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sun traverses the sky. As improved efficiency means improved yield, use of
trackers can make quite a difference to the income from a large plant.
Need For Solar Tracker:
The energy contributed by the direct beam drops off with the cosine of
the angle between the incoming light and panel.
The sun travels through 360
degrees east west a day, but from the
perspective of any fixed location the visible portion 180 degrees during a 1/2 day
period. Local horizon effects reduce this somewhat, making the effective motion
about 150 degrees. A solar panel in a fixed orientation between the dawn and
sunset extremes will see a motion of 75 degrees on either side, and thus,
according to the table 2-2, will lose 75% of the
energy in the morning and
evening Rotating the panels to the east and west can help recapture these losses.
A tracker rotating in the east west direction is known as a single-axis tracker.
The sun also moves through 46 degrees north south over the period of a
year. The same set of panels set at the midpoint between the two local extremes
will thus see the sun move 23 degrees on either side, causing losses of 83% a
tracker that accounts for both the daily and seasonal motion is known as a dual
axis tracker.
Table 2.2 Direct power lost (%) due to misalignment (angle I)
Misalignment (angle
I
)
Direct power lost (%)=1-cos(I)
0
0
0
1
0
0.015
3
0
0.14
8
0
1
23
0
8.3
30
0
13.4
45
0
30
75
0
>75
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Passive Trackers: Use the sun’s radiation
to heat gases that move the
tracker across the sky.
Active Trackers: Use electric or hydraulic drives and some type of
gearing or actuator to move the tracker.
Open Loop Trackers: Use no sensing but instead determine the position
of the sun through prerecorded data for a particular site
Passive Trackers: Passive trackers use a compressed gas fluid in two canisters
each place in west and east of the tracker. The mechanism is in such a way that
if one side cylinder is heated other side piston rises causing the panel to tilt over
the sunny side. This affects the balance of the tracker and caused it to tilt. This
system is very reliable and needs little maintenance.
Active Trackers: Active trackers measure the light
intensity from the sun by
using light sensors to determine where the solar modules should be pointing.
Light sensors are positioned on the tracker at various locations in specially
shaped holders. If the sun is not facing the tracker directly there will be a
difference in light intensity on one light sensor compared to another and this
causes to determine in which direction the tracker has to tilt with the help of the
stepper or dc motor in order to be facing the sun.