Single-Axis Solar Tracker

Overview

A single-axis solar tracker is a motorized mounting structure that rotates a long row of photovoltaic modules about one horizontal north-south axis so the panels follow the sun from east in the morning to west in the evening. By keeping the modules closer to perpendicular to the sun for more of the day, a tracker lifts annual energy yield 15–25% over a fixed-tilt rack at a modest increase in cost and maintenance. Horizontal single-axis trackers dominate utility-scale solar in low and mid latitudes because they are mechanically simple, robust and cheap to install at gigawatt scale.

The product is organized as one independent row. Its backbone is the torque tube, turned by a slew drive and carried on a bearing assembly. Modules attach through the module rails. A tracker controller computes where to point, a self-power supply makes the row independent of trench cabling, and a driven-pile foundation holds the whole row down.

Torque Tube

The torque tube is the rotating spine that runs the length of the row, often 60–90 m. It is built from a dozen or more tube sections of hot-dip galvanized steel, 100–140 mm across, joined end to end by bolted tube couplers that transmit torque without slip. Because a long slender tube is prone to wind-driven oscillation, aerodynamic dampers are spaced along the row. These rotary friction or hydraulic units bleed energy out of any galloping or flutter motion, which has caused field failures on early trackers when wind speeds matched the structure's natural frequency.

Slew Drive

The slew drive sits near the centre of the row and rotates the torque tube through roughly ±55° to ±60°. Its core is a slew drive gear, a self-locking worm-and-wheel set with a 50:1 to 70:1 ratio that holds the tracker at any angle without a separate brake. A DC drive motor turns the worm input, and a drive encoder reports the actual tilt angle back to 0.1°. The gear and motor sit in a sealed cast drive housing rated IP66 against grit and rain. A single drive can rotate the whole row because the torque tube is stiff enough in torsion to carry the load to the ends.

Bearings and Module Mounting

Between drive points the torque tube rides on the bearing assembly. Each pier carries a bearing housing with a maintenance-free polymer journal that lets the tube rotate freely for decades without lubrication, located by a tube saddle clamp. Every steel member is tied to the array earth through a grounding lug for lightning and fault protection.

The module rail system holds the PV modules to the tube. Cross purlins of galvanized C-section span the tube and bolt to it through rail brackets set at the right chord angle. Anodized aluminum module clamps, mid-clamps between modules and end-clamps at the row ends, grip the module frames. Layouts are described as 1P (one module in portrait per chord) or 2P (two stacked), trading row height against wind load.

Controller and Tracking Logic

The tracker controller is the brain of the row. Its control board runs a solar-ephemeris algorithm that computes the sun's position from the date, time and GPS coordinates, then commands the drive to the matching angle. An inclinometer verifies the achieved tilt in closed loop, and the motor driver, an H-bridge with stall detection, energizes the gearmotor. A defining feature is backtracking: in early morning and late evening the controller deliberately points the row away from the ideal sun angle so that one row does not shade the next, a calculation that depends on row spacing and ground slope.

A wind sensor feeds the safety logic. Above a configurable threshold of 20–30 m/s the controller drives the row to a flat or steep stow position that minimizes wind load, protecting the structure in storms. A mesh radio links each row controller to the plant SCADA so operators can monitor angle, motor current and faults across thousands of rows, and issue a fleet-wide stow command. Everything mounts in a weatherproof controller enclosure.

Self-Power Supply

Trenching power and signal cable to every row is expensive, so each row is made self-sufficient by the self-power supply. A small auxiliary PV panel of 50–100 W charges a LiFePO4 battery through an MPPT charge controller. The battery runs the controller and drive motor through the night and through overcast spells, so the only thing leaving the row is the DC string cabling for the main modules and the wireless data link. This arrangement cuts installation labour sharply and removes a large source of field wiring faults.

Foundation and Use

The row stands on a foundation of driven piles, W-section galvanized steel hammered 1.5–2.5 m into the ground at each bearing point, capped by bolted pile caps that carry the bearings and drive. Pile driving avoids concrete and lets a tracker field go up fast across large flat or gently rolling sites. Single-axis trackers are the default choice for utility solar farms in sunbelt regions; they are less common in high latitudes or on steep, broken terrain where fixed racks or dual-axis trackers fit better.