARRAY
Daily Useful Energy(kWh) = H ×η× PR ×PP
PP = Peak power of PV array
H = full sunshine hours
η = efficiency of battery
PR = performance ratio (actual output/theoretical output)
PP = Daily Useful Energy (Wh)/[H ×η× PR]

PERFORMANCE RATIO
The standard solar radiation unit, kWh/m2, is usually given for an
average year or for an average day in a month or year. It is also
known as peak sun hours or full sun hours.
For example a PV module rated at 80Wp which has 1200 peak sun
hours falling on it over a year at STP will produce: 80Wpx1200sun
hours = 96,000Wh or 96kWh. However this is for ideal conditions
which in reality occur only in laboratories.
In a real grid-tied PV system one could expect perhaps 75-80% of
that, while in a stand-alone-system about 60-70% could be
expected.
The difference between the actual energy yield or output of a PV
system and the theoretically possible energy yield is known as the
performance ratio.

PV MODULES & LAMINATES
A PV module is composed of interconnected photovoltaic cells
encapsulated between weather-proof covering (usually glass) and
black plate (usually a plastic laminate). It will also have one or more
protective bypass diodes. The output terminals, either in a junction box
or in the form of output cables, will be on the back. Most PV modules
come with frame. Those without frames are termed as laminates. In
some cases the back plate is also glass which gives higher fire rating
but increases the weight.

CHARGE CONTROLLER
A charge controller (CC) or regulator regulates the
fluctuating voltage (due to cloud cover, rain etc) from
solar PV to protect the battery unit.
Provide information and warnings to the user on the
state of the system’s battery, PV array currents and
load currents.
Protects a battery from overcharging and complete
discharging.
Sometimes provide secondary functions such as
disabling lighting circuits during the hours of daylight.
A solar panel produces current during day time but at
night time it can consume a small amount of current
as well. CC prevents backflow (with the help of a
backflow resistor) of current to PV panel.

INVERTER
It converts DC (direct current) into AC (alternating current)
It is required to run any mains appliance
It consumes a small amount of energy to operate
It can be costly and sometimes temperamental

GRID-TIED INVERTERS
Grid tied inverters convert the DC electricity produced by PV array into single-phase
or three-phase electricity at a voltage and frequency suitable to be fed into the grid.
Inverters are available in a range of sizes and are rated in Wp, the peak wattage of
the PV array they are connected to. They are also called grid-connected inverters,
synchronous inverters or utility-intertie inverters.
Different types of inverters are available for different array configurations: central
inverters which serve a single installation, inverters for single string of modules or for
multiple strings and for single module. In case of large arrays if there is unavoidable
partial shading of the array or if parts of the array are oriented in different directions
or have different inclinations, several inverters may be required.
The inverter also needs to disconnect itself automatically from the grid if the grid is
turned off by the utility for maintenance. The situation in which grid has been turned
off by the utility and inverter keeps putting a voltage on the grid is termed as
islanding. This needs to be prevented as it would present hazard for the electricians
working on the grid.

BATTERIES
Batteries are needed to store energy
Batteries are the most vulnerable part of the PV system
They are usually specified as voltage and capacity in Amp-hours
E = V x capacity
A 12V 100Ah battery stores up to 1200 Wh, enough energy to run a
10W light bulb for 120hours

BATTERY CHEMISTRY
Discharging
Pb + PbO2 + 2H2SO4 2 PbSO4 + 2H2O
Electrolyte turns to water, plates turn to lead sulphate
Charging
Pb + PbO2 + 2H2SO4 2PbSO4 + 2H2O
Positive plate turns to lead oxide, negative plate turns to
lead, electrolyte turns to sulphuric acid.

BATTERY SELECTION
Cost
Application
Ease of maintenance
Life expectancy

STATE OF CHARGE AND DEPTH OF
DISCHARGE
A state of charge (SOC) of 100% corresponds to a completely
charged battery and an SOC of 0% corresponds to a completely
discharged battery.
SOC would be used as a “fuel gauge” to indicate the charge left in a
battery.
Depth of discharge (DOD) is the converse of SOC. If a battery has a
DOD of 80% this corresponds to a SOC of 20%.
DOD + SOC always equals 100%.

LIFE EXPECTANCY - I
For good life expectancy, batteries
mustn’t be discharged too much. It is
highly recommended to increase the
battery size rather over discharging
Even though battery capacity at high
temperatures is higher, battery life is
shortened. Battery life is reduced at
higher temperatures - for some batteries
for every 10 degrees C over 25, battery
life is cut in half.

SOC/DOD MEASUREMENT
SOC/DOD can be evaluated by measuring the specific gravity of the
battery electrolyte with the help of a hydrometer.

BATTERY MAINTENANCE - I
Although maintenance is critical to the long-term life of a battery bank, it is not a substitute for poor
system design or sub-standard installation. No amount of regular maintenance can compensate
for the effects of an improperly sized or an incorrectly installed battery bank. Poor design or
incorrect installation can be expensive, often resulting in additional battery bank purchases.
Once a system has been designed and installed properly, daily charging of the battery bank is
perhaps the most important factor influencing the longevity of an FLA battery bank. Both under-
and over-charging batteries can reduce the life of the battery. It is important to optimize systems to
meet the load requirements of the application, while taking into account the specific nature of the
charging sources available.
Batteries are simply an energy storage device, so it's critically important that a three-stage charge
control mechanism is provided that can be optimized for the most efficient charging of the battery
bank, regardless of the charging source.
The three stages of charging typically associated with daily charging cycles in an FLA battery
bank are bulk, absorption and float charging. Bulk charging refers to a higher rate of initial
charging that brings a battery to an 80 percent to 90 percent full state of charge and regulates at a
pre-determined voltage set-point. Absorption charging is the stage immediately following bulk
charging. The current is reduced to prevent over charging while maintaining the battery at a
specific voltage set-point for a period of time, allowing it to complete the last 10 percent to 20
percent of the charge cycle. Float charging is the final stage of three-stage charging. The charge
current and voltage are reduced to maintain a full battery, providing just enough charging to
compensate for self discharge. Since temperature variations affect batteries, using a charging
system with the ability to measure battery temperature will ensure that batteries will receive a
proper charge.

BATTERY MAINTENANCE - II
As flooded lead acid (FLA) batteries charge, hydrogen gas is produced and vented in the process.
This off-gassing of hydrogen reduces the electrolyte level in the FLA battery and so periodic
"watering" of the batteries with distilled water is required to ensure maximum life. Distilled water
should only be added to fully charged batteries that are in float charge mode.
No matter how frequently a battery bank is watered, do it according to a regular schedule and take
advantage of the opportunity to do a routine check of terminal connections. A poor electrical
connection anywhere in the system, whether caused by a loose connection or corrosion, can lead
to poor performance.
Always wear protective clothing, gloves and goggles when working with batteries. The electrolyte
in an FLA battery is a solution of acid and water, so take extra precaution to avoid contact with
skin and clothing.

OVERVIEW OF VARIOUS TYPES OF
BATTERIES

CABLE SIZING
Volt Drop (Vd) = Resistance X Current X Length in meters
• Should not exceed 5% on DC side
• Should not exceed 1% on AC side
Cross sectional
area (mm2)
Max Current
(amps)
Resistance
mW/meter
0.5 4.25 37
1 8.5 19
2 17 9
4 28.5 4.5
6 41.5 3

LIGHTENING
Lightning takes the easiest path to ground, it should be provided an
easier path than going through the PV system – lightning conductor and
earthing rod.
PV systems can be damaged by direct or nearby lightening strikes which
induce voltages, current and magnetic fields in the installation,
sometimes even destroying it completely.

LIGHTENING
The effects in general can be categorized as under.
Direct strike: if there is no lightening protection system, the lightening will
flow over the installation and more or less destroy it completely – structural
damage and fire can also result.
Indirect strike: in this case the lightening current flows through the
installation cables and utility cables – serious damage is likely
Near strike(<500m): magnetic fields induce voltage surges in cables which
can cause damage
Distant strike (>1000m) – mainly capacitive effect, usually not so dangerous

LIGHTENING
Damaged PV Damaged Inverter
Voltage surge Arrester

ORIENTATION OF PV MODULES - I
Ideal PV array should be kept at an angle perpendicular to
the sun’s incoming radiation but in reality most arrays are
fixed at a particular angle.
By choosing correct angle and orientation it is possible to
optimize the output of a PV system.
Just how crucial angle of inclination and orientation are
depends very much on the diffuse solar radiation
component.

ORIENTATION OF PV MODULES - II
For locations in northern hemisphere, PV should be
ideally facing south and north for southern hemisphere.
It is simplest to mount solar panels at a fixed tilt and just
leave them there.
However, since the sun is higher in the summer and
lower in the winter, more energy can be captured by
adjusting the tilt of the panels.
Adjusting the tilt four times a year is often a good
compromise between optimizing the energy on panels
and optimizing time and effort spent in adjusting them.

ORIENTATION OF PV MODULES - III
There are various formulae equations to determine the optimum tilt
angle for fixed panels. Tilt angles can be set to capture energy around
the year or to capture energy during the preferred season (summer or
winter).
One of the practiced formula, for example, is to tilt panels at an angle
that is 0.9 times the latitude. In countries where the latitude is greater
than 10°, panels can also be inclined at an angle equal to the latitude of
the site in order to receive the maximum irradiation throughout the year,
or to an angle slightly greater (latitude + 10° or latitude + 20°) to receive
maximum irradiation during the least favorable months.

SOLAR TRACKING SYSTEMS
Greater energy capture can be achieved by
using single or dual axis tracking mechanism
that will keep the PV array pointing towards
the sun from dawn to dusk.
A single axis east–west tracking installation
can yield up to nearly 30% more energy in a
year than a fixed array. A dual axis set-up,
which also tilts the array to follow the sun’s
changing altitude, can produce around 40%
more, both at the cost of higher capital and
maintenance costs.
Passive trackers are also becoming available
for solar PV installations. These use the
solar-induced expansion of a low boiling
point compressed gas fluid to keep the
panels pointing at the sun, and viscous
dampers to minimise wind shake.

SYSTEM LAYOUT - CONSIDERATIONS
Siting of the array – security, access, distance, lightning
Siting of the batteries – temperature, ventilation,
container, access for maintenance.
Siting of the controller – easy access
Cable lengths
Capabilities and training of the user
Maintenance skills available. Day to day, regular
scheduled, emergency repair

PV OUTPUT ESTIMATION
Solar radiation data for the site
The orientation of the module(s) ( i.e. South, East, West)
The tilt angle or angle of inclination of the modules
The performance ratio of the system

SHADING
Types of Shading
Occasional shading
Recurring shading

BYPASS DIODE
Cells connected in series, also called strings, increase the voltage output; while
cells connected in parallel increase the current. Each string of cells is usually
protected by a bypass diode. These prevent damage through overheating
occurring to the module if a cell is shaded or defective – the so called hot spot
effect. – and limits the subsequent drop in output in the concerned module and
other modules in the array.

CUSTOMER SATISFACTION
Attention to
client’s
need
Appropriately
designed
system
Quality
components
Quality
installation
Proper
training
Affordable
Reliable
after sales
services

DESIGN OF GRID-TIED PV SYSTEM
Maximum investment = $35000
Available shade-free roof area = 51m2 (L =8.5, W=6m)
Orientation = Due South
Inclination = 45°
Estimated net installed cost =$5500/kWp
Selected cell type = mono crystalline (require 9m2/kWp)
Site temperature range = -10°C to 40°C
Module operating temperature range = -10°C to 70°C
System size?
No. of modules needed?

Maximum system size that can be bought from the available investment =
$35000/$5500 = 6.36kWp
Maximum system the available roof area can have = 51m2/9m2/kWp =
5.67kWp
The largest possible system is within the budget limit!

No. of modules needed?
Information needed:
Module peak power
Module dimensions (length and width)
Selected modules: Output=165Wp, L=1.61m, W=0.81m
No. of modules required = 5670Wp/165Wp = 34.4 modules
The initial estimate suggests 34 modules of capacity 34 x 165 = 5.61kWp

Module arrangement/layout
Can 34 modules fit on the roof?
Modules in landscape format:
Roof length/modules length = 8.5m/1.61m = 5.27
Roof width/module width = 6/0.81 =7.41m
Maximum modules = 5 x 7 =35 modules
Modules in portrait format:
Roof length/modules width = 8.5m/0.81m = 10.49
Roof width/module length = 6/1.61 = 3.73m
Maximum modules = 10 x 3 =30 modules
34 modules thus can be used but in landscape format.

Voltage design
Module specifications on the data sheet
MPP-voltage VMMP (at 25C) = 35.35V
MPP-current IMMP (at 25C) = 4.67A
Open circuit voltage VOC (at 25C) = 43.24V
Short circuit current ISC (at 25C) = 5.10A
Voltage temperature coefficient Tc (VOC) =-168.636mV/C
Current temperature coefficient Tc (ISC) = 2mA/C
Power coefficient Tc (PN) = -0.42%/C

Module operating temperature range = -10°C to 70°C
VOC ( at -10C) = 43.24V + 35(0.168636V) = 49.14V
VMPP ( at -10C) = 35.35V + 35(0.168636V) = 41.25V
VMPP ( at 70C) = 35.35V - 35(0.168636V) = 27.76V
The highest voltage VOC will be at -10C i.e. 49.14V. And the voltage range at
MPP will be between 27.76V and 41.25V.

Inverter selection -I
Number of inverters
In installation of up to 5 or 6kWp and where the roof surface has a uniform
orientation and inclination and is free of shade, the use if a single inverter
usually makes sense.
Inverter power rating
The power rating of inverter is determined by the peak power of the array.
The peak power of the array is for standard test conditions (STC) which in
practice rarely occur. For this reason the size of the inverter can usually be
about 5% to 10% lower than the peak power rating of the array but the
maximum input currents and voltage of the inverter should never be
exceeded.
Inverter power rating = (0.90 – 0.95 ) x PV array peak power
PV array peak power = (1.05 – 1.10 ) x inverter power rating
Peak power of the array has been determined as 5.61kWp(34 modules x
165Wp), so an inverter of 5.61 x (0.90 - 0.95) = 5.05 – 5.33 kW shall be
appropriate.

Inverter selection –II
Inverter specifications on the data sheet
Maximum PV array power, PPV Max = 6 kW
DC Nominal Power, PDC Nominal = 4.5kW
Minimum peak power tracking voltage, VPV lower = 125V
Maximum peak power tracking voltage, VPV upper = 750V
Maximum DC input voltage, VDC max = 750V
DC Nominal Current, IDC Nominal = 9.35A
Maximum DC current IDC max = 22.50 A

The aim of this step is to decide on the number of modules in a string. The string
voltage needs to be within both the upper and lower limit of the inverter MPP voltage
range, i.e. the voltage range within which the inverter will track the MPP of the string.
The open circuit voltage of the string also needs to be checked to ensure that it is
below the maximum inverter input voltage. The maximum MPP voltage of the
modules occur at -10C and the minimum occurs at 70C.
How many modules can be connected in series?
Modules are usually series-connected in strings, one for each inverter DC input
terminal. The input DC voltage range of the inverter will determine the number of
modules to be connected together in each string as under.
Maximum number of modules = VPV upper/ VMPP (at -10C) = 750V/41.25V = 18.2
Minimum number of modules = VPV lower / VMPP (at 70C) = 125V/27.76V = 4.5
So in order to stay within the voltage range at which the inverter will track MPP of
array, the number of modules in each string must not be fewer than 5 and not be
more than 18.
Voltage limits and module
configuration

The maximum voltage at the inverter input will occur at -10C during open
circuit operation (i.e. a cold winter day, the sun suddenly appears from
behind the clouds). The number of modules in strings must be chosen so
that under no circumstances does the string voltage go above the DC
voltage input range of the inverter. If it did, the inverter could be damaged.
Maximum number of modules = VDC max /Voc (at -10C) = 750V/49.14v = 15.3
So the earlier figure of 18 modules has been reduced to 15 modules in
order to keep below the maximum DC voltage input of the inverter.

Array configuration
Number of strings = planed number of modules/number of modules per
string
Decision has to be made with customer about number of modules!
Possible configuration arrangement for 30 modules.
With single central inverter
2 strings of 15 modules or 3 strings of 10 modules
For 34 modules with multi-string inverter
2 strings of 11 and 1 of 12

Configuration A – 10 modules in
series, 3 strings in parallel
VMPP (at 70C) = 10 x 27.76V = 277.6V
This value is above the lower limit of MPP voltage range V PV lower (125V) –
acceptable
VMPP (at -10C) = 10 x 41.24V = 412.4V
The value is below the upper limit of the MPP voltage range V PV upper
(750V)- acceptable
Voc (at -10C) = 10 x 49.14V = 491.4V
This value is below the maximum acceptable inverter input voltage V DC max
(750V) – acceptable
The current at MPP IMPP of a string has a value of 4.67A. Connecting 3
strings in parallel will give 14.01A. The value is above the inverter DC
nominal current I DC nominal but still below the maximum DC current IDC max.

Configuration B – 15 modules in
series, 2 strings in parallel
VMPP (at 70C) = 15 x 27.76V = 416.4V
This value is above the lower limit of MPP voltage range V PV lower (125V) –
acceptable
VMPP (at -10C) = 15 x 41.24V = 618.6V
The value is below the upper limit of the MPP voltage range V PV upper
(750V)- acceptable
Voc (at -10C) = 15 x 49.14V = 737.1V
This value is below the maximum acceptable inverter input voltage V DC max
(750V) – acceptable
The current at MPP IMPP of a string has a value of 4.67A. Connecting 2
strings in parallel will give 9.34A. The value is just over the inverter DC
nominal current I DC nominal and below the maximum DC current IDC max.

Deciding between configuration
A and B
In both configurations V and I outputs are within the respective V and I input
ranges for the inverter, so either is possible. The more the modules in a
string the higher the voltage will be. Because higher voltage means lower
cable losses, configuration B will be preferred over configuration A.
connecting modules in series is simpler, quicker and reduces cost and
possibility of incorrect connections.

SUMMARY
Thus keeping within the budgetary constraints and the size of the available
roof surface the following system design emerge.
PV array peak power – 4.5 kWp
Number of modules – 30 x 165Wp
Configuration – 2 strings of 15 modules
Central inverter with a DC nominal power rating of 4.5 kW and maximum PV
array power rating of 6 kW.
Other deign details are possible employing different modules and inverters.

PV MOUNTING
Material
Aluminum and stainless steel are the most common, galvanized steel is
also used
Structures
Roof mounting
Roof integrated
Free standing
Façade mounting

PV MOUNTING
Shading
Cable run length
Cable protection
Array installation
Array maintenance
Lightning protection
Animals, children and thieves

FACTORS AFFECTING SYSTEM SIZING
AND DESIGN
Solar Resource
System Loads
Total Energy Demand
Maximum Power Demand
System Efficiency
Days of Autonomy
Length of cable runs

QUICK PV OUTPUT ESTIMATION
Solar radiation data for the site
The orientation of the module(s) ( i.e. South, East, West)
The tilt angle or angle of inclination of the modules
The performance ratio of the system

SYSTEM LAYOUT - CONSIDERATIONS
Siting of the array – security, access, distance, lightning
Siting of the batteries – temperature, ventilation, container, access for
maintenance.
Siting of the controller – easy access
Cable lengths
Capabilities and training of the user
Maintenance skills available. Day to day, regular scheduled, emergency
repair

SIZING PV ARRAY
Daily Useful Energy(kWh) = H ×η× PR ×PP
PP = Peak power of PV array
H = hours of full sunshine
η = efficiency of battery
PR = performance ratio (actual output/theoretical output)
PP = Daily Useful Energy (Wh)/[H ×η× PR]

PV SYSTEM SIZING
E = H ×ηsys×WPV
(E = G ×ηsys× WPV)
WPV = Peak power of PV array
H = Full sunshine hours
η sys = Total system efficiency (performance ratio)
WPV = E/[H ×η sys]

PV SYSTEM SIZING
ηsys = ηPV x ηcc x ηinv x ηbatt x ηdis
Where
ηPV = Efficiency of PV panel with regards to its MPP output ( typically
around 80%)
ηcc = Efficiency of charge controller, around 98%
η inv = Efficiency of inverter, around 90%
ηbatt = Efficiency of battery, around 80%
ηdis = Efficiency of distribution cables, around 98%

BATTERY SIZING
Q = (E X D)/(DOD x ηinv x ηcb )
Where
Q = Total energy to be stored in batteries
E = Daily energy requirement
D = Days of autonomy (number of days of storage required)
DOD = Allowed depth of discharge
η inv = Efficiency of inverter
η cb = Efficiency of inverter

ASSESSING ELECTRICITY CONSUMPTION
Prediction can be misleading
Appliance power ratings not accurate.
Metering actual consumption advisable

EXAMPLE - SYSTEM SIZING
Daily energy
requirement
(Wh)
Hours of use
per day (h)
Total Power
(W)required
Quantity
Power rating
of appliances
(W)
Load/applianc
e
3
3
11
CFL-hall and
living room
1.5
1
20
CFL-Kitchen
0.2
2
100
Lights-outside
and garage
1
1
60
TV
0.4
1
700
microwave
0.1
1
400
Food mixer
Average -5
1
80
Refrigerator
Totals
H = 4.5 peak sun hours
Overall system efficiency = 60%
Days of autonomy = 5
DOD = 50%
η inv = 90%
η cb = 97%

Daily energy
requirement
(Wh)
Hours of use
per day (h)
Total Power
(W)required
Quantity
Power rating of
appliances (W)
Load/appliance
99
3
33
3
11
CFL-hall and
living room
30
1.5
20
1
20
CFL-Kitchen
40
0.2
200
2
100
Lights-outside
and garage
60
1
60
1
60
TV
280
0.4
700
1
700
microwave
40
0.1
400
1
400
Food mixer
400
Average -5
80
1
80
Refrigerato
949
1493
Totals

Wp = 949/(4.5 x 0.6) = 351Wp
Q = (5 x 949)/(0.5 ) = 9.49kWh
= 9.49/24 = 395Ah

HEALTH AND SAFETY - BATTERIES
Batteries are heavy. Make sure that they can be lifted comfortably
and plan the maneuver in advance. Wear proper footwear.
Sulphuric acid used is corrosive to skin and clothes. When filling
batteries ensure that there is proper protective gloves, goggles,
clothing to hand.
Although the voltages are generally low and safe batteries can
supply very high currents. Care must be taken to ensure that
terminals do not become shorted and that cables are fused.
Batteries give of explosive hydrogen gas. Ensure proper ventilation,
and do not smoke or use naked flames in their vicinity.

ENVIRONMENTAL IMPACTS OF PV
PV systems do not produce any carbon dioxide during their operation.
Although indirect emissions of CO2 occur at other stages of the lifecycle,
these are significantly lower than the avoided emissions.
PV does not involve any other polluting emissions or the type of
environmental safety concerns associated with conventional generation
technologies.
There is no pollution in the form of exhaust fumes or noise.
Contrary to other power generation technologies, the decommissioning of
PV systems is unproblematic.
Recycling of PV modules is possible.

solar PV

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (20)

Similaire à solar PV

Similaire à solar PV (20)

Dernier

Dernier (20)

solar PV