Hybrid energy systems for off-grid remote telecom tower in Odisha, India

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1 This article was downloaded by: [Orissa University of Agriculture & Technology] On: 26 September 2013, At: 21:25 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK International Journal of Ambient Energy Publication details, including instructions for authors and subscription information: Hybrid energy systems for off-grid remote telecom tower in Odisha, India Sonali Goel a & Sayed Majid Ali a a School of Electrical Engineering, KIIT University, Bhubaneswar, India Accepted author version posted online: 29 Jul 2013.Published online: 10 Sep To cite this article: Sonali Goel & Sayed Majid Ali, International Journal of Ambient Energy (2013): Hybrid energy systems for off-grid remote telecom tower in Odisha, India, International Journal of Ambient Energy, DOI: / To link to this article: PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the Content ) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at

2 International Journal of Ambient Energy, Hybrid energy systems for off-grid remote telecom tower in Odisha, India Sonali Goel and Sayed Majid Ali School of Electrical Engineering, KIIT University, Bhubaneswar, India (Received 14 May 2013; accepted 4 July 2013) Hybrid energy systems are increasingly being applied in areas where grid extension is considered uneconomical. Their costs can be minimised through proper equipment sizing and load matching. This paper reports the results of optimisation of solar wind hybrid energy system for remote telecom site which is located at the coastal island (20.33 N latitude and E longitude) in Kendrapara district of Odisha, India. The present power supply system has been optimised using HOMER (Hybrid Optimization Model for Electric Renewables) software (2.68 version) package developed by National Renewable Energy Laboratory (NREL), Colorado, USA. From the load demand and different equipment sizing, the net present cost, costs of energy and operating costs were determined and compared with only diesel generator system. Keywords: HOMER; PV; wind; hybrid 1. Introduction India currently has about 400,000 telecom towers and poised to increase to 450,000 towards the end of 2013 (Anonymous 2013). A large portion of these towers is not connected to the electricity grid or does not have access to reliable electricity implying they have to install backup power systems in order to run without interruptions. Diesel generators (DGs) have been the choice of telecom operators despite their higher operating expenses (OPEX) and carbon imprint. Telecom towers are estimate to burn 2 billion litres of diesel (around 500 million barrels) annually at a cost of $18,232 million (Moury, Khandoker, and Haider 2012). On an average, about $4740 is being spent annually to fulfil the diesel requirements of a single telecom tower. These high input costs also results in high pollution. While the government has been trying to convert these towers to renewable energy forms, most of the tower operators have been very slow to implement this change. The renewable energy ministry had asked telecom companies to reduce their dependency on conventional fuels and consider alternatives for partly powering telecom towers. Indus Towers, the largest with over 1 lakh towers in India, planned to set up 2500 solar towers by the end of this year. Viom Networks, which operates more than 38,000 towers across India, plans to run more than one-fourth of this number on alternative energy within the next two years. It plans to run 2000 towers on solar power alone by 2013 (Moury, Khandoker, and Haider 2012). Each tower requires energy from 1000 to 3000 W (older installation consumes more power when compared with new ones because of technological advancement). Assuming average power consumption of each tower is 1200 W then total CO 2 emission is lakh tonne per hour by all these towers if we assume that all are running on state electricity. In India, about 70% telecom towers are in rural areas. Presently in rural areas, only 33% power requirements of telecom towers are met by grid electricity while 67% by diesel generators (Anonymous, 2011). The DGs are of kva capacity and consume about 3 L of diesel per hour and produce 2.63 kg of CO 2 per litre. For every kwh of grid electricity consumed, 0.84 kg of CO 2 is emitted. Total CO 2 emission is about 5 million tonnes due to diesel consumption and 8 million tonnes due to grid power per annum. Extensive use of DG has very adverse effects on the environment as it emits higher amount of CO 2 and other green house gas (GHG) emission causing global warming. During twentieth century, global surface temperature has increased by 0.74 C(Chowdhury, Roy, and Aziz 2009). The move from diesel to solar and other alternative sources of energy will result in a reduction of 5 million tonnes of CO 2 emissions as well as a saving of huge amount in operating expenses for telecom tower companies. Solar energy has proven to be a reliable and economical method of powering telecomunication system in places where conventional electricity is unavailable or impractical (Anonymous, 2007). Move to renewable energy sources can generate millions of carbon credits that could offset the OPEX on their towers. Thus, by replacing DGs with solar wind hybrid power systems in telecom towers, more than 5 million tonnes of carbon emissions could be prevented from entering the atmosphere. India, with its average irradiance (5 kwh/m 2 /d), has excellent opportunity to explore solar photovoltaic (SPV) Corresponding author. sonali19881@gmail.com 2013 Taylor & Francis

3 2 S. Goel and S. Majid Ali power to meet this challenge of onsite power generation. Also wind speed in coastal region is almost above the cutin speed of wind turbines (WTs) throughout the year. As most of the base stations are located in open spaces and exposed to sunlight and wind, solar wind hybrid systems make the most feasible solution for powering the telecom sites in coastal areas of our country. Coupled with a DG and battery backup for uninterrupted power supply, photovoltaic (PV) wind hybrid systems are most viable and exciting alternatives to reduce the power cost and total operating expenditure thereby providing a sustainable and reliable solution to the power problem in telecom sites. Nema et al. (2010) of Department of Energy, MANIT, Bhopal, studied the most feasible configuration of a standalone PV/wind hybrid energy system with DG as a backup for cellular mobile telephony base station sites in isolated areas of Central India. They concluded that this system is more cost effective and environmental friendly over the conventional DG and also reduced the emission of carbon dioxide and other harmful gasses in the environment. With the help of HOMER (Hybrid Optimization Model for Electric Renewables), they found that the solar wind hybrid energy system is most viable power solution for mobile base station in Indian sites over conventional DG. Bajpai et al. (2009) made the simulation of various types of renewable energy-based power system models for powering stand-alone base transceiver station (BTS) sites using HOMER. Based on the simulation results, it is observed that SPV-FC (fuel cell)-battery hybrid system with maximum power point tracker is most economic solution compared to single storage system. Moury et al. (2012) compared the grid-connected BTS with the SPV model by using HOMER and found that the SPV system is more economical with lower cost of energy (COE) than traditional system. In all these papers, the focus is solely on feasibility study of renewable energy for powering BTS sites. Table 1. Equipment Solar PV array WT Battery DG Converter Equipment used in telecom site. Specifications 10 kwp Module type ES-250M60B 5.1 kwp ac generator Rotor diameter 5.24 m Hub height 25 m Cut-in speed 2.7 m/s Cut-out speed 35 m/s 1250 Ah, 2 V each 48 no. used in two strings 20 kva, 0.8 pf 12 kw 2. Present architecture of site The basic component of the PV wind DG system that is installed in the telecom site is shown in Figure 1. The electrical energy generated from the PV wind DG system is fed directly to the BTS load through the charge controller and battery unit. The energy that is stored in the battery is used to supply the power during low power production or at night when only WT is functional. DG is used in the system as the secondary backup power supply as SPV arrays and WT are not 100% reliable energy sources. In cloudy or rainy day, output electrical power from SPV cells can be very low which might cause a significant problem and also in case of WT, sometimes wind speed may come below cut-in speed which may cause poor or no power generation. DG can supply power when both solar wind battery systems fail to supply power to the load. As the load of the BTS is dc, but the DG and WT produce ac, converter is used to convert ac to dc. It also regulates the power flow from each of the sources, acting as charge controller or boosting up the power. The details of the systems configuration used in the site are given in Table 1. Figure 1. Hybrid system used in telecom site.

4 International Journal of Ambient Energy 3 Figure 2. Solar radiation with clearness index. Figure 3. Wind speed in different months in the site. In this paper, the simulation result of hybrid renewable energy system is analysed and compared with only DG system in off-grid remote conditions. 3. Energy resources for hybrid power system For this hybrid system, the meteorological data of solar radiation and hourly wind speed were imported from NASA site and were analysed by using HOMER. Figure 2 shows the variation of solar radiation and clearness index of the site. The average solar radiation of the site is 4.7 kwh/m 2 /d. Wind speed also varies seasonally. Average wind speed of the area is 4.36 m/s. Figure 3 shows the monthly wind speed variation of the site. Average energy consumption of the site is 23 kwh/d with a peak load demand of 2.0 kw. Figure 4 shows the Figure 4. Daily load profile of telecom tower. daily load profile, and Figure 5 shows monthly load pattern of the telecom tower. 4. System analysis For the simulation analysis, salvage value of 10% (except battery) and O&M (operation and maintenance) as 10% Figure 5. Load of telecom tower in different months.

5 4 S. Goel and S. Majid Ali Table 2. System equipment and cost. Element Initial cost ($/kw) Replacement cost ($/kw) O&M ($/kw) Life time (years) Solar system WT Battery 268 (per unit) 268 (per unit) 13 (per unit) 8 Converter DG (per hour) 10 (15,000 h) Figure 6. Architecture of solar wind DG system. were taken. Actual cost of solar system, WT, battery unit and DG was collected from the Executive Engineer, BSNL maintenance division, Cuttack, for analysis purpose. The simulations were performed using HOMER to get the optimised sizing, cost, electrical production and emissions. Cost, O&M and lifetime of all the elements are presented in Table 2. For simulation purposes, DG sizes of 8, 12 and 16 kw and battery of 24 and 48 numbers were selected. The present load of the tower having 1 BTS is 22.7 kwh/d. Another two loads of 55 and 83 kwh/d were considered keeping in mind that in future two more BTS will be commissioned at the site. Similarly, different values of other variables like global radiation, wind speed and diesel price were taken for sensitivity analysis. Simulation results of existing renewable system-i (PV wind DG) and the traditional system-ii (DG only) are presented below PV wind DG system (system-i) SPV array of 10 kw, WT of 5.1 kw and DG of 20 kva capacity with 48 numbers of tubular gel batteries in two strings are installed at the telecom site. The system architecture is shown in Figure 6. The component-wise net present cost (NPC) of the system is shown in Figure 7, while the simulation results at 22.7 kwh/d load, 4.7 kwh/m 2 /d of solar radiation and 4.36 m/s wind speed with diesel price of 0.9 USD per litre is shown in Figure 8. The cost summary of the system is presented in Table 3. The levelised COE of the solar wind DG system was found to be higher ($0.839/kWh) than wind-diesel system Figure 7. Cash flow of the system-i.

6 International Journal of Ambient Energy 5 Figure 8. Optimised system with existing resources. Table 3. Cost summary of the solar wind DG system (system-i). Load (kwh/d) Parameters NPC ($) 79, , ,725 Operating cost ($/year) Levelised COE ($/kwh) Diesel consumption (L/year) Excess electricity production/year (%) CO 2 production (kg/year) ,781 at lower load of 22.7 kwh/d. But at higher load of 55 and 83 kw/h, this model has the lowest COE over all other systems. The COE of this system varies from $0.839 to $0.506/kWh with annual diesel consumption ranging from 97 to 6752 L as the load varies from 22.7 to 83 kwh/d. Excess electric energy production decreases from 45.2% to 1.10% as load increases from 22.7 to 83 kwh/d. As load increases, COE decreases while the NPC and operating cost increases. Higher operating cost at higher loads may be due to higher amount of diesel consumption at higher loads. The NPC of this system varies from $79,755 to $175,725 as the load varies from 22.7 to 83 kwh/d. This may be due to expenditure of higher amount of operating cost at higher loads. Optimised values of the components that were found out for this system were 10 kw SPV arrays, 24 batteries in a single strings, DG of 8 kw and 12 kw converter (6 kw inverter and 6 kw rectifier). Figure 9. System architecture of only DG system DG system (system-ii) The system architecture and the NPC of this system are shown in Figures 9 and 10. The cost summary of this system is presented in Table 4. For simulation, 8 kw DG, 24 batteries for storage of energy for emergency backup, 6 kw inverter and 6 kw rectifier were considered. The levelised COE of this system was found to be $0.966/kWh at lower load of 22.7 kwh/d. The COE of this system varies from $0.966 to $0.568/kWh with annual diesel consumption ranging from 12,130 to 7932 L as the load varies from 22.7 to 83 kwh/d. Excess electric energy production decreases from 31.7% to 0.35% as the load increases from 22.7 to 83 kwh/d. As load increases, COE decreases while the NPC and operating cost increases. Higher operating cost at higher loads is due to higher amount of diesel consumption at higher loads. The NPC of this system varies from $91,786 to $197,343 as the load varies from 22.7 to 83 kwh/d. This may be due to higher amount of operating cost at higher loads. GHG emissions The GHG emissions of these two systems are shown in Table 5 which indicates that system-i discharge very negligible amount of pollutants when compared with system-ii.

7 6 S. Goel and S. Majid Ali Figure 10. Table 4. NPC of DG system. Cost summary of the DG system ( system-ii). Load (kwh/d) Parameters NPC ($) 91, , ,343 Operating cost ,644 15,245 ($/year) Levelised COE ($/kwh) Diesel consumption ,551 (L/year) Excess electricity production/year (%) CO 2 production (kg/year) 12,130 23,967 33,048 Table 5. GHG emissions by two systems at 22.7 kwh/d load. Emission (kg/year) Pollutant System-I System-II Carbon dioxide ,374 Carbon monoxide Unburned hydrocarbons Particulate matter Sulphur dioxide Nitrogen oxides At lower load of 22.7 kwh/d, the consumption of diesel fuel is reduced from 4699 to 97 L in system-i when compared with system II, which not only saves cost but also has greater importance for the environment by reducing emission of 12,117 kg of CO 2 to the atmosphere when compared with system-ii. 5. Conclusion When the results of NPC, COE, operating cost and excess electricity are compared between the two systems, it is seen that at all the three levels of loads, lower COE and operating cost were obtained in system-i. Also, installing renewable elements like solar PV array coupled with WT has lots of economical and environmental advantages. It reduces the operating expenses as well as COE when compared with conventional DG systems in off-grid remote areas thereby making telecommunication sustainable and economically profitable. Acknowledgements The authors are grateful to the Dean, School of Electrical Engineering, KIIT University, Bhubaneswar and Executive Engineer, Maintenance Division, Bharat Sanchar Nigam Ltd, Cuttack for providing facilities for carrying out the research work. References Anonymous Solar Energy in Telecommunication. Bechtel Telecommunication Technical Journal 5 (1): Anonymous Consultation Paper on Green Telecommunication. Telecom Regulatory Authority of India. Anonymous Case for Telecom to Shift from Diesel to Renewable. Greenpeace. Bajpai, P., N. P. Prakshan, and N. K. Kishore Renewable Hybrid Standalone Telecom Power System Modelling and

8 International Journal of Ambient Energy 7 Analysis. TENCON, 2009, IEEE. doi: /09. Chowdhury, S. A., V. Roy, and S. Aziz Renewable Energy Usage in the Telecommunication Sector of Bangladesh: Prospect and Progress. In 1st International Conference on the Developments in Renewable Energy Technology (ICDRET), Dhaka, Bangladesh, 1 5. Moury, S., M. N. Khandoker, and S. M. Haider Feasibility Study of Solar PV Arrays in Grid Connected Cellular BTS Sites. IEEE. doi: /12. Nema, P., R. K. Nema, and S. Rangnekar PV-Solar/Wind Hybrid Energy System for GSM/CDMA Type Mobile Telephony Base Station. International Journal of Energy and Environment 1 (2):