Wind loads on heliostats and photovoltaic trackers of various aspect ratios

For the layout of solar trackers the wind loads on the structure have to be known. They can be calculated by using wind load coefficients given in literature. But so far these values are only valid for aspect ratios of the panel (width to height) of about 1.0. Therefore the wind load coefficients for heliostats of aspect ratios between 0.5 and 3.0 were determined to close this gap. As solar trackers are exposed to the turbulent atmospheric boundary layer the turbulence of the approaching flow has to be modeled. As a reliable method at reasonable cost wind tunnel measurements were chosen. Solar trackers of 30 m2 panel size were investigated at a model scale of 1:20. Wind direction and elevation angle of the panel were varied to investigate especially the constellations at which the highest wind loads are expected (critical load cases). By spires and roughness elements a wind profile and a turbulence intensity of the modeled wind according to typical sites for solar trackers were achieved. The loads were measured by a high frequency force balance placed underneath the models. Additionally measurements of the pressure distribution on a panel with aspect ratio of 1.2 were performed to better understand the effects that lead to the peak values of the wind load coefficients. A significant impact of the aspect ratio was measured. For the critical load cases the aspect ratio dependencies of the accordant peak wind load components were determined. By these the peak wind loads on solar trackers of varies aspect ratios can be calculated. Regarding the single solar tracker components the main results are: Higher aspect ratios are advantageous for the dimensioning of the foundation, the pylon and the elevation drive but disadvantageous for the azimuth drive

Determination of wind loads on heliostats

By boundary layer wind tunnel measurements the wind loads on heliostats were investigated for conditions with no or only insufficient values available in literature: • Aspect ratio: For aspect ratios of the mirror plane (width / height) between 0.5 and 3.0 the wind load coefficients were determined. For the critical load cases (combinations of elevation angle and wind direction of highest wind loads) formulas for the calculation of the impact of the aspect ratio were gained. • Wide gap: By measurements of a heliostat with one wide central gap between the mirror facets it turned out that wide gaps are of impact especially on the hinge moment. • Wind fence: The impact of a wind fence at different heliostat field densities was investigated. For low field densities only small load reductions were measured. Future work should investigate the significance of the similarity of the energy spectrum at the critical scales

Zu Alfred Momberts Nachlass im Moskauer Sonderarchiv

Grüner F, Buselmeier M. Zu Alfred Momberts Nachlass im Moskauer Sonderarchiv. Heidelberg. Jahrbuch zur Geschichte der Stadt. 1999;4:249-254

A holistic approach for low cost heliostat fields

The AutoR-project takes a holistic approach to reduce the cost of heliostat fields: Wireless control and energy supply enables to use smaller heliostats which need less steel per mirror area (but usually have high wiring cost). A low cost but high efficient drive system is chosen which reduces energy consumption to a minimum amount and leads to low cost for PV cell and energy storage. The usual boundary layer wind tunnels tests for heliostats are proven regarding energy spectra to avoid oversizing of steel structure and drives or failures because of underestimations of the loads. The concepts for wireless control and energy supply, the wind tunnel investigations and the first rim drive heliostat prototype are presented