Challenging weather conditions are becoming the new normal for solar developers and system owners, who require new measures to minimize risk and ensure returns.
Understanding the importance of wind testing and how different types of wind forces affect tracker design and production can help power producers secure the right single-axis tracker technology for their site and region.
A variety of elements affect how the wind affects Solartacker on each individual job site, ranging from local weather phenomena and topography to the influence of other nearby structures or objects. Because no two PV sites are the same, each requires site-specific customization, making these projects more complex to design.
If wind profiles are not properly incorporated into a tracker's design, asset owners can face a number of events such as: B. remediation costs and downtime as well as lower energy yields, and ultimately miss their financial goals.
Looking at the technical intricacies involved in designing for different types of winds and understanding how proper tracker testing can affect tracker design features like stoke angles and damping drives drives stable aerodynamics for long-term performance .
There's something in the wind
Careful assessment of a site's wind conditions allows asking the right questions from the start.
Variability in wind speed, turbulence and direction can all have unexpected effects on solar tackers and their surroundings. Understanding wind effects helps designers and EPCs account for uncertainties and optimize yield.
Wind effects can be divided into three main categories: static, dynamic and aeroelastic.
Static wind forces exert an even and constant pressure on a tracker that can cause deformation or flexing of the structure that affects the performance and accuracy of the tracking mechanism.
Dynamic wind forces are less predictable, fluctuating in speed and direction, which can cause significant vibration and stress on a tracker, reducing tracking accuracy and causing panel misalignment and component wear and tear. To account for these dynamic wind loads, advanced aerodynamic models that account for turbulence, gusts, and other variations should be used.
Aeroelastic wind forces occur when a tracker interacts with the surrounding airflow. Aeroelastic effects include resonant vibration, torsional flutter, and torsional gallop, all of which can cause uncontrolled vibration or oscillation that leads to misalignment, reduced tracking accuracy, or component failure. Tracker design must focus on combating these effects in order to achieve aerodynamic stability.
Tracker design must focus on combating these effects to achieve aerodynamic stability, according to Canadian engineering firm RWDI, which specializes in wind testing. Every component in a tracker's structure must be evaluated to ensure optimized resistance to wind loads. A number of potential failures need to be considered, including:
Resonant vibration, which occurs when the frequency of a gust of wind matches the structure's natural frequency, which can lead to catastrophic failure.
Torsional flutter, which is a self-excited aerodynamic instability that can cause large amplitudes in the array's torsional motion, resulting in tracker failure.
Torsion canter that uniquely involves a vertical movement. Tracker failure occurs when high wind speeds overcome the resistance of the structure.
Not only is understanding wind effects critical to device design, but knowing how to weather gusts of wind can optimize a tracker's performance. For example, knowing about abnormal wind on a certain part of a PV construction site means that a windbreak could be used to reduce wind speed and turbulence, improve tracker stability and accuracy. Sophisticated sensors could be deployed to detect wind variations and adjust a tracker's position to optimize energy production. It is also possible to reduce a tracker's profile, increase its rigidity or construct it with special materials that resist wind loads and aeroelastic effects.
Taking the wind out of tracker design with testing
Wind tunnel testing plays a crucial role in the development of solar tackers. Small-scale models are used to assess how a new tracker might cope with any number of wind conditions, revealing design limitations early in development. After adjustments to the design, an inexpensive full-size tracker can be produced that minimizes risk.
Updraft terrain simulation is one of the critical components of wind tunnel testing. This type of simulation replicates real-world obstacles that could affect wind forces, such as B. Trees and buildings or even other rows of trackers on the site.
Updraft behavior simulation includes different elevation curves, modifiable surface roughness, moving barriers, and displays of various wind events, including such phenomena as hurricanes and tornadoes.
Bend with the wind through stagnation angles
Stagnation angles and associated static and dynamic wind loads must be carefully considered when designing a wind-resistant solar tacker. A useful mitigation strategy is damping, which dissipates or controls vibrational energy or oscillations in a system.
Dampers are an important part of developing an optimal stowing strategy, especially for solar tackers at 0° stowing, which are susceptible to torsional forces that cause twisting and spinning along the axis of a torque tube. During the development of a wind-resistant 1P tracker, various tilt angles were tested in a wind tunnel to develop an optimal stowage strategy. The tests showed that lower tilt angles caused lower static loads on the structure and less force on the overall system. A 0° inclination angle provided the lowest coefficient value as the lateral load was close to zero.
Higher tilt angles introduced additional stresses on the structure, requiring more foundations or increased foundation and torque tube sizes to withstand additional lateral forces. In contrast, a 0° stowage strategy with the right degree of overdamping and stiffness to resist deformation was found to require fewer foundations.
The ideal design for a 0° jam should balance stiffness, cushioning and weight to control tracker costs, protect assets and maintain efficiency. While stowing at high bank angles can be safe, it can result in increased wind loads on foundations and other parts of the structure, requiring more rigid systems or overdamped designs to mitigate dynamic variations that cause aerodynamic instability.
Proper damping - which limits vibration and oscillation - is critical to ensure the stability of a Solartacker system. Determining the right amount and type of cushioning depends on a variety of factors, such as: B. the stowing angle of the design, the wing length and the mass of the structure.
Again, testing is key. A system that is underdamped can become unstable and require costly mitigation measures such as B. additional dampers to address torsional forces that could otherwise cause damage or even failure of the tracker.
For the 1P solar tacker discussed in the previous section, which had a 0° stowage strategy and a 30-40 m blade length, it was found that two to four dampers per row were sufficient to achieve a properly damped structure create.
Because quality testing is essential to determine the right configuration, you should choose an experienced tracker solution provider with damper expertise that can meet project specifications, budget, and timelines.
Take the wind out of instability with multi-row tests
Testing a tracker design cannot be done in isolation. It is imperative to conduct multi-row testing to balance stiffness and damping to maximize performance and mitigate long-term risks. Positioning, shielding, and wind vortices can all affect the aeroelastic performance of different segments of a solar array in different ways.
Multi-row testing rotates the table to simulate multi-angle wind testing to determine the effects of static and dynamic wind on the perimeter and center rows of a system. Pushbuttons can determine peak static and dynamic wind loads to provide coefficient values required to design optimized 0° stagnation angles. The values also help determine the ideal number of foundations and most cost-effective span height.
While a 0° stagnation angle was ideal for the example 1P tracker, with all rows behaving the same when wind blew over the panels in the stagnation, the edge zones received higher loads in a preview position before affecting the central zones downwind .
It is important to verify aeroelastic effects to maintain efficiency, avoid mechanical wear, reduce downtime and decrease efficiency. Multiple row testing improves the overall design of a system and allows strategy adjustments to ensure fringes do not adversely affect the central rows of the array.
Taking the wind out of a system's sails
Pluck tests - in which a tracker is pulled and released to simulate a gust of wind and evaluate its dynamic behavior - validate the stiffness and damping ratio of a solar tacker system. The process also includes high and low amplitude tests and a shake test. Results are compared to aeroelastic wind test results to balance the design.
It is essential to include the specified rotation angles in the Pluck test calculations to accurately predict potential rotations of up to 15°. A pluck test that accounts for lower angles may be easier to simulate, but it could affect accuracy.
Proper pluck testing ensures a tracker will perform as expected in real wind conditions and avoid costly downtime. Choose a tracker solution provider with extensive pluck testing experience and a skilled engineering team capable of validating existing aeroelastic wind reports.
Go like the wind with the right racking partner
When evaluating tracking technologies, consider manufacturers with extensive wind tunnel testing that can provide robust data to support these questions:
Has the tracker manufacturer conducted extensive multi-row static, dynamic and aeroelastic wind tunnel tests in recent years? Can they prove their tracker design meets the tolerances specified in these tests?
Can they demonstrate that their design meets the tolerances specified in these tests, including natural frequency, attenuation, field height, chord length, tracker length, and GCR?
What is the critical wind speed that the system can withstand during normal operation and storage? Are there specific calculations showing how these velocities are calculated using data from the aeroelastic wind report?
Can the tracker manufacturer demonstrate that its design accommodates all specified pressures and wind tunnel specific load combinations beyond standard building code requirements?
If the tracker manufacturer's design does not use dampers, can they verify that their tracker will not experience adverse aeroelastic effects during normal operation and storage?