Solar tracking systems are among the most thermally dynamic mechanical environments that a coupling will ever encounter. A tracker drive motor, gearbox, and drive shaft begin each day at ambient temperature — which in desert solar installations can be below freezing on winter mornings — and reach operating temperature by midday, when direct solar irradiance on the tracker structure combined with high ambient temperatures can push structural steel temperatures to 60 to 80°C above the morning baseline. This thermal cycle repeats every day for the 25 to 30-year design life of the solar installation, accumulating thousands of thermal expansion and contraction cycles on every structural member and drive component.
The coupling connecting the tracker’s drive motor and actuator to the torque tube or slewing drive must absorb the lateral shaft offset that results from this daily thermal expansion without transmitting destructive radial forces to the motor or gearbox bearings — and it must do this reliably for decades, in an outdoor environment with UV exposure, dust, temperature extremes, and minimal maintenance access. The Oldham coupling addresses this challenge with its lateral offset absorption capability, its dry-running polymer disc, and its availability in corrosion-resistant materials appropriate for outdoor installation.
A typical horizontal single-axis tracker (HSAT) consists of a steel torque tube supported on bearings at regular intervals along its length, driven by a linear actuator or a slewing drive at the central support. The motor and gearbox are mounted on a fixed support structure adjacent to the drive point, with a coupling connecting the gearbox output shaft to the torque tube drive interface.
As the tracker structure heats up during the day, the steel torque tube and the motor support structure expand thermally. Because the two structures have different geometries, different orientations relative to the sun, and different thermal masses, they do not expand at exactly the same rate or in exactly the same direction. The result is a daily cycle of lateral shaft offset between the gearbox output shaft and the torque tube drive axis — an offset that may be 0.2 to 0.8 mm at peak temperature differential depending on the installation geometry and the distance between the motor mount and the torque tube bearing.
A rigid coupling in this position transmits the thermal misalignment as a bending load on both the gearbox output shaft bearing and the torque tube bearing. Over thousands of daily thermal cycles — approximately 3,650 cycles per decade — this cyclic load is a fatigue loading that progressively reduces bearing life. In a solar installation designed for 25 years of operation with minimal maintenance access, premature bearing failure from coupling-induced loads is an unacceptable failure mode.
Horizontal single-axis trackers use either a centralised drive system — one motor and gearbox per row of panels, connected to the torque tube at the row’s centre — or a distributed drive system with individual drives at each panel. In both configurations, the coupling at the gearbox-to-torque-tube interface must accommodate the thermal misalignment described above.
The Oldham coupling is used in this position specifically for its zero-bearing-load lateral offset accommodation. A flexible coupling that imposes spring-back forces — bellows or beam designs — would transmit the cyclic thermal misalignment as a cyclic radial load on the gearbox bearing: exactly the fatigue loading that must be avoided in a 25-year maintenance-minimised installation. The Oldham coupling absorbs the offset through its sliding disc with zero reaction force, protecting the gearbox and torque tube bearings from coupling-induced fatigue loads throughout the installation’s service life.
Tracker drive systems do not require zero backlash in the same way that precision servo systems do — the panel positioning accuracy required for maximum energy harvest is typically in the range of ±0.1 to ±0.5 degrees, which is achievable with a coupling that has modest backlash. However, in tracker designs with encoder-based closed-loop position control, the encoder coupling connection does require zero backlash for stable control loop operation.
Dual-axis trackers (both azimuth and elevation tracking) are used in concentrated photovoltaic (CPV) and concentrated solar power (CSP) applications where tracking accuracy requirements are more stringent — typically within ±0.05 degrees to maintain focus on a small receiver. These systems use servo-controlled drives with encoder feedback, and the coupling requirements combine the precision of a servo application with the outdoor environment challenges of a solar tracker.
In CPV and CSP trackers, Oldham couplings appear at both the encoder connection (zero backlash, electrical isolation, zero bearing load on the encoder) and the main drive connection (lateral offset absorption from thermal expansion, zero bearing load on the precision drive gearbox). Stainless steel hubs and PEEK discs are typically specified for these outdoor precision applications — the stainless steel providing corrosion resistance in coastal or humid desert environments, and PEEK providing the temperature stability needed for continuous outdoor operation in high-ambient-temperature climates.
The outdoor environment of a solar installation introduces material requirements beyond those encountered in typical industrial applications:
UV exposure: Standard acetal (POM) is susceptible to UV degradation over extended outdoor exposure. UV radiation breaks down the polymer chain, causing surface chalking, embrittlement, and increased brittleness. In outdoor tracker applications with direct sunlight exposure, a UV-stabilised acetal grade or an alternative disc material should be specified. Carbon-fibre-filled PEEK is inherently black and absorbs UV without degradation, making it a suitable outdoor disc material. If shielding the coupling from direct sunlight with a simple cover or guard is feasible, standard acetal discs can be used with confidence.
Condensation and moisture cycling: Daily temperature cycling from cold mornings to hot afternoons creates condensation on cold metal surfaces during the cool-up phase. In coastal or humid desert environments, salt-laden condensation is particularly corrosive to aluminium hubs. Standard aluminium 6061 without special surface treatment will develop corrosion in these environments over a 25-year service life. Anodised aluminium provides better corrosion resistance; hard-anodised aluminium is more durable still. For coastal or salt-fog environments, 316L stainless steel hubs are the conservative specification that avoids corrosion concerns entirely.
Temperature extremes: Desert solar installations experience temperature swings from below -20°C on winter nights to above +60°C ambient in summer afternoons, with coupling component temperatures reaching higher still due to direct solar heating. Acetal’s low-temperature brittleness — it becomes significantly more brittle below 0°C — means that a disc replacement or emergency maintenance action in cold conditions carries a risk of brittle fracture if a disc is handled carelessly. PEEK’s much lower cold-temperature brittleness makes it a more robust specification for installations in cold-night climates.
Solar tracker installations typically cover large areas — a utility-scale solar farm may have thousands of tracker drives spread across hundreds of hectares. The cost of maintaining each coupling individually is therefore a significant operational consideration, and minimising maintenance frequency is a primary design goal.
The Oldham coupling’s replaceable disc architecture is well suited to this constraint. When disc replacement is eventually required — typically after several years in a correctly specified solar tracker application — the replacement takes five minutes per coupling without shaft re-alignment or disturbing the mounting structure. A maintenance technician with a small kit of replacement discs and a torque wrench can service multiple couplings per day. Compare this with bellows couplings that require full replacement and re-alignment, which takes significantly longer and may require two technicians.
For utility-scale installations, the operating company should establish a disc replacement programme based on the expected service life for the specific installation conditions — climate, operating cycle, and disc material — and pre-stock sufficient replacement discs for the full installation. The cost of stocking spare discs is minimal compared to the cost of an unplanned maintenance dispatch to a remote tracker row.
| Tracker Type / Location | Hub Material | Disc Material | Key Reason |
|---|---|---|---|
| HSAT, inland arid site | Anodised aluminium | UV-stabilised acetal or PEEK | Low humidity, UV protection priority |
| HSAT, coastal or humid site | 316L stainless steel | PEEK | Salt spray and condensation resistance |
| HSAT, cold climate (below -20°C) | 316L stainless steel | PEEK | Low-temperature toughness, no cold brittleness |
| Dual-axis CPV/CSP tracker | 316L stainless steel | PEEK | Precision + outdoor environment + long service life |
Solar tracker drives combine three requirements that individually appear in other applications but rarely together: lateral offset absorption from thermal expansion across daily temperature cycles spanning 50 to 80°C; long service life in outdoor environments with UV, moisture, and temperature extreme exposure; and minimal maintenance access in large distributed installations. The Oldham coupling addresses all three through its sliding disc mechanism — which absorbs thermal misalignment without bearing loads throughout decades of daily cycling — and its material options, which provide the UV, temperature, and corrosion resistance appropriate for each installation climate. Correctly specified with stainless steel hubs and PEEK discs for demanding environments, and with UV-stabilised materials for direct sunlight exposure, an Oldham coupling in a solar tracker drive will operate reliably for the full 25 to 30-year design life of the installation with nothing more than periodic disc inspection and replacement as its maintenance requirement.
Browse our Oldham coupling range for outdoor and solar applications with stainless steel hub and PEEK disc options, or contact our team for material selection guidance specific to your installation climate and tracker design.
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