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Energy a nd Power Engineering, 2013, 5, 194-197 doi:10.4236/epe.2013.54B037 Published Online July 2013 (http://www.scir p.org/journal/epe) Copyright © 2013 SciRes. EPE Application Research of Off-grid Home Photovolt aic Pow- er System in Shaanxi Northern Region Ke Cheng1, Liu Hao2, Jie Yang1 1School of Power and Energy, Northwestern Polytechnical University, Xi’an, Chin a 2Shaan xi Regional Electri c Power Group Co., LTD., Xi’an, China Email: cksolar@sohu.com Received February, 2013 ABSTRACT Because working performance of off-grid home photovoltaic power system is influenced by factors of solar radiation, ambient temperature and installation angle, this research established power supply model, analyzed working perfor- mance and optimized system configuration, by referencing weather conditions of Yulin and Yan’an and those factors. Results showed that under given solar radiation and ambient temperature, difference of installation angle can cause 30% to 40% difference of performance. In order to meet power demand, installation angles of Yulin and Yan'an were se- lected as 40 degree and 30 degree, and annual output power were 1.44 kWh/Wp and 1.32 kWh/Wp. Based on those results, the config ura tion o f Yul in a nd Ya n'an was 150 Wp and 170 Wp, and annua l outp ut po wer was 172.70 kWh and 179.66 kWh. Systems optimized above can meet the mid-sc ale de mand in S haa nxi northern region and b uild t heo retical foundation of application. Keywords: Off-grid Home Ph otovoltaic Power System; Photovoltaic; Sola r 1. Introduction Shaanxi northern reg ion is located in the north of Shaan- xi province, including Yulin and Yan’an, belonging to semi-arid monsoon climate zone. With sufficient sun- shine, the mean sunshine hours are 6-8 hours a day, 2600-2900 hours a year and the solar global radiation is 5000-5500 MJ/m2. These areas have favorable conditions of developing and utilizing solar energy. B y the i nfluence of Maowusu desert and Loess plateau, some residents in this area live in t he scatte red and outfield, so electr icit y is unavailable for them because the diffic ulty of power grid exten sion, o ff-grid home photovoltaic power system pro- vide them an effective way to solve those problems. Off-grid home photovoltaic power system consists of PV modules, batteries, controllers and inverters. As power generation equipment, the performance of PV modules is greatly influenced by environmental fac- tors[1-2]. In order to give full play to the performance of the system, this research established power supply model, analyzed working performance and optimized system configuration, which laid a theoretical foundation for the application of off-grid home photovoltaic power system in these areas b y refe re nci ng weat her cond itio ns o f Y ulin and Yan’an as well as other factors such as solar radia- tion, ambient temperature and installatio n angle. 2. Electricity Load Dispersed rural ho usehold s can ge nerall y be divid ed into low, mid-scale and high levers according to their elec- tricity consumption level. The low levers primarily use light, the mid-scale levels ad d TV and t he hig h l eve l s add washing machines and refrigerators. The purpose of this research is to meet the demand of mid-level peasant households according to actual electricity price and pho- tovoltaic power generation cost. The electricity con- sumption has list in Table 1. According to the table above, the peak power of mid- level rural household is 101.6 W, daily electricity con- sumption is 0.428 kWh, annual electricity consumption is 156.2 kWh. 3. Weather Conditions Shaanxi northern region has the most abundant solar energy resources in Shaanxi province, including Yulin and Table 1. Electrical load of rural ho usehold. Appliances Number Powe r Working hours Synchronization Coefficient Peak Powe r CFL 3 9 5 0.8 21.6 TV 1 70 4 1 70 Satellite receiver 1 10 4 1 10 K. CHENG ET AL. Copyright © 2013 SciRes. EPE 195 Yan’an. Yulin is located in the northern of Shaanxi province and situated from 107°28'-111°15'E longitude to 36°57'-39°34'N latitude, with the annual average tem- perature is 10℃ and average sunshine hours are from 2500 to 2900 hours. Yan'an is situated from 107°41 '-110°31'E longitude to 35°21'-37°31'N latitude , con- nected with the southern part of Yan'an. Its annual aver- age temperature is 11℃ and average sunshine hours are from 2300 to 2700 hours[3]. Their su ns hi ne r ad i ati o n and average temperature in every month are showed in Fig- ures 1 and 2. 4. Performance Prediction 4.1. Theory Model According to the working principle of photovoltaic cells, the factors effect working efficiency of photovoltaic cell, and in accordance with the characteristics of semicon- ductor PN junction[4-5], relationship between photovol- taic battery output current and output voltage can be showed use the follow equation: Figure 1. Monthly averaged sol ar r adiation incide nt. Figure 2. M o nthly a v eraged s o lar r adiatio n incident. () {exp[] 1} s ph sat s sh qV RI II InKT V RI R + =−− + − (1) Among it : I—output current of photovoltaic panels(A) V—output voltage of photovoltaic panels(V) q—char ge quantity a n electroni c contai ns (l.6×10-19C) K—disposal of Boltzmann ' s constant(l.38×10-23 J/K) T—surface temperature of photovoltaic panels(K) n—ideal factor of photovoltaic panels(n = 1.5) Isat—reverse saturation current of photovoltaic panels, can be expressed as follows: 3 11 [] exp[()] gap satrr rr qE T II TkA TT =⋅− (2) Among it: Tr—reference temperature of the photovoltaic panels Irr—reverse saturation current when photovoltaic cell work in tempera ture bo undary Tr (0k) Egap—required energy when semiconductor materials across the clearance From formula (2) we can see reverse saturation current Isat is the function of temperature T. Secondly, Iph, pro- duced by photovoltaic panels, is c ha nge b y the cha nge of sunshine intensity and atmospheric temperature. The relationship between them is: [( )] 1000 i ph scrri K IITT s= −−× (3) Among it: Iscr—the measured short circuit current value when photovoltaic cell work in the reference temperature and sunlight condition is 1 kW/m2 Ki—temperature coefficient of photovoltaic panel’s short circuit current (mA/K) si一sunshi ne intensi ty (kW/m2) The output power P is the product of current I and voltage V. The relation can be showed use formula (4): () {exp[] 1} ph s sat s sh P VIVI qV RI VI nKT V RIV R = = + −− + − (4) We can see sunshine intensity and atmospheric tem- perature can affect the performance of photovolta ic cell. 4.2. Performance Simulation In light of the theory above, we arrange PV modules to- ward south, monthl y simulate and calculate the electrici- ty generation performance of 1 Wp PV modules on dif- K. CHENG ET AL. Copyright © 2013 SciRes. EPE 196 ferent installation angle, based on the date of local solar radiation and the average temperature every month. The results have showed in Fig ur es 3 and 4: We can come to the conclusion that 10°installation angle of photovoltaic module can obtain the maximum mont hly o utput p o wer in Ma y in Shaa nxi northern region, which Yulin is 0.15 kWh/Wp, Yan’an is 0.13 kWh/Wp. It is because in May the local sunshine radiation reach the highest lever throughout the year. At the same time, the temperature is not high and temperature influence is not big. 4.3. Configuration Optimization According to the results of performance simulation, we can get the electricity generation performance of PV module s in different installation angles, as showed in Figure 5: We can find that the maximum annual output power occurs when the installation angle is 40° in Yulin and 30 ° in Yan’an, and they are 1.44 kWh/Wp and 1.32kWh/Wp. In both cities we can get the minimum output power when the installation angle is 90°, and they are 0.96 kWh/Wp and 0.84 kWh/Wp. Figure 3. M o nthly a v eraged out put powe r of Yul in. Figure 4. M o nthly a v eraged out put powe r of Yan'a n. The designed target of the off-grid photovoltaic power system is to balance the average power generation in each month and meet the electricity demand when the output power reach minimum lever. In another word, we don’t see the annual power output or total power output as the highest goal. It is more incline to calculate the worst case and part of sunshine may be abandoned in the month which sunshine is sufficient. Therefore, it is ne- cessary to further analysis minimum output power in different installation angle, the result is show in Figure 6: Compare the minimum monthly output power in all installation angles, in Yulin it can reach the maximum 0.11 kWh/Wp when the installation angle is 40°and in Yan’an it can reach the maximum 0.09 kWh/Wp when the installation angle is 30°. So according to the instal- lation angles above, assumes that the charge and dis- charge loss is 20% and consider the battery energy sto- rage need in three days, as well as the contro ller, i nverter safety margin, the basic configuration is as follows: Figure 5. Ye a rly o utput power under different ins tallation angle. Figure 6. M ini mize monthly average d output power of dif- ferent installation angle. K. CHENG ET AL. Copyright © 2013 SciRes. EPE 197 According to the configuration, the output power ca- pacity of the off-grid home p hotovoltaic po wer system is 172 .70 kWh in Y ulin, 17 9.66 kWh in Y an’an, more tha n the mid-scale farmers' annual electricity consumption, can solve their problems of use electricity. 5. Conclusions This research studied the off-grid home photovoltaic power system in Shaanxi northern region according to the meteorological data, the establishment of perfor- mance model, and gets the following conclusions: 1) In the same area, solar radiation and ambient tem- perature are certain, but we can choose the best installa- tion angle, different installation angle can lead to 30% - 40% gap of the performance in the s yst e m. 2) Off-grid home photovoltaic power system should meet the demand of electric ity consumption when the output power reaches minimum. I n light of this principle, the installatio n angle should be 4 0°in Yulin and 30°in Yan’an. 3) According to the installation an gle abo ve, the power generation of PV modules can reach 1.44 kWh/Wp in Yuli n and 1. 32 kWh/W p in Ya n’an, so t he ann ual powe r output of 150 Wp and 170 Wp systems is 172.70 kWh and 179.66 kWh, which can meet the electricity demand in mid-scale rural families. The off-grid home photovoltaic power system has been widely used in Shaanxi northern region, we will optimize the system further with considering the actual situatio n, suc h as wind , snow, dirt and o t her factor s . REFERENCES [1] H. Sheng and Z. Q. Zeng, “Solar photovoltaic technolo- gy,” Beijing: Chemical Industry Press, 2005. [2] A. Li, “Solar P hotovoltaic Systems Engin eering,” Beijing: Beijing Industrial University Press, 2001. [3] B. Z. Wang, “Calculation of solar radiation of the slope ground Sol ar Energy,” Vol. 3, 2000, pp. 16-17 [4] J. Q. Wang, “Stand-alone Photovoltaic Power System Power Elect roni cs Technology,” Vol. 3, 2009 , pp. 53-47. [5] W. T. Li, “Analysis and Calculation of the Best Angle of Photovoltaic Array of Village without Electricity in Qinghai Province,” Qinghai Technology, Vol. 4, 20 03 , pp. 35-37. |