The efficiency of solar power plants – including photovoltaic (PV) and solar thermal technologies – depends on how closely the collectors are able to track the course of the sun. The more precise and trouble-free these collectors operate, the more efficient and therefore more profitable the plants will be.
Rolling and plain bearings, as well as linear units from Schaeffler are making an important contribution here. These units have high rigidity and high load-carrying capacities and operate reliably even under extreme operating conditions. With its extensive range of products and specialist expertise for materials, coatings and seals, Schaeffler is an important development partner and supplier for projects that involve parabolic troughs, solar towers, Dish Stirling systems and Fresnel power plants.
In addition to standard bearings, engineered solutions for specific customer requirements are also provided. Depending on the type and design of power plant, suitable rolling bearings include slewing rings, angular contact roller bearings, ball screw drives, housed units and radial insert ball bearings, as well as track rollers. Plain bushes, spherical plain bearings and linear units are also provided.
Plain bearings for single-axis tracking systems
Schaeffler has expanded its range of plain bearings for solar energy applications. As well as ELGOGLIDE plain bearings, which have proven themselves over several years, the product range also includes metal-polymer composite plain bearings and ELGOTEX plain bearings.
ELGOGLIDE is a sliding layer that comprises a technical woven material with support fibres, Teflon fibres and a synthetic resin matrix. The advantages of these bearings are that they are maintenance-free units and offer very high load-carrying capacities, particularly if very high loads are present on one side combined with swivelling movements.
The characteristics of metal-polymer composite plain bearings come from the composite material, which enables low-wear sliding characteristics, as well as high load-carrying capacity and good thermal conductivity. The excellent formability of the material also enables customer-specific components to be engineered for various rotary, linear and swivel motions.
The composite materials used for ELGOTEX bearings are resistant to corrosive media and offer continuously low-friction, low-wear sliding characteristics, ensuring maintenance-free operation. ELGOTEX comprises two intertwined, wound layers. The internal sliding layer – which is embedded in a resin matrix with fillers and solid lubricants – is made from synthetic and PFTE fibres. The external layer comprises continuous glass fibres (filament) in epoxy resin. A specific winding angle of the glass fibres stabilises the layer, which significantly increases the strength of the plain bushing.
AXS angular contact roller bearings for double-axis tracking
Rolling bearings such as Schaeffler’s AXS angular contact roller bearings are used in double-axis tracking systems for solar thermal plants, including solar towers and Dish Stirling power plants. Typical applications include reflector adjustment systems. High load-carrying capacity, rigidity and positioning accuracy play a critical role here. These characteristics are absolutely key in enabling secure, smooth, vibration-free bearing operation for solar collectors. The bearings must also support high forces and moments, for example, during sudden gusts of wind. The bearing supports are therefore critical for the reliability and cost effectiveness of the solar power plant.
AXS angular contact roller bearings can be integrated in new and existing designs. The geometry of the bearing rings is identical, which means no mistakes can occur during fitting. Simple, turned bearing seats are sufficient for supporting the bearing rings manufactured using forming methods. In addition, special lubricants (both grease and oil) ensure that the bearings have very low maintenance requirements.
Modular System for Automation Tasks
Schaeffler’s Linear Technology Business Unit is a systems supplier that provides complete linear drive systems (linear actuators, tables and modules) designed to match specific customer requirements. A wide range of standard driven, ready-to-use linear units are also available, both for the manufacture of solar collectors and PV modules, as well as for solar tracking applications.
The linear units are based on anodised aluminium profiles and are modular in their design, which means optimum systems can be designed to specific customer requirements. In many applications, the stable, rigid design eliminates the need for complex frames. The compact design facilitates the integration and installation into handling and production facilities for solar panels.
Linear units are also available as monorail guidance systems and shaft guidance systems. The drive function is performed by a ball screw drive, toothed belt drive or direct drive. Schaeffler can supply the full range of accessories for power transmission applications, delivering driven linear units as complete systems that are ready-to-fit and ready-for-use (including control systems).
Seals and coatings
The prevailing environmental conditions place very high demands on the development and design of the bearings for solar power plants. The environment – often desert regions – is usually characterised by arid, dusty conditions combined with high temperatures that fluctuate significantly. These conditions require bearings that use reliable sealing technologies that prevent particles from entering the bearing and which keep the high-quality bearing grease inside the bearing, as well as special materials and coatings that protect the bearing from corrosion.
Schaeffler offers a modular sealing system comprising a variety of sealing principles, systems, design elements and combinations. As a leader in the field of innovative surface and coating technologies for many years, Schaeffler has been able to optimise the functionality of rolling bearing surfaces and precision components that are subjected to high loads.
Schaeffler’s Surface Technology Centre carries out research and development, transferring innovations from laboratory scale to volume production processes. Zinc and zinc alloys are predominantly used for anti-corrosion protection. Under the Corrotect brand name, Schaeffler has launched various coatings such as zinc (Corrotect ZK), zinc iron (Corrotect ZI) and zinc nickel (Corrotect ZN).
The sliding partner (shaft/pin) of plain and spherical plain bearings, for example, can be coated with chromium mixed oxide (LC layer) on a columnar chromium layer (Durotect CK+) in order to provide anti-corrosion protection and to improve the friction properties. Combining a basic layer with a soft sliding layer improves not only the running-in behaviour of the bearings but also the friction and wear properties.
Durability and resistance to corrosion are often underestimated but are important criteria in ensuring the high-reliability, long operating life, low-maintenance requirements and cost efficiency of solar power plants. Schaeffler offers durable, long life bearings with operating life up to 20 years.
For more information on Schaeffler’s bearings for solar energy applications, please email or visit the website at www.schaeffler.co.uk.