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Summary

Wind Stow is a protective mechanism that commands single-axis trackers to a specified angle when wind conditions exceed safe operating limits. PlantPredict supports two wind stow implementations: PlantPredict Wind Stow (threshold-based comparison using wind gust speed) and Array Technologies Wind Stow (external API-based calculation using proprietary algorithms). Wind stow has the highest priority in the tracker angle determination hierarchy, overriding both base tracking and irradiance optimization.

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Inputs

NameSymbolUnitsDescription
Wind Stow Type——PlantPredict or ArrayTechnologies
Wind Gust Speedvgustv_{gust}m/sWind gust speed from weather data (PlantPredict)
Wind Stow Thresholdvthresholdv_{threshold}m/sUser-defined threshold for stow activation (PlantPredict)
Wind Stow Angleαstow\alpha_{stow}degreesUser-defined stow position (PlantPredict)
Current Tracker Angleαcurrent\alpha_{current}degreesTracker rotation angle before wind stow check
Minimum Tracking Limit—degreesMinimum tracker rotation angle (ATI)
Maximum Tracking Limit—degreesMaximum tracker rotation angle (ATI)
Nighttime Stow Angle—degreesStow angle for nighttime (ATI)
ATI Wind Stow Type——Array Technologies wind stow algorithm variant (ATI)

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Outputs

NameSymbolUnitsDescription
Commanded Tracker Angleα\alphadegreesFinal tracker rotation angle after wind stow logic

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Detailed Description

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Override Hierarchy

Wind stow has the highest priority in PlantPredict’s tracker angle determination: Final Angle=Wind Stow>Irradiance Optimization>Base Tracking\text{Final Angle} = \text{Wind Stow} > \text{Irradiance Optimization} > \text{Base Tracking} When wind stow is activated, it overrides both the base tracking angle and any irradiance optimization adjustments.

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PlantPredict Wind Stow

PlantPredict’s built-in wind stow uses a threshold comparison with wind gust speed. Activation condition: Activate Stow={true,if vgust>vthresholdfalse,otherwise\text{Activate Stow} = \begin{cases} \text{true}, & \text{if } v_{gust} > v_{threshold} \\ \text{false}, & \text{otherwise} \end{cases} Stow angle calculation: When activated, the tracker moves to the stow angle while preserving the directional sign: α=sign(αcurrent)×αstow\alpha = \text{sign}(\alpha_{current}) \times \alpha_{stow} where sign(αcurrent)\text{sign}(\alpha_{current}) returns +1 for positive angles (west-facing), -1 for negative angles (east-facing). Zero stow angle handling: If the stow angle equals zero, a small non-zero value prevents numerical issues: α={0.001×sign(αcurrent),if αstow=0°sign(αcurrent)×αstow,otherwise\alpha = \begin{cases} 0.001 \times \text{sign}(\alpha_{current}), & \text{if } \alpha_{stow} = 0° \\ \text{sign}(\alpha_{current}) \times \alpha_{stow}, & \text{otherwise} \end{cases} Requirements: PlantPredict Wind Stow requires WindGust data in the weather file. Wind gust values are not synthesized from mean wind speed.

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Array Technologies Wind Stow

Array Technologies Wind Stow uses an external API to calculate wind stow angles based on proprietary algorithms. API endpoint: 
https://wind-stow.api.arraytechinc.com/simulation
Request parameters:
  • Minimum tracking limit angle
  • Maximum tracking limit angle
  • Nighttime stow angle
  • Array Technologies wind stow type (algorithm variant)
  • Weather time series data
  • API authentication key
Response: The API returns time series data containing ModuleTrackerAngleWindStow for each timestep. When the returned wind stow angle differs from the calculated tracking angle, PlantPredict:
  1. Updates the rotation angle to the wind stow angle
  2. Recalculates surface angles from the new rotation
  3. Recalculates incidence angles based on updated surface orientation
Caching: If multiple DC fields share identical wind stow parameters (min/max tracking limits, nighttime stow angle, ATI wind stow type), PlantPredict reuses the API response from the first field to avoid redundant API calls.

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References

  • Banks, D. (2013). Tracker wind loading and stow strategies. Solar America Board for Codes and Standards.