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(ii) Two-axes passive solar tracker
Passive trackers use either internal or external computers to calculate the position of
the solar disk. Following the initial setup of the system, tracking of the solar spot by
the shading disk or the instrument attached to the tracker should not normally vary
except when the power is removed from the tracker and/or the computer operating
the tracker, or when the time used to calculate the solar position is incorrect.
- check that the clock time used in the calculation of solar position is accurate to better
than 15 seconds for tracking of instruments with a 2° field of view or greater. The smaller
the FOV, the greater the time accuracy required.
- on days when the solar spot is visible on the target, check tracker alignment. If not
aligned follow the procedures below and/or in the manual.
- determine if the power to the tracker has been disrupted either at the main power
panel or within the cabling to and within the tracker.
- for friction-driven drives check for slippage of the drive disks (see the tracker operating
manual for the proper procedure).
- for gear-driven drives, if slippage occurs, check gear alignment or if one or more gears
have broken teeth (see the tracker operating manual for proper procedures).
- check to ensure that the tracker has not changed its physical position, either in level
or location (e.g., the tracker has not been bumped accidentally).
- a tracker mechanical malfunction or software failure can also cause a loss of tracking
capability. The operator should refer to the tracker operating manual in such cases.
(iii) Two-axes active solar tracker
An active tracker corrects for small variations in the pointing of a passive system. Such
a system requires that the tracker not operate in active mode during periods where
the solar signal is below a defined solar irradiance threshold. During such periods, the
active tracker should operate in a mode similar to a two-axes passive system. Following
the initial setup of the system, tracking of the solar spot by the shading disk or the
instrument attached to the tracker should not normally vary except when the power
is removed from the tracker and/or the computer operating the tracker.
- clean the active sensing unit on the tracker daily and following occurrences of
precipitation.
- check that the clock time used in the calculation of solar position is accurate to better
than 15 seconds for tracking of instruments with a 2° field of view or greater. The smaller
the FOV, the greater the time accuracy required.
- on days when the solar spot is visible on the target, check tracker alignment. If not
aligned follow the procedures below and/or in the manual.
- determine if the power to the tracker has been disrupted either at the main power
panel or within the cabling to and within the tracker for a time greater than that which
the active sensing unit can correct.
- check the operation of the active sensing unit. This can be accomplished by covering
the active sensor and manually positioning the tracker to within the acceptance limits
of the active sensor with the power turned off. By turning on the power to the tracker
(ensuring that any computer programs are operating correctly) the active sensor should
move the tracker into correct alignment. If this does not occur, technical assistance
in further checking the operation of the active sensor is required.
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