Unravelling Polymers

The Definitive Blog on Polymers by Poly Fluoro Ltd.

Solar Tracker Bearings - Cost Benefits from Injection Moulding

Our foray into Solar Tracker Bearings over the past few years has not come without a fair share of learnings.

While, the initial assumptions we had regarding the bearing design and polymer grade selection have not altered much, we have had to revise our understanding of the manufacturing process significantly.

Primarily, a solar tracker bearing needs to conform to a few parameters in order to be suitable for the application involved:

  1. Lightweight – this is essential because the more load the bearing places on the solar tracker mechanism, the higher the inefficiency of the system. Solar energy is sensitive to net energy losses within the system and the bearing should not be a drag on energy

  2. Low coefficient of friction – the smoother the motion of the bearing, the easier the system can move. Again, if it requires extra load to rotate the bearing within its casing, it leads to a new energy loss

  3. UV resistant – since the bearing is being used in a solar application, it is essential that the polymer does not degrade over the 15-20 years that the system is expected to be operational

  4. Load resistant – while different projects have different parameters on how much load the bearing needs to take, it is safe to assume that a single solar tracker bearing would need to withstand somewhere between 700-1200 Kgs of load without experiencing any fatigue or deformation over time

  5. Low cost – with most projects needing about 1000-2000 sets of bearings per megawatt, there is a high volume of bearings needed for a single project. One reason that standard pillow block bearings are not used in these projects is that they are prohibitively expensive in comparison to the polymer bearing assemblies
     

Below, we look at some of the key learnings along the above metrics and evaluate how our understanding has changed and allowed us to offer a more tailored and effective solution for this product.

  Existing designs Poly Fluoro designs Benefits
Weight Machined from rods, so parts tend to be bulky Injection moulded using special lattice structure Injection moulding offers significant weight reduction of up to 40%
Grade of polymer UHMWPE or PA6 Special blend of thermoplastic with PTFE PA6 has high moisture absorption, while UHMWPE is not injection mouldable in its standard form. Poly Fluoro uses special blends to give a low moisture absorption polymer that has the benefits of PTFE's self-lubricating properties
UV resistance Usually black pigment Uses HALs HALs offer a far superior resistance to UV radiation over the long term
Coefficient of friction 0.15-0.2 0.1 Using a thermoplastic-PTFE blend allows us to reduce coefficients of friction to within 0.1 and possibly below
Load capacity 700-1100 Kgs 700-1100 Kgs Poly Fluoro designs offer the same load capacity, but at much lower part weights
Cost 1X 0.6X The use of injection moulding allows us to lower material consumption, machining cost and gives a much higher productivity overall. This brings the cost down significantly

 

To summarise – we too had initially opted for the machining route in making these bearings. However, we find that using injection moulding allows us the freedom to lower the part weight, improve the blend of the polymer grade being used and increase productivity, thereby reducing cost while enhancing the effectiveness of the part.

The downside to injection moulding is that it requires a significant up-front cost in making the mould. However, our understanding is that the mould cost is effectively recovered within the first 1500-2000 sets of bearings made. In other words, a project that requires many thousands of bearings would recover the cost quite quickly. Furthermore, since the life of the mould is anywhere between 150,000 and 200,000 sets of bearings, solar companies would save significantly by standardising a bearing design and using this across multiple projects.
 

Poly Fluoro Ltd. is currently making solar tracker bearings under the brand name: HelioGlide. We offer standard sizes of bearings which can be incorporated even in smaller projects, where the total requirement may not be high.

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