Wind damage of single axis tracking structures has been the subject of much discussion within the solar industry over the past two years or so. Why is this the case?
Wind damage is not something new in solar structures. But since a solar tracker is a structure that is moving and something that can rotate, it is something that is more prone to suffer from wind failures if it is not appropriately designed.
What has happened in recent years is that panels have been growing in size and solar trackers have been growing in size. What’s more is that in the beginning, all solar plants were installed at sites that were flat and wind loads were not so high. In the last few years solar trackers and panels have been installed almost all over the world, and in some places that experience higher wind speeds than in the past.
Certain attention has been drawn to 2P (two-in-portrait) trackers in terms of wind. Why do you think this is the case?
Wind affects both 1P and 2P trackers, the impacts are not related to the form factor. It is true that according to how that structure is dimensioned, it can experience instability at different wind speeds. And contrary to what many people would think, the tracker configuration [1P vs 2P] is not the key factor for the tracker’s wind resilience. Tracker design and stow strategy are the most important factors.
In the beginning the structures were designed only considering the building codes [for wind] and would only consider static loads – and they were considered by the [solar] industry as being insufficient. Then with these wind tunnel tests and wind tunnel scale models, the know-how and expertise has developed. Firstly, we started learning more about dynamic effects and more recently about aeroelastic effects.
And how is this knowledge being put into practice?
At the moment we have developed the Dy-wind strategy for a solar tracker that we claim is the most advanced in the market. We can now simulate, with CFD modeling, how an entire solar tracker plant is going to behave. By changing a few parameters, we know what kind of wind speed a tracker is going to be able to stand. We can also adapt parameters like the size of the panel, the length or width, and what is going to happen if you change the stow strategy – bigger panels can be stowed in a way in which they work as a wind shield.
The consequence of all of this knowledge, besides the impact of the stow strategy that I mentioned, is that the 1P tracker will require reinforcement of the tracker by adding dampeners – sometimes up to six per tracker. Keep in mind that dampeners don’t only have to be installed, they have to be maintained. And they [1P trackers] also have had to reinforce the piles.
In terms of the 2P tracker that we manufacture, we had to reinforce the torque tube, so that it could stand this twisting effect related to galloping and fluttering effect. We also introduced multi-slewing drives and the rails that support the panels. Sometimes rows of the panels can also be made shorter. But these are two different strategies: you either reinforce some elements of the tracker, like the torque tube or the piles, or you can add dampeners.
In the case of 2P trackers, it is not that dampeners don’t work – they do. But they are very expensive [on a 2P tracker] in comparison to a 1P configuration making it a better strategy to reinforce other elements of the tracker. The effect [of the reinforcement] is that there is a higher [resonant] frequency of the tracker so that it doesn’t start this instability. Overall, it is a matter of design.
And how is Soltec introducing this improved robustness into the market?
We have recently launched the SF8 tracker, a new model that is specially designed for larger panels. We have introduced DY-wind design, which is a new stow strategy, and it also integrates new, more advanced algorithms and electronics. So, we are sure we are offering to the market a solution that is the right one for almost all wind and almost all locations.
What is the benefit of multiple slewing drives?
The normal 1P tracker only has a slewing drive in the middle of the tracker, and then it has a motor and a tracker controller. A multi-drive tracker means that instead of having only this blocking mechanism in the center of the tracker, the slewing drive, it has more than one. When you have more than one blocking mechanism, like in Soltec’s case more than one slewing drive along the tracker, you are blocking the tracker in several points – so it behaves more [like] a fixed racking. It means there isn’t the freedom for the fluttering or galloping effects. It is almost static.
Does the additional robustness that is built into the SF8 affect the cost?
Not necessarily. The SF8 is bigger. Instead of working for three strings, which is the case on the SF7, the configuration is for four to six strings. This means that there are fewer controllers, fewer parts, per watt peak. With the SF8 design, we balance the increase in some elements, like the slewing drives, with increasing the number of panels and wattage that can be installed on a single tracker. So, the tracker is 22% stronger than the SF7, it can withstand high winds even with larger panels.
By increasing the size, some of the additional cost can be balanced – is that right?
That’s right.
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