While the Covid 19 pandemic has caused deep pains across many industries, the world has been careful not to ignore the ever-present threat of global warming. Indeed, with the advent of the coronavirus, many nations have looked towards the renewable energy sector as a magic bullet. Not only do investments in renewable energy allow for a boost in economic activity, but the move away from fossil fuel-based power sources ensures that we continue to aim for the reduction in emissions that remain so vital to our planet’s future.
Some nations, such as Spain, have set aggressive targets for themselves, stating that by 2050 they will be 100% based on renewable energy. Others, such as the UK, have already started setting domestic records for the number of days in which coal-based power has not been required. India has also pledged to move towards solar energy, with many of the projects running well ahead of schedule. Recently, the Adani Group has been awarded the largest such contract on record, underlining the seriousness with which the government is approaching renewable energy.
At Poly Fluoro, we have delved deep into the renewables sector through our involvement in solar tracker bearings. We engaged in the first of such projects in mid-2018, when the industry was still ramping up and when new technologies were only just being understood. The learnings we have uncovered have allowed us to further invest and develop our own polymer technologies, with the aim that we are positioned to take on any project and offer the technical support and guidance needed by our clients.
Before we go into these learnings, let us first understand the purpose of the solar tracker bearing.
For all solar projects, the efficiency of the system is maximised when the installed panels are able to maximise their harvest of the sun’s radiation. Since the sun moves across the sky, the angle of the panels needs to alter as the day progresses. To facilitate this, a tracker is installed, which rotates the panels at the required rate. Since the tracker itself consumes power, it is vital to ensure that the energy expended in rotating the panels does not exceed the extra power generated by this system. It is for this reason that a smooth functioning bearing is essential. The solar tracker bearing clamps around the square tube on which the panels are fixed. The tracker rotates the square tube and the bearing’s job is to allow for this rotation with minimal friction.
Some of our key learnings are as follows:
For the most part, a solar tracker bearing needs to match the size of standard square tubes. Since most projects would prefer to use off-the-shelf square tube dimensions, the bearings need to be designed accordingly.
In India, the sizes of 75mm, 100mm, 120mm, and 150mm would be most common. Here too, the preference is for 100mm tubes, as this maximises the number of panels that can be installed on a single length of tube, but minimises on the weight of the tube itself.
Our designs have focussed on creating a uniform bearing for the 100 square tube. In doing so, we have studied the dimensions of existing bearings to understand how much load and friction the part would be submitted to.
Our experience has shown that while erstwhile bearings demand the use of UHMWPE for solar tracker bearings, this polymer becomes problematic as volumes increase. The main reason is that UHMWPE is not injection mouldable. This means that parts need to be machined. Machining is time consuming, expensive, and it also results in a very heavy final component.
Other candidates include POM (Polyacetal), HDPE, and Nylons. Each of these has advantages, although our preference has been towards POM, as it offers both strength and an ease of moulding. While HDPE is lightweight, it is not nearly as strong as POM. Nylon is the least preferred because it tends to swell when there is moisture. While Nylon bearings may have done well in projects where the climate is dry, the use of Nylon in more humid conditions would not be advisable.
Other than the polymer, the key lies in what additives one incorporates. There are three primary factors to consider. The first is strength – which is managed by the choice of polymer. A typical solar tracker bearing of 100 square would need to accommodate at least 1000-1500 Kgs of vertical load. The second criterion is friction. The use of friction reducing additives is required in making solar tracker bearings, as it greatly enhances efficiency. Experience has shown us that there is a balance needed here. Too little friction can also be a bad thing, as it may cause the panels to rotate due to wind loads. Finally, the bearing needs to be UV resistant. Poly Fluoro has explored the impact of different fillers on UV resistance. While many manufacturers simply add carbon black and claim that the part is resistant to UV, this can be misleading. Our own research shows that the addition of black pigment can only withstand UV up to a point. In most cases, the bearing will begin to deteriorate within 2-3 years. The more expensive option is to use HALS (Hindered amine light stabilizers), which work by ensuring that the UV radiation is managed within the first 0.1mm of the part’s surface. HALS would allow the solar tracker bearing to have a life of 25-30 years, which is what is required when considering a solar project.
While smaller projects may opt for machining, it is our belief that an injection moulded part is most suitable for solar tracker bearings.
Using a special honeycomb or lattice structure, the bearings can be made lightweight, but strong enough to take heavy loads. Furthermore, with a cycle time of only under two minutes, the manufacture of a solar tracker bearing can be done in a fraction of the time it would take to machine the bearing from a rod or sheet.
The combined impact of the weight reduction and lower cycle time results in a cost saving of over 50% in some cases. For large projects, where tens of thousands of bearings are needed, the machining route is both financially wasteful and unlikely to meet any stringent project timelines.
We hope the above information has been useful in better understanding the structure of the solar tracker bearing. As projects grow in size, we expect to come across more learnings. In the meantime, Poly Fluoro is proud to be one of the pioneers in this space. Our library of solar tracker bearings allows us to take on projects of different sizes and volumes, while offering both a quality product and a genuine academic understanding of the engineering behind it.