Civil Engineering Reference
In-Depth Information
the other hand, if the array is not normal to the sun, the sun angles on the
two cells are different, giving two different currents:
(
)
(
)
I
=
I
cos
45
+
δ
, and I
=
I
cos
45
−
δ
1
o
2
o
The motor current is therefore:
(
)
−
(
)
I
=−=
I
I
I
cos
45
+
δ
I
cos
45
−
δ
m1
2
o
o
Using Taylor series expansion:
2
h
(
)
=
()
+⋅′
()
+
′′
()
+
fx h
+
fx
h f x
fx
L
2!
we can express the two currents as the following:
I
=
I
cos
45
−
I
δ
sin
45
, and
1
o
o
I
=
I
cos
45
−
I
δ
sin
45
2
o
o
The motor current is then
(8-11)
I
=−=
I
I
2
I
δ
sin
45
°
m
1
2
o
=
2
I
δδ
if is in radian
o
Small pole-mounted panels can use one pole-mounted suntracker. Large
array, on the other hand, is divided into small modules, each mounted on
its own single-axis or dual-axis tracker. This simplifies the structure and
eliminates the problems related with large motion.
8.7
Peak Power Point Operation
The suntracker drives the module mechanically to face the sun to collect the
maximum solar radiation. However, that, in itself, does not guarantee the
maximum power output from the module. As was seen in
Figure 8-16
,
the
module must operate electrically at a certain voltage which corresponds to
the peak power point under the given operating conditions. First we examine
the electrical principle of the peak power operation.
If the array is operating at voltage V and current I on the i-v curve, the
power generation is P = V · I watts. If the operation moves away from the
above point, such that the current is now I +
∆
I, and the voltage is V +
∆
V,
the new power is as follows:
