Module 5

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• Electrical installations of high-rise buildings: Distribution systems – rising main,
cable system - Installation of lifts, standby generators, fire pumps - electric schematic
drawing.

• Selection of standby Diesel Generator set (DG set) –power rating - Continuous, Prime
and Standby power ratings- installation and essential protections-Introduction to
Automatic Mains failure (AMF) systems.

• Energy Conservation Techniques in electrical power distribution - Automatic Power

Factor Correction (APFC) panel – Principle of operation and advantages.

• Introduction to Solar PV Systems, off-grid and on-grid systems, Solar panel

efficiencies design of a PV system for domestic application-Selection of battery for
off-grid domestic systems.

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Advantages of APFC

• Consistently high power factor under fluctuating loads.

• Eliminate power factor penalty

• Lower energy consumption by reducing losses

• Continuously sense and monitor load

• Automatically switch on/off relevant capacitor steps for consistent power supply

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HIGH RISE BUILDINGS
• Special features applicable for high-rise apartment buildings
 High rise residential apartments are those buildings having a height above
ground level of more than 15 m.
 Lift machine rooms or the water tanks will not be taken into account in
fixing the height of the building.
 These buildings come under the section 54 of the Electricity Act
2003 and rule 50(A) of the Indian Electricity Rules 1956.
 The electric power supply arrangement in the high rise apartment
buildings are normally provided through a transformer sub station
which receives power at 11kV on the high voltage side.

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• S U B STATIONS
 Normally, out door type transformer sub stations are not
permitted at the premises of high rise apartments.
 However, out door transformers with cable end boxes on both HT
and MV sides can be permitted with special emphasis on safety
measures.
 Only dry type transformers will be permitted to be installed in
the basement floor or above the ground floors.
 If the total connected load of the apartment is 50 kVA and
above, separate transformer shall be installed by the promoter /
owner at his cost.
 If the common and essential loads exceed 100 kVA, it is advisable to
install a separate transformer for this purpose by the promoter / owner.
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 Fire pump capacity is not to be included in assessing the total connected load.

 For calculating the connected load, a minimum of 1.2 kW for single phase
connection and 5 kW for three phase connection shall be used if exact
information is not available. Otherwise, a uniform rate of 50 W/m2 shall be used
for working out the total connected load.

 A diversity factor not exceeding 2 is included in deciding the maximum demand

for the apartment.

 Emergency supply disconnection facility using push button shall be provided at a

conspicuous place in the ground floor, preferably at a height of 2.75m from the
floor level.

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• P RIMARY AND S E C ON D A RY PROTECTION
 If there is only one transformer, an H T load break switch fuse unit or a
vacuum circuit breaker may be used as the primary controlling unit.
 H T load break switch is adequate for capacities below 1000 kVA. For higher
ratings, vacuum circuit breakers are to be used.
 If there are more than one transformer in the same premise, the H T switch
board shall have an H T load break isolator of adequate capacity on the incomer
side as a group controller and HT S F U or VCB as out going for
controlling individual transformers.
 The H T metering arrangement shall be arranged on the primary control unit.
 Only tamper proof digital TO D (Time of Day) meters shall be provided for
metering the energy consumption.

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 The metering current transformer shall be of single ratio; single core type and no
extra tapping points are permitted on this CT.
 Tappings from the metering Potential Transformer (PT) can be
permitted through separate fuses for connection to the indicating lamps, volt meters,
power factor meter and watt hour meter.
 A circuit breaker of adequate capacity shall be provided on the secondary
side of the transformer.
 Oil filled circuit breakers or oil filled switch fuse units shall not to be used in high rise
buildings.
 Low set earth fault protection using neutral CT need not be insisted for transformers
feeding high rise buildings where, Low tension metering is provided for individual
consumers.
 How ever E L C B (Earth leakage circuit breakers) shall be provided on all consumer
distribution boards and other motor loads excepting the fire pump motors.
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M E T E R I N G PA N E L
 For high rise apartment buildings, the metering panel shall be located at the ground
floor level.
 The maximum number of outlets from a metering panel will be limited to eight
in the case of three phase supply and twelve in the case of single phase system.
 The energy meters for the individual consumers are to be provided by the promoter of
the building and these meters have to be certified by the competent authority before being
installed in the metering panel.
 Fuse/ M C B protection shall be provided for every energy meter. Locking and
sealing facility shall also be provided on all metering panels, main switch boards,
HT switch board etc to prevent theft of energy or to prevent crime.
 Unmetered spare outlets are not permitted in MSB, SSB’s and in the metering panels.

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• CABLING
 Cables from the metering panel to various floors shall be routed through cable ducts only.
 There shall be access to these cable ducts from all floors.
 Fire barriers shall be provided in the cable ducts at all floor levels inside the ducts.
This is to prevent the spread of fire to upper floors in the event of a fire breaking out in
a lower floor.
 The grid power cables and the generator cables shall be segregated inside the duct.
 Other service cables like telephone, net work, C C T V cable etc shall not be provided in
the cable ducts for power.
 Aluminium armoured cables are preferred up to the distribution boards of the
individual consumers. Beyond the distribution board copper wires are preferred
for reasons of convenience and reliability.

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• D ISTRIBUTION BOARDS

 Factory assembled distribution boards with IP42 protection (Double door) is

the best choice for apartments.

 The incomer device for these distribution boards shall be an RCBO or

E L C B + M C B (30 mA sensitivity) of appropriate rating depending on the
connected load.

 The out going MC Bs shall be of B-characteristics for light and resistive

loads and of C- characteristics for highly inductive loads.

 The maximum number of ways permitted for three phase distribution

board is only 8.

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• EMERGENCY P O W E R S U P P LY

 A stand by generator of adequate capacity is to be provided for every apartment building to meet the
emergency needs and essential loads in case of a power failure.

 The capacity of the generator shall be a minimum of 20 % of the connected load of the apartment.

 When generator supply is extended to individual consumers, it shall be carried out

through a separate emergency distribution board.

 The generators shall conform to the requirements of the Pollution Control Board and shall be
housed in an acoustic enclosure to limit the sound level below 70 dB.

 The exhaust pipe of the diesel generator set shall also be extended to the top of the building.
 If the generator is to be installed on any floor above the ground level, structural fitness of the building
will have to be ascertained to check whether the building will be able to carry the static and
vibratory loading of the generator.

 A separate room shall be provided with proper oil drainage facility. An emergency engine stopping
arrangement also is to be provided out side the generator room.

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 All electrical rooms accommodating the transformer, switch boards,
metering panels, generator etc shall be located with easy access and proper
ventilation.

 Adequate clearances are also to be guaranteed for easy maintenance work.

 The details of electrical installations of a High rise apartment building with

twelve floors (G+11) which includes forty residential apartments and three
penthouses are shown below. The ground floor is set apart for common
facilities and each upper floor has four flats up to tenth floor and the eleventh
floor has three pent houses.

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 The details of the common service panel are shown in figure .

 This panel caters to the lighting requirements of common areas like entrance
lobby, stair ways, car parks, equipment rooms, external lights etc.

 Supply to the lifts, domestic pumps, fire pumps and other building services
are also provided from this panel.

 The total energy consumption from this panel is separately metered and the
total cost is shared by the owners of the residential flats as part of the monthly

maintenance charges .

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 Emergency and standby generation
• Intended to provide an alternate source of power if the normal source of power
fails
• Classified as follows
– Emergency power systems
– Standby power systems

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• Emergency power system: An independent reserve source of electric energy that, upon
failure or outage of the normal source, automatically provides reliable electric power
within specified time to critical devices and equipment whose failure to operate
satisfactorily affect the health and safety of personnel or result in damage to property.

• Standby power system: An independent reserve source of energy that, upon failure or
outage of the normal source provides electrical power of acceptable quality so that the
user’s facilities may continue in satisfactory operation.

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 General considerations
• Engine driven AC generator sets are used for industrial and commercial buildings as
a source of power.

• Main prime movers used in engine driven type generators are diesel engines, gas
turbines and steam turbines.

• Gas turbine generators are lighter in weight than diesel engine sets, run more quietly
and require less cooling and combustion air leading to lower installation costs

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• Gas turbine generator sets are more expensive than diesel engine generator sets,
require more starting time

• Another factor is fuel supply,If fuel is stored in tanks, it should be stored away
from the generators

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Ratings of standby generator sets
• When selecting the right generator for any application, one key place to
start is with the generator’s ratings.
• Ratings will provide insight into how much power the generator is
capable of producing.
• They also define how and what types of applications it can be used for.
• These ratings helps to buy a generator capable of providing proper
coverage for the needs within the constraints of budget and efficiency.
• There are three basic rating types – prime, continuous, and standby.

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Prime Generator
• A prime generator is one that serves as the primary source of power for the
operation.
• It is designed to work long term.
• The prime generator is designed to offer a variable power load that is drawn over
time.
• The most common use for a prime generator is for establishing a location that is
away from other sources of power, such as a remote building site or hard-to-access
area.
• They are used for power lighting, sound systems, and facilities at various events
and locations that may frequently change, such as for staging or ceremonies.

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Continuous Generator

• A continuous generator is one that is used much like the primary power source.

• It is generally designed to work on a consistent basis as the primary source of

power for the facility or function.

• The difference between a continuous and a prime generator is that the continuous
form does not offer a variable amount of power. Instead, it is designed to provide a
steady power load over the entire time frame it is used.

• They are often used in mining, military, and agriculture.

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Standby Generators

• A standby generator is a backup generator, one used for emergency use

only.

• It generally has the ability to run for a short amount of time as the main
power supply.

• It is meant to run just long enough to get the other prime power back
online.

• Standby generators can be usable in many situations, including residential,

commercial, and industrial areas. The amount of time they can run varies
significantly.
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 Arrangement of standby generating system
• Normal operating conditions- load
supplied from utility supply
• Upon loss of this supply Q3 is tripped,
the generator set is started and load is
supplied by the standby generator set by
closing the CB Q2
• Critical loads are supplied from UPS
• UPS is equipped with static switch
which will bypass the rectifier/inverter
module in case of an internal fault in the
UPS and ensure continuous supply of
electric power to the critical loads

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Emergency/standby power supply arrangement

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 Installation requirements of standby generators
• Minimum 1m clearance shall be provided on three sides of the generator set, minimum
2m clearance shall be provided between them.
• Fuel tank of DG sets shall be installed outside the generator room.
• Exhaust pipe of DG sets shall maintain a minimum height of 1.8m clearance from the
floor level
• Voltmeters and frequency meters shall be connected before the circuit breaker in the
generator control panel.
• Watt hour meter and ammeters in each phase shall be provided.
• For generators of 500kVA and above, kVA/kW meter and pf meter shall also be
provided
• Changeover switches of approved makes is permitted for capacities up to and including
800A .

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• Provide thermal O/L relay in the generator circuit.

• Generator room shall be made of non inflammable materials.

• Standard size of earthing cables and conductors for generators shall be provided.

• Proper protection schemes should also be provided for generators.

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Automatic Mains Failure(AMF)
• Automatic mains failure (AMF) panels – also referred to as automatic transfer switch
(ATS) panels – make the power, switch to emergency standby generators in the event
of a significant loss of mains power or total blackout.

• There are three main types of AMF units

Using Microcontroller in the unit itself

Using PLC (Programmable Logic Control) for control action

With the help of Relay Mechanism

A relay based system is described for control action. Elements which are used are
voltage monitoring relay/phase failure detector (PFD), Overload Relay and Air Circuit
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• The system continuously monitors the voltage level from the mains.

• If the voltage is dropped below the allowed level, this system will switch the Load
to Generator (auxiliary supply) and switch back to the mains when the voltage is
back to nominal required normal level.

• Continuity of supply to load is achieved with the help of AMF unit.

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Block diagram of AMF

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• Power from mains supply is continuously monitored by PFD with the help of relay unit.

• It gives signal to the ACB for its operation / protection.

• When fault occurs in the mains supply PFD detects the fault and disconnect the mains
supply form the load side by tripping the ACB.

• Generator will start automatically

• When generator runs at rated RPM & frequency then the ACB will operate & supply is
given to the load form the generator.

• Phase Failure Detector: It is an electro mechanical device used in power system

engineering to protect a load from damage due to failure in any of the phases supplying
power to the load. It automatically cuts off the load from supply if one of the individual
phase becomes faulty. It automatically cuts off the load from supply.

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• Phase Failure Detector will operate in following conditions;

i) Unbalanced Voltage

ii) Single Phase or Phase loss

iii) Overload Condition

iv) Power Outage

v) Phase Reversal

• It monitor both Generator as well as Mains side parameter. Any above mentioned
condition will cause PFD to operate & give signal to ACB as well as control signal
is generated .

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Energy conservation techniques in lighting

• Electric lighting is a major energy consumer.

• Enormous energy savings are possible using energy efficient equipment, effective
controls, and careful design

• Electric lighting design also affects visual performance and visual comfort by
maintaining adequate and appropriate illumination while controlling reflection and
glare.

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 Techniques implemented
• Installation of CFL in place of incandescent lamps.

– CFLs use about 2/3 less energy than standard incandescent bulbs, give the same
amount of light, and can last 6 to 10 times longer

• Installation of energy-efficient fluorescent lamps in place of “conventional”

fluorescent lamps

– There are a few styles worth noting; these models are simply labeled as “T-12”, “T-
8”, or “T-5”

– The names come from the size of their diameter per eighth inch. For example, a T-12
lamp is 12/8 inch in diameter (or 1 1/2 inch); a T-8 lamp is 8/8 inch in diameter (or 1
inch); a T-5 lamp is 5/8 inch in diameter.
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• The recommended style of fluorescent lighting is a T-8

• T-8 lights are the most cost effective

• More efficient than standard T-12 fluorescent lamps, which have poor color
rendition and cause eye strain

• T-8 lamps provide more illumination, better color, and don't flicker

• T-5 lamps are the most energy efficient and also tend to transmit the best color;
however, they are expensive.

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Installation of occupancy/motion sensors to turn lights on and off where
appropriate

• Lighting can be controlled by occupancy sensors to allow operation whenever

someone is within the area being scanned.

• When motion can no longer be detected, the lights shut off.

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Use an automated device, such as a key tag system, to regulate the electric
power in a room

• The key tag system uses a master switch at the entrance of each guest room,
requiring the use of a room key-card to activate them

• Using this technique, only occupied rooms consume energy because most
electrical appliances are switched off when the keycard is removed (when the
guest leaves the room)

• Along with lighting, the heating, air-conditioning, radio and television may also be
connected to the master switch

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Replace all exit signs with light emitting diode (LED) exit signs

• Multiple LEDs, properly configured, produce equivalent lighting and consume

95% less electricity than incandescent bulbs and 75% less than energy-efficient
compact fluorescent lamps

• 20 year life cycle and eliminates maintenance

• LED exit signs are the expensive, but are also the most efficient exit signs
available.

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Use high efficiency exterior lighting

• Include mercury vapor, metal halide and high pressure sodium

• HID lighting is mostly utilized in floodlight, canopy, area fixtures outdoors etc

• The best type for any application depends on the area being lighted and mounting
options.
Add lighting controls such as photo sensors or time clocks
• Photo sensor controls monitor daylight conditions and allow fixtures to operate
only when needed
• Photo sensors detect the quantity of light and send a signal to a main controller to
adjust the lighting
• Time controls save energy by reducing lighting time of use through
preprogrammed scheduling.
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Star certification
• Earning the ENERGY STAR certification means the product meets strict
energy efficiency guidelines set by the US Environmental Protection Agency
• Lighting products that have earned the ENERGY STAR label deliver
exceptional features, while using less energy.
• Saving energy helps you save money on utility bills and protects the
environment by reducing greenhouse gas emissions.
ENERGY STAR Certified Light Bulbs:
• Use about 70-90% less energy than traditional incandescent bulbs
• Last at least 15 times longer and saves electricity costs over its lifetime
• Meet strict quality and efficiency standards that are tested by accredited labs
and certified by a third party.
• Produce about 70-90% less heat, so it’s safer to operate and can cut energy
costs associated with home cooling.
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• ENERGY STAR certified ceiling fan/light combination units:
– Are 40% more efficient than conventional fan/light units
– Use improved motors and blade designs
– Provide quality, cutting edge design, and the latest in efficient technology.

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 Energy conservation in power
• ENERGY STAR certified room air conditioners come with better materials
• Offer additional convenience, comfort and energy-savings, including the ability to:
– turn off the unit remotely using your phone or computer;
– schedule changes to temperature settings based on your needs
– receive feedback on the energy use of the product
– use 10 percent less energy and saves electricity cost.
• An ENERGY STAR certified solar water heating system can cut your
annual hot water costs in half
Life expectancy of certified solar water heating systems is 20 years

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 Energy conservation in motors
• Motors and drives constitute two third of the energy consumed by manufacturing
industry.
• The efficiency of conversion of this electrical energy , is of the order of 85%
• There are three important losses in motor, the largest being the resistive loss of
windings(I2R loss)
• The next loss is that of magnetic circuit(known as iron loss) which varies with
both voltage and frequency
• Third is windage and friction loss which varies with motor speed

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 Energy efficiency-Induction motors
• Induction motors have long been the workhorses of industry for fixed speed
applications
• They are applied to variable speed duties through the use of variable frequency
inverters.
• This electronic equipment allow the voltage and frequency supplied to the motor
to be accurately controlled and hence very effective variable speed performance
can be achieved over a wide operating range.
• The efficiency of standard induction motors can be significantly improved by
using more materials in the motor.

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• Energy efficient motors are

– more expensive than standard motors

– lower noise and vibration

– lower operating temperature

– greater ability to accelerate high inertia loads

– Less affected by voltage variations

• An alternative method of reducing losses in the motor would be to use low

magnetic loss materials such as silicon iron, which have losses of about one-fifth
of those in conventional material.
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Improvements to increase efficiency of motors include

• use of lower loss steel, longer core, thicker wire, thinner laminations smaller air
gap between stator and rotor , copper instead of aluminum bars in the rotor,
superior bearings and a smaller fan.

• Energy efficient motors now available in India, have 3-4% of higher efficiency
than standard motors.

• B.I.S stipulates that energy efficient motors are to operate without loss of
efficiency at loads between 75% and 100% of rated capacity

• The power factor is to be the same or higher than standard motors.

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Automatic Power Factor Correction (APFC)

• An APFC panel is an electrical panel that is used to improve the power factor of electrical
systems.

• The power factor is a measure of how efficiently electrical power is being used, and it is
calculated by dividing the real power (measured in watts) by the apparent power (measured
in volt-amperes).

• A low power factor means that electrical energy is being wasted, which can result in
increased electricity bills and reduced efficiency.

• APFC panels are used to correct the power factor by automatically adjusting the amount of
reactive power (measured in VARs) that is being used in the electrical system.
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• An APFC panel typically consists of a microprocessor-based controller, a capacitor
bank, and a contactor.

• The controller monitors the power factor and activates the contactor to switch the
capacitor bank on or off as needed to maintain a desired power factor.

• The capacitor bank consists of a series of capacitors that are connected in parallel with
the load to supply reactive power to the system.

• APFC panels are commonly used in industries and commercial buildings where the
power factor is low due to the use of inductive loads such as motors and transformers.

• By improving the power factor, APFC panels can help to reduce electricity bills and
improve the efficiency of electrical systems.
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 Solar Photo Voltaic Systems
• PV systems generate electricity directly from sunlight.
• Electricity can be used directly or can be stored in batteries/fed to grid
• Most suitable for homes with a flat roof or with slanting roof facing
south
Types of PV electrical systems
There are two general types of design for PV power systems are
• Grid connected or utility interactive systems
• Stand-alone or off grid PV systems
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Grid connected system
• Designed to operate in parallel with and
interconnected with the utility grid.
• Primary component is the inverter or power
conditioning unit (PCU).
• Inverter converts DC power produced by
the PV array into AC power consistent with
the voltage and power quality required by
the utility grid.
• Bidirectional interface is made between PV
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• When the PV output is greater than the on site load demand ,PV system feed the
grid .

• When electrical demand is greater than the PV system output, the balance of
power required is drawn from the electric utility.

• Main Safety issue is PV system should not feed to utility grid when grid is down
for service or repair.

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Stand-alone system

• It is designed to operate independent

of the electric utility grid.

• Supply DC/AC loads.

• Most suited for remote locations

where there is no utility supply.

• Drawbacks are 1)batteries wont last

forever 2) wastage of surplus energy.

• Need replacement every 5-6 years

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 PV system components
Basic components are
1) Solar PV modules
2) Array mounting racks
3) Grounding system
4) Junction box
5) Surge protection
6) Inverter
7) Meters
8) Disconnector
9) Battery bank
10) Charge controller
11) Battery disconnect
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1) Solar PV modules
• Solar cell is the basic building block of a PV module.
• Many cells wired together form PV module (10W-300W) and many
modules form PV array.
• Rating of a module is the maximum power the module can produce under
standard test conditions with 1kW of sunlight per sq.meter at a temperature
of 25° C in air
Types of solar modules
• Mono crystalline- high performance solar cells (efficiency 15-19%)
• Poly-crystalline- standard solar cells (efficiency 11-15%)
• Amorphous – thin film solar cells( efficiency 5-8%)
• Hybrid solar modules (combines two technologies for manufacture)

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2) Array mounting racks

• Orientation of PV array affects its performance.

• Best location of PV system is flat roof and south facing roof.
• On roof mounted systems, PV array is mounted on fixed racks parallel to the roof
and lifted off few centimeters above the roof surface to allow airflow that will
keep the surface cool.
• Solar modules can also be placed on the ground either on a fixed pole or a tracking
mount.
• Mounting racks are adjustable such that angles can be set for PV modules to
follow the sun.
• Tracked PV arrays can increase system’s daily energy output by 25%-40%.
• Tracking systems are not recommended for home solar applications

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3) Grounding system
• Provides low resistance path from PV system to ground to protect the system from
current surges, lightning strikes or equipment malfunctions.
• Provides protection from shock caused by ground fault.
• All system components and any exposed metal including equipment boxes, frames and
PV mounting equipment should be properly grounded.

4) Junction box

• Output wires from individual PV modules are run to the junction box
• Junction box includes safety fuse or circuit breaker for each string and also includes a
surge protector
5) Surge protection
• Protect the system from power surges due to lightning.
• Lightning surge is a sudden increase in voltage above the design voltage
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6) Inverter

• Converts DC power of PV to AC power to feed domestic loads

• Also takes function of power conditioning
– Reduce voltage fluctuations
– Ensuring pure sinusoidal wave for grid connected systems
– Ensuring 50 Hz frequency of electricity
Criteria for selecting a grid connected inverter: The following factors should be considered
for selection
– DC voltage of PV module
– Quality of inverter such as efficiency, voltage regulation and good frequency
– Manufacturer warranty
– MPPT capability

7) Metering

• Provides easy access to various parameters of the system and allows us to check whether
the system is operating properly or not
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8) Disconnector

• Automatic and manual type

• Ensure proper shut down of system for repair and maintenance

9) Battery bank

• Store DC power of PV system during daytime for later use

• Different types of batteries used in solar system are
– Lead acid batteries
– Alkaline batteries- high cost, used for extremely cold temperatures

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10) Charge controller
• Necessary for systems with battery back up
• Prevents overcharging and over discharging of batteries
• Selection based on
– PV array voltage – The controller’s DC voltage input must match the nominal
voltage of the solar array
– PV array current – The controller must be sized to handle maximum current
produced by the PV array
The charge controller must be selected such that it does not interfere with the proper
operation of the inverter

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 Typical design for home application
Design steps
Step 1) Determine the load to be served in watt-hours/day
Step 2) Determine the average solar energy available on at least a month by
month basis
Step 3) Calculate the size of solar panel that is required to meet the load
demand under the worst month conditions
Step 4) Calculate the size and type of battery that is needed to provide the
required reliability of power
Step 5) Determine the type of charge controller
Step 6) Determine the inverter capacity

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1) Determining load to be served in watt-hours per day
• Determine the power rating in watts of each of the appliances to be used in the
household.
• Estimate the number of hours per day that each appliance will be used.
• For each appliance multiply the power rating in watts by the hours of use to get
watt-hour/day.
• Calculate the total watt hour per day for all appliances taken together.

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2) Determining average solar energy available on at least a month
by month basis

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3) Size of solar panel required to meet the load
• Solar panels should produce 30% more energy that is required by the user.
• Watt – hour /day to be generated by the solar panel is about 130% of the watt
hour needed by the equipment in the household.
• Panel generation factor (PGF) is an important component used in deciding solar
panel size
• There are several factors that influence performance of the solar panels and we
need to apply corrections for the same.
• Corrections include
– 15% for ambient temperature above 25ᵒC (85% derating)
– 5% loss due to sunlight not striking straight on the panel (95%)
– 10% for loss due if there is a no MPPT charge controller 90% derating
– 5% allowance for dirt collected on the solar panel (95% derating)
– 10% allowance for the panel being below specification and for ageing (90%)
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• Therefore panel generation factor is obtained by multiplying the lowest Wh/day by
the derating factor
• Number of PV modules required is calculated
• Number = (Panel size required/rated Wp of the PV module)

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4) Battery sizing
• Deep cycle battery is preferred for PV systems
• Batteries shall be large enough to operate the appliances at night and cloudy
days
• Depth of discharge of the battery should not be large to have good life of
battery
• The following assumptions are made for selecting the capacity of the
battery bank
Battery efficiency is assumed to be 85%
Depth of discharge is assumed to be 50%
Cloudy days are assumed to be 2
• Battery voltage levels are chosen based on the wattage capacity of the plant
– 12V for up to 500W capacity
– 24V for up to 1000W capacity
– 48V for up to 2000W capacity

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5) Selection of charge controller
• Basic functions include
– Block reverse flow of current
– Prevent battery over charging
– Prevent battery over discharging
– Protect battery from overload
– Display battery status and flow of power
The charge controller is specified in terms of current and voltage.
It is selected to match the voltage of the PV array and batteries.
Should operate at 30% more than the short circuit current of the array.
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6) Selection of inverters
• Basic qualities of inverter for PV applications are
– Power quality- “Utility Interactive”
– Voltage input- inverter’s DC input should match the PV array
– AC power output
– Surge capacity
– Frequency and voltage variation
– Efficiency
– Integral safety disconnects
– MPPT
– Automatic load shedding
– Warranty
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 SOLAR PV SYSTEM SIZING

1. Determine power consumption demands

The first step in designing a solar PV system is to find out the total power and energy
consumption of all loads that need to be supplied by the solar PV system as follows:
1.1 Calculate total Watt-hours per day for each appliance used. Add the Watt-hours
needed for all appliances together to get the total Watt-hours per day which must be
delivered to the appliances.
1.2 Calculate total Watt-hours per day needed from the PV modules. Solar panels
should produce 30% more energy that is required by the user. Watt – hour /day to be
generated by the solar panel is about 130% of the watt hour needed by the equipment in
the household Multiply the total appliances Watt-hours per day times 1.3 (the energy lost
in the system) to get the total Watt-hours per day which must be provided by the panels.

Example: A house has the following electrical appliance usage:

• One 18 Watt fluorescent lamp with electronic ballast used 4 hours per day.
• One 60 Watt fan used for 2 hours per day.
• One 75 Watt refrigerator that runs 24 hours per day with compressor run 12 hours and
off 12 hours.
The system will be powered by 12 Vdc, 110 Wp PV module.
Solution

Determine power consumption demands

Total appliance use = (18 W x 4 hours) + (60 W x 2 hours) + (75 W x 24 x 0.5 hours)
= 1,092 Wh/day

Total PV panels energy needed = 1,092 x 1.3 = 1,419.6 Wh/day.

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2. Size the PV modules

Different size of PV modules will produce different amount of power. The peak watt (Wp)
produced depends on size of the PV module and climate of site location.

We have to consider panel generation factor which is different in each site location. The
panel generation factor is 3.43 kWh/m2/day. To determine the sizing of PV modules, calculate
as follows:

2.1 Calculate the total Watt-peak rating needed for PV modules

Divide the total Watt-hours per day needed from the PV modules (from item 1.2) by panel
generation factor (3.43) to get the total Watt-peak rating needed for the PV panels needed
to operate the appliances.

Total Wp of PV panel capacity needed = 1,419.6 / 3.4 = 413.9 Wp

2.2 Calculate the number of PV panels for the system

Divide the answer obtained in item 2.1 by the rated output Watt-peak of the PV modules
available to you. Increase any fractional part of result to the next highest full number and
that will be the number of PV modules required.

Result of the calculation is the minimum number of PV panels. If more PV modules are
installed, the system will perform better and battery life will be improved. If fewer PV
modules are used, the system may not work at all during cloudy periods and battery life
will be shortened.

Number of PV panels needed = 413.9 / 110 = 3.76 modules

Actual requirement = 4 modules

So this system should be powered by at least 4 modules of 110 Wp PV module.

3.Inverter sizing

An inverter is used in the system where AC power output is needed. The input rating
of the inverter should never be lower than the total watt of appliances. The inverter
must have the same nominal voltage as your battery.
For stand-alone systems, the inverter must be large enough to handle the total amount
of Watts you will be using at one time. The inverter size should be 25-30% bigger than
total Watts of appliances.

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 In case of appliance type is motor or compressor then inverter size should be minimum
3 times the capacity of those appliances and must be added to the inverter capacity to
handle surge current during starting.
For grid tie systems or grid connected systems, the input rating of the inverter should
be same as PV array rating to allow for safe and efficient operation.

Total Watt of all appliances = 18 + 60 + 75 = 153 W

For safety, the inverter should be considered 25-30% bigger size.
The inverter size should be about 190 W or greater.

4. Battery sizing

The battery type recommended for using in solar PV system is deep cycle battery.
Deep cycle battery is specifically designed for to be discharged to low energy level
and rapid recharged or cycle charged and discharged day after day for years. The
battery should be large enough to store sufficient energy to operate the appliances at
night and cloudy days. To find out the size of battery, calculate as follows:

4.1 Calculate total Watt-hours per day used by appliances.

4.2 Divide the total Watt-hours per day used by 0.85 for battery loss.

4.3 Divide the answer obtained in item 4.2 by 0.6 for depth of discharge.

4.4 Divide the answer obtained in item 4.3 by the nominal battery voltage.

4.5 Multiply the answer obtained in item 4.4 with days of autonomy (the number of days
that you need the system to operate when there is no power produced by PV panels)
to get the required Ampere-hour capacity of deep-cycle battery.

Battery Capacity (Ah) = (Total Watt-hours per day used by appliances x Days of
autonomy) / (0.85 x 0.6 x nominal battery voltage)

Total appliances use = (18 W x 4 hours) + (60 W x 2 hours) + (75 W x 12 hours)

Nominal battery voltage = 12 V

Days of autonomy = 3 days

Battery capacity = [(18 W x 4 hours) + (60 W x 2 hours) + (75 W x 12 hours)] x 3

(0.85 x 0.6 x 12)

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 Total Ampere-hours required 535.29 Ah

So the battery should be rated 12 V 600 Ah for 3 day autonomy.

5. Solar charge controller sizing

The solar charge controller is typically rated against Amperage and Voltage capacities. Select
the solar charge controller to match the voltage of PV array and batteries and then identify
which type of solar charge controller is right for your application. Make sure that solar charge
controller has enough capacity to handle the current from PV array.

For the series charge controller type, the sizing of controller depends on the total PV input
current which is delivered to the controller and also depends on PV panel configuration (series
or parallel configuration).

According to standard practice, the sizing of solar charge controller is to take the short circuit
current (Isc) of the PV array, and multiply it by 1.3

Solar charge controller rating = Total short circuit current of PV array x 1.3

PV module specification

Pm = 110 Wp

Vm = 16.7 Vdc

Im = 6.6 A

Voc = 20.7 V

Isc = 7.5 A

Solar charge controller rating = (4 strings x 7.5 A) x 1.3 = 39 A

So the solar charge controller should be rated 40 A at 12 V or great er

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