Energy a nd Power Engineering, 2013, 5, 194-197
doi:10.4236/epe.2013.54B037 Published Online July 2013 (http://www.scir
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
Received February, 2013
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 Yanan 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 Yanan, 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 Yanan 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
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
receiver 1 10 4 1 10
Copyright © 2013 SciRes. EPE
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}
ph sat
Among it :
Ioutput current of photovoltaic panels(A)
Voutput voltage of photovoltaic panels(V)
qchar ge quantity a n electroni c contai ns (l.6×10-19C)
Kdisposal of Boltzmann ' s constant(l.38×10-23 J/K)
Tsurface temperature of photovoltaic panels(K)
nideal factor of photovoltaic panels(n = 1.5)
Isatreverse saturation current of photovoltaic panels,
can be expressed as follows:
[] exp[()]
satrr rr
Among it:
Trreference temperature of the photovoltaic panels
Irrreverse saturation current when photovoltaic cell
work in tempera ture bo undary Tr (0k)
Egaprequired 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:
[( )]
ph scrri
IITT s= −−×
Among it:
Iscrthe measured short circuit current value when
photovoltaic cell work in the reference temperature and
sunlight condition is 1 kW/m2
Kitemperature coefficient of photovoltaic panel’s
short circuit current (mA/K)
sisunshi 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}
= =
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-
Copyright © 2013 SciRes. EPE
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 1installation
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 4 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 9, 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 4and in
Yan’an it can reach the maximum 0.09 kWh/Wp when
the installation angle is 3. 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
Figure 6. M ini mize monthly average d output power of dif-
ferent installation angle.
Copyright © 2013 SciRes. EPE
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 in Yulin and 3in
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 .
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