Heliostat Wind Loads

Heliostat pv trackers

The heliostat wind load and aerodynamics research group aims to improve our current understanding of the turbulence characteristics in the atmospheric boundary layer (ABL) through the use of detailed experimental measurements in a large-scale wind tunnel.

Developing methods for wind load reduction can assist heliostats to be designed from lighter materials that would lower the manufacturing and installation costs of the heliostat field in a concentrating solar thermal (CST) power tower (PT) system.

The heliostat wind load and aerodynamics research group is continually looking for potential industrial/research collaborators, as well as potential PhD students, both locally and globally. Information about how to apply for an Australian Solar Thermal Research Institute (ASTRI) postgraduate research scholarship in the heliostat project at the University of Adelaide, is available online, or to discuss potential collaboration, please contact us.

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  • Background

    Heliostat mirrors

    The motor drives, support structure and mirror of a heliostat account for up to 80% of the heliostat capital cost (Kolb et al. 2011), but this can be reduced with an accurate estimation of the wind loading on these components to maintain the structural integrity while achieving good optical performance (Pfahl et al. 2017).

    Heliostats are designed to maintain structural stiffness during operation at different elevation angles and with sufficient structural strength to withstand the maximum wind loads during high-wind conditions when aligned parallel to the ground in the stow position. This requires a detailed understanding of the turbulent phenomena in the lowest 10 m of the atmospheric surface layer where heliostats are positioned. The research outcomes would allow the development of reliable engineering tools to predict and further optimise the wind loads on heliostats in various configurations.

    References
    Kolb, G.J., Ho, C.K., Mancini, T.R. & Gary, J.A. (2011), Power Tower Technology Roadmap and Cost Reduction Plan, SAND2011-2419, Sandia National Laboratories, Albuquerque, USA.
    Pfahl, A., Coventry, J., Röger, M., Wolfertstetter, F., Vásquez-Arango, J.F., Gross, F., Arjomandi, M., Schwarzbözl, P., Geiger, M. & Liedke, P., Progress in heliostat development, Solar Energy, 152, 2017, 3-37.

    The research challenge

    Design wind codes for large physical structures, such as buildings with heights of the order of 100 m, adopt a simplified gust factor method for the calculation of wind loads. This is not applicable to heliostats positioned at heights below 10 m with natural frequencies of an order of magnitude larger than standard-sized buildings, hence heliostats have previously been designed using mean and peak wind load coefficients derived from experimental data in systematic wind tunnel studies.

    Wind tunnel experiments have developed accurate methods for reproducing theoretical mean velocity and turbulence intensity profiles to represent the atmospheric surface layer (ASL), nominally the lowest 100 m of the ABL. However, the spectral distribution of the velocity fluctuations is shifted to higher frequencies in smaller-scale boundary layer wind tunnels. Hence, the absence of the most energetic vortices generated in the lower frequency region of the spectra through wind tunnel experiments can lead to discrepancies in the calculated peak wind loads, such as the drag forces and overturning moments in operating positions and the lift forces and hinge moments in stow position.

    The frequency distribution of eddies is important, as the sizes of the energy-containing eddies causes higher pressure differences over the surface of a heliostat mirror. This requires a detailed understanding of the temporal and spatial distributions of the turbulence characteristics in the lowest 10 m of the surface layer. This is best obtained by reliable and extensive wind tunnel and field measurements for the development of design wind guidelines for heliostats and the validation of computational models.

  • People

    A/Professor Maziar Arjomandi

    A/Professor Maziar Arjomandi
    Research Director

    Expertise:
    Fluid mechanics, heat transfer, hybrid technology development.

    Dr Matthew Emes

    Dr Matthew Emes
    Research Associate

    Expertise:
    Atmospheric boundary layer turbulence, aerodynamics, concentrated solar systems.

    Ms Azadeh Jafari

    Ms Azadeh Jafari
    PhD Candidate

    Expertise:
    Atmospheric boundary layer, solar thermal systems.

    Mr Jeremy Yu

    Mr Jeremy Yu
    PhD Candidate

    Expertise:
    Bluff body aerodynamics, concentrated solar systems

  • Partners & collaborators

    The heliostat wind load and aerodynamics research group actively collaborates with researchers around Australia. Current collaborators include:

    This work is supported by ARENA through the Australian Solar Thermal Research Initiative (ASTRI)

  • Facilities & equipment

    The research facility for the study of highly turbulent wind engineering flows utilises the large-scale Adelaide wind tunnel. Key components of the wind tunnel facility include:

    Geometries of four spire sets

    Geometries of four spire sets

    Wind engineering test section containing spires, roughness elements with velocity and force measurement rigs

    Wind engineering test section containing spires, roughness elements with velocity and force measurement rigs.


    Specialised wind engineering techniques and flow measurement devices are used for characterisation of the turbulent flow approaching the heliostat;

    • Large cross-section (3 m × 3 m) and development length (17 m) with spires and roughness elements for generation of the atmospheric boundary layer;
    • Hot-wire anemometry and multi-hole pressure probes, including post-processing of velocity measurements to obtain derived quantities of turbulence;
    • Simultaneous diagnostics, able to couple measurements of temperature, velocity and ambient conditions;
    • Specialised two-dimensional traverse system, controlled through Matlab on an in-house computer
    Telescopic pylon design (left) and pressure tap locations on the heliostat mirror surface (right) (Emes et al. 2017).

    Telescopic pylon design (left) and pressure tap locations on the heliostat mirror surface (right) (Emes et al. 2017).

    Force measurements and pressure distributions on scale-model heliostats;

    • Square heliostat mirrors with chord lengths 0.1 m to 0.8 m (in increments of 0.1 m)
    • Telescopic pylon design allowing variation of elevation axis height from 0.3 m to 0.6 m
    • Hinge design allows modification of the heliostat elevation angle with respect to the horizontal
    • Four three-axis load cells to measure the three force components are mounted on a 3 m diameter turntable for modification of the azimuth angle
    • Pressure taps on the heliostat surface monitor the non-uniform pressure distributions
    • In-house image processing, post-processing and data analysis, including capability to extract derived quantities, such as turbulence intensity, power spectra and integral length scales
  • Research data

    Lift and hinge moment coefficients on isolated heliostats in stow position
    (Emes et al. 2017)

    Detailed experiments were conducted on a series of heliostat mirrors of different chord lengths (c) and at a different elevation axis heights (H) in the simulated ABL generated using two configurations of spires and roughness. Force and surface pressure measurements were analysed to relate the lift force and hinge moment coefficients on the stowed heliostat to the turbulence characteristics of the ABL.

    Schematic diagram of the wind tunnel setup

    Schematic diagram of the wind tunnel setup

    Peak pressure coefficient distribution on the mirror surface of the stowed heliostat (U = 13 m/s, Iu = 10%)

    Peak pressure coefficient distribution on the mirror surface of the stowed heliostat (U = 13 m/s, Iu = 10%)

    Key experimental parameters

    • Heliostat mirror chord length, c = 0.3-0.8 m (in increments of 0.1 m)
    • Heliostat elevation axis height, H = 300-600 mm
    • Velocity profiles of the two spire sets (SR1 and SR2) are approximated by power law profiles with roughness exponent α = 0.12 and 0.14, respectively
    • Freestream velocity, U = 11 and 15.5 m/s
    • Reynolds number, Re = 0.88×106, 1.24×106
    • Turbulence intensity, Iu = 6-13%

    Key data provided

    Peak stow lift and hinge moment coefficients calculated from force measurements on different-sized heliostat mirrors exposed to two configurations (SR1 and SR2) of spires and roughness.

    Emes, M., Arjomandi, M., Ghanadi, F., & Kelso, R. (2017). Effect of turbulence characteristics in the atmospheric surface layer on the peak wind loads on heliostats in stow position. Solar Energy, 157, 284-297. https://doi.org/10.1016/j.solener.2017.08.031

    Lift and hinge moment coefficients on tandem heliostats in stow position
    (Emes et al. 2018)

    Schematic diagram of the tandem heliostat configuration

    Schematic diagram of the tandem heliostat configuration

    Key experimental parameters

        Heliostat mirror chord length, c = 0.3-0.8 m (in increments of 0.1 m)
        Heliostat elevation axis height, H = 300-600 mm
        Longitudinal gap ratio, d/c = 0.1-5
        Velocity profiles of the two spire sets (SR1 and SR2) are approximated by power law profiles with roughness exponent α = 0.12 and 0.14, respectively
        Freestream velocity, U = 11 m/s
        Reynolds number, Re = 8.8×105
        Turbulence intensity, Iu = 6-13%

    Key data provided

    See Table 2 in the article (access via link below) for all of the data points.

    Downloadable spreadsheet of Velocity Profiles

    Emes, M., Ghanadi, F., Arjomandi, M., & Kelso, R. (2018). Investigation of peak wind loads on tandem heliostats in stow position. Renewable Energy, 121, 548-558. https://doi.org/10.1016/j.renene.2018.01.080

    Drag coefficients on normal heliostats

    Pressure coefficient distribution on a normal heliostat for peak drag (left) and hinge moment (right)

    Pressure coefficient distribution on a normal heliostat for peak drag (left) and hinge moment (right)

    Key experimental parameters

    • Heliostat mirror chord length, c = 0.8 m
    • Heliostat elevation axis height, H = 500 mm
    • Velocity profile approximated by power law profile with roughness exponent α = 0.14
    • Freestream velocity, U = 11 m/s
    • Reynolds number, Re = 8.8×105
    • Turbulence intensity, Iu = 13%

    Heliostat wind load spreadsheet

    Wind load predictions for heliostats are not provided in design codes because of their non-standard shape and the changes in wind velocity and turbulence in the lowest 10 m of the atmospheric boundary layer (ABL). The ASTRI heliostat spreadsheet estimates the design wind loads on different heliostat sizes based on:

    (1) the dependence of wind load coefficients on turbulence intensity derived in our wind tunnel experiments,

    (2) the expected wind speed and turbulence intensity profiles in the full-scale ABL.

    Mean and peak design loads are calculated for a square-shaped heliostat based on the mean wind speed and the relevant aerodynamic coefficient. Critical load cases show the maximum value of the heliostat loads and aerodynamic coefficients for each load case.

  • List of publications

    Listed below are the recent publications arising out of the heliostat wind load and aerodynamics research group. Direct links to the published articles (via digital object identifiers, DOIs), or where available, accepted versions of manuscripts, can be found by clicking the hyperlinks below.

    Journal articles

    1. Emes, M.J., Jafari, A., Coventry, J. and Arjomandi, M. (2020), The influence of atmospheric boundary layer turbulence on the design wind loads and cost of heliostats, Solar Energy, 207, 796-812. doi:10.1016/j.solener.2020.07.022
    2. Jafari, A., Emes, M., Cazzolato, B., Ghanadi, F. and Arjomandi, M. (2020), Turbulence characteristics in the wake of a heliostat in an atmospheric boundary layer flow, Physics of Fluids, 32(4), 045116. doi:10.1063/5.0005594
    3. Emes, M.J., Arjomandi, M., Kelso, R.M. and Ghanadi, F. (2019), Turbulence length scales in a low-roughness near-neutral atmospheric surface layer, Journal of Turbulence, 20:9, 545-562. doi:10.1080/14685248.2019.1677908
    4. Emes, M.J., Jafari, A., Ghanadi, F. and Arjomandi, M. (2019), Hinge and overturning moments due to unsteady heliostat pressure distributions in a turbulent atmospheric boundary layer, Solar Energy, 193, 604-617. doi:10.1016/j.solener.2019.09.097
    5. Jafari, A., Ghanadi, F., Emes, M.J., Arjomandi, M. and Cazzolato, B.S. (2019), Measurement of unsteady wind loads in a wind tunnel: scaling of turbulence spectra, Journal of Wind Engineering and Industrial Aerodynamics, 193, 103955. doi:10.1016/j.jweia.2019.103955
    6. Jafari, A., Ghanadi, F., Arjomandi, M., Emes, M. & Cazzolato, B. (2019). Correlating turbulence intensity and length scale with the unsteady lift force on flat plates in an atmospheric boundary layer flow. Journal of Wind Engineering and Industrial Aerodynamics, 189, 218-230. doi:10.1016/j.jweia.2019.03.029
    7. Yu, J., Emes, M., Ghanadi, F., Arjomandi, M. & Kelso, R. (2019). Experimental investigation of peak wind loads on tandem operating heliostats within an atmospheric boundary layer. Solar Energy, 183, 248-259. doi:10.1016/j.solener.2019.03.002
    8. Emes, M., Ghanadi, F., Arjomandi, M., & Kelso, R. (2018). Investigation of peak wind loads on tandem heliostats in stow position. Renewable Energy, 121, 548-558. doi:10.1016/j.renene.2018.01.080
    9. Emes, M., Arjomandi, M., Ghanadi, F., & Kelso, R. (2017). Effect of turbulence characteristics in the atmospheric surface layer on the peak wind loads on heliostats in stow position. Solar Energy, 157, 284-297. doi:10.1016/j.solener.2017.08.031
    10. Emes, M., Arjomandi, M., & Nathan, G. (2015). Effect of heliostat design wind speed on the levelised cost of electricity from concentrating solar thermal power tower plants. Solar Energy, 115, 441-451. doi:10.1016/j.solener.2015.02.047

    Conference papers

    1. Emes, M.J., Jafari, A. & Arjomandi, M., Wind Load Design Considerations for the Elevation and Azimuth Drives of a Heliostat, in SolarPACES, 2019, AIP Conference Proceedings: Daegu.
    2. Jafari, A., Emes, M., Cazzolato, B., Ghanadi, F. and Arjomandi, M., An Experimental investigation of unsteady pressure distribution on tandem heliostats, in SolarPaces. 2019, AIP Conference Proceedings: Daegu.
    3. Arjomandi, M., Emes, M., Jafari, A., Yu, J., Ghanadi, F., Kelso, R., Cazzolato, B., Coventry, J. & Collins, M., A Summary of Experimental Studies on Heliostat Wind Loads in a Turbulent Atmospheric Boundary Layer, in SolarPACES, 2019, AIP Conference Proceedings: Daegu.
    4. Emes, M.J., Jafari, A., Ghanadi, F. and Arjomandi, M. (2019), A method for the calculation of the design wind loads on heliostats, AIP Conference Proceedings: Casablanca, 2126(1), 030020. doi:10.1063/1.5117532
    5. Jafari, A., Ghanadi, F., Emes, M., Arjomandi, M. & Cazzolato, B. (2018). Effect of Free-stream Turbulence on the Drag Force on a Flat Plate. In Proceedings of the 21st Australasian Fluid Mechanics Conference. Adelaide, Australia.
    6. Emes, M., Jafari, A. & Arjomandi, M. (2018). Estimating the Turbulence Length Scales from Cross-Correlation Measurements in the Atmospheric Surface Layer. In Proceedings of the 21st Australasian Fluid Mechanics Conference. Adelaide, Australia.
    7. Emes, M., Yu, J., Jafari, A., Ghanadi, F., & Arjomandi, M. (2017). Experimental Investigation of the Wind Loads on Heliostats. In Proceedings of the Asia Pacific Solar Research Conference 2017. Melbourne, Australia: Australian PV Institute. Retrieved from http://apvi.org.au/solar-research-conference/proceedings-apsrc-2017/
    8. Jafari, A., Emes, M., Ghanadi, F., & Arjomandi, M. (2017). The Effect of Turbulence Intensity on the Peak Wind Loads on Heliostats. In Proceedings of the Asia Pacific Solar Research Conference 2017. Melbourne, Australia: Australian PV Institute. Retrieved from http://apvi.org.au/solar-research-conference/proceedings-apsrc-2017/ Voluptatem accusantium doloremque
    9. Emes, M. J., Ghanadi, F., Arjomandi, M., & Kelso, R. M. (2017). Optimisation of the size and cost of heliostats in a concentrating solar thermal power tower plant. In The European Conference on Sustainability, Energy & the Environment 2017. Brighton, UK. Retrieved from https://papers.iafor.org/submission36612/
    10. Ghanadi, F., Emes, M., Yu, J., Arjomandi, M., & Kelso, R. (2017). Investigation of the atmospheric boundary layer characteristics on gust factor for the calculation of wind load. In AIP Conference Proceedings Vol. 1850. doi:10.1063/1.4984496
    11. Ghanadi, F., Yu, J., Emes, M., Arjomandi, M., & Kelso, R. (2017). Numerical investigation of wind loads on an operating heliostat. In AIP Conference Proceedings Vol. 1850. doi:10.1063/1.4984497
    12. Emes, M. J., Arjomandi, M., Ghanadi, F., & Kelso, R. M. (2017). Wind tunnel investigation of turbulence characteristics in the atmospheric surface layer. In Wind Energy Science Conference. Copenhagen, Denmark.
    13. Emes, M., Ghanadi, F., Arjomandi, M., & Kelso, R. (2016). An experimental technique for the generation of large-scale spanwise vortices in a wind tunnel. In Proceedings of the 20th Australasian Fluid Mechanics Conference (pp. 1-5). Perth, Australia: Australasian Fluid Mechanics Society.
    14. Emes, M., Arjomandi, M., Kelso, R., & Ghanadi, F. (2016). Integral length scales in a low-roughness atmospheric boundary layer. In Proceedings of the 18th Australasian Wind Engineering Society Workshop (pp. 1-4). McLaren Vale, South Australia: AWES. Retrieved from http://www.awes.org/archives/workshop-proceedings/
    15. Coventry, J., Arjomandi, M., Barry, J., Blanco, M., Burgess, G., Campbell, J., Emes, M., . . . Yu, J. (2016). Development of the ASTRI heliostat. In V. Rajpaul, & C. Richter (Eds.), Proceedings of International Conference on Concentrating Solar Power and Chemical Energy Systems, as published in AIP Conference Proceedings Vol. 1734 (pp. 020005-1-020005-8). Cape Town, South Africa: American Institute of Physics. doi:10.1063/1.4949029
  • Contact us

    For enquiries regarding data, collaborative work and PhD opportunities:

    Dr Matthew Emes
    Centre for Energy Technology
    School of Mechanical Engineering
    The University of Adelaide
    SA 5005 Australia
    matthew.emes@adelaide.edu.au