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Study of a solar PV–diesel–battery hybrid power system for a remotely located population near Rafha, Saudi Arabia
Energy 35 (2010) 4986e4995
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Study of a solar PVedieselebattery hybrid power system for a remotely located population near Rafha, Saudi Arabia Shafiqur Rehman*, Luai M. Al-Hadhrami Center for Engineering Research, Research Institute, King Fahd University of Petroleum and Minerals, KFUPM Box 767, Dhahran-31261, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 9 April 2010 Received in revised form 13 August 2010 Accepted 17 August 2010
This study presents a PVediesel hybrid power system with battery backup for a village being fed with diesel generated electricity to displace part of the diesel by solar. The hourly solar radiation data measured at the site along with PV modules mounted on fixed foundations, four generators of different rated powers, diesel prices of 0.2e1.2US$/l, different sizes of batteries and converters were used to find an optimal power system for the village. It was found that a PV array of 2000 kW and four generators of 1250, 750, 2250 and 250 kW; operating at a load factor of 70% required to run for 3317 h/yr, 4242 h/yr, 2820 h/yr and 3150 h/yr, respectively; to produce a mix of 17,640 MWh of electricity annually and 48.33 MWh per day. The cost of energy (COE) of diesel only and PV/diesel/battery power system with 21% solar penetration was found to be 0.190$/kWh and 0.219$/kWh respectively for a diesel price of 0.2$/l. The sensitivity analysis showed that at a diesel price of 0.6$/l the COE from hybrid system become almost the same as that of the diesel only system and above it, the hybrid system become more economical than the diesel only system. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Renewable energy PVediesel hybrid system Solar radiation Battery
1. Introduction In this period of time, the electrification of rural areas has become an effective instrument for the sustainable development of such regions in both developing and developed countries. During last couple of decayed, an increasing interest has been observed in the deployment of medium to large scale windediesel, PVediesel and windePVediesel hybrid power systems for rural electrification in various countries around the globe. There are many indications that there is a large potential market for such systems, and though there are an increasing number of demonstration projects but a true market for such systems has yet to emerge [1]. Baring-Gould [2] outlined the foundations for hybrid power systems architecture and design and presented hybrid systems as an optimum approach for stand-alone power supply options for remote area applications. Wichert et al. [3] studied techno-economical characteristics of hybrid power systems and outlined the expected future directions for the development of hybrids. According to authors, the hybrids power systems were found to be more favorable when the cost of diesel fuel transportation was incorporated in the analysis. Hunter
* Corresponding author. Tel.: þ966 3 8603802/þ966 502085496 (mobile); fax: þ966 3 8603996. E-mail addresses: [email protected] (S. Rehman), [email protected] (L.M. Al-Hadhrami). 0360-5442/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2010.08.025
[4] studied in detail the technical and operational characteristics of windediesel hybrid systems and found that among various disadvantages of diesel only generation in remote areas, there has to be a stand-by diesel generator to be used only when repairs or maintenance are being performed. According to Hunter [4] this could be handled by introducing wind energy generation to the existing diesel only system. Mahmoud and Ibrik [5] reported that the utilization of PV systems for rural electrification in Palestine is economically more feasible than using diesel generators or extension of the high voltage electric grid. Kamel and Dahl [6] assessed the economics of hybrid power systems versus the diesel generation technology in a remote agricultural development area. Their optimization results showed that hybrid systems are less costly than diesel generation from a net present cost perspective even with the high diesel fuel price subsidies. The hybrid power systems exhibit higher reliability and lower cost of generation than those that use only one source of energy [7e13]. Bakos and Soursos [14] conducted techno-economic assessment of an autonomous hybrid PV/diesel hybrid power system installed in a bungalow complex in Elounda, Crete. In remote areas which are far from the grids, the electric energy is supplied either by diesel generators or small hydroelectric plants. Under such circumstances, the supply of diesel fuel becomes so expensive that hybrid diesel/photovoltaic generation becomes competitive with diesel only generation [15]. Schmid et al. [16] reported that PV systems with energy storage connected to
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Fig. 1. Trend of per capita energy consumption in Saudi Arabia.
existing diesel generators, allowing them to be turned off during the day, provide the lowest energy costs. The authors suggested that in Northern Brazil it is economical to convert diesel systems up to 50 kW peak power into hybrid systems. According to Wies et al. [17] and Dufo-López and Bernal-Agustın [18] the solar PV/diesel hybrid power systems provide a reduction in operation and maintenance costs and air pollutants emitted in to the local atmosphere compared to that of a diesel only system. Nfah et al. [19] studied a solar/diesel/battery hybrid power systems to meet the energy requirements of a typical rural household in the range 70e300 kWh/yr and found that a hybrid power system comprising a 1440Wp solar PV array and a 5 kW single-phase generator operating at a load factor of 70%, could meet the required load. Bala and Siddique [20] presented an optimal design of a solar PVediesel hybrid mini-grid system for a fishing community in an isolated islanddSandwip in Bangladesh. Their study revealed that the major share of the cost was for solar panels and batteries. In the coming time, the technological development in solar PV technology and economic production of batteries would make rural electrification in the isolated islands more promising and demanding. A pre-feasibility of windePVebattery hybrid system was performed for a small community in the east-southern part of Bangladesh, [21]. The hybrid system analysis has showed that for a small community consuming 53,317 kWh/year, the cost energy was 0.47USD/kWh with 10% annual capacity shortage and produced 89,151 kWh/year electricity in which 53% came from wind and the remaining 47% from solar [21]. Hrayshat [22] presented a detailed techno-economic analysis of an optimal autonomous hybrid PV/diesel/battery system to meet the load of an off-grid house, located in a remote Jordanian settlement. The hybrid system with 23% of photovoltaic energy penetration and comprised of 2 kW PV array, a 4 kW diesel
generator and two storage batteries in addition to 2 kW converter was found to be the optimal system and economically feasible for diesel prices greater than 0.15 $/L. Dihrab and Sopian [23] proposed a hybrid power system to generate power for grid-connected applications in three cities in Iraq. Results showed that it is possible for Iraq to use the solar and wind energy to generate enough power for villages in the desert and rural areas. Lau et al. [24] studied the possibility of implementing the hybrid photovoltaic (PV)/diesel energy system in remote areas of Malaysia. The investigators demonstrated the impact of PV penetration and battery storage on energy production, cost of energy and number of operational hours of diesel generators for the given hybrid configurations. Abdullaha [25] presented the cost-effectiveness of the solar PV system and the solar/hydro schemes for rural electrification employing the HOMER simulation software. Their results have shown that combined power schemes are more sustainable in terms of supplying electricity compared to a stand-alone PV system due to prolong cloudy and dense haze periods. The present study aims at penetrating the existing diesel power plant through solar photovoltaic system with battery backup to reduce the diesel consumption and at the same time maintain a continuous supply of power to the inhabitants of the village.
Fig. 2. Cumulative power installed capacity (MW) of Saudi Arabia.
Fig. 3. Annual peak load (MW) of Saudi Arabia.
2. Background Saudi Arabia is a vast country with total area of 2,149,690 km2 and having international boundary of 4431 km (bordering countries: Iraq 814 km, Jordan 744 km, Kuwait 222 km, Oman 676 km, Qatar 60 km, UAE 457 km, Yemen 1,458 km). Most of the cities and village are either connected with the national electrical grid or with the isolated grids. Most of the remotely located villages get power through diesel generating power plants. It is really cumbersome to
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surface station pressure, global solar radiation) were measured at Rawdat Ben Habbas village from 13 September 2005 till 18 November 2008. The 40-m tall tower is shown in Fig. 6. The data retrieved through on-site visits and remotely using mobile network data services. The geographical coordinates of the data collection/ proposed project site were 29 8.2820 N latitude, 44 19.8170 E longitude and 443 meters altitudes above mean sea level. 3.1. Meteorological data Fig. 4. Annual energy production (GWh) in Saudi Arabia.
maintain regular supply of fuel and to ensure the continuous electricity supply during breakdowns and scheduled shutdowns of the diesel units. In Saudi Arabia, the per capita energy consumption has reached to 20 kWh/day in 2008 compared to 19.4 kWh/day in 2007, i.e. a net increase of 3.1% in one year [26], as shown in Fig. 1. A maximum of 10% increase in per capita energy was observed in 2004 compared to that in 2003. On an average over 25 years period from 1984 till 2008, 4.1% annual increase in per capita energy per day has been observed [26] which is really significant and needs to be addressed immediately. Moreover, the total installed capacity of the Kingdom in year 2005 was 32,301 MW which increased to 34,825 MW in 2006, an increase of 7.81% and then further increased by 6.1% and 6.21% in the years 2007 and 2008 compared to 2006 and 2007, respectively, as can be seen from Fig. 2. A jump of 11.89% (i.e. from 31,240 MW to 34,953 MW) was observed in peak load in year 2007 compared to that in 2006, as shown in Fig. 3. Again, in 2008, the peak load demand increased by another 8.72% which shows a continuous increasing trend in peak load. The annual energy production (as shown in Fig. 4) from all conventional sources increased by 3.01%, 5.02% and 7.17% during 2006, 2007, and 2008 compared to 2005, 2006 and 2007, respectively. These numbers indicate a progressively increasing production of energy which is reflective of growing energy demands. The total fuel consumption reached 49,740 thousands TOE in year 2008 compared to that of 45,760 TOE in 2007, a net increase of 8.7%, as seen from Fig. 5. Around 3.5% increases were observed in the years 2007 and 2006 compared to those in 2005 and 2006, respectively. Kingdom of Saudi Arabia has vast open land and is the largest producer and supplier of fossil fuels in the world but still encouraging utilization of clean and renewable sources of energy.
Data were recorded every 10 min on a removable data storage card. The wind speed data were measured at 20, 30, and 40 m height above the ground. At each height two sensors were installed. The surface air temperature ( C), relative humidity (%), surface station pressure (mbar), and global solar radiation (GSR, W/m2) data were also measured at 2 m above the ground surface. The monthly mean values of the GSR obtained using daily totals during each month are shown in Fig. 7. April to September higher radiation intensities were observed with highest in June and lowest in December. Similarly, the monthly average diurnal profiles of GSR showed peak intensity around 12 o’clock during all the months of the year as can be seen from Fig. 8. 3.2. Village load data description The hourly electrical load data for the year 2005 was obtained for the village and load analysis was performed. The maximum
3. Site and data description The data collection site at Rawdat Ben Habbas village is an open area from all directions except a couple of warehouse shades and diesel storage tanks in the far vicinity of the wind mast. The site, which is a diesel power plant, is located on the international highway leading to Jordan and is secured. The meteorological data (wind speeds, wind direction, air temperature, relative humidity,
Fig. 5. Annual fuel consumed (Thousands TOE) in Saudi Arabia.
Fig. 6. Meteorological sensors used for measurements.
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Fig. 7. Monthly mean daily global solar radiation at the site.
value of the load recorded was 4.370 MW and occurred on 14 July, 21 July, 31 July and 18 August 2005. The peak was recorded at 15:00 hours. The annual load factor for this area was 0.45. However, the monthly load factor varied between 0.49 in April (low demand) and 0.71 in August (high demand). Fig. 9 shows the hourly load demand for the peak summer day (July 14, 2005). As evident from the graph, the demand increased during the day time due to higher air conditioning load. The average demand for the day was approximately 3.3 MW. The load variation for a typical winter week day (January 03, 2005) is shown in Fig. 10. As shown, the demand was much lower than the summer day. The peak value for the day was only 1.8 MW and was recorded in the evening. During JanuaryeFebruary and NovembereDecember, the peak load appeared at around 18:00 hours while two peaks were observed during March and April at 00:00 and 14:00 hours, as shown in Fig. 11. From June to October the peak load was found to be around 14:00 with highest load of more than 4000 kW during the month of August. 4. PVedieselebattery hybrid power system Hybrid power systems can consist of any combination of wind, photovoltaics, diesel, and batteries. Such flexibility has obvious
advantages for customizing a system to a particular site’s energy resources, costs, and load requirements. In the present case, a PVeDiesel hybrid power system with battery backup and a power converter is used to design and meet the load requirements of the village under investigation. The schematic diagram of the PVeDieseleBattery hybrid model used in this study is depicted in Fig. 12. The hybrid power system optimization tool HOMER [27] developed by NREL has been used in the present study and the details of the same are given in next paragraph. 4.1. HOMER software hybrid power system modeling tool HOMER [27] is primarily an optimization software package which simulates varied renewable energy sources (RES) system configurations and scales them on the basis of net present cost (NPC) which is the total cost of installing and operating the system over its lifetime. It firstly assesses the technical feasibility of the RES system (i.e. whether the system can adequately serve the electrical and thermal loads and any other constraints imposed by the user). Secondly, it estimates the NPC of the system. HOMER models each individual system configuration by performing an hourly time-step simulation of its operation for
Fig. 8. Diurnal variation of global solar radiation during different months of the year.
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project lifetime, including initial set-up costs (IC), component replacements within the project lifetime, maintenance and fuel. Future cash flows are discounted to the present. HOMER calculates NPC according to the following equation [27] NPC ¼ TAC/CRF
(1)
where TAC is the total annualized cost ($). The capital recovery factor (CRF) is given by [18]: CRF ¼ i(1 þ i)**N/(i þ i)**N
Fig. 9. Typical summer day load demand for the village (July 14, 2005).
where N is the number of years and ‘i’ is the annual real interest rate (6% in the present case). HOMER assumes that all prices escalate at the same rate, and applies an ‘annual real interest rate’ rather than a ‘nominal interest rate’. NPC estimation in HOMER also takes into account salvage costs, which is the residual value of power system components at the end of the project lifetime. The equation to calculate salvage value (S) is S ($) ¼ Crep (Rrem/Rcomp)
Fig. 10. Typical winter day load demand for the village (January 03, 2005).
one year duration. The available renewable power is calculated and is compared to the required electrical load. Following calculations of one-year duration, any constraints on the system imposed by the user are then assessed; e.g. the fraction of the total electrical demand served or the proportion of power generated by renewable sources. Net present cost (NPC) represents the life cycle cost of the system. The calculation assesses all costs occurring within the
(2)
(3)
where Crep is the replacement cost of the component ($), Rrem is the remaining life of the component (t) and Rcomp is the lifetime of the component (t). Annual savings are estimated by subtracting the annualized costs for each supply method from each other, giving the overall saving or loss for each year. Year 0 will have a negative figure as the initial cost (IC) of the hybrid RES exceeds that of the grid-only system. Finally, the annual savings are cumulatively summed to provide the cash flow for the duration of the project. Published payback times for grid-connected small-scale systems range from 7 years (IC aided by large rebates) [28] to 11.2 years [29], 15 years [30] and as high as 30 years [31]. 4.2. HOMER software input data The main input data include the hourly solar radiation and load data; technical specifications and cost data of diesel generators, photovoltaic modules, power converters, batteries; system
Fig. 11. Diurnal variation of load during different months of the year.
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Batteries Nominal capacity of each battery (Ah) ¼ 1,900 Nominal voltage of each battery (V) ¼ 4 Round trip efficiency (%) ¼ 80 Minimum state of charge (%) ¼ 40 Number of batteries per stack ¼ 10 Number stacks considered ¼ 0, 20, 30 and 40 Number of batteries considered ¼ 0, 200, 300 and 400 Nominal capacity of each stack considered ¼ 0; 380,000 Ah (1520 kWh); 570,000 Ah (2280 kWh), and 760,000 Ah (3040 kWh) Minimum battery life (years) ¼ 5 Expected lifetime throughput (MWh) ¼ 2113.8; 3170.7; and 4227.6 Cost of battery (US$/battery) ¼ 1100 Replacement cost of battery (US$/battery) ¼ 1000 Operation and maintenance cost of batteries (US$/battery/ year) ¼ 10
Fig. 12. PVediesel hybrid model with battery backup.
controls; economic parameters; and system constraints. The details of solar radiation and load data has been given above in the preceding paragraphs and the values of remaining data are given below: Control parameters Minimum renewable energy fractions (MRF) considered ¼ 0%, 20%, 30% and 40% Annual real interest rate ¼ 6% Plant working life span ¼ 20 years Diesel price considered (US$/l) ¼ 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 Dispatch strategy: cyclic charging and Apply setpoint state of charge ¼ 80% Operating reserve: as percent of load, hourly load ¼ 10% As percent of renewable output, solar power output ¼ 10% Photovoltaics modules Photovoltaic sizes considered (kW) ¼ 0, 2000, 3000, 4500, and 5000 Cost of photovoltaic array (US$/kW) ¼ 5000 Replacement cost of photovoltaic array (US$/kW) ¼ 5000 Operation and maintenance cost of PV array (US$/kW/year) ¼ 50 Photovoltaic modules were considered as fixed Working life of photovoltaic panels (years) ¼ 20 Power converter Power converter sizes considered (kW) ¼ 0 and 3000 Cost of power converter (US$/kW) ¼ 900 Replacement cost of power converter (US$/kW) ¼ 900 Operation and maintenance cost of power converter (US$/kW/ year) ¼ 0 Working life span of power converter (years) ¼ 15 Inverter efficiency (%) ¼ 90
Diesel generators Generator 1 sizes considered (kW) ¼ 0, 1000, 1250, 1500, and 1750 Generator 2 sizes considered (kW) ¼ 0, 750, 1000, and 1250 Generator 3 sizes considered (kW) ¼ 0, 1750, 2000, 2250, and 2500 Generator 4 sizes considered (kW) ¼ 0, 150, 250, and 500 Lifetime operating hours (hours) ¼ 20,000 Minimum load ratio (%) ¼ 30 Capital cost (US$/kW) ¼ 1521 Replacement cost (US$/kW) ¼ 1521 Operation and maintenance cost (US$/hour) ¼ 0.012 5. Results and discussion Based on the above input, a total of 448,000 runs were made which comprised of 28 sensitivities and 16,000 simulations for each sensitivity run. A high speed computer, Pentium D, with 3.2 GHz speed, 2 GB ram took 3 h, 43 min and 9 s to complete the required simulation. The HOMER suggested an optimal PVedieselebattery hybrid power system for the village with 2000 kWp PV panels (21% solar energy penetration); four generators with rated power of 1250, 750, 2250 and 250 kW; 300 batteries; and 3000 kW sized power converter. The suggested optimal hybrid power system was found to have a capital cost of 19,874,500$ with an annual operating cost of 1,996,715$, total net present cost (NPC) of 42,776,660$ and levelized cost of energy (COE) of 0.219$/kWh, as shown in Table 1. The diesel only power system was found to be the most economical power systems with a diesel price >0.6$/l but turned un-economical at a diesel price of 0.8$/l. The energy output and the economical analysis of the proposed hybrid systems and the related sensitivity analysis is provided in the forthcoming paragraphs. 5.1. Energy yield analysis The proposed PVedieselebattery hybrid system was able to meet the energy requirement of the village with 21% solar photovoltaic power penetration in to the existing diesel only power system. Table 2 summarizes the energy contribution by solar PV system and the existing four generators. As seen from this table, 79% of the energy is supplied by the diesel generators and the remaining 21% by the solar PV system. The proposed 21% solar PV penetration system was found to be optimal in terms of excess energy i.e. only 0.67% or 118,631 kWh of the energy was in excess.
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Table 1 Optimal PVedieselebattery hybrid power system for the village.
With 30% solar PV penetration, the excess energy was 3.48% and 9.94% for 42% penetration. The monthly mean power contribution of PV systems to the hybrid power system remain almost the same with slight variation of maximum and minimum of 466 kW and 341 kW in September and December, respectively, as shown in Fig. 13. The total power generated by all the generators (Gen) was found to be maximum in August and minimum in March. The annual diesel consumption variation with solar energy fraction is depicted in Fig. 14. It is evident from this figure that solar power penetration has direct impact on fuel consumption and thereof fuel conservation. Furthermore, the number of running hours of the generators
decreased with an increase in solar energy penetration in to the existing diesel only power system, as can be seen from Fig. 15. The number of running hours of the largest unit of the diesel decreased drastically compared to that of smaller units. This means that the larger units will have longer life and will require lesser maintenance.
Table 2 Energy contribution of different sources. Production PV array Generator Generator Generator Generator Total
1 2 3 4
kWh/yr
%
3,634,638 4,121,250 2,367,724 6,137,742 668,763
21 23 17 35 4
17,640,122
100
Fig. 13. Monthly mean power contribution by solar PV and diesel power systems.
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Fig. 14. Effect of solar PV penetration on diesel consumption.
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Fig. 16. Effect of solar PV penetration on GHG emissions.
5.3. Economical analysis
Fig. 15. Effect of solar PV penetration on number of running hours of diesel generators.
5.2. Green house gas (GHG) emissions The proposed pdedieselebattery hybrid power system with 21% PV penetration could avoid addition of 3321.1 (15,877.83e12,566.72) tons of GHG equivalent of CO2 annually in to the local atmosphere of the village under consideration. Furthermore, during the lifetime of the hybrid power plant, a total of 66,422 tons of GHG could be avoided from entering in to the local atmosphere of the village which will further improve the health of the local inhabitants and results in reduction of their medical bills. The reduction in the quantity of different air pollutants for 21% PV penetration compared to that diesel only power plant is given in Table 3. Almost 21% decrease in each pollutant is noticed for a 21% PV penetration in to the existing diesel only power system. The reduction in total GHG with increasing PV penetration of 20, 30 and 40% is depicted in Fig. 16 which shows visible positive impact on GHG reduction.
The total costs of each component of the hybrid power systems, including mainly the PV panels, four generators, battery bank and power converter, are shown in Fig. 17 and the breakup of capital, replacement, O & M, fuel and salvage costs is given in Table 4 and the corresponding annualized costs are included in Table 5. It is evident, that bulk of the total net present cost (NPC) is accounted for diesel generating sets and the least for batteries. The annualized capital cost of PV panels was 871,846$ while that of diesel units it was 596,735 $ but the corresponding O & M costs were 10,000$ and 173,523$. Furthermore, the fuel cost for diesel sets was 928,640$ and zero in case of PV system. The COE increases with the increasing cost of diesel, as seen from Fig. 18. The COE also increases with increasing solar PV penetration at lower diesel prices < 0.6$/l. At a diesel price of 0.6$/l and more the diesel only power system becomes un-economical compared to PVedieselebattery hybrid power systems as seen from Fig. 18. Furthermore, Each MWh of electricity produced from renewable sources results in to conservation of about 1.7 barrels of fuel which means a revenues earning of 136$. In the present case, the PV system contributes 3694.6 MWh electricity which means a saving of 6281 barrels of fuel and hence a foreign earning of 502,470$ annually. In 20 years time, the integration of PV systems in to the existing diesel only system can result in revenue savings of more than ten millions dollars. Additionally, the utilization renewable energy sources will also result in earning carbon credits of around 20$ for each ton of GHG avoided from entering in to the atmosphere. In the present scenario, a total of 66,420$ could be earned annually as a result of avoidance of 3321 tons of GHG from entering in to the atmosphere. Over the lifetime of the hybrid power plant
Table 3 Annual GHG emissions for hybrid power system. Pollutant
Carbon dioxide Carbon monoxide Unburned hydrocarbons Particulate matter Sulfur dioxide Nitrogen oxides
Emissions (kg/yr) Diesel only
21% PV Penetration
15,460,978 38,163 4227 2877 31,048 340,533
12,227,066 30,181 3343 2275 24,554 269,305
Fig. 17. Cash flow summary of various components of the hybrid power system.
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Table 4 Summary of various costs related to the PVedieselebattery hybrid power system. Component
Capital ($)
Replacement ($)
O&M ($)
Fuel ($)
Salvage ($)
Total ($)
PV Generator 1 Generator 2 Generator 3 Generator 4 Surrette 4KS25P Converter System
10,000,000 1,901,250 1,140,750 3,422,250 380,250 330,000 2,700,000 19,874,500
0 2,942,278 2,405,716 3,761,287 797,156 273,840 1,126,617 11,306,891
1,146,993 570,686 437,899 873,320 108,391 34,410 0 3,171,698
0 3,124,448 2,285,842 4,713,078 528,058 0 0 10,651,425
623,610 404,896 269,614 192,073 94,851 81,556 561,249 2,227,850
10,523,383 8,133,766 6,000,593 12,577,864 1,719,003 556,694 3,265,368 42,776,660
Table 5 Summary of annualized cost of the hybrid power system. Component
Capital ($/yr)
Replacement ($/yr)
O&M ($/yr)
Fuel [$/yr]
Salvage ($/yr)
Total ($/yr)
PV Generator 1 Generator 2 Generator 3 Generator 4 Surrette 4KS25P Converter System
871,846 165,760 99,456 298,367 33,152 28,771 235,398 1,732,750
0 256,521 209,741 327,826 69,500 23,875 88,224 985,786
100,000 49,755 38,178 76,140 9450 3000 0 276,523
0 272,404 199,290 410,808 46,038 0 0 928,640
54,369 35,301 23,506 16,746 8270 7110 48,932 194,234
917,477 709,139 523,159 1,096,596 149,871 48,535 284,690 3,729,464
be developed and practical aspects of the development, operation, maintenance and thereof improvement should studied. Acknowledgement The authors are thankful to the Research Institute of King Fahd University of Petroleum and Minerals for providing financial and technical support required for the study presented in this paper. References
Fig. 18. Effect of solar PV penetration on levelized cost of energy (COE).
more than 1.3 millions of dollars could be collected as part carbon credit benefit.
6. Concluding remarks An attempt was made to explore the possibility of utilizing power of the sun to reduce the dependence on fossil fuel for power generation to meet the energy requirement of a small village Rowdat Ben Habbas located in the north eastern part of the Kingdom. The existing diesel only system with four diesel generating units of 1500, 1000, 1750 and 250 kW with diesel price of 02 $/l was found to be most economical power system with levelized cost of energy (COE) of 0.19$/kWh. The next best system with 21% solar PV (2000 kWp) penetration; four diesel generators of 1250, 750, 2250 and 250 kW; battery bank (300); and a power converter of 3000 kW with a COE of 0.219$/kWh was economical at a diesel price of 0.2$/l. With increasing fuel price the diesel only system was found to becoming less economical and at a fuel price of 0.60$/l and above, the diesel only system became un-economical compared to that of hybrid power system. It is recommended that a demonstration hybrid power system with 20% solar PV penetration should
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S. Rehman, L.M. Al-Hadhrami / Energy 35 (2010) 4986e4995 [16] Schmid AL, Hoffmann CAA. Replacing diesel by solar in the Amazon: short-term economic feasibility of PVediesel hybrid systems. Energy Policy 2004;32:881e98. [17] Wies RW, Johnson RA, Agrawal AN, Chubb TJ. Simulink model for economic analysis and environmental impacts of a PV with Diesel battery system for remote villages. IEEE Trans Power Systems 2005;20(2):692e700. [18] Dufo-López R, Bernal-Agustín JL. Design and control strategies of PVediesel systems using genetic algorithms. Solar Energy 2005;79(1):33e46. [19] Nfah EM, Ngundam JM, Tchinda R. Modelling of solar/diesel/battery hybrid power systems for far-north Cameroon. Renewable Energy 2007;32: 832e44. [20] Bala BK, Siddique SA. Optimal design of a PVediesel hybrid system for electrification of an isolated islanddsandwip in Bangladesh using genetic algorithm. Energy for Sustainable Development 2009;13:137e42. [21] Sanjoy KN, Himangshu RG. Prospect of windePVebattery hybrid power system as an alternative to grid extension in Bangladesh. Energy 2010;35:3040e7. [22] Hrayshat ES. Techno-economic analysis of autonomous hybrid photovoltaicedieselebattery system. Energy for Sustainable Development 2009;13: 143e50. [23] Dihrab SS, Sopian K. Electricity generation of hybrid PV/wind systems in Iraq. Renewable Energy 2010;35:1303e7. [24] Lau KY, Yousof MFM, Arshad SNM, Anwari M, Yatim AHM. Performance analysis of hybrid photovoltaic/diesel energy system under Malaysian conditions. Energy 2010;35:3245e55.
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[25] Abdullaha MO, Yunga VC, Anyia M, Othmana AK, Hamida KBA, Taraweb J. Review and comparison study of hybrid diesel/solar/hydro/fuel cell energy schemes for a rural ICT Telecenter. Energy 2010;35:639e46. [26] Electricity: growth and development in the Kingdom of Saudi Arabia. Ministry of Water and Electricity, Office of the Deputy Minister, Information & Statistics Center; 2008. [27] Lambert T, Lilienthal P. HOMER: the micro-power optimization model. Software developed by NREL; 2004. Available from:, http://www.mistaya.ca/homer/MicropowerSystemModelingWithHOMER.pdf. [28] Rhoads-Weaver H, Grove J. Exploring joint green tag financing and marketing models for energy independence. In: Conference proceedings of global windpower, NREL. Available from: http://www.ourwind.org/windcoop/pdfs/ AWEA_Paper.pdf. [29] Yang D. Local photovoltaic wind hybrid system with battery storage or grid connection. NREL. Available from: http://www.chem.jyu.fi/ue/frame_left/ UEsem2005-Yang.pdf. [30] Edwards JL, Wiser R, Bolinger M, Forsyth T. Building a market for small wind: the break-even turnkey cost of residential wind systems in the United States. Berkeley, CA (US): Ernest Orlando Lawrence Berkeley National Laboratory. Available from: http://www.osti.gov/energycitations/product.biblio.jsp?osti_ id¼823465. [31] Forsyth T, Tu P, Gilbert J. Economics of grid-connected small wind turbines in the domestic market. National Renewable Energy Laboratory (NREL). Available from: http://www.nrel.gov/docs/fy00osti/26975.pdf.
Contents lists available at ScienceDirect
Energy journal homepage: www.elsevier.com/locate/energy
Study of a solar PVedieselebattery hybrid power system for a remotely located population near Rafha, Saudi Arabia Shafiqur Rehman*, Luai M. Al-Hadhrami Center for Engineering Research, Research Institute, King Fahd University of Petroleum and Minerals, KFUPM Box 767, Dhahran-31261, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 9 April 2010 Received in revised form 13 August 2010 Accepted 17 August 2010
This study presents a PVediesel hybrid power system with battery backup for a village being fed with diesel generated electricity to displace part of the diesel by solar. The hourly solar radiation data measured at the site along with PV modules mounted on fixed foundations, four generators of different rated powers, diesel prices of 0.2e1.2US$/l, different sizes of batteries and converters were used to find an optimal power system for the village. It was found that a PV array of 2000 kW and four generators of 1250, 750, 2250 and 250 kW; operating at a load factor of 70% required to run for 3317 h/yr, 4242 h/yr, 2820 h/yr and 3150 h/yr, respectively; to produce a mix of 17,640 MWh of electricity annually and 48.33 MWh per day. The cost of energy (COE) of diesel only and PV/diesel/battery power system with 21% solar penetration was found to be 0.190$/kWh and 0.219$/kWh respectively for a diesel price of 0.2$/l. The sensitivity analysis showed that at a diesel price of 0.6$/l the COE from hybrid system become almost the same as that of the diesel only system and above it, the hybrid system become more economical than the diesel only system. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Renewable energy PVediesel hybrid system Solar radiation Battery
1. Introduction In this period of time, the electrification of rural areas has become an effective instrument for the sustainable development of such regions in both developing and developed countries. During last couple of decayed, an increasing interest has been observed in the deployment of medium to large scale windediesel, PVediesel and windePVediesel hybrid power systems for rural electrification in various countries around the globe. There are many indications that there is a large potential market for such systems, and though there are an increasing number of demonstration projects but a true market for such systems has yet to emerge [1]. Baring-Gould [2] outlined the foundations for hybrid power systems architecture and design and presented hybrid systems as an optimum approach for stand-alone power supply options for remote area applications. Wichert et al. [3] studied techno-economical characteristics of hybrid power systems and outlined the expected future directions for the development of hybrids. According to authors, the hybrids power systems were found to be more favorable when the cost of diesel fuel transportation was incorporated in the analysis. Hunter
* Corresponding author. Tel.: þ966 3 8603802/þ966 502085496 (mobile); fax: þ966 3 8603996. E-mail addresses: [email protected] (S. Rehman), [email protected] (L.M. Al-Hadhrami). 0360-5442/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2010.08.025
[4] studied in detail the technical and operational characteristics of windediesel hybrid systems and found that among various disadvantages of diesel only generation in remote areas, there has to be a stand-by diesel generator to be used only when repairs or maintenance are being performed. According to Hunter [4] this could be handled by introducing wind energy generation to the existing diesel only system. Mahmoud and Ibrik [5] reported that the utilization of PV systems for rural electrification in Palestine is economically more feasible than using diesel generators or extension of the high voltage electric grid. Kamel and Dahl [6] assessed the economics of hybrid power systems versus the diesel generation technology in a remote agricultural development area. Their optimization results showed that hybrid systems are less costly than diesel generation from a net present cost perspective even with the high diesel fuel price subsidies. The hybrid power systems exhibit higher reliability and lower cost of generation than those that use only one source of energy [7e13]. Bakos and Soursos [14] conducted techno-economic assessment of an autonomous hybrid PV/diesel hybrid power system installed in a bungalow complex in Elounda, Crete. In remote areas which are far from the grids, the electric energy is supplied either by diesel generators or small hydroelectric plants. Under such circumstances, the supply of diesel fuel becomes so expensive that hybrid diesel/photovoltaic generation becomes competitive with diesel only generation [15]. Schmid et al. [16] reported that PV systems with energy storage connected to
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Fig. 1. Trend of per capita energy consumption in Saudi Arabia.
existing diesel generators, allowing them to be turned off during the day, provide the lowest energy costs. The authors suggested that in Northern Brazil it is economical to convert diesel systems up to 50 kW peak power into hybrid systems. According to Wies et al. [17] and Dufo-López and Bernal-Agustın [18] the solar PV/diesel hybrid power systems provide a reduction in operation and maintenance costs and air pollutants emitted in to the local atmosphere compared to that of a diesel only system. Nfah et al. [19] studied a solar/diesel/battery hybrid power systems to meet the energy requirements of a typical rural household in the range 70e300 kWh/yr and found that a hybrid power system comprising a 1440Wp solar PV array and a 5 kW single-phase generator operating at a load factor of 70%, could meet the required load. Bala and Siddique [20] presented an optimal design of a solar PVediesel hybrid mini-grid system for a fishing community in an isolated islanddSandwip in Bangladesh. Their study revealed that the major share of the cost was for solar panels and batteries. In the coming time, the technological development in solar PV technology and economic production of batteries would make rural electrification in the isolated islands more promising and demanding. A pre-feasibility of windePVebattery hybrid system was performed for a small community in the east-southern part of Bangladesh, [21]. The hybrid system analysis has showed that for a small community consuming 53,317 kWh/year, the cost energy was 0.47USD/kWh with 10% annual capacity shortage and produced 89,151 kWh/year electricity in which 53% came from wind and the remaining 47% from solar [21]. Hrayshat [22] presented a detailed techno-economic analysis of an optimal autonomous hybrid PV/diesel/battery system to meet the load of an off-grid house, located in a remote Jordanian settlement. The hybrid system with 23% of photovoltaic energy penetration and comprised of 2 kW PV array, a 4 kW diesel
generator and two storage batteries in addition to 2 kW converter was found to be the optimal system and economically feasible for diesel prices greater than 0.15 $/L. Dihrab and Sopian [23] proposed a hybrid power system to generate power for grid-connected applications in three cities in Iraq. Results showed that it is possible for Iraq to use the solar and wind energy to generate enough power for villages in the desert and rural areas. Lau et al. [24] studied the possibility of implementing the hybrid photovoltaic (PV)/diesel energy system in remote areas of Malaysia. The investigators demonstrated the impact of PV penetration and battery storage on energy production, cost of energy and number of operational hours of diesel generators for the given hybrid configurations. Abdullaha [25] presented the cost-effectiveness of the solar PV system and the solar/hydro schemes for rural electrification employing the HOMER simulation software. Their results have shown that combined power schemes are more sustainable in terms of supplying electricity compared to a stand-alone PV system due to prolong cloudy and dense haze periods. The present study aims at penetrating the existing diesel power plant through solar photovoltaic system with battery backup to reduce the diesel consumption and at the same time maintain a continuous supply of power to the inhabitants of the village.
Fig. 2. Cumulative power installed capacity (MW) of Saudi Arabia.
Fig. 3. Annual peak load (MW) of Saudi Arabia.
2. Background Saudi Arabia is a vast country with total area of 2,149,690 km2 and having international boundary of 4431 km (bordering countries: Iraq 814 km, Jordan 744 km, Kuwait 222 km, Oman 676 km, Qatar 60 km, UAE 457 km, Yemen 1,458 km). Most of the cities and village are either connected with the national electrical grid or with the isolated grids. Most of the remotely located villages get power through diesel generating power plants. It is really cumbersome to
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surface station pressure, global solar radiation) were measured at Rawdat Ben Habbas village from 13 September 2005 till 18 November 2008. The 40-m tall tower is shown in Fig. 6. The data retrieved through on-site visits and remotely using mobile network data services. The geographical coordinates of the data collection/ proposed project site were 29 8.2820 N latitude, 44 19.8170 E longitude and 443 meters altitudes above mean sea level. 3.1. Meteorological data Fig. 4. Annual energy production (GWh) in Saudi Arabia.
maintain regular supply of fuel and to ensure the continuous electricity supply during breakdowns and scheduled shutdowns of the diesel units. In Saudi Arabia, the per capita energy consumption has reached to 20 kWh/day in 2008 compared to 19.4 kWh/day in 2007, i.e. a net increase of 3.1% in one year [26], as shown in Fig. 1. A maximum of 10% increase in per capita energy was observed in 2004 compared to that in 2003. On an average over 25 years period from 1984 till 2008, 4.1% annual increase in per capita energy per day has been observed [26] which is really significant and needs to be addressed immediately. Moreover, the total installed capacity of the Kingdom in year 2005 was 32,301 MW which increased to 34,825 MW in 2006, an increase of 7.81% and then further increased by 6.1% and 6.21% in the years 2007 and 2008 compared to 2006 and 2007, respectively, as can be seen from Fig. 2. A jump of 11.89% (i.e. from 31,240 MW to 34,953 MW) was observed in peak load in year 2007 compared to that in 2006, as shown in Fig. 3. Again, in 2008, the peak load demand increased by another 8.72% which shows a continuous increasing trend in peak load. The annual energy production (as shown in Fig. 4) from all conventional sources increased by 3.01%, 5.02% and 7.17% during 2006, 2007, and 2008 compared to 2005, 2006 and 2007, respectively. These numbers indicate a progressively increasing production of energy which is reflective of growing energy demands. The total fuel consumption reached 49,740 thousands TOE in year 2008 compared to that of 45,760 TOE in 2007, a net increase of 8.7%, as seen from Fig. 5. Around 3.5% increases were observed in the years 2007 and 2006 compared to those in 2005 and 2006, respectively. Kingdom of Saudi Arabia has vast open land and is the largest producer and supplier of fossil fuels in the world but still encouraging utilization of clean and renewable sources of energy.
Data were recorded every 10 min on a removable data storage card. The wind speed data were measured at 20, 30, and 40 m height above the ground. At each height two sensors were installed. The surface air temperature ( C), relative humidity (%), surface station pressure (mbar), and global solar radiation (GSR, W/m2) data were also measured at 2 m above the ground surface. The monthly mean values of the GSR obtained using daily totals during each month are shown in Fig. 7. April to September higher radiation intensities were observed with highest in June and lowest in December. Similarly, the monthly average diurnal profiles of GSR showed peak intensity around 12 o’clock during all the months of the year as can be seen from Fig. 8. 3.2. Village load data description The hourly electrical load data for the year 2005 was obtained for the village and load analysis was performed. The maximum
3. Site and data description The data collection site at Rawdat Ben Habbas village is an open area from all directions except a couple of warehouse shades and diesel storage tanks in the far vicinity of the wind mast. The site, which is a diesel power plant, is located on the international highway leading to Jordan and is secured. The meteorological data (wind speeds, wind direction, air temperature, relative humidity,
Fig. 5. Annual fuel consumed (Thousands TOE) in Saudi Arabia.
Fig. 6. Meteorological sensors used for measurements.
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Fig. 7. Monthly mean daily global solar radiation at the site.
value of the load recorded was 4.370 MW and occurred on 14 July, 21 July, 31 July and 18 August 2005. The peak was recorded at 15:00 hours. The annual load factor for this area was 0.45. However, the monthly load factor varied between 0.49 in April (low demand) and 0.71 in August (high demand). Fig. 9 shows the hourly load demand for the peak summer day (July 14, 2005). As evident from the graph, the demand increased during the day time due to higher air conditioning load. The average demand for the day was approximately 3.3 MW. The load variation for a typical winter week day (January 03, 2005) is shown in Fig. 10. As shown, the demand was much lower than the summer day. The peak value for the day was only 1.8 MW and was recorded in the evening. During JanuaryeFebruary and NovembereDecember, the peak load appeared at around 18:00 hours while two peaks were observed during March and April at 00:00 and 14:00 hours, as shown in Fig. 11. From June to October the peak load was found to be around 14:00 with highest load of more than 4000 kW during the month of August. 4. PVedieselebattery hybrid power system Hybrid power systems can consist of any combination of wind, photovoltaics, diesel, and batteries. Such flexibility has obvious
advantages for customizing a system to a particular site’s energy resources, costs, and load requirements. In the present case, a PVeDiesel hybrid power system with battery backup and a power converter is used to design and meet the load requirements of the village under investigation. The schematic diagram of the PVeDieseleBattery hybrid model used in this study is depicted in Fig. 12. The hybrid power system optimization tool HOMER [27] developed by NREL has been used in the present study and the details of the same are given in next paragraph. 4.1. HOMER software hybrid power system modeling tool HOMER [27] is primarily an optimization software package which simulates varied renewable energy sources (RES) system configurations and scales them on the basis of net present cost (NPC) which is the total cost of installing and operating the system over its lifetime. It firstly assesses the technical feasibility of the RES system (i.e. whether the system can adequately serve the electrical and thermal loads and any other constraints imposed by the user). Secondly, it estimates the NPC of the system. HOMER models each individual system configuration by performing an hourly time-step simulation of its operation for
Fig. 8. Diurnal variation of global solar radiation during different months of the year.
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project lifetime, including initial set-up costs (IC), component replacements within the project lifetime, maintenance and fuel. Future cash flows are discounted to the present. HOMER calculates NPC according to the following equation [27] NPC ¼ TAC/CRF
(1)
where TAC is the total annualized cost ($). The capital recovery factor (CRF) is given by [18]: CRF ¼ i(1 þ i)**N/(i þ i)**N
Fig. 9. Typical summer day load demand for the village (July 14, 2005).
where N is the number of years and ‘i’ is the annual real interest rate (6% in the present case). HOMER assumes that all prices escalate at the same rate, and applies an ‘annual real interest rate’ rather than a ‘nominal interest rate’. NPC estimation in HOMER also takes into account salvage costs, which is the residual value of power system components at the end of the project lifetime. The equation to calculate salvage value (S) is S ($) ¼ Crep (Rrem/Rcomp)
Fig. 10. Typical winter day load demand for the village (January 03, 2005).
one year duration. The available renewable power is calculated and is compared to the required electrical load. Following calculations of one-year duration, any constraints on the system imposed by the user are then assessed; e.g. the fraction of the total electrical demand served or the proportion of power generated by renewable sources. Net present cost (NPC) represents the life cycle cost of the system. The calculation assesses all costs occurring within the
(2)
(3)
where Crep is the replacement cost of the component ($), Rrem is the remaining life of the component (t) and Rcomp is the lifetime of the component (t). Annual savings are estimated by subtracting the annualized costs for each supply method from each other, giving the overall saving or loss for each year. Year 0 will have a negative figure as the initial cost (IC) of the hybrid RES exceeds that of the grid-only system. Finally, the annual savings are cumulatively summed to provide the cash flow for the duration of the project. Published payback times for grid-connected small-scale systems range from 7 years (IC aided by large rebates) [28] to 11.2 years [29], 15 years [30] and as high as 30 years [31]. 4.2. HOMER software input data The main input data include the hourly solar radiation and load data; technical specifications and cost data of diesel generators, photovoltaic modules, power converters, batteries; system
Fig. 11. Diurnal variation of load during different months of the year.
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Batteries Nominal capacity of each battery (Ah) ¼ 1,900 Nominal voltage of each battery (V) ¼ 4 Round trip efficiency (%) ¼ 80 Minimum state of charge (%) ¼ 40 Number of batteries per stack ¼ 10 Number stacks considered ¼ 0, 20, 30 and 40 Number of batteries considered ¼ 0, 200, 300 and 400 Nominal capacity of each stack considered ¼ 0; 380,000 Ah (1520 kWh); 570,000 Ah (2280 kWh), and 760,000 Ah (3040 kWh) Minimum battery life (years) ¼ 5 Expected lifetime throughput (MWh) ¼ 2113.8; 3170.7; and 4227.6 Cost of battery (US$/battery) ¼ 1100 Replacement cost of battery (US$/battery) ¼ 1000 Operation and maintenance cost of batteries (US$/battery/ year) ¼ 10
Fig. 12. PVediesel hybrid model with battery backup.
controls; economic parameters; and system constraints. The details of solar radiation and load data has been given above in the preceding paragraphs and the values of remaining data are given below: Control parameters Minimum renewable energy fractions (MRF) considered ¼ 0%, 20%, 30% and 40% Annual real interest rate ¼ 6% Plant working life span ¼ 20 years Diesel price considered (US$/l) ¼ 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 Dispatch strategy: cyclic charging and Apply setpoint state of charge ¼ 80% Operating reserve: as percent of load, hourly load ¼ 10% As percent of renewable output, solar power output ¼ 10% Photovoltaics modules Photovoltaic sizes considered (kW) ¼ 0, 2000, 3000, 4500, and 5000 Cost of photovoltaic array (US$/kW) ¼ 5000 Replacement cost of photovoltaic array (US$/kW) ¼ 5000 Operation and maintenance cost of PV array (US$/kW/year) ¼ 50 Photovoltaic modules were considered as fixed Working life of photovoltaic panels (years) ¼ 20 Power converter Power converter sizes considered (kW) ¼ 0 and 3000 Cost of power converter (US$/kW) ¼ 900 Replacement cost of power converter (US$/kW) ¼ 900 Operation and maintenance cost of power converter (US$/kW/ year) ¼ 0 Working life span of power converter (years) ¼ 15 Inverter efficiency (%) ¼ 90
Diesel generators Generator 1 sizes considered (kW) ¼ 0, 1000, 1250, 1500, and 1750 Generator 2 sizes considered (kW) ¼ 0, 750, 1000, and 1250 Generator 3 sizes considered (kW) ¼ 0, 1750, 2000, 2250, and 2500 Generator 4 sizes considered (kW) ¼ 0, 150, 250, and 500 Lifetime operating hours (hours) ¼ 20,000 Minimum load ratio (%) ¼ 30 Capital cost (US$/kW) ¼ 1521 Replacement cost (US$/kW) ¼ 1521 Operation and maintenance cost (US$/hour) ¼ 0.012 5. Results and discussion Based on the above input, a total of 448,000 runs were made which comprised of 28 sensitivities and 16,000 simulations for each sensitivity run. A high speed computer, Pentium D, with 3.2 GHz speed, 2 GB ram took 3 h, 43 min and 9 s to complete the required simulation. The HOMER suggested an optimal PVedieselebattery hybrid power system for the village with 2000 kWp PV panels (21% solar energy penetration); four generators with rated power of 1250, 750, 2250 and 250 kW; 300 batteries; and 3000 kW sized power converter. The suggested optimal hybrid power system was found to have a capital cost of 19,874,500$ with an annual operating cost of 1,996,715$, total net present cost (NPC) of 42,776,660$ and levelized cost of energy (COE) of 0.219$/kWh, as shown in Table 1. The diesel only power system was found to be the most economical power systems with a diesel price >0.6$/l but turned un-economical at a diesel price of 0.8$/l. The energy output and the economical analysis of the proposed hybrid systems and the related sensitivity analysis is provided in the forthcoming paragraphs. 5.1. Energy yield analysis The proposed PVedieselebattery hybrid system was able to meet the energy requirement of the village with 21% solar photovoltaic power penetration in to the existing diesel only power system. Table 2 summarizes the energy contribution by solar PV system and the existing four generators. As seen from this table, 79% of the energy is supplied by the diesel generators and the remaining 21% by the solar PV system. The proposed 21% solar PV penetration system was found to be optimal in terms of excess energy i.e. only 0.67% or 118,631 kWh of the energy was in excess.
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Table 1 Optimal PVedieselebattery hybrid power system for the village.
With 30% solar PV penetration, the excess energy was 3.48% and 9.94% for 42% penetration. The monthly mean power contribution of PV systems to the hybrid power system remain almost the same with slight variation of maximum and minimum of 466 kW and 341 kW in September and December, respectively, as shown in Fig. 13. The total power generated by all the generators (Gen) was found to be maximum in August and minimum in March. The annual diesel consumption variation with solar energy fraction is depicted in Fig. 14. It is evident from this figure that solar power penetration has direct impact on fuel consumption and thereof fuel conservation. Furthermore, the number of running hours of the generators
decreased with an increase in solar energy penetration in to the existing diesel only power system, as can be seen from Fig. 15. The number of running hours of the largest unit of the diesel decreased drastically compared to that of smaller units. This means that the larger units will have longer life and will require lesser maintenance.
Table 2 Energy contribution of different sources. Production PV array Generator Generator Generator Generator Total
1 2 3 4
kWh/yr
%
3,634,638 4,121,250 2,367,724 6,137,742 668,763
21 23 17 35 4
17,640,122
100
Fig. 13. Monthly mean power contribution by solar PV and diesel power systems.
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Fig. 14. Effect of solar PV penetration on diesel consumption.
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Fig. 16. Effect of solar PV penetration on GHG emissions.
5.3. Economical analysis
Fig. 15. Effect of solar PV penetration on number of running hours of diesel generators.
5.2. Green house gas (GHG) emissions The proposed pdedieselebattery hybrid power system with 21% PV penetration could avoid addition of 3321.1 (15,877.83e12,566.72) tons of GHG equivalent of CO2 annually in to the local atmosphere of the village under consideration. Furthermore, during the lifetime of the hybrid power plant, a total of 66,422 tons of GHG could be avoided from entering in to the local atmosphere of the village which will further improve the health of the local inhabitants and results in reduction of their medical bills. The reduction in the quantity of different air pollutants for 21% PV penetration compared to that diesel only power plant is given in Table 3. Almost 21% decrease in each pollutant is noticed for a 21% PV penetration in to the existing diesel only power system. The reduction in total GHG with increasing PV penetration of 20, 30 and 40% is depicted in Fig. 16 which shows visible positive impact on GHG reduction.
The total costs of each component of the hybrid power systems, including mainly the PV panels, four generators, battery bank and power converter, are shown in Fig. 17 and the breakup of capital, replacement, O & M, fuel and salvage costs is given in Table 4 and the corresponding annualized costs are included in Table 5. It is evident, that bulk of the total net present cost (NPC) is accounted for diesel generating sets and the least for batteries. The annualized capital cost of PV panels was 871,846$ while that of diesel units it was 596,735 $ but the corresponding O & M costs were 10,000$ and 173,523$. Furthermore, the fuel cost for diesel sets was 928,640$ and zero in case of PV system. The COE increases with the increasing cost of diesel, as seen from Fig. 18. The COE also increases with increasing solar PV penetration at lower diesel prices < 0.6$/l. At a diesel price of 0.6$/l and more the diesel only power system becomes un-economical compared to PVedieselebattery hybrid power systems as seen from Fig. 18. Furthermore, Each MWh of electricity produced from renewable sources results in to conservation of about 1.7 barrels of fuel which means a revenues earning of 136$. In the present case, the PV system contributes 3694.6 MWh electricity which means a saving of 6281 barrels of fuel and hence a foreign earning of 502,470$ annually. In 20 years time, the integration of PV systems in to the existing diesel only system can result in revenue savings of more than ten millions dollars. Additionally, the utilization renewable energy sources will also result in earning carbon credits of around 20$ for each ton of GHG avoided from entering in to the atmosphere. In the present scenario, a total of 66,420$ could be earned annually as a result of avoidance of 3321 tons of GHG from entering in to the atmosphere. Over the lifetime of the hybrid power plant
Table 3 Annual GHG emissions for hybrid power system. Pollutant
Carbon dioxide Carbon monoxide Unburned hydrocarbons Particulate matter Sulfur dioxide Nitrogen oxides
Emissions (kg/yr) Diesel only
21% PV Penetration
15,460,978 38,163 4227 2877 31,048 340,533
12,227,066 30,181 3343 2275 24,554 269,305
Fig. 17. Cash flow summary of various components of the hybrid power system.
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S. Rehman, L.M. Al-Hadhrami / Energy 35 (2010) 4986e4995
Table 4 Summary of various costs related to the PVedieselebattery hybrid power system. Component
Capital ($)
Replacement ($)
O&M ($)
Fuel ($)
Salvage ($)
Total ($)
PV Generator 1 Generator 2 Generator 3 Generator 4 Surrette 4KS25P Converter System
10,000,000 1,901,250 1,140,750 3,422,250 380,250 330,000 2,700,000 19,874,500
0 2,942,278 2,405,716 3,761,287 797,156 273,840 1,126,617 11,306,891
1,146,993 570,686 437,899 873,320 108,391 34,410 0 3,171,698
0 3,124,448 2,285,842 4,713,078 528,058 0 0 10,651,425
623,610 404,896 269,614 192,073 94,851 81,556 561,249 2,227,850
10,523,383 8,133,766 6,000,593 12,577,864 1,719,003 556,694 3,265,368 42,776,660
Table 5 Summary of annualized cost of the hybrid power system. Component
Capital ($/yr)
Replacement ($/yr)
O&M ($/yr)
Fuel [$/yr]
Salvage ($/yr)
Total ($/yr)
PV Generator 1 Generator 2 Generator 3 Generator 4 Surrette 4KS25P Converter System
871,846 165,760 99,456 298,367 33,152 28,771 235,398 1,732,750
0 256,521 209,741 327,826 69,500 23,875 88,224 985,786
100,000 49,755 38,178 76,140 9450 3000 0 276,523
0 272,404 199,290 410,808 46,038 0 0 928,640
54,369 35,301 23,506 16,746 8270 7110 48,932 194,234
917,477 709,139 523,159 1,096,596 149,871 48,535 284,690 3,729,464
be developed and practical aspects of the development, operation, maintenance and thereof improvement should studied. Acknowledgement The authors are thankful to the Research Institute of King Fahd University of Petroleum and Minerals for providing financial and technical support required for the study presented in this paper. References
Fig. 18. Effect of solar PV penetration on levelized cost of energy (COE).
more than 1.3 millions of dollars could be collected as part carbon credit benefit.
6. Concluding remarks An attempt was made to explore the possibility of utilizing power of the sun to reduce the dependence on fossil fuel for power generation to meet the energy requirement of a small village Rowdat Ben Habbas located in the north eastern part of the Kingdom. The existing diesel only system with four diesel generating units of 1500, 1000, 1750 and 250 kW with diesel price of 02 $/l was found to be most economical power system with levelized cost of energy (COE) of 0.19$/kWh. The next best system with 21% solar PV (2000 kWp) penetration; four diesel generators of 1250, 750, 2250 and 250 kW; battery bank (300); and a power converter of 3000 kW with a COE of 0.219$/kWh was economical at a diesel price of 0.2$/l. With increasing fuel price the diesel only system was found to becoming less economical and at a fuel price of 0.60$/l and above, the diesel only system became un-economical compared to that of hybrid power system. It is recommended that a demonstration hybrid power system with 20% solar PV penetration should
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