There are many ways to make solar modules follow the course of the sun. This article provides a brief overview on the basics of single-axis solar tracker concepts, the clearly dominating tracker technology in the solar segment.
Single-axis trackers, also called 1-axis solar tracker systems, consist of a module mount structure that drives the solar modules on a trajectory relative to the sun’s path position using a single pivot point to rotate. There are three categories of single axis trackers: horizontal single-axis tracker (HSAT), vertical single-axis tracker (VSAT) and tilted single-axis tracker (TSAT). The axis of rotation is horizontal with respect to the ground and the solar module is oriented parallel to the axis of rotation in HSAT systems. In VSAT systems, the axis of rotation is vertical with respect to the ground. As VSAT systems follow the sun around a vertical axis, they need larger space compared to HSAT to avoid negative shading impacts on yield. There are also tilted HSAT (HTSAT) systems in the market where the solar panels are mounted with an optimum tilt at the horizontal axis.

According to technical specification IEC / TS 62727, all trackers with the axis of rotation between the horizontal and vertical are considered as tilted single-axis trackers (TSAT), but these products are very rare. TSAT have a rotation axis placed between the horizontal and vertical axis.

The axis of HSAT systems can be oriented either in East-West (E-W) or North-South (N-S) configurations. In N-S axis configuration the modules follow the sun in E-W tracking direction. In case of the E-W horizontal oriented axis the solar panels can only rotate to follow the sun in its elevation angle. E-W axis configuration is not commonly used because the collected energy yield is quite lower than in N-S axis configurations. HSAT systems are the most widely used in practice, as they come with simple and robust mechanics, which often trade off the smaller collection of radiation with respect to the dual-axis trackers.
Jacobson & Jadhav1 from Stanford University showed that single-axis horizontal tracking provides much higher output than single-axis vertical tracking below 65° N and S, whereas output is similar elsewhere.
However, solar trackers offer only little benefit over optimal tilting for higher latitudes above 75° N and 60° S. When considering optimal output and LCOE reduction but not CAPEX reduction, single-axis horizontal tracking (HSAT) is recommended for utility-scale PV parks.
The text is an excerpt from the TaiyangNews Report Solar Trackers: First Comprehensive Technology Overview with Product Specs For A Key Component With Increasing Share In Utility-Scale Solar Power Plants – The TaiyangNews Market Survey Report can be downloaded for free here.
A comprehensive overview on Solar Trackers  was provided by Dr Olga Papathanasiou, TaiyangNews, during the TaiyangNews Solar Tracker Conference; the recording can be viewed here.