Modal testing of VAST Solar’s Heliostats

CMP Engineers were delighted to be involved recently in VAST Solar’s concentrated solar power project for Mt Isa which is designed to deliver 50 MW of baseload power. The system uses an extensive array of mirrors (known as heliostats) to focus sunlight on to receivers which generate and store power via an innovative molten salt storage technology.

The heliostats, which pivot to track the movement of the sun throughout the day, need to accurately maintain their shape in order to ensure optimal focusing of the sunlight. One of the challenges is to achieve a balance between weight, stiffness and cost of the structure supporting the heliostats. Excessively flexible support structures may result in the heliostats experiencing destructive resonance due to vortex shedding when wind blows across the structures.

To test for this, CMP Engineers placed a number of accelerometers across the heliostat support structure. We then measured the accelerations that occurred when the structure was excited (either by (carefully!) striking the framework supporting the mirror, or by statically deflecting one corner of the structure and then releasing it). This was repeated at numerous locations and in several directions around the heliostat in order to fully cover the range of potential mode shapes.

Processing the resulting data provided us with information on the natural frequencies of the structure, and associated mode shapes. This will be used by VAST Solar to refine their designs for the Mt Isa project.

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