Power Generation From Concentrated Solar-Heated Air Using Buoyancy-Induced Vortices

Abstract

Thermally-stratified air layers overlying solar-heated ground are exploited for power generation by the deliberate formation of intense buoyancy-induced vertical columnar vortices, similar to naturally-occurring desert “dust devils.” In hot-climate regions, such buoyancy-driven columnar vortices occur spontaneously with core diameters of 1–50 m at the surface and heights up to one km, leading to flows with considerable angular and axial momentum. Unlike “dust devil” vortices, which are typically free to wander laterally and are therefore susceptible to crosswind, anchored columnar vortices are deliberately triggered and confined within a domain laterally bounded by an azimuthal array of stationary ground-mounted vertical vanes, and are sustained by continuous entrainment of heated air passing between these vanes. Hot air near the solar-heated ground plane sustains the anchored vortex, and electric power is generated by using the resulting rotational and vertical flow induced by an “anchored” vortex to drive a vertical-axis wind turbine coupled to an electric generator. This novel approach to the collection of solar energy provides a low-cost, scalable, and sustainable method for generation of electric power from vast amounts of solar-heated air in arid regions. Meter-scale laboratory experiments have demonstrated the nucleation and sustainment of strong, buoyancy-driven vortices above a thermally controlled ground plane. The present investigation focuses on fundamental mechanisms of columnar vortex formation, evolution, and dynamics using stereo particle image velocimetry (PIV), with particular emphasis on scaling and assessment of the available mechanical power. The strength and scaling of theses vortices can be significantly altered by adjustment of the vanes and the rate of sensible heat uptake by the air flow, related to the “buoyancy flux”. Recent outdoor tests of a meter-scale prototype coupled with a simple vertical-axis turbine placed on a surface directly heated by solar radiation, have demonstrated continuous rotation of the turbine with significant extraction of kinetic energy from the column vortex, in both the absence and presence of crosswind.