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The design of a photovoltaic/biomass hybridelectrical energy system for a rural village inCambodiaS. Sou a , W. Siemers b & R. H. B. Exell ca The Joint Graduate School of Energy and Environment, King Mongkut's University ofTechnology Thonburi , 126 Pracha-Uthit Road, Bangmod, Tungkru, Bangkok, 10140,Thailandb The Joint Graduate School of Energy and Environment, King Mongkut's University ofTechnology Thonburi , 126 Pracha-Uthit Road, Bangmod, Tungkru, Bangkok, 10140,Thailandc The Joint Graduate School of Energy and Environment, King Mongkut's University ofTechnology Thonburi , 126 Pracha-Uthit Road, Bangmod, Tungkru, Bangkok, 10140,ThailandPublished online: 30 Mar 2011.

To cite this article: S. Sou , W. Siemers & R. H. B. Exell (2010) The design of a photovoltaic/biomass hybridelectrical energy system for a rural village in Cambodia, International Journal of Ambient Energy, 31:1, 3-12, DOI:10.1080/01430750.2010.9675803

To link to this article: http://dx.doi.org/10.1080/01430750.2010.9675803

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International Journal of Ambient Energy, Volume 31, Number 1 January 2010

The design ofa photovoltaic/biomass hybride l e c t r i c a lenergy systemfor a ruralvillage inC a m b o d i aS. Sou*, W. Siemers** andR. H. B. Exell***

S Y N O P S I SA hybrid renewable energy system, consisting of a1 . 2 7 kWp solar photovoltaic generator, a 15 k W ebiomass gasif icat ion system and a 7.28 k W hbattery backup, has been designed for theelectrif icat ion of a representat ive vil lage, namelyChhouk Ksach in Cambodia, which is not currentlyconnected to the electrical power grid and wherecar batter ies are used for electr i f icat ion. Thehybrid system is designed to ensure that the loaddemand is supplied for 24 hours a day throughoutthe year. The photovoltaic generator al lows thegasif ication system to shut down when the loaddemand is small during daytime hours. The systemhas an electrical generation capacity of 34,376 kWhper year of which 4% is generated by the photo-voltaic system and 96% by the biomass gasificationsystem. The annual load demand is 24,518 k W h ,of which 90% is taken directly from the biomassgasif ication system, 3% is taken directly from thephotovoltaic system and 7% is taken from thebackup battery. The annual net loss is estimatedto be 2,878 kWh leaving an energy surplus of6 , 9 8 0 kWh, which can be used for chargingexternal batteries.

I N T R O D U C T I O NElectrical energy generation for a local distributiongrid, from renewable energy resources through acombined power scheme, is promising for remoteand poor communi t ies in developing countr iescompared wi th e lectr icity solely based on aconventional generator or a central ised gridextension [1–3]. Hybrid electrical energy systemsgive a reliable energy supply [4, 5], a high level ofsustainabil i ty [6] , and flexible expansion whi ledemands increase without interrupting the wholes y s t e m .

Many hybrid systems have been designed andoptimised through different s imulat ion softwaretools [4]. Most of these tools deal with hybridenergy systems which are combinat ions ofphotovoltaic systems, wind turbines and dieselgenerators using battery storage; none of themare designed for photovoltaic/biomass hybridrenewable energy systems. The optimum designsare achieved if the minimal net present cost or thelowest level ised cost of energy is reached.However, these designs would leave a highpercentage of unmet load demand, which wouldlead to system failures.

Cambodia already has some experience withsmall gr ids based on hybrid renewable energysystems [7, 8] , i .e. the combinat ion of a con-ventiona l energy source, commonly a d ieselgenerator, wi th one or more renewable energytechnologies. Examples can be found incombinat ions of a photovoltaic system or abiomass gasif ication system with diesel generatorto produce electricity for rural electrif ication. Thesystems encountered dif f icul ties because the

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* Socheath Sou, The Joint Graduate School of Energy andEnvironment, King Mongkut’s University of TechnologyThonburi, 126 Pracha-Uthit Road, Bangmod, Tungkru, Bangkok10140 Thailand.* * Werner Siemers, The Joint Graduate School of Energy andEnvironment, King Mongkut’s University of TechnologyThonburi, 126 Pracha-Uthit Road, Bangmod, Tungkru, Bangkok10140 Thailand.* * * Robert H. B. Exell, The Joint Graduate School of Energy andEnvironment, King Mongkut’s University of TechnologyThonburi, 126 Pracha-Uthit Road, Bangmod, Tungkru, Bangkok10140 Thailand. (To whom all correspondence should bea d d r e s s e d )© Ambient Press Limited 2010

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Design of a photovoltaic/biomass hybrid electrical energy system for a rural village in Cambodia Sou, Siemers, Exell

designs were made ignor ing the demand. Theresult ing poor s iz ing lead to over- or under-ut i l isat ion and system fai lures, unsustainableelectrical energy production and poor electricalq u a l i t y .

The aim of this study was to develop a modelfor designing photovoltaic/biomass hybridsystems by matching the demand and supply inorder to provide dependable and sustainable off-grid electr icity services for poor and remotevillages in Cambodia where there is no electricitygrid and car batter ies are used for domestice l e c t r i f i c a t i o n .

S T U D Y S I T E

Site selection and profile. A vi l lage, namedChhouk Ksach, was selected for the study basedon three criteria: (1) being representative for thewhole country, (2) having no electricity grid and(3) using car batter ies as a main source ofelectri f icat ion. The vil lage is in Baray district ofKampong Thom province, 120 km from PhnomPenh and 55 km from Kampong Thom town.Figure 1 shows the location of the vi llage on a mapof Cambodia.

The village has a population of 1,869, in 352houses, concentrated in an area of about 0 . 5 k m2.The major source of income is f rom riceproduction, which accounts for about 51.3% ofthe total population; 46% of the population have

incomes from activities such as labour outside thevil lage (23.5%), small in-house businesses (13.4%)and domestic animal husbandry (9.1%). Theremaining 2.7% have unclear sources of income.

Even though this village has no electricity gridconnection, 86.6% of households are electri f iedby indiv idually owned car batter ies, which arenormally designed and used for vehicles, with a5-year l i fet ime. The recharging cyc le var iesbetween 3 and 7 days. Battery charging by adiesel generator is common practice not only inthis v i l lage but also throughout the country.Currently, there are two battery rechargingstations operat ing 6 to 8 hours dai ly in ChhoukK s a c h .

Load profile. There are 352 houses in the village,but some of them are abandoned and some aretemporary. A survey via quest ionna ires, di rectinterviews and site visits was conducted over 188households which use electricity and are expectedto use the electricity service from the project. Theelectr ical energy consumption of these 188households represents the load demand in thevi llage and was used as the baseline for furthercalculations in this study.

The research survey showed that about 64.7%of the households own a televis ion, of which15.57% are colour TVs, and 46.62% of house-holds owning a television also have a VCD player.The electric energy consumption patterns of the

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F i g u r e 1Map of the Kingdom ofCambodia showing thelocation of Chhouk Ksach.

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Design of a photovoltaic/biomass hybrid electrical energy system for a rural village in Cambodia Sou, Siemers, Exell

households do not dif fer much from one toanother, the minimum electrical energy consump-tion being about 2 kWh per household per monthand the average about 5.5 kWh per household perm o n t h .

The daily energy consumption in the vi l lagewas estimated at 43.12 kWh while the peak powerdemand would reach 9 kW. This electrical energyconsumption is low due to the l imitat ion andinconvenience of using car batteries.

Lessons learned from rural electr i f icat ionsystems, where small grids are available, help toestimate the expected increase in the electricalenergy consumption for the vi l lage with theproposed hybrid system, assuming that thevi l lagers wil l change or upgrade the ir e lectr icequipment. In particular, we assume that 10 W D Cfluorescent lamps wi l l be changed to 20 W A C

fluorescent lamps, 9 W DC incandescent lampswill be changed to 11 W AC incandescent lampsand black and white TV sets will be changed to14 inch AC colour TV sets. The estimated dailyenergy demand is estimated to reach 67.12 k W h ,or 24,518 kWh per year, (Table 1).

Colour televisions, f luorescent lamps and VCDplayers are the main electrical appliances. It isnoteworthy that appliances such as refrigeratorscommonly used elsewhere are not used in thisvi l lage ( ice f rom the local market being usedinstead). The predicted load profi le shown inFigure 2 has a low electrical energy consumptionin the daytime, with practically no difference fromone hour to another. The peak power demandincreases sharply in the evening with a peak of1 5 kW at 20:00 making a big difference betweenthe daytime and night time loads.

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T a b l e 1 Estimated daily electrical energy demand of Chhouk Ksach after the installation of the hybrid renewableenergy system.

Number of Estimated energyA p p l i a n c e s Rated power ( W ) a p p l i a n c e s Operation time (h) consumed (kWh)

Fluorescent lamp 2 0 1 8 6 3 . 5 0 1 3 . 0 2Incandescent lamp 1 1 1 1 4 . 0 0 0 . 4 8Colour television 8 0 1 2 2 4 . 0 0 3 9 . 0 4VCD player 3 5 5 2 4 . 5 0 8 . 1 9Audio player 9 1 7 4 . 5 0 0 . 6 9Stereo player 2 5 3 1 4 . 5 0 3 . 4 9Standing/floor fan 4 5 1 4 3 . 5 0 2 . 2 1

T o t a l 6 7 . 1 2

F i g u r e 2Predicted load profile ofChhouk Ksach village afterinstallation of the hybridrenewable energy system.

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an AC line, as shown in Figure 4. The AC couplingtechnique is convenient when different generatorsare used, when the distribution is required overlong distances, and when system expansion isrequired [10]. When there is an electrical energysurplus the backup battery is charged. The storedelectr ical energy is taken from the batteryto supply the load when the demand exceedsthe electr ical energy produced by the maingenerators, or when the generators fail.

The design method. The technologies arechosen in accordance with the locally avai lablerenewable energy resources, namely solar radiation

Solar irradiance. In Cambodia, the study of solarradiation data is still at an early stage and the dataare not ready for use. Therefore, the NASA data-base [9], derived from satell ite surveys conductedbetween 1995 and 2005, is used for the calculationof solar energy in this study.

At the geographical coordinates of ChhoukKsach vi llage, 12°24′ North and 105°05′ East, theaverage global annual solar insolation incident on ahorizontal surface is 5.21 k W h m– 2 per day with anaverage daily maximum irradiance of 0.76 kW m– 2.The variation of solar irradiation depends on thetropical and monsoon seasons. Early in the year,during the dry season, ir radiation is quite high,decreasing towards end of the year in the rainyseason, see Figure 3. The daily ir radiat ionincreases f rom January to Apri l and thendecreases gradually until December.

Woody biomass. Planting fast growing trees forenergy is a pract ical method for biomassproduction in rural areas in Cambodia. Theplantation of fast growing trees can be either inpublic places or in indiv idual home gardens.Therefore, people can earn an income by sellingwood fuel to the power plant. Also, the villages nearChhouck Ksach have large unused land areas.

S Y S T E M D E S I G N

Proposed hybrid system configurat ion. T h econfiguration of the hybrid system depends on theavailable renewable energy sources (solar andwood) and the electricity demand. The simplestway is to couple all electrical energy generators to

F i g u r e 3Average over 11 years(1995–2005) of solarirradiation on a horizontalsurface each day of they e a r .

F i g u r e 4 The proposed configuration of an AC coupledhybrid energy system.

Day of year

k W h m– 2 d– 2

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and woody biomass, together with the loadprofile, Figure 2. The use of a single renewablesystem is not recommended in this study. I f aphotovoltaic system alone is used, the investmentcapital is huge, whi le a gasi f ier for smalldecentral ised power generat ion can only beoperated continuously 6–8 hours per day [11].Therefore, the photovoltaic system is used tosupply all the load demand during the daytime [12]while the gasif ier is used in the evening when theload demand is greatest.

Spreadsheet sof tware is used to design thehybr id renewable energy electric ity supply forthe vi l lage. The energy supply consists of aphotovoltaic system, a biomass gasif icat ionsystem, and a backup battery. The spreadsheetmodel uses as input the hourly load demand and

the hourly solar radiation in one year. The modelcalculates the electrical energy generated by thephotovoltaic system and supplied to the loaddemand each hour. The unconsumed electr icalenergy is used to charge the backup battery untilthe battery is full . If the electrical energy producedby the photovoltaic generator cannot meet theload demand, the battery has to supply the load.The model does the electrical energy balance andcalculates the electrical energy surplus from thehybrid system. We require that the energy outputfrom the photovoltaic system should meet the loaddemand during the daytime and the energy of thebattery should meet the demand at night. Theannual unmet demand is assumed to be zero.Figure 5 i l lustrates the steps in the power andenergy calculation in and out of each component.

F i g u r e 5Calculation steps for thedesign of a hybrid energys y s t e m .

S t a r t

Solar Energy ( Ep v) B i o m a s sLoad Demand ( Ed m d) E n e r g y

Battery Energy ( Eb a t , d i s c h) ( Eb i o)

N o

N o Ed m d , r e m 1 = Ep v – Ed m d( ? )

Ed m d , r e m 2 = Eb a t , d i s c h – Ed m d , r e m 1Ed m d , r e m 2 < Eb i o

Y e s

( ? ) Ed m d , r e m 1 < 0 ( ? ) Ed m d , r e m 1 = 0Eb a t , d i s c h > 0 Ed m d , r e m 1 = 0 S t o p

Y e sEd m d , r e m 1 > 0

Eb a t , c h

( ? )Eb a t , c h > Eb a t , d i s c h N o S t o p

S Y M B O L S

S t a r t Y e s

Input data Es u r p l u s = Eb a t , c h – Eb a t , d i s c h

P r o c e s s

Decision( ? ) Ew a s t e

Es u r p l u s > 0 Y e s ( B C S )S t o r a g e

N oT e r m i n a t o r

Flow direction S t o p

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Design of a photovoltaic/biomass hybrid electrical energy system for a rural village in Cambodia Sou, Siemers, Exell

Power output from PV array. The net powergenerated from the photovoltaic array is obtainedfrom the eff icienc ies of devices used by thee q u a t i o n :

P( p v ) = A I ηm Rf η i n v ( 1 )

w h e r e :A is total surface area of the array, m2,I is hourly solar radiation, kW m– 2,ηm is the module conversion efficiency 12.7%,Rf is the reduction or loss factor of the system,0.78, andη i n v is the efficiency of the inverter, 90%.

The net power for the load is then:

P( n e t , p v ) = P( p v ) ( 1 – S M ) ( 2 )

where the safety margin (SM), or the fractionalloss of the distribution network, is 0.1.

Calculation of battery energy charge/discharge.The available energy to be stored in the backupbattery is:

E( b a t , c h ) = E( e x ) ηc o n t ηc h ( 3 )

w h e r e :E(bat,ch) is the energy to be stored in battery, kWh,E( e x ) is the excess energy f rom load con-sumption, kWh,ηc o n t is the efficiency of the battery chargingcontroller, 90%, andηc h is the eff iciency of battery charging pluswiring losses, 85%.

The backup battery is protected by a chargingcontroller and cannot be overcharged.

The energy avai lable for the load supply bydischarging the battery is assumed to pass severalelectronic devices, including the inverter andcharge control ler. The safety margin on thedistribution network is also included. Thus:

E( b a t , d i s c h ) = E( b a t ) ηc o n t ( 1 – S M ) ( 4 )

w h e r e :E( b a t , d i s c h ) is the net energy from the battery forsupplying to the load, kWh,

E( b a t ) is the energy stored within battery, kWh,ηc o n t is the ef f iciency of the battery chargecontroller, 0.85%, and,

The safety margin (SM) of the distr ibut ionnetwork is 0.1.

The depth of discharging (DoD) level mustnot exceed 60%, otherwise the backup batterywould be damaged and its l ifetime would bereduced [13, 14].

Power output from biomass gasification. In orderto meet the energy demand, the power outputmust at least equal the peak power required bythe load:

P( n e t , o u t ) = P( p - l o a d ) ( 5 )

where P( p - l o a d ) is the peak power required by theload, kW.

In this case, P( n e t , o u t ) is the net electrical powerwhich is available for the load supply taking intoaccount the safety margin of the distribut ionsystem. Therefore the power output from thegenerator is:

P( g a s , o u t ) = P( n e t , o u t ) / ( 1 – S M ) ( 6 )

where the safety margin (SM) of the distributionnetwork is 0.1.

The power output from the generator can becalculated by using the expression below:

P( g a s , i n ) = P( g a s , o u t ) / ηs y s ( 7 )

w h e r e :P( g a s , o u t ) is the power output of the gasifier, kW,a n dηs y s is the eff iciency of the gasif ication system,

2 3 . 4 % .

Energy input of gasifier. The energy input to thegasifier is derived from the power input requiredby the gasif ication process over a period of time.Therefore, the energy input to the gasifier is:

E( g a s , i n ) = P( g a s , i n ) H o u r s ( 8 )

w h e r e :P( g a s , i n ) is the power input to the gasifier, kWa n dE( g a s , i n ) is the energy input to the gasif ier, kWh.

Rate of fuel input. From the power input to thegasifier, the rate of fuel input can be found. TheLeucaena leucocephala tree is used for thiscalculation. Thus:

Rf u e l = P( g a s , i n ) / L H V ( 9 )

w h e r e :LHV is the calorif ic value or lower heating value

of the fuel, 14.83 MJ/kg at moisture content1 5 % ,

E( g a s , i n ) is the energy input to the gasif ier, kWh,a n dRf u e l is the fuel burning rate, kg/h.

System sizing method. The system sizing usingthe spreadsheet follows the fol lowing procedure.

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Design of a photovoltaic/biomass hybrid electrical energy system for a rural village in Cambodia Sou, Siemers, Exell

( 1 ) The s ize of the photovol ta ic array and thestorage capacity of the backup battery arechosen to meet the load demand during thedayt ime and at night a fter the biomassgasifier has been shut down.

( 2 ) The capaci ty of the gasif ier is chosen tosupply all the peak load power, which occursin the evening at 20:00, Figure 2. The gasifieris set to operate at this peak load power for6 hours per day from 18:00 to 23:59.

( 3 ) If there is a shortage of the electrical energysupply from the photovoltaic system and thebattery, the gasifier needs to start operationbefore 18:00 in order to maintain theelectrical supply continuously for 24 hours.

( 4 ) Fina l ly, the s ize of the PV array and thecapaci ty of the battery are readjusted andthe model calculat ion is repeated unt i l theload demand is satisf ied.

RESULTS AND DISCUSSION

Minimum system components. After severaltrials, the minimum size of the PV array andbattery capaci ty which can supply the requiredelectrical energy to the load was determined;

( 1 ) Start ing with the surface area of a photo-vol taic panel, 0.63 m2, and rated power of0 . 0 8 kWp avai lable in Cambodia, the model

finds that a 10 m2 photo-voltaic array rated at1 . 2 7 kWp is required by the hybrid system.

( 2 ) A backup battery capable of stor ing anddelivering 4.37 kWh is needed. A total batterycapacity of 7.28 kWh is needed to del iver4 . 3 7 kWh at 60% state of discharge.

( 3 ) The biomass gasif icat ion system should berated 15 k W e .

The hybrid system can then provide electricalenergy to the load to meet the demand all the time.

Demand and supply curves in the hybrids y s t e m . The power generated each hour by eachcomponent of the system is shown in Figure 6assuming the solar ir radiance has its annualaverage value each hour. Since the power loadduring the daytime is quite low, the photovoltaicsystem alone is responsible for the daytime load.In the evening, the biomass gasif ication systemstarts to produce electr icity to supply energyduring the peak load period. The backup batterysupplies the load after the photovoltaic systemhas stopped and before the biomass system hasstarted. The battery stores excess e lectr icalenergy from the biomass system before midnightand supplies this energy to the load after mid-night when the biomass gasi f icat ion system isclosed down. Figure 6 also shows the relationshipbetween the generated energy and the load

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F i g u r e 6 Hourly comparison between the power generated by the photovoltaic array and by the biomass gasificationsystem, the energy stored in the backup battery, and the hourly load demand of Chhouk Ksach.

Hour of day

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curve. The left vertical axis represents the powerscale (kW) for the photovoltaic generator, thebiomass generator and the load demand. Theright vertical axis represents the backup batteryenergy (kWh).

The simulated result in Figure 7, using thesolar radiation values shown in Figure 3, showsthe battery charge state. The battery is onlypartially discharged during the dry season (hours721 to 2,881), but reaches almost 60% dischargedur ing the wet season (hours 5,041 to 6,481).Therefore, the hybrid system can provide all theenergy needed throughout the year.

Electrical energy balance. The hybrid system isest imated to generate 34,376 kWh per year, ofwhich 4.4% are generated by the photovol ta icsystem and 95.6% are generated by the biomassgenerator. The total losses are est imated to be2 , 8 7 8 kWh per year, or 8.4% of the total energygenerated. The energy flows are shown in Figure 8.It should be noted that the energy flows into andout of the battery balance each other (without anyapparent loss) because the losses in the system

have been est imated separate ly. These lossesinc lude losses in each electrical component,mismatch losses, and distribution or cable losses.

The consumption by the load is 24,518 k W hper year, of which 4% is directly from the photo-voltaic system, 89% is directly from the biomassgenerator, and the ba lance of 7% is from thebattery. The consumption by the load is less thanthe total generated energy available, so there issurplus energy amounting to 6,980 kWh per yearwhich can be used to charge portable batteries forhouseholds not connected to the village grid.

Electrical energy surplus. The electrical energysurplus from the photovoltaic generator is zerobecause any unused electrical energy is stored inthe battery which is never ful ly charged during thedaytime. The biomass gasifier, on the other hand,is always operating at its full capacity and there isan energy surplus as soon as the battery is fullycharged. The calculations show that the surplusenergy in the second half of the year is 10% loweron average than in the f irst half. This is becausethere is less solar radiation in the second half of

Hour of year

F i g u r e 7 The maximum and the minimum amounts of energy stored in the battery each hour in a one-yearsimulation. Zero on the vertical scale means depth of discharge is 60%.

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the year than in the first half and the battery isalmost fully discharged at this time.

The electrical energy surplus of 6,980 kWh cancharge about 22 70 Ah 12 V car batteries per day.If an average recharging cycle is 5 days, then 110households in the village, each using one battery,wil l benefit from the surplus electrical energy. Theportable external batteries can be connected tothe system only during the 6 hours of operation ofthe biomass gasification generator in the evening,when the backup battery is ful l and the loaddemand is less than the biomass generation power.

Biomass gasif ication operation and fuelr e q u i r e m e n t . In the model, the biomass gasifier isassumed to operate 2,190 hours per year with anoveral l eff iciency of 23.4%, generating 15 kW ofelectr ica l power for the load. The speciesLeucaena leucocephala is taken as an example toestimate the amount of wood requi red. Togenerate 1 kWh, the gasifier consumes 1.14 kg ofwoody biomass since the lower heating value ofthe woodchips is 14.83 MJ/kg [15] and themoisture content is 15%. In Cambodia, this fastgrowing tree is very popular for biomassgasif ication technology as it is easy to grow in theCambodian cl imate. The production has beenestimated at about 11.30 t/ha per year at 15%moisture content. The wood can be harvestedtwice per year [16]. Assuming that only 80% of thetotal production is harvested, we need 5 ha ofland area for growing the trees. The harvestedvolume of the trees and the harvesting area arealmost the same as found in a study in India [11].

C O N C L U S I O NThis paper descr ibes a method for designing aphotovoltaic/biomass hybrid energy system for asmall distributed electricity grid at v i l lage level.Deta i ls of a system suitable for the vi l lage ofChhouk Ksach, Kampong Thom Province inCambodia are given. The system designed wouldgive the village a self-sufficient electricity supplyindependent of imported conventional fuel. Thereare many vi l lages similar to Chhouk Ksach inCambodia for which a photovol taic/biomasshybrid energy system could be designed in thesame way.

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F i g u r e 8 Energy flows within the photovoltaic/biomass hybrid system. All numerical values are kilowatt-hours peryear (kWh/y). Some of the energy flows shown have a rounding error of one unit in the least significantd i g i t .

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Design of a photovoltaic/biomass hybrid electrical energy system for a rural village in Cambodia Sou, Siemers, Exell

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