What Is a Slewing Bearing?

A slewing bearing—also known as a slewing ring or turntable bearing—is a large-diameter rolling-element bearing designed to support heavy loads while enabling rotational movement between two structures. Unlike standard bearings that typically handle only radial or axial loads, slewing bearings are engineered to simultaneously manage axial loads (vertical forces), radial loads (horizontal forces), and tilting moments (overturning forces).

Core components: A slewing bearing consists of several key elements working together to provide reliable rotation under load. The inner ring and outer ring serve as the load-carrying structural rings, typically manufactured from forged alloy steel such as 50Mn or 42CrMo. Between them, rolling elements—either steel balls or cylindrical rollers—transfer loads and enable rotation. A cage or spacer maintains proper spacing between rolling elements to prevent metal-to-metal contact and reduce friction. Seals protect the raceway from contaminants and retain lubricant. Mounting holes are uniformly spaced around the bearing for secure installation.

Working principle: The rolling elements operate within precision-ground raceways in the inner and outer rings. Under load, the rolling elements distribute forces across the raceway surfaces, enabling smooth rotation while supporting combined loads. The raceway geometry and material properties determine the bearing's load capacity and fatigue life.

Common types: Single-row four-point contact ball bearings are the most versatile and cost-effective, suitable for light to medium loads. Double-row ball bearings provide higher axial and moment capacity. Crossed roller bearings offer the highest precision and rigidity. Three-row roller bearings deliver extreme load capacity for the heaviest applications. For solar tracking, single-row four-point contact bearings integrated with worm gear drives are the most common configuration.

The Role of Slewing Bearings in Solar Tracking Systems

Solar tracking systems rotate photovoltaic panels to follow the sun, increasing energy yield by 20-35% compared to fixed installations. At the core of each tracking system is a slewing bearing—or more accurately, a slewing drive assembly that integrates a slewing bearing with a worm gear drive mechanism.

A patent for solar power generation equipment describes a slewing bearing with a worm wheel mechanism enabling precise positioning of solar panels. The design includes a base, ring frame, worm wheel, and worm, with a positioning hole and limiting hole system for fixing the worm wheel after installation—facilitating maintenance or replacement.

Another patent application details a slewing bearing for driving solar panels that incorporates a deformable gap structure to offset crosswind loads, ensuring normal operation under lateral forces. This innovation addresses a key challenge in solar tracking: maintaining performance under varying wind conditions.

Key Technical Requirements for Solar Tracker Slewing Bearings

Precise positioning: Solar trackers require smooth, low-torque rotation with fine angular accuracy to optimize panel orientation relative to the sun. An electric slewing drive using a worm gear mechanism provides precise control over speed and position. Typical positioning accuracy requirements are within ±2 degrees for single-axis trackers and within ±0.5 degrees for dual-axis trackers.

Self-locking: The worm gear's self-locking property ensures the system maintains position even when power is off—critical for keeping panels oriented correctly during wind loading or power interruptions. This self-locking capability eliminates the need for additional brakes or holding systems, reducing cost and complexity.

Environmental durability: Solar trackers operate outdoors in varying conditions: high temperatures, UV radiation, dust, and rain. Sealed housing and robust materials ensure durability and minimal maintenance. Slewing bearings for solar trackers must withstand temperature ranges from -20°C to 70°C and exposure to UV radiation without degradation.

Low maintenance: Remote or difficult-to-access tracker installations benefit from sealed, long-life bearings that reduce service visits and maintenance costs. Many solar tracker operators expect 10+ years of maintenance-free operation.

Design Features of Solar Slew Drives

A solar slewing drive typically integrates:

• A slewing bearing as the load-bearing element, handling radial, axial, and tilting moments

• A worm gear mechanism transmitting motor rotation, providing high torque and self-locking

• An electric motor for fine-tuned, accurate positioning

The slewing drive provides high torque output (typical ratings up to 4,800 Nm) with gear ratios around 55:1. The worm gear design allows for compact packaging while delivering the torque needed to rotate heavy solar panels.

Key design considerations:

• Sealing: Heavy-duty rubber seals or sealed housing to prevent moisture and dust ingress

• Corrosion protection: Zinc or epoxy coatings, or stainless steel variants for long-term outdoor exposure

• Lubrication: Extended or maintenance-free options preferred for remote installations

• Mounting: Bolt-mounted design for easy installation and replacement

Types of Solar Tracking Systems and Their Slewing Bearing Requirements

Single-Axis Trackers

Single-axis trackers rotate panels around one axis, typically horizontal or vertical. They require:

• One slewing drive per tracker row (or per two rows for some designs)

• Lower torque requirements than dual-axis trackers

• Gear ratios typically 40:1 to 60:1

• Positioning accuracy within ±2 degrees

Dual-Axis Trackers

Dual-axis trackers rotate panels around both horizontal and vertical axes, enabling precise sun tracking throughout the day and across seasons. They require:

• Two slewing drives per tracker (one for each axis)

• Higher torque requirements for the vertical axis drive

• Higher positioning accuracy (±0.5 degrees)

• More robust sealing due to more complex geometry

Large-Scale Solar Farms

Utility-scale solar farms (50MW+) require:

• Hundreds or thousands of slewing drives

• Consistent quality across large volumes

• Reliable supply chain and logistics support

• Extended maintenance intervals to minimize operational costs

How to Select the Right Slewing Bearing for Solar Tracking

Load Analysis

Calculate the loads the slewing bearing must support:

• Axial load: Weight of the solar panels and support structure

• Radial load: Wind loads and seismic forces

• Tilting moment: Overturning forces from wind pressure on panels

Wind load is typically the dominant factor in solar tracker slewing bearing selection. Design wind speeds range from 90 km/h to 180 km/h depending on location and code requirements.

Environmental Assessment

Evaluate the operating environment:

• Temperature range: Affects lubricant viscosity and seal performance

• Humidity and rainfall: Influences corrosion protection requirements

• Saltwater exposure: Requires enhanced corrosion protection for coastal installations

• Dust and sand: Affects seal selection and lubrication intervals

Slewing Bearing Configuration

For solar applications, consider:

• Gear type: External gearing with worm drive is standard for solar trackers

• Gear ratio: Typically 40:1 to 60:1 for single-axis, up to 100:1 for dual-axis

• Sealing: IP 65 rating or higher for dust and water resistance

• Corrosion protection: Zinc-epoxy coating or specialized plating

Quality and Certification

For solar farm projects, quality certification is essential:

• ISO9001 and TUV certification

• Material test certificates and hardness records

• Dimensional inspection reports

• Traceability from raw material through finished product

Emerging Trends in Solar Slewing Bearings

Lubrication-free designs: Mobile solar tracker applications increasingly use slewing ring bearings with polymer plain bearings that run completely without maintenance and lubrication. Cityfreighter uses lubrication-free slewing ring bearings in solar tracker mechanics.

Wind load compensation: Recent patent designs incorporate gap structures between the drive outer ring and load-bearing outer ring to offset crosswind loads. A disc spring provides elastic deformation, allowing the bearing to compensate for lateral forces while maintaining normal operation.

Smart monitoring: Integration of sensors for position feedback, temperature, and vibration enables predictive maintenance and remote monitoring of tracker performance.

Higher torque density: Advances in gear design and materials allow slewing drives to deliver higher torque in smaller packages, enabling more compact and cost-effective trackers.

How LDB Bearing Supports the Solar Energy Industry？

LDB Bearing supplies precision slewing bearings and slew drives for solar tracking systems. Products use verified 50Mn and 42CrMo forged alloy steel with induction-hardened raceways to 55–62 HRC and gear teeth to 50–60 HRC. Customizable configurations include gear type, seal options, coatings, and lubrication for various environmental conditions.

LDB's solar slewing bearing capabilities:

• Single-row four-point contact slewing bearings integrated with worm gear drives

• Custom gear ratios and torque ratings for specific tracker designs

• Seal options including heavy-duty rubber and labyrinth designs

• Corrosion-resistant coatings for outdoor and coastal installations

• Application engineering support for load calculations and tracker integration

• Full dimensional records retained for every bearing sold

LDB provides application engineering support for load calculations and tracker integration, retaining full dimensional records for every bearing sold. Serving 73 countries with over 500,000 units in service, LDB delivers the quality, precision, and reliability that solar energy applications demand.

Contact LDB Bearing today to discuss your solar tracker slewing bearing requirements.