A case study of Solar Powered Base stations - Simple search234252/FULLTEXT01.pdf · A Case Study of Solar Powered Cellular Base ... of Solar power PV cell construction, ... are thin

A Case Study of Solar Powered Cellular Base Stations

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DEPARTMENT OF TECHNOLOGY


By

Geetha Pande

September 2009

Master’s Thesis in Energy Systems

Supervisor/Examiner: Dr. Taghi Karimpanah


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ACKNOWLEDGEMENTS

First of all, I would like to thank my supervisor and examiner Dr.Taghi Karimpanah

for his able guidance and support to perform the thesis work. I am also grateful to Ulf

Larsson, head of Master of Science program, for providing me the opportunity to

perform the thesis.

I would also like to thanks Dalarna university library staff for providing me required

articles for the thesis work. Apart from this I am also grateful to all those who directly

or indirectly contributed to the completion of my thesis work.

Finally, I can’t forget my family members in India and friends for their

encouragement and support during my stay abroad.


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ABSTRACT

Green power, environment protection and emission reduction are key factors

nowadays in the telecom industry. Balancing of these modes while reducing the

capital and operational costs are of prime importance. Cost efficient and reliable

supply of electricity for mobile phone base stations must be ensured while expanding

the mobile phone network. In this context, solar energy, using sophisticated

photovoltaic cell technology, is considered to be playing very important role.

Currently, companies such as ABI research, Flexenclosure AB, etc believe that the

solar powered cellular base stations are capable of transforming the telecom industry

into one of the greenest in the world. Hence, lot of research is in progress across the

globe to use solar power in telecom industry.

In this thesis work, the significance of solar power as renewable energy source for

cellular base stations is reviewed. Moreover, simulation software called PVSYST4.37

is used not only to obtain an estimate of the cost of generation of solar power for

cellular base stations but also to obtain the system parameters such as the number of

modules, batteries and inverters needed for designing the solar powered cellular base

stations. The simulations were carried out for the Grid-Connected and the Stand-

Alone solar power systems by considering the cases of New Delhi, India and

Stockholm, Sweden.

The PVSYST4.37 simulation results shows that the power generation costs for the

grid connected solar powered system is less compare to standalone solar powered

system both in New Delhi, India as well as in Stockholm, Sweden.


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INDEX

CHAPTER 1

1.1 INTRODUCTION...................................................................................................5

1.2 THESIS OBJECTIVE.............................................................................................6

1.3 ORGANISATION OF THESIS..............................................................................6

CHAPTER2

SOLAR POWER AS RENEWABLE ENERGY

2.1Introduction...............................................................................................................7

2.2Solar Photo Voltaic(PV) Technologies.....................................................................8

2.3Construction of PV cell.............................................................................................8

2.2.2Material used for PV cell........................................................................................9

2.2.3PV array Design and Sun tracking.......................................................................10

2.2.4Types of Solar Powered Systems.........................................................................10

2.3Solar power as Renewable energy in India.............................................................12

CHAPTER3

SOLAR POWER FOR CELLULAR BASE STATIONS

3.1Introduction............................................................................................................13

3.2Power requirement of cellular Base Stations.........................................................14

CHAPTER4

Simulation Using PVSYST 4 Software......................................................................15

CHAPTER5

Simulation Results and Analysis.................................................................................16

CHAPTER6

CONCLUSIONS AND FUTUREWORK....................................................................39

REFERENCES.............................................................................................................40


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CHAPTER 1

1.1 Introduction

Now a day’s developing countries across Asia and Africa are hit with the serious

energy crisis. Fulfilling the power demand of the people for the basic necessities itself

is much a bothered situation. Hence, people started looking towards permanent and

imperishable sources of energy called renewable sources of energy such as solar and

wind energy [1]. The positive aspect of use of renewable energy sources in

developing countries is that they are available in plenty and also pollution free [2].The

cost efficient production of energy using renewable sources is still a major problem in

developing countries. Hence, it is difficult to replace immediately the existing

traditional energy resources with the renewable sources.

Due to the reach of mobile telephony among the people in remote villages, the service

providers are pressured for finding a working solution to the energy crisis. Thus the

provision to power the base stations for mobile operators with renewable energy is

gaining importance steeply.

Traditional Global System for Mobile communications (GSM) [3] equipment is

targeted to the urban environments only. Vendors and operators of the GSM

equipment have been facing difficulty to meet certain challenges in remote rural areas

such as it costs much, expensive to run, uses much power and is difficult in deploying

in rural areas with limited electricity supply, lack of skilled engineers and poor roads.

Hence it is very important to take into consideration all these problems before

deploying solar powered base stations [1].

Before the actual deployment of the solar powered base stations it is very essential to

get an estimate of not only the number of the photovoltaic (PV) cells [4], inverters [3],

batteries and generators required but also the cost of production of energy per unit. In

order to do so it is always suggested to design and simulate the deployable solar

powered base stations using software such as PVSYST4.37 [6]. PVSYST software

has used to study the requirement of cooling demand [5] in solar powered base

stations in developing countries like Morocco. Moreover, this software can be used to

design and simulate the deployment of solar powered base stations in countries like

India, Sweden or any country by considering geographical and other design

parameters for solar power. Hence, the use of PVSYST software will enable to design

and simulate cost efficient deployable solar powered base stations.


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1.2 Thesis Objectives:

The objectives of this thesis work is to

Study the significance of Solar Power as renewable energy

Design and analyse the use of Solar power for cellular base stations using

PVSYST4 simulation software

Design and Costs analysis for implementation of Solar powered cellular base

stations in New Delhi, India and Stockholm, Sweden using PVSYST4

simulation software.

Comparison of Simulation results of New Delhi, India and Stockholm,

Sweden.

1.3 Organisation of the Thesis

The entire thesis is organised as follows:

Chapter2 gives an overview about the significance of Solar power, working principle

of Solar power PV cell construction, material used for PV cell, different types of Solar

powering systems and Solar power in India.

Chapter3 describes Solar power for base stations and power needed for base stations.

Chapter4 gives description of basic knowledge of PVSYST software.

Chapter5 describes simulation results for grid connected system and stand alone

system for New Delhi (India), Stockholm (Sweden).

Chapter6 describes conclusions and future work to be done.

References are numbered continuously and listed at the end of the thesis.


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CHAPTER 2

Solar Power as Renewable Energy

2.1 Introduction

Currently, our society’s energy demands are fulfilled using conventional energy

sources such as water, coal, oil, natural gases or uranium. The production of energy

using these conventional sources is a cause of concern of many environmentalists.

The major problems can be quoted as follows:

1. It causes atmospheric pollution, climate changes or nuclear waste and thus can

endanger our living condition on the earth.

2. The extensive use of these limited conventional energy sources may result in

complete depletion of energy sources and hence, there is no guarantee of

energy supply for future.

The above mentioned problems can be solved by using renewable energy sources

such as Sun and Wind.The renewable energy sources use natural resources and do not

cause any pollution. Hence they are termed as Green Energy sources[2].Moreover,

these renewable energy sources only use a small part of the flow that is why they

cannot damage natural surrounding and also do have the risk of being depleted.

Sun is considered as a potential source of renewable energy. Hence, the use of solar

energy for applications such as generation of electricity, running of automobiles, etc is

becoming popular. The generation of electricity using solar energy is done using

photovoltaic technology (4).The term ‘Photovoltaic’ is a combination of two words.

They are ‘photo’ meaning ‘light’ and ‘voltaic’ meaning electricity. Generally,

photovoltaic is abbreviated as ‘PV’. The solar PV cell works on the principle of

conversion of sun light into electricity. For generation of electricity in large amounts,

an array of solar PV cells are either connected in series or parallel. Despite high cost

of PV cells, solar power is considered as an alternative source of energy in many parts

of the world.

The solar energy incident on the surface of the earth is different in different parts of

the world. Hence, it is not possible to install same solar PV plants in all parts of the

world. Before making a decision about the installation of a solar PV plant, it is

essential to see the solar energy map. Solar energy map, as shown in figure (1), gives

information about the solar radiation intensity in different parts of the world. As

shown in figure (1) different parts of the world are classified into 7 different regions

based on the annual average solar irradiance kWh/square meter. As it can be seen

from solar energy map that solar energy can be a very good source of energy in

Tropical countries like India compare to the Nordic countries such as Sweden.


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Figure 1: Solar Energy Map [7]

2.2 Solar Photovoltaic (PV) Technologies:

Solar PV technology is about generation of electricity from sunlight. This technology

involves construction of PV cell, materials used for PV cell construction and the

design of PV cell array.

2.2.1 Construction of PV Cell:

Sunlight can be converted to electricity by PV cell. There will be no air or water

pollution occurs. PV cells consist of two semiconductor layers. The two layers are

charged oppositely. One layer is having positive charge and other is negative charge .

When light falls on the cell semiconductors absorb photon from light. When electrons

travel from negative layer to positive layer electricity is produced.

Construction of PV cell can be compared with diode with PN junction .The junction

absorbs the energy of light. Silicon system is used to transfer electron –proton from

the photons .In electric load electric load electron flow in the circuit is used [4].

The basic circuit of PV effect converts the photon energy into voltage across the pn

junction is shown in figure (2)

Figure 2. Basic construction of PV cell in daily life [8]


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Figure 3.Conversion of photon energy into voltage across the pn

Junction by PV [4]

2.2.2 Material Used for PV cell:

The capital cost per watt and conversion efficiency of solar energy depends on PV

cell. So it is having more importance in solar energy system. The economic

competiveness of PV electricity depends on capital cost and conversion

efficiency .The following are the different types of materials used for PV cells. They

are: Single-Crystalline Silicon, Polycrystalline and semi crystalline Silicon, Thin –

Film Cell, Amorphous Silicon, Spheral Cell, Conctrate Cell and Multifunction Cell.

Single crystalline Silicon: This is commonly used cell material. The conversion

efficiency is 14% to 18%.The cost of this material is $20 to $25 per pound.

Polycrystalline and Semi crystalline Silicon: The manufacturing method of this

material is quick and cheap. The cost is low due to low conversion efficiency. It is

both in thick as well as thin film.

Thin film cell: This is the new type upcoming in the market. Copper indium

dieselinide (CuInSe2or CIS) ,cadmium telluride (CdTe),and gallium arsenide(GaAs)

are thin film materials whose thickness is very less that is few micrometers. As less

material is used in the cell the cost of power is less. Cadmium telluride is the low cost

thin film material.

light

Electric load Pcontact

Current direction

ncontactt


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Amorphous Silicon: It is only 2-um-thick.It uses only 1%of the material comparing

with crystalline silicon. The efficiency is only 50percent of the crystalline silicon and

cost is less.

Spheral cell: The cost of this material is $1 per pound. Thickness is 2um.The

conversion efficiency is high that is 16 to 20%

Concentrator Cell: It is focusing on small area with high efficiency (37%).The

disadvantage with this is that it requires focusing optics.

Multifunction Cell: In this electricity is generated by using red and infrared light. Blue

and ultraviolet is not used for the electricity. It has high efficiency(34%) and cost is

also high[4].

2.2.3 PV Array Design and Sun tracking

The factors that influence the electrical design of the solar photovoltaic array are the

sun intensity and the sun angle

Sun Intensity:

The photo current is highest during sunny day. When sunlight is less power goes

down as shown in fig. When sun intensity is less there is decrease in circuit current.

For different sun intensity ,the efficiency is same.

I

Higher sun intensity

Lower sun intensity

V

Figure4. Power change in different sun intensity [4]

Sun angle:

The cell output current is expressed as 𝐼 = 𝐼𝑂 cos 𝜃 ,where I is the current with

vertical sun impinging, and theta is the angle to the vertical position. This law is

applied when sun angle is 0 to 50 degrees. When angle is more than 50 degrees there

is decrease in relative current. There will be no power generation when angle is more

than 85degrees.

Sun Track: When PV module is installed on tracker with an actuator which follows

the sun more energy is collected .There are 2 types of trackers.

1. One axis tracker

2. Two axis tracker[4]

2.2.4 Types of Solar powered systems:

Grid Connected Systems

Grid connected system have solar panel ,mounting for panels, wiring, inverter. When

rays from sun falls on solar panels DC electricity is produced. This DC passes to


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inverter where the voltage is converted to AC (this is for base stations).Then surplus

electricity goes to mains grid.

Figure5. Block diagram of grid connected PV system [4]

Stand Alone Systems

PV stand alone system have the following componets.1.Solar array

2.Batteries3.Inverter4.Switches.The power from PV rays passes to batteries, from

batteries it passes to inverter where DC is converted to AC.From inverter the

power passes to base station. The PV standalone system is shown as follows.

solar arrays (1,2) Batteries AC loads

Figure6. PV standalone power system with battery (4)

Stand Alone Hybrid System

This system does not depend on single power source. Multiple power sources

are used .There are two types of stand alone hybrid systems. Standalone

hybrid system with diesel. Standalone hybrid system with fuel [4].

Hybrid system with diesel

As diesel is more advantageous for providing power so in hybrids diesel

generator are used with PV or wind. In some case battery also used with diesel.

Battery is used when there is daily fluctuations in load and diesel generator is

used for long term fluctuations [12].

Inverter

Switch

and Fuse

SOLAR

POWER

INVERT

ER

MAIN

GRID SUN

USER

(LOAD)


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Hybrid with fuel cell

In this system in place of diesel engine fuel cell is used in urban areas.

Because diesel emits high carbon. So it is not advisable to use diesel engine.

In fuel cell emissions are veryless.The emissions are 25gm per MWh. In fuel

cell electricity is produced by chemical reaction which does not change

electrode and electrolyte material. The construction of fuel cell is shown in fig.

Electricity is generated when Hydrogen and oxygen combined from air.

Figure7. Block diagram of hybrid standalone solar system [5]

2.3 Solar power as renewable energy in India: In India renewable energy is produced by using different sources such as solar power,

biomass and wind power. The total renewable energy produced is (9220 )4.As there is

possibility of diminishing conventional energy sources so there is necessity use

renewable energy sources such as wind and solar. In India use of Solar power is less

than 1 million tone(mtoe)[11].

The solar Isolation in India is 1700-2500 kwh/kwp per year. Solar radiation is 4 to7

kwh/m2/day. The subsidies are given to the companies which produce power from

solar power. For selling solar energy products Ministry of Renewable energy is

helping some organizations to open solar shops .So that everybody can buy solar

products. The shops are named as Akshay Urja Shops. Loans are provided for setting

up this kind of shops. In India no net metering is there[9].

VNL is the company in India which is providing power for GSM base station from

solar power. The power used is 150W.Flat surface collectors are used for capturing

solar power.VNL is the company that is using renewable energies for GSM base

stations. First option is solar energy and second is wind power .Using renewable

energy sources for power is economical..VNL is focusing main on rural areas in India

[10].

PV

array

Backup

generato

r,fuelcell

Battery

Capacito

r

End

user

End

user

Cooler

Inverter


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CHAPTER 3

Solar Power for Cellular Base stations

3.1 Introduction

A cellular base station is a wireless system and makes use of microwave radio

communication technology. The base station acts as an interface between either two

mobile phones or between a mobile phone and a fixed phone. Generally these base

stations are made up of several antennas mounted on a metallic tower and a house of

electronics at the base of the tower as shown in Fig (8).The antennas are connected to

the base with cables.

The base station antennas are used for transmitting as well as receiving the radio

signals to and fro from mobile phones. Generally, these antennas are mounted on the

top of the tower so that obstacles such as trees, high rise buildings, hills, etc should

not obstruct the radio signals. Usually, three antennas are mounted on the top of the

tower to cover the specified region. Among three antennas two are used for receiving

and one is for transmitting. Though these antennas are operated at different

frequencies they are well separated from each other to avoid interference of emitted

power from each other.

At the bottom of the tower a small house of electronic circuits comprising of power

amplifiers, used to generate strong signals and this power amplifiers are connected to

mounted antennas with long cables. The base station also has supporting components

such as base station controllers using computers and AC/DC rectifiers to convert AC

power to DC power. Many base stations have a DC power back up system in the form

of batteries connected either in series or parallel and these batteries supply power to

the base station during blackout or power failure.

The area covered by base station signals is called cell [3].Based on the amount of area

covered the base stations can be classified as Macro cell base station, Micro cell base

station, Pico cell station and Femto cell base station. Femto cells cover the smallest

area and they are deployed in a room. Pico cells are deployed in offices or shopping

malls and they cover more area than femto cells. Micro cells can cover blocks of

buildings in an urban locality and cover area more than pico cells. Macro cells cover

the largest area among all the cells and generally they are deployed in rural areas or

on high ways.

3.2 Power requirements of Cellular Base Stations

The power needed for the radio base station depends on the number of calls at that

time. For different regions traffic is different. During night time signal traffic is low


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when compared to day time. So it is difficult to find actual power needed for the base

station. The power needed for the radio base station (RBS2202 in for one cabinet)

Figure.8 Illustration of solar powered cellular base station [1, 14]

varies between 800w to 3200wattb [5].The average power for whole year is 1400watt

for a Macro base station. The equivalent average power in MWh per year for a macro

base station can be computed as 12.3 MWh. If the site container contains more than

one cabinet then the power needed may be more. As in RBS (radio base station) there

are air conditioner and heat exchanger, electronics also present. So the power is used

by all the components. The highest amount of power needed for the by macro RBS IS

3200W.Micro base station needs 110 watts. If minilink is there the power is

150watts.RBS and electrical exchanges are connected by minilink [5].


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CHAPTER 4

Simulation Using PVSYST4 Software

Photovoltaic system (PVSYST) is a software used for study of photovoltaic system.

This software is used for grid connected, standalone, pumping, DC grid connected

system. This software is mostly used by engineers, architectures, researchers and

educational institutes. It is developed by University of Geneva ,Switzerland.

It is divided into 3 parts and the front page of the software is shown in figure (9).

1. Preliminary design

2. Project design

3. Tools

Figure9. Front page of PVSYST4.0 software [6]

Preliminary design:

In this presizing is done for grid connected, standalone, pumping system. This is

used for initial designing of PV system.

Project Design: In this stage simulation is done using some of the data from preliminary design. In

this we get detailed report with results.

Tools:

In this various solar tools such as solar geometry, Mateo etc. [6] are available for

the project design.


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CHAPTER 5

Simulation Results and Analysis

5.1 Solar Powered Cellular Base Station for New Delhi, India:


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5.1.1 Grid Connected Systems for New Delhi:

Figure10.Design of Grid connected solar powered base station [6]

Preliminary Design (Presizing) results (New Delhi):

In this preliminary design location (New Delhi, India)is selected to which simulation

is to be performed. So when location is selected longitude and latitude of that location

are automatically shown. For the preliminary design the module used is standard.

The PV cells are monocrystalline.The nominal power is 8Kwp and collector area is

67m2.Total investment cost is 60553 euro for 14.1MWh and energy price is

0.39eur/Kwh.

PV

ARR

AY

INVERTE

R

BASE

STATION


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Project Design results (New Delhi):

In this data from preliminary design is used. The estimate of the cost .39euro obtained

by preliminary design is set as one of the project goals and other project goal is power

required that is 12.3Mwh/year by base station.

In this PV module HIT and model HP-1317 manufactured by Sanyo is used. Total

number of modules used are 960.Array total nominal power is 13Kwp with module

area of 121m2.The inverter used is Sunny boy SWR 1100u.Total of 10 inverters used.

Total investment cost is 102624euro and energy cost is .39euro/Kwh and performance

ratio is 75.1%.


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20


21


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5.1.2 Standalone Systems for New Delhi:

Fig(11) Design of Standalone solar powered base station[6]

Preliminary Design (Presizing) results (New Delhi)

In this When location is selected latitude 28.8N and longitude 77.2E is automatically

defined. The nominal power of array is 7.8Kwp.Total investment is 88624euro and

energy price is 1.24Eur/KWh.

PV

array

Backup

generato

r,fuelcell

Battery

Capacito

r

End

user

Base

Station

Cooler

Inverter


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Project Design results

In this Si –mono PV module of model MW870 is taken. Manufacturer is Eni

Technologies .The total number of modules are 112 with a nominal power of 7.8kwp.

and module area is 75.5 m2.Total investment is 32215euro,total yearly cost is

15469euro/year, energy cost is 1.24euro/kWh.In this TXE1700/OPzs1500 model

battery is used. Battery pack contains 48 units. In this 37 fluorescent lamps of 18

w/amp,100TV,magnetoscope/pc are used.1fridge is used. Performance ratio is 66.4%.


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25


26


27


28


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5.2 Solar Powered Cellular Base Station for Stockholm, Sweden:

5.2.1 Grid Connected Systems for Stockholm:

Preliminary Design (Presizing) results:

In this presizing when location Stockholm(Sweden) is selected latitude 59.1N

longitude 17.6E is automatically defined. Tilt angle of 30deg and azimuth is 0 deg is

taken.


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In this standard module of monocrystalline cells are used. Nominal power is

13.1KWp and collector area is 109m2.The total investment cost is 89606 eur and

energy price is 0.65Eur/kwh.Which is more when comparable to India.


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Project design is performed based on the data obtained from preliminary design. In

this HIT PV module of model HIP -1317 is used. Total 960 modules with a nominal

power of 13kwp is used. Array area is 121m2.One inverter of model EN18 is used.

Performance ratio is 77.6%.Total investment with taxes is 94772euro and energy cost

is 0.66euro/kWh.Without taxes total investment is 78977euro.


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33


34

5.2.2 Standalone Systems for Stockholm

Preliminary Design (Presizing) results:

In Preliminary design when location Stockholm(Sweden) is selected latitude 59.1N

and longitude 17.6E is automatically selected.

In this PV array nominal power is 68Kwp.Total investment cost is 403133euro and

energy price is 3.37eur/KWh.


Project design is based on data obtained from preliminary design. In this PV module

of Si-poly is used. It is manufactured by SED and model is Biber(solar tile)The

number of modules are 6066 with a module area of 2284m2 is taken. The total

number of batteries used is 244 with voltage of 48V.Total investment is

64856euro.Energy cost is 3.37eur/kwh.


35


36


37


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CHAPTER 6

Conclusions

The simulation results of the solar powered macro cellular base station suggests that it

is very cost efficient to deploy grid connected system compare to standalone system

either in New Delhi, India or in Stockholm, Sweden. Simulation results show that

estimate of the cost of production was found to be 0.39 euro/kwh for grid connected

system compare to 1.24euro/kwh for standalone system in New Delhi, India. In

Stockholm, Sweden it is found that Grid system will cost 0.66euro/kwh compare to

3.37euro/kwh for Standalone.

It can also be concluded that system design for standalone system is more complicated

compare to grid connected as the standalone system contains batteries and generators

apart from inverters and PV modules. This adds extra constraint to the design.

Grid connected systems are suitable if the supply of solar energy is reliable. In other

words it is suggested to use grid connected system in summers in India. If the supply

of solar energy is not reliable like during monsoon season in India or anytime of the

year in Stockholm, Sweden then it is suggested to use standalone system though it is

costly compare to grid connected system. Hence there is always trade off between

reliability and cost efficiency while deploying solar powered cellular base stations.

Future Work

The obtained simulation results can be compared with the practically implemented

solar powered cellular base stations in New Delhi, India and Stockholm, Sweden.


39

REFERENCES

1. http://www.pegrocoinvest.com/news/flexenclosure- launches-unique-green-base-station

2. Renewable Energy Power for a Sustainable Future edited by Godfrey Boyle

3. Wireless Communications: Principles and Practice, 2nd Edition by Theodore Rappaport

4. Wind and Solar POWER SYSTEMS Design, Analysis, and Operation, Mukund R.Patel

5. Cost Analysis on Solar Powered Radio Base Station with cooling Demand, by Christer Olsson,

Högskolan Dalarna, Master’s Level Thesis, No.10.March 2002.

6.http://www.google.com/search?hl=en&source=hp&q=pvsyst+v4.33&rlz=1R2ADRA_enSE336&aq=

7&oq=PVSYS&aqi=g3g-s1g6

7. http://www.rise.org.au/info/Applic/Solarpump/image003.jpg

8. http://www.ekotek-energija.com/PV_Basics_Part1-hr.htm

9.http://www.globalgreen.org/solarreportcard/SolarReportCard.pdf (India)

10.Solar Imperative: Using sustainable energy for mass deployment of GSM installations in rural India,

White Paper by Anders Hansson, February 2008

11.http://www.kpmg.de/docs/080402_Oil_Gas_Scenario_India_032008.pd

12. www.utilityfree.com/powerstation2.html

13. http://www.unu.edu/unupress/unupbooks/uu24ee/uu24ee0j.htm

14http://www.vnl.in/tag/fuel/

15. http://www.solarbuzz.com/Moduleprices.htm

.

http://www.rise.org.au/info/Applic/Solarpump/image003.jpg

http://www.ekotek-energija.com/PV_Basics_Part1-hr.htm

http://www.globalgreen.org/solarreportcard/SolarReportCard.pdf

http://www.utilityfree.com/powerstation2.html

http://www.unu.edu/unupress/unupbooks/uu24ee/uu24ee0j.htm

http://www.vnl.in/tag/fuel/

http://www.solarbuzz.com/Moduleprices.htm

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A case study of Solar Powered Base stations - Simple search234252/FULLTEXT01.pdf · A Case Study of Solar Powered Cellular Base ... of Solar power PV cell construction, ... are thin