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Design and Operational Experience of PoweringBase Transceiver Station in Indonesia by Usinga Hybrid Power SystemP. A. Dahono', M. F. Salam", F. M. Falah 2, G. Yudha2, Y. Marketatmo', and S. Budiwibowo'1. Institute of Technology Bandung, Bandung, Indonesia.2. PT. LEN, Bandung, Indonesia.

3. PT. Indosat, Jakarta, Indonesia.Abstract - The design of small hybrid power system forpowering base transceiver s ta tion (BTS) is described in thispaper . The energy for powering the BTS is obtained by using acombination of wind power, solar cell, and utility line. The sizingmethod for this kind of hybr id power supply is proposed. In

order to verify the proposed design method, a pilot pro ject ofpowering a 4000-Watt BTS is implemented. Operationalexperience of this kind hybrid power supply is reported in thispaper. It is found that a hybrid approach is useful to reduce thecost of powering BTS in remote areas.

I. INSTRODUCTIONIndonesia has more than ten thousands small islands those

are distributed around the equator. In these islands, most ofelectrical power is generated by using diesel generators.Generating electrical power by using diesel generators is veryexpensive. Moreover, during rainy and wind seasons, it isdifficult to send fuels to the island because the sea wave isvery high. It is desirable to create a power generation systemthat is self sufficient. The president of Indonesia has declaredto create many energy self-sufficient villages and islands.Indonesia has targeted to install more than 1000 MW windpower plants and 10000 MW solar power plants by 2025.

PT. Indosat is one of cellular telephone company inIndonesia who has more than 13,000 BTSs. About half ofthem are located in remote areas. PT. Indosat has a problem ofpowering the remote BTSs especially during wind and rainyseasons. At present, one remote BTS usually consumes 2000liters of diesel fuel every month. In some remote regions, theprice of fuels can be very expensive several times higher thanthe normal price. In recent years, PT. Indosat has a program toimprove the reliability of the BTSs by using alternative energysources those are available locally. As Indonesia is located atthe equator, the solar energy is the first choice. At present,however, solar cell is still considered very expensive. In orderto reduce the size of solar cell, wind power is considered as agood alternative especially in east part of Indonesia. Bycombining wind and solar energy sources, it is expected that areliable power supply can be obtained without too much costpenalty.

In this paper, the design and sizing of hybrid power systemfor small BTSs in Indonesia are presented. Combination ofwind and solar energy sources are used as the main source andutility line is used as a backup. The operational experience that

is obtained from a pilot project during the last six months isreported. It is found that the designed system is working asexpected.

II. POWER SYSTEMDESIGNThe power consumption of BTSs is almost constant from timeto time. For small BTSs, the average power demand is about4000 Watt. Hal f of this power is used for air conditioningsystem. The telecommunication equipment itself is jus tconsuming 1500 Watt. The rest is for lighting and monitoringsystem.In this pilot project, it has been decided to design a systemthat is not so different to the existing scheme. The scheme ofconventional power system of BTS is shown in Fig. 1. TheBTS is usually powered by the utility line. A diesel generatoris usually used as the back-up. Air condition and lightingsystems are powered from the AC bus. By using a rectifier, theac power is converted into 48V dc power. The battery andtelecommunication equipment are connected directly to the48V de bus. The battery is usually designed to give at least 6hours back-up time.In remote areas, however, diesel generator is usually themain source. For small BTSs, about 2000 liters diesel fuel isrequired every month. In remote areas or small islands, themain problem is how to send the fuel. Just in several years, thefuel cost may exceed the price of the BTS itself.The first choice is using PV and wind power generationsystems that produce ac voltage as shown in Fig. 2. By usingthis configuration, the operating procedure of the BTS is notchanging at all. Unfortunately, the efficiency of this system islow and the power converter systems are expensive. Thesecond choice is using a system as shown in Fig. 3. In thissystem, the wind and PV power plants produce dc voltage. Asthe required power converters are smaller than the one in Fig.2, the efficiency is better and the cost is cheaper. In this case,however, the setting point of the existing rectifier must bemodified to take into account the existence of PV and windcharge controllers. The second configuration is the one that isimplemented in this project.In this pilot project, the site is selected arbitrarily. The sitemay not the optimal place for PV or wind power but it isselected because the access is easy. Moreover, the governmenthas selected Bali island as to be a green island. The selected

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Utility

ACload

. . . . ~ 1 ) i , " ' 1 I:~ G e n s e tL 48Vdc

Wind

. 1 I ~ I ~ P V IDC AC

C C

DC loads

ACloads

I UtilityL

Rectifier48Vdc

DieselGenset

Battery

Fig. 3. The second configuration.

site is located in Girisari village, Bali island. Before the hybridpower system is installed, the BTS is powered by the utilityline. No diesel generator back-up is provided because thereliability of utility line in Bali is considered good. Theaverage energy consumption of this BTS is 96 kWh/day.Every day, the energy consumption of the telecommunicationequipment is 1500x24 Wh or 36 kWh.According to the data, the average wind speed in this area is

not so good. It is just about 4-5 m/s. Though the average speedis low, the peak speed can be very high. This is a problemduring the design of wind tower. As the average speed is low,the wind power cannot be relied as the main source. In thispilot project, the installation of wind power is just to get

DCloads

experience of using wind for power ing BTSs. The generalspecification of the sys tem is shown in Table 1.The general specification of wind power sys tem is shown in

Table 2. The ins talled wind turbine has maximum capacity of2500 Watt. The maximum power is reached when the windspeed is 12 m/s. The generator used in this pilot projec t is asurface-mounted permanent magnet three-phase ac generator.The output of the generator is rectified by using a dioderectifier . The output of rectifier is connected to the dc busthrough a battery charge controller. The charge controller isbasically just a buck chopper that controls the battery voltage.Neither pitch controller nor maximum power controller areprovided in the charge controller.According to the data, the average sunshine hour in this site

is between 7 to 8 hours a day during the dry season andbetween 5 to 6 hours a day during the rainy season. As theaverage energy consumption is 36 kWh, the installed PVmodule must be larger than 4000 Wp. It is decided to install4800 PV array tha t is divided into two modules. The genera lspecification of PV module is shown in Table 3. If it is notbecause of good location for PV or wind but it is r ather goodonly the telecommunication equipment will be powered bysolar and wind power sources. The battery is designed to givea backup time for 24 hours. According to the average windspeed in the area, it is designed to use a 2500 Watt windturbine. The solar module is s ized as 4800 Watt system that isdivided into two 2400 Watt arrays. Each array is connected tothe de bus through a solar charge controller. The chargecontroller is basically a buck converter that operates accordingto the de bus voltage. No maximum power point tracker isprovided in this solar charge controller.The battery is designed to provide back-up time for 24

hours. Thus, the minimum ampere-hour of the battery must be1500x24/48=750 Ah. Considering the battery maximum andminimum charge conditions, a battery bank of 1200 Ah wasselected. The minimum charge level of the battery wascontrolled to be 30 %. When the minimum charge level isreached, the recti fier is act ivated by the sys tem control ler tocharge the battery bank.

Utility

ACloads

. . . . ~ . ] ) i , " ' l I . ~ G e n s e tL 48Vdc

DC loadsFig. 1. Scheme of conventional BTSs.

Fig. 2. First configuration of hybrid system.

Winda lJ ACC

Battery

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Table 1. General system specification.PVand Wind Power Curve

., PhotovoltaicSystem

.,BatteryBank

.,ChargeController

.,PVSupport System

.,Wind Turbine,Wind Tower., Protection Panel.,Remotemonitoring

: PolycristalinePV,4.8 kWp (48pes,@ 1OOWp): DeepCycleOPzV,57.6 kWh(48 block,@ 100Ah): PWM,48 Vdc, 120Ampere,: FreeStanding,on top shelter for 4800Wp: 2500Watt, 48 Vdc, includedCharge controller: 24 meter SelfSupport, steel galvanize: AC and DCprotection system: Dataacquisitionand communicationvia GPRS

Table 2. Specification of wind power plant. Fig. 4. PV, wind, and load power curves in Jnuary 9,2009.TypeRated PowerRotor positionRotor diameterNumber of bladesBlade materialRotor speedCut-in speedNominal rated speedGenerator typeSafety systemTail length

: SKEA LPN-2500E: 2500 Watt: upwind: 5.0 m:3: Fiberglass-reinforced: 450 rpm: 2.5 mls: 10 mls: Angular type, magnet permanent: " ecliptic safety by turning tail vane gOO andelectric brake ": 2800 mm

PVand Wind Power Curve

Table 3. General Specification of PV module. Fig. 5. PV, wind, and load curves in March 14,2009.

cellNo. Of Cells and connectionsNominal VoltageDimensionTypical maximum power (Pmax)Voltageat maximumpower (Vmp)Current at maximum power (Imp)Short-circuit current (Is

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main rectifier is deactivated when the battery voltage hasincreased up to 90 percent of battery charge condition. Someadjustment on the setting point of charge controller is going onto maximize the energy production by PV and wind.PT. Indosat has considered this pilot project as successfully.Based on this experience, PT. Indosat has a plan to installsimilar 50 hybrid power system for powering the BTSs. Thefinal target is converting about 2.5% of all BTSs into greenBTSs. This target is in accordance to the national target ofusing renewable energy sources.At present, PT. Indosat has a plan to use a biodiesel that isproduced locally to improve the reliability of the BTSs insome remote islands. PT. Indosat has just finishedcommissioning a small plant that produces a biodiesel with acapacity of 30 kiloliters per month. The biodiesel is producedfrom jathropa oil. By using this small plant, most of BTSs inBali and Lombok islands that belongs to PT. Indosat will begreen. If this project is successful, other projects using otheroil plants will follow.

IV. CONCLUSIONA small hybrid power system has been proposed to supply asmall BTS in Indonesia. The system consists of wind, PV, andutility sources. Measurement results shown that the system hasperformed as expected. As the average speed is very low,wind energy cannot be relied to supply BTS. The PV power ispromising because we have almost do day without sunshine.Optimization is still required to maximize the utilization ofrenewable energy sources.

REFERENCES[1] H. Gumhalter, Power Supply Systems in Communications Engineering,

Part2: Equipment Engineering and Planning Instructions, Wiley, 1985.[2] W. Reeve, DC Power System Design for Telecommunications, Wiley,

2007.

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