Diesel-solar electricity supply for remote monasteries Zoran Nikolić, Vladimir M. Shiljkut, and Dušan Nikolić Citation: J. Renewable Sustainable Energy 5, 041815 (2013); doi: 10.1063/1.4813068 View online: http://dx.doi.org/10.1063/1.4813068 View Table of Contents: http://jrse.aip.org/resource/1/JRSEBH/v5/i4 Published by the AIP Publishing LLC.

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JOURNAL OF RENEWABLE AND SUSTAINABLE ENERGY 5, 041815 (2013)

Diesel-solar electricity supply for remote monasteries Zoran Nikolic´,1,a) Vladimir M. Shiljkut,2,b) and Dusan Nikolic´3,c) 1

Institute of the Technical Sciences of the SASA, Knez Mihailova str. 35, 11000 Belgrade, Serbia 2 Electricity Distribution Company “Elektrodistribucija Beograd,” Masarikova str. 1-3, 11000 Belgrade, Serbia 3 Entura, 89 Cambridge Park Drive, Hobart, Tasmania, Australia (Received 30 January 2013; accepted 18 June 2013; published online 22 July 2013)

This paper proposes a hybrid autonomous electricity supply system for monasteries as a specific type of load. Chilandar monastery (Mount Athos, Greece) was presented as a case study. Taking into consideration specific location, historical significance, present and future needs of the monastery, and peculiar life style of its inhabitants, a new hybrid system for 400 kWh daily energy consumption and 80 kW peak load have been designed, proposed and elaborated here. It is based on combined use of three new diesel aggregates and a field of photovoltaic panels. Paper further outlines the methodology for selection and sizing up of power generating sources and other equipment. The primary goal for the new system was the reduction of diesel fuel and operational costs. Finally, cost-benefit analysis results of the proposed hybrid system C 2013 AIP Publishing LLC. are presented as well. V [http://dx.doi.org/10.1063/1.4813068]

I. INTRODUCTION

Holy Mountain of Athos (Agion Oros) is one of the most sacred and the most respected places in Christian Orthodox faith. It is located in Northern Greece, in Athos peninsula. Athos peninsula is completely surrounded by Aegean sea, and it is remoted from mainland and its power system. The entire population of Mount Athos consists only of male orthodox monks. Today, they spend their lives in the same way their predecessors did in previous centuries—in prayers, meditation, and work.1 They live in 20 monasteries, several skities (monastic communities) and dozens of particular hermitages (monks’ cells), usually very distant from one another. Hence, from the beginning of electrification, only small, autonomous electrical power generation systems were designed and commissioned in Mount Athos. Isolated power generation systems for supplying customers with peak loads under 100 kW and daily electricity consumption less than 1000 kWh were mostly powered by diesel aggregates (DAs). However, diesel generation brings the following problems: • • • • •

High investment (capital) costs High operational costs Transportation of diesel fuel to remote and isolated locations of diesel generation station can be problematic, especially during winter Diesel generators demand constant maintenance If run at low loads, diesel aggregates have increased fuel consumptions as well as gas emissions.

Autonomous generation of electrical power in the monasteries in Mount Athos has to fulfill some particular conditions, which are mandatory in this specific area:2 a)

Email: [email protected] Email: [email protected] c) Email: [email protected] b)

1941-7012/2013/5(4)/041815/14/$30.00

5, 041815-1

C 2013 AIP Publishing LLC V

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J. Renewable Sustainable Energy 5, 041815 (2013)

Electrical power source should not produce neither noise nor vibrations Electrical power generation must be ecologically acceptable as much as it is possible Diesel fuel consumption should be minimal The system must operate autonomously The system should be highly reliable It is essential that the maintenance of the system should be minimal Above all, system should have capital and operational costs as low as possible.

Technical demands described above, led to the development of the power system in Chilandar monastery, based on diesel aggregates. It provides the necessary electric energy to the monastery and recharges electrical energy storage batteries during day. Without supply interruption, these batteries supply the consumers in the monastery during night, without any noise. Diesel aggregates use diesel fuel, which is becoming increasingly expensive. Renewable energy sources are an attractive option and cheaper option, however they provide highly intermittent power supply. Taking into account these facts, hybrid supplying systems have some advantages,3 which cover the deficiencies of both systems’ types. A. Higher operational reliability of hybrid system

Reliability of supply and reduction of interruption periods are achieved by combining more sources, from which the electricity can be obtained. Photovoltaic panels (PV) demand less maintenance compared with diesel aggregates, reducing that way the operational interruptions as well as the efforts for the periodical maintenance of the equipment.4 B. Reduction of noise and dangerous gasses emission

Diesel aggregates emit polluting particles in the air as well as the noise during their normal operation. In that aspect, they differ significantly from renewable energy sources, whose technologies are complementary to environment protection. C. Continuous supply

Connecting diesel aggregates and PV panels in parallel operation with accumulating batteries increases the ability of acceptance of striking and starting currents of electrical motors. This way, the system becomes less susceptible to supply interruptions. D. Extended operational lifetime of the equipment

Alternating operation of two diesel electrical aggregates, powered in the optimal operational regime, allows the maximal operational lifetime of these machines. Additionally, the optimal regime of battery discharging contributes to their extended operational lifetime as well. E. Costs reductions

Renewable energy source or hybrid power source proved itself as very beneficial electricity generation system, taking into account the savings in fossil fuel consumption and lower maintenance costs. For a conventional diesel aggregates system, in a remote area, fuel and fuel transportation costs are usually quite high, as well as repair and maintenance costs. At the same time, renewable energy sources have high investment costs and very low operational and maintenance costs. II. CASE STUDY—MONASTERY CHILANDAR

The old diesel aggregate station in Chilandar monastery was built by the end of 20th century, with three diesel electrical generators, electric energy storage batteries, and uninterruptible power supply (UPS).5 The reasons for its modernization are its amortization, need to reduce diesel fuel consumption, and environment pollution.

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Nikolic´, Shiljkut, and Nikolic´

J. Renewable Sustainable Energy 5, 041815 (2013)

A. The present system description

The scheme of the present power generation system in Chilandar monastery is shown in Fig. 1. The biggest diesel aggregate, manufactured by English producer, Wilson, has the rated power of 135 kVA. The second aggregate is one of the Italian producer, Meccalte, of 60 kVA rated power. The third, the smallest one, aggregate was made by Uljanik, having rated output power of 55 kVA. The batteries for energy storage, produced by Sonnenschein, have the rated voltage of 360 V and five-hours-lasting capacity of 250 Ah. These batteries, via an inverter of rated power 60 kVA, produced by Sicon, supply the power grid in the monastery at standard voltage 3  380 V, 50 Hz. One diesel aggregate starts its operation at 7:00 AM, taking the whole consumption load of the monastery.6 In the same moment, UPS device changes its operation mode automatically, from DC/AC into AC/DC, and starts to recharge the batteries. At 9:30 PM, the diesel aggregate switches off and the entire electricity supply comes from accumulation batteries. Diesel aggregates do not operate in parallel with battery inverter. Basic device which allows autonomous operation of diesel aggregates station in general is UPS. Two devices were integrated in it: the rectifier for battery recharging and inverter for transforming DC voltage to AC voltage. Also, inverter tracks batteries state of charge and determines the time of switch-on and operation of diesel aggregates. Battery recharging process is performed by IU characteristic, with current constraint, while variable voltage constraint, versus ambient temperature, is 410 V, by 20  C.

FIG. 1. Single-phase connecting scheme of three diesel electric power aggregates, rated powers 55 kVA, 60 kVA, and 135 kVA and the system for uninterrupted supply in existing diesel aggregates station.

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Nikolic´, Shiljkut, and Nikolic´

J. Renewable Sustainable Energy 5, 041815 (2013)

B. Energy balance

Daily load chart of present diesel aggregates station was recorded in June 2008.7 The load recording started at 7:00 AM, when a diesel aggregate was turned on, and electrical load begins to increase significantly. First of all, the UPS device changes its operational regime from inverter to rectifier and starts to recharge the batteries (see Fig. 2). Besides that, there are also few different devices, like water heaters (boilers), compressors, machines, etc., which start to operate then. In 2008, the UPS loaded diesel aggregate with 12 kW, during several hours. After that period, the load decreased and around 5:00 PM dropped to very low value. Currently, monastery is experiencing reconstruction and expansion works, so it is estimated that future electricity needs will be higher than present. It has been estimated that daily electricity consumption in Chilandar monastery is about 223 kWh, during summer period. During daylight, the amount of 141 kWh can be spent on different devices and other consumers. Around 82 kWh are used for battery recharging, while during night about 63 kWh of that energy are delivered back to consumers (total efficiency rate is 0.76). Such amount of energy can be generated only by diesel electrical aggregates. To preserve silence and piece of the monks during night, electricity supply can be obtained from highquality lead-acid accumulating batteries, without the need for maintenance. Commonly, during night, only high priority consumers and devices are supplied—mainly emergency lighting in corridors, cells of the monks, and guests’ rooms. Diesel aggregates mainly operate up to 20.000 working hours. However, diesel aggregates with higher rated powers do not have such long operational lifetime, if they operate at lower loads, i.e., in unfavorable regimes. C. Deficiencies of the present system for autonomous supply

Existing technical solution, shown in Fig. 1, operates since 1997 and still supplies the monastery with electricity of high quality.6,7 During that operational period, however, some deficiencies of that solution have bee noticed: •

During morning hours, the stronger diesel aggregate is turned on, which supplies the batteries with maximal power. Soon after that, other consumers are fed, with the start of morning activities of monks and their guests. Few hours later, consumption load decreases significantly, and this aggregate becomes very poorly loaded.

FIG. 2. Load chart of diesel aggregates station, during daylight and night, with total electrical energy of 223 kWh=day.

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041815-5 • • • •

•

Nikolic´, Shiljkut, and Nikolic´

J. Renewable Sustainable Energy 5, 041815 (2013)

This problem is especially emphasized in late afternoon, by additional load reduction, even though the aggregate with lower rated power is turned on instead of the first one. Sometimes also happened that the aggregate turned out of operation, in consequence of high, striking loads, which inverter could not hold on. During some winter nights, when batteries were not able to accumulate and deliver energy amount sufficient to increased monastery’s needs, diesel aggregates turned on automatically. However, it has been noticed that diesel aggregates operate mainly underloaded, with increased, specific fuel consumption (l/kWh). Consequently, the emission of exhausted gases is increased, too. Inverter does not have enough power to secure and hold on the early morning overloads and to “cover” turn-offs of diesel aggregate.

III. A PROPOSAL OF HYBRID SOLUTION FOR MONASTERY SUPPLY

Our proposal of hybrid solution for supplying the monastery with electric power consists of photovoltaic panels, diesel aggregates, accumulating batteries, and power converters. There are several articles and papers dedicated to modeling of such systems:8 optimal choice of their components9,10 as well as practical realizations.11,12 A. Possible ways for fuel consumption reduction

The reduction of diesel fuel consumption and, consequently, the reduction of annual operational costs of hybrid power plants have been analyzed even for the cases with rated powers higher than several MW.13 These reductions can be achieved using several methods: 1. The use of renewable energy sources

In spite of the existence of several types of renewable sources, which can be used practically and efficiently, the most appropriate for use in monasteries where minimal maintenance, low noise and no visual impact are imperative, are PV panels, which convert solar energy directly into electricity. Optimal conditions for appliance of such supply have been analyzed in many papers, e.g., Ref. 14. 2. More efficient use of fuel in diesel aggregates

By operating diesel aggregates in optimal operating point, it is possible to achieve the diesel fuel consumption of about 0.3 l per generated kWh of electrical energy. That is about 40% less consumption, compared with average 0.5 l per kWh of electrical energy, which is achieved, nowadays, using the present technical solution and existing aggregates. 3. More efficient electricity use

Using electrical devices of class “A” and high-efficiency power consumers, it is possible to achieve significant savings of electrical power. Besides that, it is necessary to turn on bigger consumers during daylight, when there is enough insolation and the electricity is the most payable. 4. The combination of previous methods

The optimal results can be achieved using more or all of the previous methods in the same time. The reduction of diesel fuel in diesel aggregates station that can be achieved using electricity more efficiently. Primarily that means the change of supplying manner of thermic consumers from electricity to other energy sources, e.g., wood, which is present here in abundance. Also, more efficient electricity use means, already mentioned, appliance of devices (electricity consumers) of the highest energy class.

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Nikolic´, Shiljkut, and Nikolic´

J. Renewable Sustainable Energy 5, 041815 (2013)

TABLE I. Monthly amount of generated electrical power from PV panels, rated power 1 kW, fixed under the optimal angle 33 towards the horizontal axis, on Mount Athos. Month

Generation (kWh)

January

71.2

February

85.7

March April

124 137

May

155

June July

153 164

August

160

September October

132 105

November

76.8

December Total

67.0 1430

B. The use of photovoltaic supply

Calculation of PV supply estimation can be found in PVGIS estimates of solar electricity generation15 for Europe and Mount Athos area. The results are shown in Table I and Fig. 3. for fixed system inclination of 33 oriented directly to the south. Nominal power of the PV system is 1.0 kW (crystalline silicon). Estimated losses due to temperature and low irradiance are 5% (using local ambient temperature), estimated loss due to angular reflectance effects are 2.5%, and other losses (cables, inverter, etc.) are 16.0%, so total PV system losses are 25.9%. Minimal electricity generation was recorded in December, only 67 kWh. Maximal generation of electricity generation is in July 164 kWh. Yearly average is 119 kWh per month. Average available time for electricity generation, TPV, in the case of rated power of PV panel of 1 kW, during summer months on Mount Athos, is maximal and reach 5.3 h. During winter months, average available time for electricity generation has minimum value of 2.16 h, 2:16 h  TPV  5:3 h:

(1)

FIG. 3. Annual electrical power generation from PV panels of rated power 1 kW, fixed under the angle 33 towards the horizontal axis.

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Nikolic´, Shiljkut, and Nikolic´

J. Renewable Sustainable Energy 5, 041815 (2013)

Average available time for electricity generation, TPV, in accordance with the examinations of PV supply possibilities, conducted in Serbia15 is in the range between 1.06 and 6.6 h. It is necessary to take into account the fact that Belgrade lies about 500 km northern from Mount Athos and has a continental climate. These results differ significantly from those, previously published in Refs. 16 and 17. The monthly average daily solar global radiation ranges are from 3.61 to 7.96 kWh/m2 in Saudi Arabia. If we divide total annual electrical power generation with rated power of PV panel, the total annual number of hours with insolation is 12 X

TA ¼

Ei

i¼1

PPV

:

(2)

In our case, total annual electricity generation, according to Table I, is 1430 kWh. Rated power of chosen PV panel is 1 kW. Hence, according to Eq. (2), total annual number of hours with insolation in Holly Mount is TA ¼ 1430 h:

(3)

This value is very similar to data obtained from examinations of PV supply possibilities, conducted in Serbia, during 2012.15 C. Efficient use of the fuel in diesel aggregates

Typical chart of specific fuel consumption in a diesel engine, of rated power 80 kW, shown in Fig. 4, points to the fact that the optimal operation of the engine is in the power generating regime, i.e., by constant speed of rotation of 1500min1 in the range from 70% to 90% of engine’s rated power.10 Loads above that power range are not recommended, because the engine would be near its overloading limit, and fuel combustion becomes worse and dark smoke appears. Low loads are bad for the engine’s operation, too, because specific fuel consumption increases significantly, fuel combustion becomes weak, and operational lifetime of the engine is shortened. The basic task was to optimize the operation of the whole power plant and to minimize the fuel consumption.

FIG. 4. Specific diesel fuel consumption versus aggregate’s load.

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Nikolic´, Shiljkut, and Nikolic´

J. Renewable Sustainable Energy 5, 041815 (2013)

Optimal operating range of diesel aggregate can be defined according to the following relation: PDA;min  DPDA;opt  PDA;max ;

(4)

where (PDA;min , PDA;max ) represents the limits of optimal range of a diesel engine operation, DPDA;opt , which can be defined as 0:6  PDA;n  DPDA;opt  0:8  PDA;n :

(5)

The basic idea was the following: diesel engines should always be loaded with constant power and to operate in the point of optimal consumption, as sources of permanent load. Current fuel consumption of diesel aggregate, FCgi , can be calculated according to the following equation, taken from Ref. 11: FCgi ðPgi Þ ¼ be;gi ðPgi Þ  Pgi ;

(6)

where Pg represents generator’s power, and be;g specific consumption by diesel engine’s braking, usually shown in (g/kWh). For diesel engines with low rated powers and medium speeds of rotation, be;g , it is common to use convex curve with minimum value of 80% of rated power, i.e., 0.8Pn;g . D. Efficient use of the batteries for energy storage

Even though the battery storage is the oldest and most familiar energy storage device, significant advances have been made in this technology in recent years to deserve more attention. Lead–acid batteries are the most common batteries used in solar applications today. Lead–acid batteries should not be discharged by more than 80% of their rated capacity or depth of discharge (DOD). Exceeding the 80% DOD shortens the lifetime of the battery.12 Operational range of the battery can be defined according to the relation Pb;min  DPb  Pb;max ;

(7)

where (Pb;min ,Pb;max ) represent the limits of battery’s operation optimal range, DPb , so 0:2  Pb;n  DPb  1:0  Pb;n :

(8)

Battery systems are quiet and non-polluting and are installed near the center of the load. These batteries have efficiencies in the range of 85%.13 A lead–acid nonaqueous (gelled lead acid) battery uses an electrolyte paste instead of a liquid. These batteries do not have to be mounted in an upright position. There is no electrolyte to spill in the case of an accident. Nonaqueous lead–acid batteries typically do not have high life cycle and are more expensive than flooded deep-cycle lead–acid batteries. Lead–acid batteries are inexpensive, readily available, and are highly recyclable, using the elaborate recycling system already in place. E. Operational principle of the system for hybrid supply of the monastery and sizing its equipment

Proposed small electric power plant should generate 400 kWh electrical energy per day, which is the forecasted quantity of electricity consumption in the monastery, Ec;n , for planning horizon. Power plant should be able to generate at least 250 kWh up to 600 kWh electric energy per day, which are limits of minimal and maximal daily consumption. Estimated daily peak load, Pc;max , will be 80 kW. The system for such sources’ power generation management, according to consumers’ demand, has been already published in some articles.14 However, for this particular case-study, we used our own system, developed relaying on technical characteristics of the system’s main components.

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Nikolic´, Shiljkut, and Nikolic´

J. Renewable Sustainable Energy 5, 041815 (2013)

The hybrid system for electricity supply should always have enough energy to feed the consumers. Available energy in the batteries, Eb , can be determined according to Eb ¼ Eg ðkÞ  Ec ðkÞ;

(9)

where Eb is the current energy in the batteries, Eg is the energy of connected sources (including batteries), and Ec is the total energy consumption of connected consumers. Available energy influences on diesel aggregate’s switch on, via generator’s switches (ON/OFF). Furthermore, there is 2 Eb ¼ 4

k X i¼1

Egi 

m X

3 Ecj 5  Bgi ;

(10)

j¼1

where Bgi is the coefficient which defines diesel aggregate’s turn on. One of two smaller diesel aggregates will switch on (Bgi ¼ 1) when Eb;1 ¼ 0:5  Eb;n . It switches off (Bgi ¼ 0) when Eb;2 ¼ 0:8  Eb;n , whereas the Eb;n represents nominal, i.e., rated energy of the battery. The biggest diesel aggregate would be turned on only in the case of some fault, when Eb;min ¼ 0:35  Eb;n Rated power of PV panels should be at such level, to be sufficient to supply the monastery during summer months exclusively with renewable energy. Therefore, we have PPV;n ¼ Ec;n =TPV ;

(11)

where TPV is defined by Eq. (1), although it is enough to accept the value TPV ¼ 5, for secure supply during all summer months. Accumulating batteries should have the capability to store the amount of energy equal to daily energy consumption, Ec;n . In order to obtain operational safety, the best solution is to have two basic diesel aggregates, which can generate at least double amount of monastery’s daily consumption. Therefore, the optimal rated power of diesel aggregate is PDA;n ¼ 2  Ec;n =24 h:

(12)

These diesel aggregates would be used alternately, never in the parallel operation. The third aggregate, with highest rated power, would be turned on only if some fault occurs. In that case, its permanent power should be greater than the peak load PDA;em  Pc;max :

(13)

Rated power of inverter should also be greater than the peak load PInv;n  Pc;max :

(14)

Hybrid power plant would be located about 700 m northern from the present, old diesel aggregating station. In the new hybrid plant, diesel aggregates (D1, D2, and D3) would be installed, and very close to it, three groups of PV panels. Inverters related to PV panels would be located in the future power plant, too. In the re-arranged old diesel aggregates station, there are batteries for energy storage (AB) and inverter with rectifier (UPS). The new hybrid system for electrical power generation (Fig. 5) would consist of PV panels, of total installed power 75 kW, as basic energy source; two diesel aggregates (D1 and D2) of rated power 55 kVA (44 kW) each; one diesel aggregate (D3) of 100 kVA (80 kW); three single-phase inverters (INV, DC/AC), rated power 25 kW each; inverter with rectifier (UPS) of rated power 125 kVA (100 kW); and accumulating battery (AB) for energy storage in amount of 400 kWh. Diesel aggregates (D1 and D2) would operate as the sources of permanent power

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041815-10

Nikolic´, Shiljkut, and Nikolic´

J. Renewable Sustainable Energy 5, 041815 (2013)

FIG. 5. Single-phase scheme of proposed, new hybrid system for electricity supply.

(of 35.2 kW), in the optimal operational point, with minimal fuel consumption per one kWh of generated electrical energy, and with minimal emission of dangerous, exhausted gases and maximal possible operational lifetime. PV panels are the basic source of electrical power, planned for priority use, while two smaller diesel aggregates (D1 and D2) represent additional sources of electricity. They would be used in periods without sufficient insolation. Third diesel aggregate, with the highest rated power, is also an additional source of electricity, planned for operation in cases with extremely high energy demand or emergency, when basic system or its parts (PVs, D1, D2) are out of order. The new solution was created under the assumption that average daily consumption in the monastery and related auxiliary buildings is 400 kWh. As already discussed, the peak load in daily load chart occurs in early morning hours (see Fig. 2), when regular daily activities start: meals preparation in the kitchen, construction works on monastery’s reconstruction and renewal, regular duties of each monk, and activities of pilgrims. Concerning the fact that the batteries would always be at least 50% of required energy amount (400 kWh), the only constraint for the peak load is inverter with rectifier (UPS), whose provided rated power is 125 kVA (100 kW). With sunrise starts the battery recharge from PV panels, via three single-phase inverters, rated power of 25 kW each, i.e., 75 kW in total. In the case of the lack of consumption in the monastery, this power corresponds to 5-h power of battery recharging. During winter period, of course, battery recharging from PVs is weaker and shorter. Diesel aggregate (D1 or D2) would start automatically, if it is necessary, when the level of stored electricity in the batteries drops under 50% of their rated capacity (and forecasted energy demand), which means under 200 kWh. Diesel aggregate would be switched off when energy stored in the batteries reached 80% of their capacity, i.e., 320 kWh. Parallel operation of diesel aggregates is not foreseen. In the case that level of energy stored, for some reason, drops to 35% of energy demand, i.e., 140 kWh, D1 or D2 would be also turned off, but reserve diesel aggregate D3, the biggest one, would be switched on. It would recharge the batteries then, in forced manner, and supply consumers in the monastery, at the same time. This diesel generator could be also switched on if normal supply fails to supply consumers in the monastery directly.

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Nikolic´, Shiljkut, and Nikolic´

J. Renewable Sustainable Energy 5, 041815 (2013)

IV. DISCUSSION A. Advantages of proposed, new system for electricity supply

The hybrid solution is created as optimal one, under the assumption that average daily consumption in the monastery and related auxiliary buildings is about 400 kWh. However, until the completion of all buildings related to the monastery’s complex and renewal of monastery itself, after disastrous fire in 2004, average daily consumption of electricity in it will be less. New supplying system is designed to meet the need for electricity during summer months almost completely from PV panels. During winter months, electricity generation would rely more on diesel aggregates D1 and D2, and fuel consumption would grow significantly. According to very uneven loads which occur during a year, the system should be flexible and to allow higher consumption of electricity in those days when it is necessary. The hybrid solution may obtain, during summer months, in normal operational conditions, 845 kWh of electrical energy from diesel aggregates and 510 kWh from PV panels, i.e., maximum 1.355 kWh per day. During those summer months, however, PV supply is sufficient to cover complete electricity consumption in the monastery. That way, by proposed hybrid solution, significant savings of diesel fuel would be achieved, in comparison with the present solution, based exclusively on diesel generators. During winter months, the hybrid solution may obtain, in normal operational conditions, 845 kWh of electrical energy from diesel aggregates and only 60 kWh from PV panels, i.e., maximum 905 kWh per day. During that period, PV supply only partially could recharge the batteries and achieve reduced savings in fuel consumption. In emergency situations, diesel aggregate D3 of rated power 100 kVA (80 kW) could obtain electricity amount of 1920 kWh per day. The only constraint for the peak load is the inverter with rectifier (UPS) of rated power 125 kVA (100 kW). Proposed hybrid solution has an important characteristic related to reliability of such systems: if UPS operation failed for some reason, or normal regime of monastery supply drops, it is possible to start reserve diesel aggregate D3 and to supply the monastery directly, with rated power of 100 kVA (80 kW). B. Annual savings of diesel fuel

Supposing that average daily electricity consumption is 400 kWh during whole year, total annual consumption in the monastery would be 146 000 kWh. With assumption that it would be only 1430 h/year, PV panels of total power of 75 kW could generate useful electrical energy of 80 974 kWh/year. We supposed that total losses in the system are 24.5%, according to EU Interactive maps for PV GIS.15 Remaining 65 026 kWh is necessary to obtain from diesel aggregates. Taking into account specific diesel fuel consumption of 0.3 l=kWh, it is possible to determine annual diesel fuel consumption of 19 508 l, necessary to generate remaining amount of electrical energy for the monastery.18,19 On the contrary, if only diesel aggregates operate, in the present regime, with average specific fuel consumption of 0.5 l=kWh, to produce complete amount of electrical energy needed in the future, i.e., 146 000 kWh/year, it is necessary to combust 73 000 l of diesel fuel per year. Hence, by realizing and applying the proposed hybrid system, annual savings would be 53 492 l of diesel fuel. Fuel consumption during each year, of course, would vary, and in winter period it would be significantly higher than during summer months. C. Operational lifetime of hybrid power plant

Previous diesel electrical power stations in Chilandar monastery had operational lifetime of 15 years. Diesel aggregates mainly operated 15 000 to 20 000 working hours, in total. After that period, they were substituted with another new ones.

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041815-12

Nikolic´, Shiljkut, and Nikolic´

J. Renewable Sustainable Energy 5, 041815 (2013)

If diesel aggregates D1 and D2 should generate 65 026 kWh of electrical energy per year, as our calculations shown, together they have to be in operation during TDA ¼

EDA 65:026 kWh ¼ 1:847 h: ¼ PD 35:2 kW

(15)

From Eq. (15) stems that in hybrid power plant, diesel aggregates should operate in total 1847 h per year or 9235 h each. It is expected that in optimal conditions and with regular maintenance, these aggregates can work up to 25 000 h or 25 years. Photovoltaic panels normally have the lifetime of 25 years, when occurs the reduction of the level of conversion of sun irradiation into electricity, for 15%. Under previously elaborated operational conditions, the lifetime of accumulating batteries would be about 9 years. Whence the lifetime of the main system’s components, PV panels, is about 25 years, proposed hybrid power plant would have its lifetime of 25 years, too. It is significantly longer than the lifetime of previous diesel electrical power stations. However, in the new plant, the batteries should be replaced each 9 years.

V. CONCLUSION

Proposed and elaborated technical solution of hybrid system with combined, different sources for electric power generation, intended for Chilandar monastery supply, is the optimal one. By this solution, the best energy efficiency of electrical power sources in Chilandar monastery would be achieved. Applying it, the following parameters and conveniences would be achieved: 1. For average daily electricity consumption of 400 kWh, annual consumption of diesel fuel would be 19 508 l, in normal operating conditions. In comparison with the operation only with diesel aggregates, yearly diesel fuel savings would be 53.492 l or 73.3%. 2. Electrical power plant would be able, even under the worst operating conditions, to generate 925 kWh/day. 3. Estimated maximal daily peak load, in the planning horizon, is 80 kW. 4. Projected lifetime of the hybrid power plant is 25 years. Besides previous and very important are the following facts: 5. Silence and peace would be provided in the monastery, without noise and vibrations, usually produced by diesel engines. 6. Proposed solution would achieve annual savings in diesel fuel of 53 492 l, compared to the present solution, based on exclusive use of diesel aggregates. 7. Environment pollution with products of diesel fuel combustion would be significantly reduced and become minimal. 8. Maintenance of the system would be minimal, because diesel aggregates would operate in the best, generation regime, as sources of constant power, in optimal operating point. 9. Minimal specific fuel consumption per generated kWh of electricity would be achieved, as well as minimal emission of exhausted gases and the lifetime of diesel aggregates would be extended. 10. With this solution, the best energy efficiency of electrical power sources in Chilandar monastery would be achieved.

ACKNOWLEDGMENTS

This work was financially supported by the Ministry of Education and Science of Republic of Serbia, through Project No. TR 36 035.

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041815-13

Nikolic´, Shiljkut, and Nikolic´

J. Renewable Sustainable Energy 5, 041815 (2013)

NOMENCLATURE

TA TPV DPDA;opt FCgi Pg be;g Pn;g DPb (Pb;min ,Pb;max ) Pb;n Ec;n Pc;max Eb Eg Ec Bgi Eb;n Ec;n PDA;em Pc;max PInv;n

Total annual number of hours with insolation (h) Daily average available time for electricity generation (h) Optimal diesel aggregate operating range (kW) Current fuel consumption of diesel aggregate (g) Generator power (kW) Diesel engine’s specific fuel consumption (g/kWh) Nominal generator power (kW) Operational range of the battery power (kW) Limits battery power of optimal operation range (kW) Nominal battery power (kW) Daily electricity consumption (kWh) Daily peak load (kW) Current energy in the battery (kWh) Energy of connected sources (including battery) (kWh) Total energy consumption of consumers (kWh) Coefficient which defines diesel aggregate’s turn on Rated energy of the battery (kWh) Daily energy consumption (kWh) Permanent diesel aggregate power (kW) Peak load (kW) Rated power of inverter (kW)

Abbreviations

UPS DC/AC AC/DC DC AC IU PV EU GIS DoD D AB INV

Uninterruptible power supply (rectifier and inverter) Inverter Rectifier Direct current Alternating current Current voltage characteristic Photovoltaic European union Geographical Information System Depth of battery discharge Diesel aggregate Accumulating battery Inverter

1

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J. Renewable Sustainable Energy 5, 041815 (2013)

10

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