Tip-Tilt Dual Axis Trackers (TTDAT): Design and Application
Imagine a seesaw mounted on a bearing fitted atop a tall strong vertical pole. Obviously, the seesaw swings around a horizontal axis. And the axis must be supported on some sort of a T-structure whose vertical leg can rotate inside the bearing we mentioned above. The bearing allows the seesaw to move horizontally (in azimuth) round the vertical axis. The seesaw swing provides the vertical tilt. Now imagine the seesaw supports on it not children but an array of panels. These two degrees of freedom give the tracker ability to track the sun throughout the day. That is one form of the tip-tilt dual axis trackers. The seesaw in the example is the H-type structure that the usual description of the tracker in literature refers to.
The axes in Tip-Tilt Dual Axis Trackers
The axes are, as a normal practice, aligned with either the east-west direction or the north south direction, but it is not compulsory. Good algorithms can help the tracker point to the sun wherever it is. This is done by optical sensors, but to cater for cloudy situations, GPS supported algorithms may help point the tracker.
It is possible for a tip-tilt dual axis tracker to have primary rotation around a nearly horizontal axis and the second axis orthogonal to the primary. No movement in the horizontal plane is allowed. This simplifies the cabling connections to the equipment on the ground.
Konza Solar Tracker Models
Konza Solar tracker models offered by Mozer LLC of USA have the array mounted on top of a vertical pole through a strong universal joint. There is absolutely no designated horizontal or vertical axis. This is perhaps the true tip-tilt concept. As per the manufacturer, this universal joint takes most of the weight of the solar array and absorbs most of the wind loading that the tracker is exposed to. Also as per their claim, the universal joint is extremely durable and will and never need greasing. A combination of east-west and north south tilts will achieve pointing anywhere on the sun. The aiming is controlled by an excellent optical tracker and custom software. As there is absolutely no rotation around a vertical axis there is no complication in connecting cabling to base mounted equipment.
Interestingly, the tilting motion on two axes is performed not by two pairs of actuators but a set of three industrial grade and weather-proof linear actuators spaced at 120 degrees intervals in a horizontal plane. The manufacturer claims their actuators never need any greasing and are sealed for life. This reduces cost and weight also.
Since there is no motion of the pole therefore, the tracker can be placed anywhere, even on a somewhat sloping ground (as long there is a firm foundation). Further, it is also suitable for a portable mobile role, eg, it can be mounted on a vehicle.
Positioning of Tip-tilt Dual Axis Trackers
Layout of multiple tip-tilt dual axis trackers on the ground is quite simple. For best positioning one needs only to ensure that the axes of rotation of all the adjacent trackers are parallel. They can be packed fairly close. In case of shading due to adjacent trackers, a bit of backtracking can be adopted. Backtracking means the arrays can be kept closer to horizontal than required for optimal tilt. Shading causes more severe effects on output than a slight loss due to backtracking. The need for backtracking will arise only when the sun is low in the sky, morning and evenings. Back-tracking is also best performed under computer control.
Limitation of Tip-Tilt Dual Axis Trackers
However, the tip-tilt dual axis trackers configuration has a limitation. Whether vehicle mounted or ground mounted, the entire weight of the system is born by the single pole. This necessarily limits the number of panels in the array.