Energy and Power Engineering, 2013, 5, 215-218
doi:10.4236/epe.2013.54B042 Published Online July 2013 (http://www.scirp.org/journal/epe)
Analysis on the Effect of Shading on the Characteristics of
Large-scale on-grid PV System in China
Yunlin Sun, Xiangzhi Li, Ruijiang Hong, Hui Shen*
School of Physics and Engineering, Sun Yat-Sen University, Guangzhou, China
Received February, 2013
ABSTRACT
Because of rich solar resource and low land cost, a lot of large-scale ground-based grid-connected PV systems have
been built in Northwest China. In this paper, some shading phenomena on a grid-connected PV system in Northwest
China are classified and analyzed. Through the I-V curve test of PV modules, it can be seen that dust influence system
performance of the grid-connected PV system. And the experimental results have shown that shading could affect the
electrical properties of PV modules. Meanwhile, same shading area on different shading positions could have different
impacts on the identical PV module.
Keywords: Large-scale; Ground-based on-grid PV System; Shading; System Performance
1. Introduction
In the process of actual installation of PV system, there
are many influencing factors. Among them, shading
which could influence the performance of PV system has
aroused common concern and research. PV modules are
generally installed in the areas of rich solar resource and
vast land. Exactly, Northwest China can provide an ideal
environment for PV modules installation because of its
widely distributed Gobi, desert and shoals. However,
under natural conditions, PV modules would be covered
by certain blocks such as leafs and guanos after longtime
use. These kinds of objects will form shadows on the
modules that would affect the performance of PV mod-
ules so that the output power reduces directly [1, 2]. On
the other hand, owing to the difference between prelimi-
nary design and actual terrain of PV system, inappropri-
ate distance between front and rear PV arrays would
cause shading phenomena too. Like the uneven and rug-
ged surface would also lead to this kind of shading in the
actual situation [3].
Obviously, partial shading will change the I-V charac-
teristics of a PV module [4]. The product of current and
voltage will increase in some part of the PV module due
to the shading, and then temperature of these areas will
rise. After longtime use, some areas will become darker
on the surface of PV module and this phenomenon is
called “hot spot” [5]. Certainly, defects of solar cell itself
could also produce heat and bring “hot spot” for PV
module even in the normal work [6]. Such cases can re-
sult in reduction of the output power of PV module, as
shadows on partial PV module, uneven irradiance on PV
array or mismatching power of PV module in a PV array
[7].
2. Classification of Shading
According to field research, it can be found that shading
phenomena on PV module differ somewhat depending on
the specific circumstances such as different regions or
PV systems [8]. On the contrary, shades have something
in common; they can be the caused by power distribution
rooms nearby, the surrounding vegetation, or sometimes
the front row arrays [9]. During the construction process,
the surface structure and ground condition may not
match exactly with design drawings. So PV arrays some-
times can not be at the same height so that the front row
shadows would cover the rear row [10].
There are many types of shading phenomena in PV
system, and they can be divided into the following cate-
gories after longtime surveys and observation on one
large ground-based grid-connected PV system.
1) The front row shading phenomenon (Figures 1, 2)
2) The surrounding plant and guano shading phe-
nomenon (Figures 3, 4)
3) The nearby power distribution room and wire pole
shading phe n o menon (Figures 5, 6)
3. The Effect of PV Array Shading on
Electrical Properties of PV Module
*Corresponding author. A PV system is constituted of many PV modules that are

Y. L. SUN ET AL.
216
connected by series and in the parallel way. If the arrays
layout is unreasonable or there are shades around the
arrays, shading will appear on some modules. In practical
situations, a modu le with shad ing in a lon g series will not
produce photovoltage, while other modules in the same
series still produce voltage normally. So there is current
going through this shaded module [11, 12]. However,
even current runs through the module, it can not produce
a normal output power without photovoltage inside. Be-
cause of this reason, the shaded module becomes a load
in the string and dissipates power because of the gener-
ated heat. So other normal modules need to work at a
higher voltage in order to maintain the total voltage of
whole series and reduce voltage loss of the shaded mod-
ule. To the normal modules, the higher voltage will cre-
ate less current and more output power loss.
Actually, the method usually used to reduce the power
loss from partial shading is to divide a string into several
parts with some bypass diodes [13]. The part with shaded
module will be isolated by the bypass diode from other
parts, so the voltage and cu rrent of this string will lose in
proportion to the shading areas. And the output power of
other not shaded parts without being protected by the
diode will not lose [14, 15].
Figure 1. Front row shadows on the rear row in tracking
PV system.
Figure 2. Front row shadows on the rear row in fixed PV
system.
Figure 3. Plant shadows on the PV module.
Figure 4. Guano shadows on the PV module.
Figure 5. Power distribution room shadows on the PV
module.

Y. L. SUN ET AL. 217
Figure 6. Wire pole shadows on the PV module.
4. The Effect of Wire Pole Shading on
Electrical Properties of PV Module
In a large grid-connected PV system in Northwest China,
aiming at wire pole shading phenomenon, some experi-
ments have been done to analyze the effect of nearby
building shading on electrical properties of PV module.
This experiment uses some poly-Si modules produced
by a China manufacturer. The module is made up by 60
pieces of solar cells (156 mm × 156 mm) connected in
series. There are three bypass diodes in one module and
each diode can protect 20 pieces of solar cells. The no-
minal parameters of the module are: Pmax = 220 W,
Vmpp = 29.0 V, Impp = 7.95 A, Voc = 36 V, Isc = 8.19
A.
As the Figure 7 shows, wire pole shadows on PV
modules in on-the-spot investigation, and each module is
numbered. Figure 8 shows six I-V curves corresponding
to six numbered modules.
Combining these two figures, it is shown that there are
no shadows on NO.2 and NO.3 module and the electrical
properties of them can be maintained. The electrical
properties of NO.1, NO.4, NO.5 and NO.6 modules with
wire pole shadows on them are affected obviously, and
their I-V curves change; as a result, their performances
have degraded. However, modules with shadows are not
in complete failure because of protections by bypass di-
odes, and their performances are different along with
different shadow position and area. Thus, it can be seen
that the properties of PV module not only could be in-
fluenced by shades like wire poles, but also change along
with the changeable sh adow position and area.
5. Summery
According to the field investigation results on a large
ground-based grid-connected PV system, this paper clas-
sifies the common shading phenomena on the grid-con-
Figure 7. Wire pole shadows on the PV modules.
Current (A)
Voltage (V)
Figure 8. Six I-V curves corresponding to six numbered
modules.
nected PV system in Northwest China. They are mainly
front row shading, plant and guano shading and nearby
building shading. Then, aiming at nearby building shad-
ing phenomenon, some experiments have been done.
From the experimental results, it can be seen that shad ing
can affect the electrical properties of PV modules.
Meanwhile, same shading area on different shading posi-
tions can cause different impacts on the identical PV
module.
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