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Introduction
Solar energy has been a part of peoples lives for thousands of years. It has been
used for drying clothes, food and other such things. The sun is also the life giver of
the world; the solar energy radiated through the atmosphere provides earth with
the energy necessary for survival. This energy is now used in a modern invention
called photovoltaic cells, which convert the suns energy into relative power. The
earth is rich in natural resources; however the earths natural resources are being
consumed at a tremendous rate. It will only be a matter of time before those
resources are depleted and the population is forced to consider otheralternatives. People can wait until every resource has been consumed and go
back to living the way mankind did over a century ago, or people can continue to
move forward and explore the possibilities of utilizing the power of something
that remains constantthe sun.
Solar water heating, where heat from the Sun is used to heat water in glass
panels on your roof. Water is pumped through pipes in the panel. The pipes are
painted black, so they get hotter when the Sun shines on them. The water is
pumped in at the bottom so that convection helps the flow of hot water out of
the top.
Photovoltaics are the direct conversion of light into electricity at the atomic level.
Some materials exhibit a property known as the photoelectric effect that causes
them to absorb photons of light and release electrons. When these free electrons
are captured, an electric current results that can be used as electricity. A number
of solar cells electrically connected to each other and mounted in a support
structure or frame is called a photovoltaic module. Modules are designed to
supply electricity at a certain voltage, such as a common 12 volts system. The
current produced is directly dependent on how much light strikes the module.
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Multiple modules can be wired together to form an array. In general, the larger
the area of a module or array, the more electricity that will be produced.
Photovoltaic modules and arrays produce direct-current (dc) electricity. They can
be connected in both series and parallel electrical arrangements to produce any
required voltage and current combination.
Activities Undertaken so far
1. Installation of LED lights in the hostel corridors.2. Proposal of a competition to motivate people to participate in sustainability
activities.
3. Survey undertaken to study the energy consumption in the hostel.Types of Solar Generation setups
1. Captive Photovoltaic2. Non-Captive Photovoltaic3. Concentrated solar thermal systems.For the purpose of generation of electrical requirements of a student hostel,
we have to use captive photovoltaic systems. The reason for this decision being
the large consumption of energy at nights.
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Captive Photovoltaic Systems
SCHEMATIC
The suns radiation generates electricity via the solar panels (photoelectric
effect) and a current constitutes and the voltages of the several panels get
added up in the combiner bus.The combiner bus is connected via a fuse (F)(to prevent damage due to
over-current) to the charge controller, which controls the flow of charge to
the battery while it charges. It is placed in order to ensure that the battery
doesnt over-charge, nor over-discharge and gets charged in the minimum
possible time, which in turn helps increase battery life by 2-3 years.
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The charge controller is connected to the battery again via a fuse and also ashunt (in the negative terminal) which just ensures minimal current is being
drawn for metering purposes. Now, the battery stores the energy
generated by the solar panels.
As most of the appliances or instruments nowadays are AC powered we
need to convert the DC current from the battery to the required AC voltage
and power ,and so the battery is connected to an inverter via a circuit
breaker(which is similar to a fuse ,except in the fact that it can be just
switched back to bring into use rather than replacing it).The inverter
converts the DC voltage to AC(~230 V) which is then given out to the AC
breaker panel or the appliances directly after ensuring all safety measures
have been covered.
NOTE : As Captive Solar PV systems are mostly off-grid, it is preferable to
have a back-up DC generator in case the PV system needs to be shut down
for maintenance. The connections linking it to the PV system are as shown
in the schematic. However, for our hostel design, we dont need the
generator as we have a grid connected system.
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Solar Modules:
A solar cell (also c
converts the energ
effect. Assemblies
solar panels.
Types of solar module
There are two type
Sizing of Solar Modul
The size of the
maximum. To esti
The number of
The insolation
Single Crys
lled photovoltaic cell) is a solid state
y of sunlight directly into electricity b
of cells are used to make solar modul
:
s of solar modules;
es:
anel generally determines the wattag
ate the size of your solar array, you'll
att-hours (wh) you plan to produce
alue at your location.
Solar Modules
Crystalline SiliconSolar Modules
talline Poly Crystalline
Thin Film
Solar Modules
device that
the photovoltaic
s, also known as
e it will put out at
need to know:
in one day.
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IMPORTANT NOTE:
We analyzed all the possibilities ( Mono and poly crystalline and thin film cells ) ,it was found that :
1>When we consider only cost, thin films are the most economical, for givenpower requirement.
2>On considering, other factors, such as installation cost, payback period andconstrained installation area, mono crystalline performs exceedingly well
compared to thin film and polycrystalline modules.
Solar panels mounting:
Solar panels are mounted on iron fixtures so that it can withstand wind and
weight of panels. The direction of panel is south facing for maximum power
tracking. The tilt angle of panels will be 13 to 25 from horizontal. This angle is
called axis tracking angle. You can set 40 degree tracking angle in the month of
December and 10 degree in the month of June. In the month of September &
March it will be 25 degree.
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CHARGE CONTROLLERS
There are basically two types of charge controllers existing today in terms offunctionality:
1.) PWM charge controllers:
These kind of charge controllers operate by sending out pulses of charge
which helps in uniform distribution of the charges on the plates of battery.
These modulate the pulse widths and slopes of the voltage and current levels
and also their rate of change. They operate in three phases :
i. Bulk phase: During the Bulk phase of the charge cycle, the voltagegradually rises to the Bulk level (usually 14.4 to 14.6 volts) while the
batteries draw maximum current. When Bulk level voltage is reached the
absorption stage begins.
ii. Absorption phase: During this phase the voltage is maintained at Bulkvoltage level for specified times (usually an hour) while the current
gradually tapers off as the batteries charge up.
iii. Float phase: After the absorption time passes the voltage is lowered tofloat level (usually 13.4 to 13.7 volts) and the batteries draw a small
maintenance current until the next cycle.
2.) MPPT charge controllers: They constantly track and maintain the
optimum voltage and current to charge the battery. They match the output of
the solar panels to the battery voltage to insure maximum charge (amps).
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For example: even though your solar panel is rated at 100 watts, you won't get
the full 100 watts unless the battery is at optimum voltage.
If your batteries are low at say 12.4 volts, then your 100 watt solar panel rated at
6 amps at 16.5 volts (6 amps times 16.5 volts = 100 watts) will only charge at 6
amps times 12.4 volts or just 75 watts. You just lost 25% of your capacity!
The MPPT controller compensates for the lower battery voltage by delivering
closer to 8 amps into the 12.4 volt battery maintaining the full power of the 100
watt solar panel! 100 watts = 12.4 volts times 8 amps
Comparison of PWM and MPPT charge controllers:
PWM MPPT
Capacity a)Available only up to 60 Amps
only
b)Can take only certain input
voltages :12V,24V,48V
c)Limits solar panel output
voltage
a) Available up to 80 Amps
b) Can take a varying range of
input voltages and hence,
reduces losses in transmission
and provides flexibility in solar
module configuration.
Cost Inexpensive;
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outperform PWM charge controllers in terms of the operating efficiency and
range of operation.
If Wp is the peak power of the solar modules that the MPPT chargecontroller handles, then the input current to the MPPT controller would be
Wp divided by nominal voltage of battery bank. Then, the MPPT charge
controller should have at least 1.2 times this value as its current input
capacity.
The input voltage of the MPPT controller should be big enough to handlethe open circuit voltages of the modules in series.
MPPT charge controllers(Major companies)
Company I Cost 12 V 24V 48 V
Morning star 60 A 565.50 $ 800 W 1600 W 3200 W
Outback 60 A 597.72 $ 900 W 1800 W 3600 W
Solar converters 60 A 581.45 $ 48 W 96 W 192 W
Xantrex 60 A 537.00 $ 720 W 1440 W 2280 W
Maximum Battery current = I; Nominal maximum solar input = V; Capacity = C
For a sample analysis ,let us consider an MPPT and a PWM charge controller from
xantrex:
For P power output from the solar panels,
No.of MPPT charge controllers=P/(110*60) {values from datasheet Xantrex
XW Solar Charge Controller MPPT 865-1030 }
Total cost =Cmppt=P*537/(110*60)=0.081*P
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BATTERIES
Types of Batteries:
Sl. No. Flooded Sealed
AGM Gel
1.Cost cost-effectiveness,
least cost per amp hour
Nearly three
times the cost
of flooded
batteries
2-3 times the
cost of
flooded
batteries
2.Maintenance require maintenance No/negligible maintenance
required
3.Size and placement Need ventilation ;
Mostly need to be keptoutdoors which hinders
working at ambient
temperature
sealed batteries conform to
situations with spaceconstraints that require you to
store your batteries in unusual
orientations or where venting
is not possible
4.Transportation classed under hazardous
materials rules, which restrict
shipping options
increased ease of
transportation
5.Life longest life less than a 2% self-discharge
rate during transport and
storage
3-7 yearsIndustrial(Traction):20 years
Industrial(Stationary):20 years
10 years 8 years
% of electrical power lost
as heat
15-20% 4% 10-16%
http://www.vonwentzel.net/Battery/01.Type/index.html
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INVERTERS:
An inverter is used in the system where AC power output is needed.
There are basically three types of inverters on the basis of the output that they
give :
Parameter\Type Square Wave Power
Inverter
Modified Sine Wave
Power Inverters
True Sine Wave Power
Inverters
Cost Least Expensive Most popular and
economical type of
power inverter
Most expensive and
best quality;
Twice the price of
modified sine wave
power inverters ofsame capcity
,generally.
Output quality The square wave it
produces is inefficient
and is hard on many
types of equipment.
It produces an AC
waveform somewhere
between a square
wave and a pure sine
wave.(Some
instruments like
motors consume more
than 30% their normal
consumption and alsomake a buzzing sound.)
It produces an AC
waveform somewhere
between a square
wave and a pure sine
wave
Capacity 500 watts or less
Usability Not suitable for
captive systems;
Cabin systems or
mobile applications
Work well in all but the
most demanding
applications and even
most computers work
well;
appliances that use
motor speed controls
or that use timers may
not work quite right
It will run practically
any type of AC
equipment
Merits Very economical and
reliable
Most appliances run
more efficiently and
use less power with a
True Sine Wave
inverter as opposed to
a Modified Sine Wave
power inverter.
Life 6 months-1 year 1-2 years 1-2 years
.
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Roof top area analysis:-
Total available area available (aftertaking out the shadowed regions)
Region Area
A 93 x 5
B 93 x 5
C 30.36 x 8
AERIAL VIEW OF ALAKANANDA HOSTEL
A
C
B
SOLAR PANELS
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Compiled data from s
The data from the survey
TYPE
SINGLE ROOMS
TRIPLE ROOMS
LED LIGHTS
DISPENSER
PC
WASHING MASHINE
TOTAL
3
Ene
urvey conducted in the hostel
has been compiled into a table :
ENERGY CONSUMPTION
639010
81645
9720
28800
3750
7000
769925
15%
51%
%
2%
gy Consumption by various
Appliances
TubeLight Fan Comp Other Devices
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3D VIEW OF THE HOSTEL
SOLAR PANELBATTERY
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Design of system:
1. Solar Panels
Model: Canadian Solar CSI CS6P-235
Peak Wattage =235 W
Module Area =1.61 m2
Therefore, No. of modules that can be installed = (2 x 93x 5 + 30.36 x
8)/1.61=728
Total Power generated = 728*235=171.08 kW
Taking output efficiency to be 95%,
Actual power generated=0.95*171.08=163 kW
Cost of each module = Rs. 28440
Total cost of modules =28440 x 728 =Rs.20,704,320.
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Power Conditioning Unit Sizing
It was observed that instead of having separately installed chargecontrollers and inverters, it was more economical and more robust in
design to have a Power conditioning unit .
It also allows the battery to charge from the grid power even when there isless power generation from the PV modules than required.
Amongst the power conditioning units that we analyzed we found, the 6KW Su-
KAM PCU 6K96 model to be best suited for our purpose. The sizing for the same
has been given below:
The PCU has a charge controller (PWM) which chargers and maintains the health
of the battery. It also has a pure sine wave inverter, which converts the DC output
of the batteries to grid A/C voltage (239 VAC). It also has a grid charger, which
provides the facility of directly utilizing the DC power generated by the solar
panels directly by converting it into 230 VAC and combining with grid supply. It
also has the required safety instrumentations, making them an ideal choice for
the required charge.
1>System Capacity = 171. 08 KW.2>Hence number of PCUs required is (171.08/6)= 29 units.3>No of solar panels approximately by each CPU = 728 / 29= 25.
From the data sheet of Canadian Solar CSI CS6P-235 solar module,
Operating Voltage = 36 V
Short Circuit Current = Isc
= 8.46 Amp.
Each of the PCUs can handle a maximum 0f 25V,
Therefore, No. of solar panel parallel module to be connected to a
PCU=1/{36/25}=0.5
This means that 2 PCUs are required for a solar panel array consisting of only
single modules in parallel.
Therefore, No. of solar panels in parallel= 50
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(as two PCUs need to handle 50 panels approximately and there are not more
than 1 solar panel in each parallel branch)
Current generated = 50 * 8.46 = 423A
This is within the maximum value that can be handled by an individual PCU (
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Battery sizing
We have taken the Su-KAM SBT 1800 battery backup as our module for building
the battery banks.
Total energy consumption per day =E =720.66 kWhr.
No. of days of autonomy of the battery=N= 1 day
Depth of discharge of battery =DoD =80%
Derating factor at 27 deg.C= d =1
Therefore, battery bank capacity = (E*N*d)/DoD=901 kWhr
Nominal input voltage for the PCU inverter=Nominal output voltage of battery
bank=Vn=96V
Approximate energy handled by a single PCU =901/29=31.07 kWhr.
Therefore, Amp-hour of battery bank connected to one PCU = 31070/96=
323.65Ahr
The Amp hour capacity of SBT1800 is 150 Ahr , so ,
No. of parallel chains in battery bank = {323.65/180}= 2
Nominal battery voltage of SBT1800 = 12 V
Now,the no. modules in every parallel chain =Vn/12=96/12=8
Total no. of batteries required = 8*2*29 = 46
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SP
SP
SP
SP
SP
SP
SP
P.C.U. P.C.U.
B B B B B B B B
B B B B B B B B
UPTO 50 UNITS
GRID
TOWARDS LOAD
NEARLY 15 SUCHMODULES
SCHEMATIC DIAGRAM OF SYSTEM
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Cost Analysis
Cost of Essential Components
Module Cost of each
module(Rs.)
No. of module Total cost(Rs.)
Solar panel 24,900 728 1,81,27,200
PCU 50,000 29 14,50,000
Battery 17100 464 79,34,400Total 2,75,11,600
Cost of Ancillary Components (based on Projected values per watt of
generated power)
Component Cost per watt(Rs.) Total Cost
Mounting
Structure
12.8 21.99 lakhs
Cables and
Transformers
7.1 12. 19 lakhs
Civil and Technical
Works
5.4 9.23 lakhs
Total 43.41 lakhs
Total cost incurred Rs 3.19 crores
Cost of electricity per unit = Rs.4.1
Savings per day = (4 * 171.08*4.35) = Rs.2976.8
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Savings per year= 2976.8 * 365 = Rs.10,86,530
Break-even time = 3.19 crores/0.108653= 29.31 years
NOTE: This system of cost analysis is inadequate for the given setup, as it doesnt
consider the life of the various components involved nor the efficiency drop over
this period of time. For a Solar Panel, the efficiency of panel drops to 90 % after
10 years and to 80 % after 10 more years. This is not the case for the PCU and the
batteries as they have to be replaced after a period of 10 years.
However, The Ministry of New and Renewable energy , Government of India
pays Rs.7 per unit of power generated by the help of rooftop solar photovoltaic
systems
Quote: a tariff of Rs. 7/- per unit for solar power generation projects with an
annual escalation of 5%. (Rs 8.09/KWh for 2009-10)
with an annual escalation varying from 3% to 5% on yearly basis up to 5years ( Rs 4.10/KWh for 2009-10)Hence the money earned by the hostel from such an arrangement will be equal to
a.)Without considering the annual escalation:
Savings per day = (8.09+4.1)*171.08*4.35=Rs.9146.19
Savings per year=9146.19*365=Rs.33,38,359
Therefore, the payback period =3.19 crores / 33,38,359=9.55 years
b.)After considering the annual escalation:
The payback period turns out to be 7.65 years.
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Carbon Footprint
Carbon dioxide released for one kilowatt-hour of electricity produced from Coal: 909 gm
Carbon dioxide released for one kilowatt-hour of electricity produced from PV: 105 gm
Reduction in carbon dioxide production per kWh: 804 gm
Total reduction in carbon dioxide production per year: (804*171.08*4.35*365) gm
218.392 tonnes of CO2.
Hence we can reduce the emission of carbon-di-oxide significantly.
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OPTIONAL COMPONENTS (suggestions to improve
efficiency and reliability)
TRACKERS AND SENSORS
There are two types of tracking systems:
Single axis tracking system.
Double axis tracking system.
Table 1:
Type Electricity production CostSingle axis tracking system Increases 20-30% relative to
fixed
Only 10-15% higher than fixed
Double axis tracking system Increases 30-40% relative to
fixed
Only 15-20% higher than fixed
systems
Source: http://www.rimlifegreentech.com/products/tracker/why.htm
METERS AND SHUNTS
Having a meter, helps in data-logging and monitoring the state of your system.This helps inclaiming warranties and also early fault detection.
Shunts are introduced if there are chances of electrical interference ,like in grid-connected
or Power generator connected systems, or to introduce an added tier of safety when it
comes to electrical discharges from batteries or other components where it is introduced.
It is basically a low-resistance path which ensures that current only flows through it and no
other crossing wires.
AC GENERATOR (BACK UP)If your system is off-grid, it is wise to have a back up AC generator, in cases of system failure or
shutdown for maintenance. It can be any kind of DC generator, linked to the inverter which then can
be used as a stand-in system for the critical loads.
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BREAKTHROUGHS
Sl.No.
Component PossibleTechnology
breakthrough
Description/Reference
1 Solar Modules 1.)SILICON
BLADES:
1.) Novel silicon micro wires can harvest nearly as much
light as traditional photovoltaic wafers, with just one
percent of the total silicon.
http://www.scientificamerican.com/article.cfm?id=phot
ovoltaic-breakthroughs-brighten-outlook-for-cheap-
solar-power
2 Charge
Controller
1.)SMPC(Switch
ed Mode PowerConversion)
This is a mode of charging being considered for
increasing power quality to batteries in order todecrease fluctuations to it and hence,reduce the
damage to battery
Efforts are being made to increase efficiencies of power
conversion though there doesnt seem to be any more
significant difference from MPPT charge controllers.
3 Batteries 1.)Ceramatec
battery
2.)Electrolysis
Breakthrough
for Solar
Storage
1.) Ceramatec says its new generation of battery would
deliver a continuous flow of 5kW of electricity over four
hours. And these batteries are expected to withstand
daily discharge/recharge cycles over 10 years (3,650
times). The batteries would hopefully sell for around
USD$2,000, which is less than 3c per kWh over the
battery's life. Conventional power from the grid typically
costs around 8c per kWh and continues to rise.
http://solarseeds.blogspot.com/2010/07/battery-
breakthrough-may-trigger-off.html
2.)http://peswiki.com/index.php/Directory:MIT:Daniel_
Nocera:Catalytic_Electrolysis#Company:
4 Inverters 1.)XPX
Technology
1.) The XPX technology, embodied in a printed circuit
board (PCB), extracts significantly more electrical energy
from any PV solar media through a combination of
patent pending design and proprietary algorithms
http://www.eosrenewabletech.com/
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EMERGING TRENDS TO REDUCE OFF-GRID
CAPTIVE SOLAR PV COSTSi. Various subsidies are being given by government in order to promote the use and installation of
captive solar PV plants in India.
ii. Batteries with longer life period are being developed in order to match their life with that ofsolar panels in order to save on replacement and maintenance costs.
iii. Stress is being laid on increased production and usage of Solar PV modules in order to bringdown the costs of the manufacturing processes. It is estimated that these costs can be brought
down by 50% with a 25% increase in solar PV consumption.
iv. The use of thin film is supposed to bring the cost of PV systems (although our analysis showednot much difference and with constrained area , it is always better to use mono crystalline solarpanels).
v. Sealed batteries are being preferred over flooded ones as the transportation costs for these aremuch less than the flooded batteries as they are not hazardous
Implementation
Currently, work is underway to supply the common room , the office, the corridors and the tech
room with electricity from solar power alone. Our hostel warden , Prof. Srinivas Reddy , has attracted
sponsors willing to invest for this issue.
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