Solar Tracker
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A solar tracker is a device for
orienting a day lighting reflector,
solar photovoltaic panel
or concentrating solar reflector or lens toward the sun. The sun's
position in the sky varies both with the seasons and time of day
as the sun moves across the sky. Solar powered equipment works
best when pointed at or near the sun, so a solar tracker can
increase the effectiveness of such equipment over any fixed
position, at the cost of additional system complexity.
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There are many types of
solar trackers, of varying costs, sophistication, and performance. One
well-known type of solar tracker is the heliostat, a movable mirror that
reflects the moving sun to a fixed location, but many other approaches are
used as well.
The required accuracy
of the solar tracker depends on the application. Concentrators, especially
in
solar cell applications, require a high
degree of accuracy to ensure that the concentrated sunlight is directed
precisely to the powered device, which is at (or near) the focal point of
the reflector or lens. Typically concentrator systems will not work at all
without tracking, so at least single-axis tracking is mandatory. Very large
power plants or high temperature materials research facilities using
multiple ground-mounted mirrors and an absorber target require very high
precision similar to that used for solar telescopes. (See heliostat.)
Non-concentrating
applications require less accuracy, and many work without any tracking at
all. However, tracking can substantially improve both the amount of total
power produced by a system and that produced during critical system demand
periods (typically late afternoon in hot climates) The use of trackers in
non-concentrating applications is usually an engineering decision based on
economics. Compared to photovoltaics, trackers can be inexpensive. This
makes them especially effective for photovoltaic systems using
high-efficiency (and thus expensive) panels.
For low-temperature solar
thermal applications, trackers are not usually used, owing to the high
expense of trackers compared to adding more collector area and the more
restricted solar angles required for Winter performance, which influence the
average year-round system capacity.
