Solar Tracker Systems: Single-Axis and Dual-Axis Options

Solar tracker systems mount photovoltaic panels on motorized frames that reorient the panels throughout the day to follow the sun's position in the sky. This page covers how single-axis and dual-axis tracker configurations work, where each type is typically deployed, and the structural, regulatory, and permitting factors that shape installation decisions. Understanding tracker options is relevant to any project where maximizing energy yield per installed panel is a primary design objective.

Definition and scope

A solar tracker is a mechanical drive system that adjusts the orientation of a solar array in response to the sun's changing azimuth and elevation. The two primary classification types are:

• Single-axis trackers (SAT): Rotate panels along one axis, typically oriented north–south, so the array tilts east-to-west across the day.
• Dual-axis trackers (DAT): Rotate panels along both a horizontal and a vertical axis, enabling continuous alignment with the sun's full three-dimensional position.

Both tracker types contrast sharply with fixed-tilt systems described in solar roof mounting systems and ground mount solar systems, where the array angle is set once at installation. The scope of tracker deployment is predominantly utility-scale and commercial ground-mount; residential rooftop installations rarely use trackers due to structural and space constraints.

According to the U.S. Energy Information Administration (EIA), a substantial share of large-scale photovoltaic capacity added in the United States uses single-axis tracking. Wood Mackenzie estimated that by 2022, roughly 80% of new utility-scale solar projects in the US incorporated single-axis trackers, reflecting the cost-per-watt improvements in tracker hardware over the preceding decade.

How it works

Both tracker types rely on a control system that calculates the sun's position using astronomical algorithms (solar position algorithms, or SPA), GPS coordinates, and real-time clock data. The National Renewable Energy Laboratory (NREL) publishes the Solar Position Algorithm used as an industry reference for tracker control logic.

Single-axis tracker mechanics:

1. A torque tube runs along the north–south length of the array row.
2. A drive motor — typically a linear actuator or slew drive — rotates the torque tube from approximately −60° (east) to +60° (west) over the course of a day.
3. The control unit updates panel angle at intervals ranging from 1 to 15 minutes depending on system design.
4. Backtracking algorithms adjust panel tilt during low-sun-angle periods to prevent inter-row shading, a feature documented in NREL technical reports on tracker yield modeling.

Dual-axis tracker mechanics:

A DAT adds a second drive axis — typically a polar or azimuth axis — allowing the panel face to remain perpendicular to direct solar irradiance at all times. The primary azimuth drive handles east-to-west rotation; the elevation drive adjusts tilt to follow the sun's seasonal arc. Dual-axis systems require more complex wiring, larger foundation footprints per panel, and more frequent mechanical maintenance intervals than single-axis designs.

Energy yield comparisons are central to the tracker vs. fixed-tilt analysis covered in solar energy production factors. NREL modeling indicates single-axis trackers typically produce 15–25% more annual energy than fixed-tilt systems at equivalent capacity; dual-axis trackers can add a further 5–10% over single-axis in high-direct-normal-irradiance (DNI) locations such as the desert Southwest.

Common scenarios

Utility-scale ground-mount projects represent the dominant deployment environment for single-axis trackers. Projects of 1 MW or larger can spread the per-watt cost of tracker hardware across enough panel capacity to achieve favorable economics. The solar-system-sizing-guide covers capacity planning concepts applicable to these installations.

Agricultural and dual-use (agrivoltaic) installations increasingly use single-axis trackers to allow crop cultivation or livestock grazing beneath raised tracker rows. Panel height, row spacing, and tilt range must be coordinated with agricultural requirements. Agricultural solar installations covers the land-use and spacing considerations in this context.

Concentrating photovoltaic (CPV) and concentrating solar power (CSP) systems almost exclusively use dual-axis trackers because concentration optics require near-perfect solar alignment — even small tracking errors cause steep efficiency losses. These applications are geographically concentrated in high-DNI regions.

Commercial carport structures occasionally incorporate single-axis trackers when the carport span and foundation depth can accommodate the additional lateral loads from tracker movement. Solar carport installations addresses the structural design constraints relevant to elevated tracker mounting.

Decision boundaries

Choosing between fixed-tilt, single-axis, or dual-axis involves evaluating five discrete factors:

1. Site latitude and DNI: Trackers deliver the largest yield gains at latitudes between 25°N and 45°N with high direct irradiance. Diffuse-irradiance-dominated climates (Pacific Northwest, for example) narrow the yield advantage of tracking.
2. Terrain slope: Single-axis trackers require relatively flat terrain (generally less than 5° cross-slope without terrain-following designs). Steep or irregular sites increase foundation costs and may make fixed-tilt more economical.
3. Structural and permitting load: Trackers introduce dynamic wind loads, seismic considerations, and electrical complexity not present in fixed-tilt arrays. Under IEC 62817 (Design qualification of solar trackers), tracker structural performance must be validated against wind, snow, and seismic loading. Permitting authorities having jurisdiction (AHJ) may require stamped structural engineering for tracker foundations. The solar installation permits and approvals page covers the AHJ process in detail.
4. Maintenance infrastructure: Trackers contain motors, bearings, gearboxes, and control electronics that require scheduled maintenance. Remote or unstaffed sites must factor in service access costs.
5. Economics relative to panel cost: As panel costs per watt have declined, the relative value of squeezing additional yield through tracking has shifted. The solar energy system costs and solar energy system roi calculator guide resources provide the financial framing for this comparison.

Safety standards applicable to tracker installations include NFPA 70 (National Electrical Code), which governs wiring and grounding of the tracker drive electronics, and UL 3703 (Outline of Investigation for Solar Trackers), which covers the safety evaluation of tracker assemblies. Inspectors reviewing tracker-based projects typically require documentation of tracker controller listings, grounding continuity, and compliance with the structural calculations submitted at permit.

References

• U.S. Energy Information Administration — Electric Power Annual
• National Renewable Energy Laboratory (NREL) — Solar Position Algorithm (SPA)
• NREL — Bifacial PV and Tracker Performance Modeling
• IEC 62817 — Design Qualification of Solar Trackers (IEC Webstore)
• NFPA 70 — National Electrical Code (NFPA)
• UL 3703 — Outline of Investigation for Solar Trackers (UL)