Slewing Bearings for Photoelectric Heating (CSP)
What Is a Slewing Bearing?
A slewing bearing (also known as a turntable bearing or slewing ring) is a large-scale rolling-element bearing designed to support heavy loads while enabling smooth rotational motion. Unlike conventional bearings, slewing bearings are typically mounted between two structures — a stationary base and a rotating platform — and can handle axial loads (vertical), radial loads (horizontal), and tilting moment loads simultaneously.
Slewing bearings are commonly used in cranes, wind turbines, excavators, and — most relevant to this article — photoelectric heating (Concentrated Solar Power) systems. They feature an inner ring and an outer ring, with rolling elements (balls or rollers) arranged between them. Many slewing bearings also include integral gear teeth (internal or external) to allow active rotation via a pinion drive.
What Is Photoelectric Heating ?
Photoelectric heating, more commonly known as Concentrated Solar Power (CSP) , is a technology that uses mirrors or lenses to concentrate sunlight onto a receiver. The receiver absorbs the concentrated solar energy and converts it into heat, which is then used to generate steam and drive a turbine for electricity production.
There are four main types of CSP systems:
- Parabolic trough systems – U-shaped mirrors focus sunlight onto a receiver tube running along the trough’s focal line.
- Power tower systems – Hundreds or thousands of flat mirrors (heliostats) track the sun and reflect sunlight to a central receiver atop a tower.
- Dish Stirling systems – Parabolic dish-shaped mirrors concentrate sunlight onto a Stirling engine at the focal point.
- Linear Fresnel systems – Flat or slightly curved mirrors reflect sunlight onto an elevated linear receiver.
In all these systems, precise solar tracking is essential. The mirrors must continuously adjust their orientation to follow the sun across the sky — and this is where slewing bearings play a critical role.
Why Do CSP Systems Require Slewing Bearings? – The Role of Dual-Axis Tracking
A CSP plant can only generate maximum electricity when its mirrors are aimed directly at the sun. Even a small angular deviation can significantly reduce energy output. This requires a dual-axis tracking system — horizontal (azimuth) rotation and vertical (elevation) tilt.
Slewing bearings provide the foundation for this tracking motion:
- Azimuth rotation: A large slewing bearing is installed between the foundation and the mirror support structure, allowing the entire assembly to rotate horizontally (typically ±120° to ±180°).
- Elevation tilt: A smaller slewing bearing or pivot bearing allows the mirror to tilt vertically (typically 0° to 90°).
Without high-quality slewing bearings, CSP systems would suffer from increased friction, positioning errors, and premature mechanical failure. The bearing must withstand continuous daily motion, high wind loads, dust, and extreme temperature variations — often in remote desert environments.
Key Features of Slewing Bearings for Photoelectric Heating Applications
Not all slewing bearings are suitable for CSP applications. The demanding environment of a solar power plant requires specific features:
- High load capacity: Must support the dead weight of mirrors, frames, and wind-induced forces.
- Smooth rotation: Low friction and consistent torque for precise sun tracking.
- High reliability: Designed for continuous operation over the full lifespan of a typical CSP plant.
- Corrosion resistance: Protection against desert dust, humidity, and temperature cycling.
- Integrated gear option: External or internal gear teeth for active drive engagement.
- Low maintenance: Sealed designs with long-lasting lubrication reduce on-site service needs.
Among the various slewing bearing types, the Four Point Contact Ball Slewing Bearing is particularly well-suited for CSP heliostats because it can handle axial, radial, and moment loads simultaneously with a single row of balls. This design offers an excellent balance of load capacity, compactness, and cost-effectiveness.
How Do Slewing Bearings Work in a Heliostat or Trough System?
In a typical CSP system, the slewing bearing operates as follows:
For a power tower heliostat:
- The slewing bearing’s outer ring is bolted to a concrete foundation or steel pedestal.
- The inner ring (equipped with external gear teeth) supports the mirror frame.
- A motor-driven pinion engages the gear teeth, rotating the inner ring and the attached mirror.
- A second slewing bearing or pivot joint handles elevation tilt.
- A controller sends positioning signals to maintain optimal sun reflection.
For a parabolic trough system:
- A Double Row Ball Slewing Bearing or Double Row Different Diameter Ball Slewing Bearing supports the trough’s collector assembly.
- The bearing allows the trough to rotate along a single axis (north-south tracking).
- The receiver tube remains stationary while the mirrors rotate around it.
The result is smooth, precise, and repeatable positioning — with minimal backlash for accurate tracking.
Core Advantages of High-Precision Slewing Bearings for CSP Plants
Using high-precision slewing bearings instead of simpler rotation mechanisms (such as plain bearings or small gearboxes) offers several distinct advantages for CSP plants:
| Advantage | Benefit for CSP System |
|---|---|
| High positioning accuracy | Maximizes solar energy collection by keeping mirrors perfectly aimed |
| Excellent moment load capacity | Handles wind forces and mirror weight without deflection |
| Long operational life | Designed for continuous outdoor service over many years |
| Low friction | Reduces motor power requirements and energy consumption |
| Integrated gear option | Simplifies drive system design and assembly |
| Sealed against contamination | Reliable operation in dusty desert environments |
For larger CSP installations requiring extreme rigidity, a Cross Roller Slewing Bearing offers higher rotational accuracy and stiffness due to its cylindrical rollers arranged in a 90° V-shaped raceway. For applications that demand maximum load capacity — such as very large heliostats or heavy trough systems — the Three-Row Roller Slewing Bearing provides separate raceways for axial, radial, and moment loads, delivering the highest load-carrying capability of any slewing bearing type.
How Do Slewing Bearings Improve Photoelectric Heating Efficiency?
Efficiency in a CSP plant is ultimately measured by electricity output per unit of sunlight. Slewing bearings improve this efficiency in several ways:
- Maximizing direct normal irradiance (DNI) capture: Precise tracking ensures mirrors are always optimally aligned, increasing thermal energy collected compared to low-precision tracking systems.
- Reducing parasitic power consumption: Low-friction bearings require less motor power to rotate heavy mirror assemblies, saving electricity that would otherwise be consumed by the plant itself.
- Minimizing downtime: Reliable slewing bearings reduce maintenance interruptions, keeping the plant operational for more hours per year.
- Enabling automated cleaning and stowing: Slewing bearings allow heliostats to rotate to a stowed position (face down) during high winds or sandstorms, protecting expensive mirrors from damage.
Real-world CSP plant experience shows that upgrading from manual or low-precision tracking to high-precision slewing bearing-based systems can significantly increase annual energy output, improving project return on investment.
Selection Guide: How to Choose the Right Slewing Bearing for Your CSP Project
When selecting a slewing bearing for a photoelectric heating application, consider the following parameters:
| Parameter | Recommendation |
|---|---|
| Static axial load | Total weight of mirror assembly × safety factor (wind and dynamic loads) |
| Dynamic torque | Based on tracking motor capacity and wind resistance |
| Bearing type | Four Point Contact Ball Slewing Bearing – most common for CSP heliostats due to its ability to handle combined loads. For lighter-duty applications, a Double Row Ball Slewing Bearing may be sufficient. For maximum rigidity, consider a Cross Roller Slewing Bearing. |
| Gear configuration | External gear for pinion drive; internal gear for space-limited designs |
| Raceway material | High-strength alloy steel with induction-hardened raceways |
| Sealing | Dual lip seals for desert dust protection |
| Rolling element material | High-carbon chromium bearing steel or other durable materials |
| Gear quality | Precision gear manufacturing for smooth tracking |
For very large CSP installations with extreme load requirements, a Three-Row Roller Slewing Bearing offers the highest capacity, with separate raceways for axial, radial, and moment loads. For applications that require simplified mounting and reduced machining, a Flanged Slewing Bearing provides pre-drilled mounting holes and a flat mounting surface, making installation faster and more cost-effective.
LDB: A Custom Slewing Bearing Manufacturer for Photoelectric Heating Systems in China
LDB is a specialized manufacturer of high-precision slewing bearings and slew drives, with extensive experience in supplying rotation solutions for photoelectric heating and concentrated solar power systems.
Our product portfolio includes both slewing bearings (heavy-duty raceway components for smooth, high-load rotation) and slew drives (integrated worm gear units for precise rotational control). Whether your CSP project requires individual slewing bearings for heliostats, trough collectors, or complete slew drive assemblies, LDB has the solution.
Why choose LDB for CSP slewing bearings?
- Customization: LDB offers tailored bolt patterns, gear tooth configurations (module, number of teeth, pressure angle), race diameters, and sealing arrangements to match any CSP system design. We also produce Flanged Slewing Bearings for simplified bolt-on mounting.
- Precision manufacturing: All slewing bearings are produced on precision CNC gear cutting machines and induction-hardened for long life. Each bearing is tested for backlash, rotational smoothness, and gear accuracy.
- Material quality: Raceways are made from high-strength alloy steel, with rolling elements from premium bearing steel. Induction hardening depth is carefully controlled for optimal wear resistance.
- Durability testing: Each unit undergoes dimensional inspection, gear runout testing, and load simulation before shipment.
- Global compliance: LDB products are manufactured in accordance with international quality standards and can be certified to meet customer-specific requirements.
- Flexible lead time: LDB works closely with customers to provide competitive delivery schedules based on project needs and order quantities.
LDB works directly with CSP project developers, heliostat manufacturers, EPC contractors, and system integrators worldwide — providing either individual slewing bearings or complete tracking solutions.
FAQ: FAQ About Slewing Bearings for Photoelectric Heating
Q1: Which type of slewing bearing is best for CSP heliostats?
A: The Four Point Contact Ball Slewing Bearing is the most common choice because it handles axial, radial, and moment loads with a single row of balls. For larger heliostats or trough systems, a Double Row Ball Slewing Bearing or Three-Row Roller Slewing Bearing may be preferred.
Q2: What is the typical service life of a CSP slewing bearing?
A: With proper design, material selection, and lubrication, a CSP slewing bearing can last for many years — matching the expected operational life of a solar power plant.
Q3: Do CSP slewing bearings require regular maintenance?
A: Minimal maintenance is required. Most LDB slewing bearings for CSP applications are sealed and pre-lubricated for long-term operation. Periodic visual inspection and re-greasing may be recommended in harsh desert environments.
Q4: Can LDB produce slewing bearings with custom gear teeth?
A: Yes. LDB manufactures slewing bearings with external or internal gears in various modules, tooth counts, and pressure angles. Gear grinding is also available for high-precision applications.
Q5: How do I request a quotation for a CSP slewing bearing project?
A: Contact LDB with your system requirements: mirror size and weight, wind load conditions, tracking speed, gear specifications, and mounting dimensions. We will provide engineering drawings and a quotation promptly.