Alt-azimuth Dual Axis Tracker
Alt-azimuth dual-axis tracker (AADAT): Design and Application
The alt-azimuth dual-axis tracker (or as correctly, azimuth-altitude dual-axis tracker) abbreviated as AADAT works quite similar to the tip-tilt dual axis in the sense that movement is possible in two orthogonal dimensions thus allowing proper tracking of the sun throughout the day. But there is a difference in the way both are structured, and hence, there are differences in operational characteristics that arise due to this.
Structure of the alt-azimuth dual-axis tracker AADAT
The primary axis is vertical and erected on the ground. The secondary axis is then normal to it and automatically horizontal. But the secondary is not fixed in space. The array is not supported at the top of the vertical structure used as support in the tip-tilt dual-axis tracker. In fact, a large horizontal ring is erected at a reasonable distance around the primary axis and the array is supported between the ring and the primary axis supported by a radial structure. This structure is used to hold the array in place. The radial structure has its inner end able to move about the vertical primary axis (the azimuth axis) while the outer end rests on vertical support which can move over the ring. The movement of this structure about the vertical gives the array its horizontal (azimuth) movement which could go as far as 270 degrees on either side or more. The elevation (or altitude) movement is provided by tilting the array towards or away from the vertical about a horizontal axis of rotation. This horizontal axis is always parallel to a tangent of the circular ring. In one design the array can make an elevation movement from a negative angle to a vertical position giving a net movement of over 90ᵒ.
In comparison with the tip-tilt dual-axis tracker, the Alt-azimuth dual-axis tracker has merits and demerits.
Such a scheme can support very large sizes of array structures. The main load is on the ground supported ring, and not on a single vertical pole. The tip-tilt tracker, because of its design cannot support large arrays.
- With this advantage, the alt-azimuth dual-axis tracker AADAT has some limitations also in comparison with the tip-tilt dual-axis tracker.
- First of all, the ring is large, the size depending primarily on the size and weight of the supported array. As a result, an adjacent tracker must be at least at a distance twice the radius of the ring on the ground. This will limit the special density of the trackers in a large system.
- Secondly, because of the wide azimuthal freedom of movement, cabling to the ground-fixed equipment can cause problems due to possible tangling. Extreme care must be taken in designing cabling routes.
- The alt-azimuth dual-axis tracker cannot be considered for a mobile PV role.
- Inter-tracker shading at lower sun angles is a limitation that must be handled both in the tip-tilt and azimuth elevation trackers. Most often back-tracking can relieve the issue.