In order to design a heliostat we have to understand the forces that will act on the structure. During a storm it’s more than likely cloudy so the heliostat only has to work in low wind-speeds. Wind-speeds in m/s x 3.6 gives the wind-speed in km/h, 20m/s = 72 km/h. which gives a pressure of 0.5 X 1.25 x 20² = 250 N/m².
|Wind speed (m/s)||Wind pressure (N/m2)|
|Lower limit||Upper limit||Upper limit|
|The wind pressure can be approximated by: Pressure = ½ x (density of air) x (wind speed)² x (shape factor)
Probably the most important environmental design criterion that must be met by a heliostat design is the wind condition. Typical requirements may be for the heliostat to meet its operating requirements in a 12 m/s wind, to survive a 22 m/s wind, and to continue to operate or move to the stow position in a 40 m/s wind (a position usually horizontal with mirrors face-up or face-down). Also, the ability to survive hail is important for any flat surface exposed to the elements. A typical hail survival criterion is 19 mm diameter hailstones impinging at 20 m/s. source: the power of the sun