Paper Menu >>
Journal Menu >>
Energy and Power Engineering, 2013, 5, 202-204
doi:10.4236/epe.2013.54B039 Published Online July 2013 (http://www.scirp.org/journal/epe)
Design of Of f-g ri d H om e P hotovoltaic Power System in
Ke Cheng, Jie Yang, Yan Chen
School of Power and Energy, Northwestern Polytechnical University, Xi’an, P. R. China
Received February, 2013
Shaanxi province has three land forms which are Shaanxi’s northern plateau, Guanzhong plain and Qinba mountain
land in the south of Shaanxi province. So the climate type is also divided into three types and the solar energy resources
distribution has a big gap between different regions. PV modules, as the core component of off-grid home photovoltaic
power system, their output power are mainly influenced by sun radiation, array tile angle, temperature and so on. Based
on the reasons above, in order to apply off-grid home photovoltaic power system in Shaanxi region, this paper designs
different systems with different configuration, and makes the performance prediction. The results show that the capacity
of PV modules reaches to the largest in Shaanxi northern region, reach minimum in Shaanxi southern region and the
output power in the winter is less than in the summer and reach minimum in the spring and autumn. In light of the
characteristics above, this research select different type and configuration in different areas systematically, and the per-
formance analysis shows that the configuration can meet the basic life demand of power to the people whose power is
Keywords: Solar; Photovoltaic Power Generation; Off-grid Home Photovoltaic Power System
It is about 870 kilometers from Shaanxi northern to
Shaanxi southern. Shaanxi province has three landforms
which are Shaanxi northern plateau, Guanzhong plain
and Qinba mountain land in south of Shaanxi. So climate
type is also divided into three types. Shaanxi northern
region belongs to warm temperate zone arid and semi-
arid climate. Guanzhong belongs to warm temperate
zone semi-humid climate and Shaanxi southern region
belongs to north subtropical humid climate. In this case,
the distribution of solar energy resource has a big gap in
different regions, especially between north and south in
Shaanxi province, the annual total sunshine radiation is
3830-5750 MJ/m2, the annual sunshine hours is 1270-
2900 hours and sunshine percentage is 28% - 64%.
Off-grid home photovoltaic power system mainly co n-
sists of PV modules, batteries, controller and inverter.
Among them PV module is the core component that
makes sun radiant energy into electricity. Power sys-
tem’s capacity is mainly influence by the sun radiation,
array tile angle, temperature and other factors[1-2].
For example, the output power of crystalline silicon
PV modules in proportion to the accepted sun radiation
intensity, power generation efficiency is inversely pro-
portional to the temperature. Based on the above reasons,
in order to apply off-grid home photovoltaic power sys-
tem in Shaanxi region, this paper designs different sys-
tem with different configuration, and makes the per-
2. Resource Condition
In Shaanxi province the annual total solar radiation is in
a high level, solar energy total reserve is 2.71 × 1015
kWh, ranking eleventh in China. The distribution char-
acteristics are the radiation in the north is more than in
the south. There is a great gap between north and south.
High value areas are located in the Shaanxi northern
along the Great Wall area and the east area of the north
of Weishui, and low v alue areas are mainly distributed in
Shaanxi sou t hern.
According to annu al total solar radiation, the solar en-
ergy resources of Shaanxi province can be divided into
three areas: the area with very adequate solar resources,
including Shaanxi northern; the area with adequate solar
resources, including the south of Shaanxi northern, Gua-
nzhong region, the northeast of Shangluo and Ankang in
Shaanxi southern; the area with relatively adequate solar
energy resources, including most areas of Hanzhong and
Ankang in Shaanxi southern. Sunshine hours and sun-
shine percentage in Shaanxi are show in Figures 1 and 2.
In the four seasons, total radiation can reach maximum
in the summer accounting for 35% of the annual total
Copyright © 2013 SciRes. EPE
K. CHENG ET AL. 203
radiation. In the summer around north of Shaanxi north-
ern area and east area of northern Weishui the total so lar
radiation reach high value. In the winter total radiation
reaches minimum and accounts for 16% of the annual
3. Electricity Load
Reference to investigation in other areas, kerosene lamp,
candles, fire and flashlight are the first choice to illumi-
nate when photovoltaic power generation is not available,
and TV, VCD, DVD and other appliances cannot use
then. After photovoltaic power generation is available,
lamp become the main lighting equipment, the use of
household electric appliances, such as TV, tape recorder
has a significant upward trend.
Figure 1. Sunshine hours in Shaanxi P rovince.
Figure 2. Sunshine perc entage in Shaanxi Province.
Design load accord ing to TV is 70 w, light is 30 w, the
basic living power can be contented . Electricity time is 4
hours, power peak is around 100 W, average load is
around 80 W.
4. Design Selection
4.1. Principle of Photovoltaic Power Generation
The solar cell of photovoltaic power generation is p-n
junction which is surface contact type. When there is no
light, it is equivalent to a diode. Otherwise the voltage
between the two sides of solar cell gets just make p-n
junction forward bias. The ideal equivalent power model
is a constant current source in parallel a diode. The ideal
I-V characteristic is:
IL- photo cur r ent
I0- saturation current of diode
q- charge quantity of electronic
k- Boltzmann constant
T- absolute temperature(K)
The output power is the product of current and voltage.
It can be show use formula (2):
4.2. Design Calculation
It has shown the solar energy resources in eight cities of
Shaanxi in Figure 3. In order to facilitate selection,
placed 100 Wp monocrystal silicon components use local
latitude as it’s tilt angle and simulate to calcu late the PV
module’s theoretical monthly output power, and the re-
sults show in Figur e 4.
The results show that th e output power in the winter is
less than in the summer for the synthesis influence of
local solar radiation and ambient temperature. Because
the power generation efficiency of PV modules is in-
versely proportional to the temperature, when the tem-
perature r i se every 1℃, the efficiency drop about 0.5%.
Figure 3. Global solar radiation in Shaanxi Province.
Copyright © 2013 SciRes. EPE
K. CHENG ET AL.
Copyright © 2013 SciRes. EPE
So in September and October, the output power reaches
minimum generally. Especially in Yulin and Yanan al-
though solar radiation is weak in the winter, output pow-
er is more than in the summer for the environment tem-
perature is below zero.
4.3. Configuration Selection
According to the power load and PV module products
series, the results are shown as in Table 1.
5. Performance Analysis Figure 5. PV module output pow er pr ediction.
According to the configuration in Table 1 and the local
meteorological data, predict the output power of solar PV
module in each area, which is shown in Figure 5.
It is assumed that the charging efficiency of battery is
90%, the working efficiency of inverter is 80%.The rela-
tionship between electricity generation and electricity
consumption in every area is shown in Figure 6. The
performance analysis results show output power of off-
grid home photovoltaic power system is more than pow-
er consumption of TV and lamp. The configuration can
meet the basic life demand of power to the people who
power is not available.
Figure 6. Output power prediction of off-grid home
photovoltaic power system.
The regional difference of solar energy resources distri-
bution and temperature is big in Shaanxi as well as lati-
tude difference. All of these are mainly influence factors
of the performance of photovoltaic power generation sys-
tem. Through the researches we can draw the conclusions:
1) The output power of PV modules varies a lot in
different areas of Shaanxi. It is mainly affected by the
solar energy resources. The output power reaches to the
largest in Shaanxi northern region, and the minimum
occurs in Shaanxi southern region.
2) Because of the synthesis influence of solar resource
and ambient temperature, output power in the winter is
less than in the summer. It reaches the minimum in the
spring and autumn.
3) According to the generating characteristics of PV
modules in Shaanxi province, different types and con-
figurations are selected in different areas systematically.
The performance analysis shows that the configuration
can meet the basic life demand of power to the people
whose power is not available.
Figure 4. Output power of 100 Wp PV component.
Table 1. Type configuration.  Divade, Z. R. Shi and H. Y. Lu, “The Pv-tech Applica-
tion Study,” Shanghai: Shanghai Jiaotong University
No Region PV Inverter Battery
1 Yulin 135 Wp 300 VA 24 V65 Ah
2 Yan’an 170 Wp 300 VA 24 V65 Ah
3 Weinan 170 Wp 300 VA 24 V65 Ah
4 Baoji 180 Wp 300 VA 24 V65 Ah
5 Xianyang 180 Wp 300 VA 24 V65 Ah
6 Hanzhong 180 Wp 300 VA 24 V80 Ah
7 Shangluo 180 Wp 300 VA 24 V80 Ah
8 An ka ng 180 W p 300 VA 24 V80 Ah
 A. Li, “Solar Photovoltaic Systems Engineering,” Beijing:
Beijing Industrial University Press, 2001.
 L. R. Wu, Z. H. Jiang, Y. P. Lu, J. W. Du, L. Qiao and H.
J. Liu, “Space Distribution Evolution Characteristics of
Sunshine Duration and Percentage in Shaanxi Province,”
Xian: Shaanxi Meteorological. 2008.1.