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INTERNATIONAL JOURNAL OF
ENERGY AND ENVIRONMENT
Volume 1, Issue 2, 2010 pp.359-366
Journal homepage: www.IJEE.IEEFoundation.org
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2010 International Energy & Environment Foundation. All rights reserved.
PV-solar / wind hybrid energy system for GSM/CDMA type
mobile telephony base station
Pragya Nema1, R.K. Nema2, Saroj Rangnekar1
1 Energy Engineering Department, Maulana Azad National Institute of Technology , Bhopal-462007
M.P., India.
2 Electrical Engineering Department, , Maulana Azad National Institute of Technology , Bhopal-462007
M.P., India.
Abstract
This paper gives the design idea of optimized PV-Solar and Wind Hybrid Energy System for
GSM/CDMA type mobile base station over conventional diesel generator for a particular site in central
India (Bhopal) . For this hybrid system ,the meteorological data of Solar Insolation, hourly wind speed,
are taken for Bhopal-Central India (Longitude 77ο.23’and Latitude 23ο.21’ ) and the pattern of load
consumption of mobile base station are studied and suitably modeled for optimization of the hybrid
energy system using HOMER software. The simulation and optimization result gives the best optimized
sizing of wind turbine and solar array with diesel generator for particular GSM/CDMA type mobile
telephony base station. This system is more cost effective and environmental friendly over the
conventional diesel generator. It should reduced approximate 70%-80% fuel cost over conventional
diesel generator and also reduced the emission of CO2 and other harmful gasses in environments. It is
expected that the newly developed and installed system will provide very good opportunities for telecom
sector in near future.
Copyright © 2010 International Energy and Environment Foundation - All rights reserved.
Keywords: Hybrid energy systems, Mobile telephony base station, Wind turbine, PV-solar,
Optimization.
1. Introduction
Obtaining reliable and cost effective power solutions for the worldwide expansion of
telecommunications into rural and remote areas presents a very challenging problem. Grids are either not
available or their extensions can be extremely costly in remote area. Although initial costs are low,
powering these sites with generators require significant maintenance, high fuel consumption and delivery
costs due to hike in fuel prices.
A sustainable alternative to power remote base station sites is to use renewable energy sources. Recent
research and development of Renewable energy sources[1] have shown excellent potential as a form of
contribution to conventional power generation systems. In order to meet sustained load demands of
mobile base station during varying natural conditions, different energy sources and converters need to be
integrated with each other for extended usage of alternative energyFor Indian remote location, one of the
most alternative solution .[2] of renewable energy sources such as wind-solar Hybrid Energy System for
mobile base station. The use of the stand-alone solar-wind with diesel backup system for the power
International Journal of Energy and Environment (IJEE), Volume 1, Issue 2, 2010, pp.359-366
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2010 International Energy & Environment Foundation. All rights reserved.
360
supply of remote areas may give an economically attractive alternative[3] for mobile telecom sector over
the use of conventional diesel generators in near future. This paper gives the design idea of wind, solar-
photovoltaic hybrid energy system.
Based on the energy consumption of mobile base station and the availability of renewable energy
sources, it was decided to implement an innovative stand alone Hybrid Energy System [4]combining
small wind turbine-generator, solar photo-voltaic panels, battery storage, advance power electronic
equipment and existing diesel generators. The system architecture employed in the hybrid system is AC-
coupled where the renewable energy sources[5] and the conventional diesel generators[6] all feed into
the AC side of the network as shown in Figure1.
Figure 1. Hybrid system schematic diagram for mobile telephony base station
National Renewable Energy Laboratory (NREL)’s, Hybrid Optimization Model for Electric Renewable
(HOMER version 2.19) [14]has been used as the sizing and optimization software tool [10]. It contains a
number of energy component models and evaluates suitable technology options based on cost and
availability of resources. In this paper the system sizing [7-9] is carried out using HOMER-optimization
and simulation software tool. Analysis with HOMER requires information on resources, economic
constraints, and control methods. It also requires inputs on component types, their numbers, costs,
efficiency, longevity, etc. Sensitivity analysis could be done with variables having a range of values
instead of a specific number.
2. Renewable energy resources for hybrid system
The availability of renewable energy resources at mobile base station sites is an important factor to
develop the hybrid system .Many parts of the India wind and solar energy is abundantly available[11].
These energy sources are intermittent and naturally available, due to these factor our first choice to
power the mobile base station will be renewable energy sources such as wind and solar. Weather data are
important factor for pre- feasibility study[12-13] of renewable hybrid energy system for any particular
site. Here the Wind and Solar energy resources data are taken from NASA[15] for Bhopal-Central India
(Longitude 77ο.23’and Latitude 23ο.21’) and shown in Table 1. In central India wind speed is an average
and sun brightness is strong.
International Journal of Energy and Environment (IJEE), Volume 1, Issue 2, 2010, pp.359-366
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2010 International Energy & Environment Foundation. All rights reserved.
361
Table 1. Weather data for the site
Month Insolation (kWh/m2) Wind Velocity m/s
January 4.880 3.350
February 5.672 3.890
March 6.325 3.395
April 6.666 3.885
May 6.876 4.956
June 5.632 5.176
July 4.021 4.796
August 4.155 4.376
September 5.112 3.666
October 5.605 3.600
November 5.123 3.500
December 4.664 3.420
Average 5.389 4.001
Maximum 6.876 5.176
Minimum 4.021 3.350
2.1 Solar energy resource
Hourly solar irradiation data for the year was collected from Environment Bhopal. Scaling was done on
these data to consider the long-term average annual resource (5.389kW h/m2/d). The clearness index for
the latitude and Average daily radiation in a year is shown in Figure 2 (i). According to solar radiation,
PV-power output are available throughout the year is shown in Figure 2 (ii). In summer solar power is
higher than winter season. In rainy season clearness index and solar power availability is lower than
summer and winter season.
Figure 2. (i) Average daily radiation in a year, and (ii) PV-Power available throughout the year
2.2 Wind energy resource
A monthly average wind dataset for Bhopal ware collected from Environment Bhopal climate. This is an
average of last ten year and indicates that annual average wind speed and shown in Figure 3. From the
above given data, wind speed probability function and average hourly wind speed throughout the year is
shown in Figure 3.
The autocorrelation factor (randomness in wind speed) is found to be 0.85. The diurnal pattern strength
(wind speed variation over a day) is 0.25 and the hours of peak wind speed is 15. Average wind speed in
the summer season is slightly higher than the winter season as shown in Figure 3 (i). The power output
throughout the year according to wind speed is shown in Figure 3 (ii).
International Journal of Energy and Environment (IJEE), Volume 1, Issue 2, 2010, pp.359-366
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2010 International Energy & Environment Foundation. All rights reserved.
362
Figure 3. (i) Average hourly wind speed for 1year, and (ii) wind power output throughout the year
3. Load pattern for mobile telephony base station
Cellular telephone service is a rapidly expanding and very competitive business world over including
developed and developing countries like India, America, European countries etc. Right now there are
55,000 different type base stations for telecom sector in India and most of them running on diesel
generators. But diesel generators are often expensive to run and more than one diesel generator are
installed for uninterrupted service. The different types of telecom base station are used according to the
technological advancement in telecommunication sector.
Recently the GSM 2/2/2 (2nd Generation Global System Mobile telephony base station) are used in all
over the world. For pre-feasibility study of designing the solar wind hybrid system considered the 2nd
Generation GSM base station. In this present study consider the power requirements for GSM telephony
base station site are about 2kW continuous. The load demand is approximate 47kWh/d and 2 kW peak.
4. Hybrid energy system components
The proposed hybrid system consists of the following:
4.1 A 7.5 kW Wind turbine
Two 7.5kW horizontal-axes, BWC-EXCEL-R/48 type [14] wind electric generators are taken for this
system. It converts wind energy into electrical energy. Availability of energy from the wind turbine
depends greatly on wind variations. Therefore, wind turbine rating is generally much higher compared to
the average electrical load. In this analysis, Wind Power’s BWCExcel-R/48 model is considered. It has a
rated capacity of 7.5 kW and provides 48 V DC. As outputs Cost of one unit is considered to be $15500
while replacement and maintenance costs are taken as $12000 and $75/year. The cost analysis is shown
in Figure 4 (i). The power curves of wind turbine are shown in Figure 4 (ii). To allow the simulation
program find an optimum solution, lifetime of a turbine is taken to be 20 years.
4.2 A 5 kW Photovoltaic array
Solar PV modules are connected in series parallel. When the sunrays strike the Solar PV panels, it
produces electricity. The Solar PV power at the site is higher than the wind power. The installation cost
of PV arrays may vary from $5.00 to $8.00/W considering a more optimistic case [1]. A 1 kW solar
energy system’s installation, and replacement costs are taken approximate as $5000 and $3000,
respectively (Figure 5). The lifetime of the PV arrays are taken as 20 years and no tracking system is
included in the PV.
4.3 Battery bank
A battery bank is used as a backup system and it also maintains constant voltage across the load. The
battery pack consists of 8(6), 48V, 305Ah, 1.83kWh batteries connected in series / parallel configuration,
two parallel sets of 8 batteries in series. Cost of one battery is $520 with a replacement cost of $370
(Figure 6). The battery stack may contain a number of batteries are 8, and 16.
International Journal of Energy and Environment (IJEE), Volume 1, Issue 2, 2010, pp.359-366
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2010 International Energy & Environment Foundation. All rights reserved.
363
(i) (ii)
Figure 4. A 7.5BWC-Excel R/48 (i) power curve, and (ii) cost curve
Figure 5. Cost curve of PV Figure 6. Cost curve of battery
4.4 Converter
A power electronic converter is needed to maintain flow of energy between the ac and dc components.
For a 1 kW system the installation and replacement costs are taken as $720 and $460, respectively. Cost
analysis shown in Figure 7. Lifetime of a unit is considered to be 15 years with an efficiency of 90%.
Consider for this hybrid system 6kW converter.
4.5 Diesel generator
The fuel consumption per year is approximate 1300 Litter for 1kW Diesel Generator. The 1 kW diesel
generator capital cost, replacement cost, operation-maintenance cost are 400$, 300$, 0.75$. The Diesel
price is used for sensitivity analysis and three discrete values (0.8, 0.85, and 0.9 $/L) were introduced. At
present, diesel price is around 0.85$/L and for a very remote location this could increase up to 0.9$/L.
Sizes to be consider for obtaining optimal hybrid system are 2kW and 5kW .This analysis shown in
Figure 8.
Figure 7. Cost curve of converter Figure 8. Cost curve of diesel generator
International Journal of Energy and Environment (IJEE), Volume 1, Issue 2, 2010, pp.359-366
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2010 International Energy & Environment Foundation. All rights reserved.
364
5. Results and discussion
The above proposed hybrid system supply the power to the mobile telephony base station continuously
throughout the year. For the analysis of this hybrid system consider four sensitivity variables (wind
speed, solar irradiation, fuel cost and Battery cost). For each of the sensitivity values simulate all the
systems in their respective. An hourly time series simulation for every possible system type and
configuration is done for a 1-year period. An optimal system is defined as a solution for hybrid system
configuration that is capable of meeting the load demand of telephony base station.
5.1 Optimization results
From the simulation result the installation of wind solar hybrid system configuration for various
locations are most suitable power solutions for telecom base station network in Indian sites. Considering
present cost analysis of a PV/Wind hybrid system is suitable for stand-alone loads around Bhopal. From
the optimization results the best optimal combination of energy system components are two 7.5kW
BWC-Excel-R/48, 2 kW PV-Array and 2 kW diesel Generator.
Total net present cost (NPC), Capital cost and cost of energy (COE) for such a system is $207,538,
$53,440 and 0.942$/kWh, respectively for one year. The detailed optimization results are shown in
Figure 9.
5.2 Simulation results
In this simulation results eliminates all infeasible combinations and ranks the feasible systems according
to increasing net present cost. It also allows a number of parameters to be displayed against the
sensitivity variables for identifying an optimal system type. The Monthly Average Electricity Production
of Hybrid Energy System for mobile telephony base station is shown in Figure 10. In this system the
total production of electrical energy is fulfil the load demand by the combination of 13% PV, 56%wind
and rest of 31% by generators.
Figure 9. Optimization results of hybrid energy system for mobile telephony base station
International Journal of Energy and Environment (IJEE), Volume 1, Issue 2, 2010, pp.359-366
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2010 International Energy & Environment Foundation. All rights reserved.
365
Figure10. Annual electricity production by different hybrid system
6. Conclusion
In India more than 1 billion peoples are mobile user. To provide better network services mobile operator
installed new mobile base stations. Power is main issue for remote or isolated areas base station, because
grid extension is not feasible. In these sites the above proposed renewable base hybrid system is most
viable solution. These solutions of power supply to the telecom base station are cost effective and
available throughout the year. The circumstance of each sites are studied in order to decide the feasible
combination of alternative energy resources. Alternate power solutions are not commonly used in mobile
telecommunication system today but are actively evaluated for remote and isolated areas over worldwide.
With the help of above pre-feasibility study the solar and wind hybrid energy system are most viable
power solution for mobile base station in Indian sites over conventional diesel generator. Although the
net present cost is high but the running and maintenance cost are low as compared to the diesel generator
power solution. Its payback time is around 15 years.
The fuel consumption is also reduced to approximate 80%.with increasing oil prices, payback times on
the investment to hybrid solar-wind powered base station sites are continuously decreasing. Considering
operating cost and maintenance cost, an autonomous site powered by wind solar hybrid system pay-off
after 2-4 years in a good sunny and windy location. The Base stations powered by the solar wind hybrid
energy system with diesel backup – are proving to be the most environmentally friendly and cost-
effective solutions for many challenging sites. Operating and maintenance costs are extremely low,
making it economical to extend cellular coverage in far-flung regions.
Solar- and wind-powered sites benefit the environment as well as the operator business case, whether
they are located in highly populated or remote areas. Due to powering the base station by hybrid
renewable energy system, it will reduce the carbon and other harmful gases emission is about 90% in
environments. Due to powering the base station by hybrid renewable energy system, it will reduce the
carbon and other harmful gases emission is about 90% in environments.
Acknowledgements
The authors acknowledge gratefully to Area Manager, BSNL-Bhopal for providing telecom base station
data used in this study. The authors also thankful to the director Dr. K.S. Panday, Maulana Azad
National Institute of Technology, Bhopal, for providing assistance to carry out the work at energy centre.
International Journal of Energy and Environment (IJEE), Volume 1, Issue 2, 2010, pp.359-366
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2010 International Energy & Environment Foundation. All rights reserved.
366
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[10] http:/www.motorola.com
[11] http:/homepage.mac.com/unarte/solar_radiation.html
[12] http://www.energysolutionscenter.org
[13] http://www.bergey.com/
[14] http: //nrel.gov./homer
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Pragya Nema - received her B.E. degree in Electrical Engineering from Govt. Engineering college of Sagar-M.P. in 1995. She-
received M.Tech. degree in Heavy Electrical Engineering from Maulana Azad College of Technology Bhopal-M.P.in 2001.She is
currently pursuing Ph.D. degree at Maulana Azad National Institute of Technology Bhopal-India. Her current research interests
include Integrated Renewable Energy System, Modeling and control of power systems.
R.K. Nema received his PhD degree in Electrical Engineering from Barkatullah University, Bhopal, India
in 2004. He is currently Associate Professor at the Department of Electrical Engineering, Maulana Aza
d
National Institute of Technology, Bhopal, India. His current research interest include power conditioning
unit for Renewable Energy storage system particularly Solar Energy, Hybrid Energy Systems, Gri
d
Interconnection of Renewable Energy sources.
Saroj Rangnekar is Professor in the Department of Energy, Energy Centre at Maulana Azad National
Institute of Technology, Bhopal. Dr. Saroj Rangnekar has 32 years of teaching & research experience an
d
received three National awards. She has published 85 papers in various International and National
Journals, Conference proceedings. Her field of interest includes hydroelectric system, control systems an
d
integrated renewable energy system, Modeling and optimization of the renewable energy sources.