Civil Engineering Reference
In-Depth Information
FIGURE 8-10
i-v characteristic of pv module shifts down at lower sun intensity, with small reduction in
voltage.
FIGURE 8-11
Photoconversion efficiency versus solar radiation. The efficiency is practically constant over a
wide range of radiation.
intensity as shown in
Figure 8-10
.
On a cloudy day, therefore, the short circuit
current decreases significantly. The reduction in the open-circuit voltage,
however, is small.
The photoconversion efficiency of the cell is insensitive to the solar radi-
ation in the practical working range. For example,
Figure 8-11
shows that
the efficiency is practically the same at 500 watts/m
.
This means that the conversion efficiency is the same on a bright sunny day
and a cloudy day. We get lower power output on a cloudy day only because
of the lower solar energy impinging the cell.
2
and 1,000 watts/m
2
8.6.2
Sun Angle
The cell output current is given by
I
=
I
cos
θ
, where I
is the current with
0
o
normal sun (reference), and
is the angle of the sunline measured from the
normal. This cosine law holds well for sun angles ranging from 0 to about 50°.
θ
