Slewing Drive Versus Linear Actuator in Solar Tracking
March 27, 2017- Slewing drives have a myriad of advantages over linear actuators in solar tracking. These include height of structure, overall angle of solar tracking rotation, and costs of (i) purchase, (ii) installation, and (iii) operations and maintenance.
Because slewing drives sit on the center axis rotation of the torque tube drive line, they can be set as close to the ground as the size of the solar panels will permit. This allows the shortest, strongest, and least expensive underlying structure to be built for supporting the solar trackers in the field, which is a considerable amount of the overall cost incurred. Linear actuators, because of their push/pull nature, must act on only a point along the chord of the exterior panel. The actuator must be mounted at some distance from the panels so they may be pushed/pulled around the center axis of rotation on the torque tubes. The trigonometry of these features requires a taller, weaker, more expensive structure to hold solar trackers being rotated through the use of a linear actuator and other related necessary accompanying components.
Slewing drives rotate 360˚ continuously, so it’s up to the solar tracking design engineer to limit their rotation at whichever angle is desired for the particular equipment. The selection is endless. For linear actuators though the size, cost, and approvals are unwieldy for anything more than +/-45˚.
The cost of purchasing a slewing drive is simplified by its sole part number and shipping point, which may be drop shipped directly to any solar field project throughout the world. Not only are linear actuators and their accompanying bill of materials required for rotation (bearings, brackets, weldaments, etc.) more expensive, but each must be cut on separate purchase orders, to separate vendors, leaving the customer to coordinate arrival of a multi-teared level of orders to arrive on-site and on time in unison.
Installation of a slewing drive is simply the fastening of the main structural bolts (normally four fasteners). There is no sub-assembly, post qualification, lubrication, inspection, or other work required. Linear actuators however must be bracketed, measured, and welded into place in a difficult field work environment.
Slewing drives are shown to last 30 years in solar applications, with some models even available in a maintenance free version. Linear actuators are known to break down often and seen as an item that must be stocked, checked, and replaced in the field as required.
These are some of the reasons that slewing drives are chosen over linear actuators in solar tracking applications.