Electric Power Generation Using Buoyancy-Induced Vortices

Thermally-stratified air layers over solar-heated ground are exploited for power generation by the deliberate formation and anchoring of intense buoyancy-induced vertical columnar vortices, similar to naturally-occurring desert “dust devils.” In hot-climate regions, these buoyancy-driven columnar vortices occur spontaneously with core diameters of 1-50 m at the surface and heights up to one km, and convert the low-grade heat in the air layer over the warm surface into “concentrated wind” with significant angular and axial momenta. Unlike the “dust devil” vortex which is typically free to wander laterally and is therefore susceptible to cross wind, the anchored columnar vortex is deliberately triggered within a cylindrical domain bounded by an azimuthal array of stationary, ground-mounted vertical vanes and is sustained by continuous entrainment of the ground-heated heated air through these vanes. Electrical power is generated by using the rotational and vertical air motions induced by the stationary vortex to drive a vertical-axis wind turbine coupled to an electric generator thus providing a low-cost, scalable, and sustainable approach 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 controlled thermal ground plane. The present investigation focuses on the fundamental mechanisms of the formation, evolution, and dynamics of the columnar vortex using stereo particle image velocimetry (PIV) with particular emphasis on scaling and strength of theses vortices which can be significantly altered by adjustment of the flow vanes and the sensible heat absorbed by the air flow or its“buoyancy flux”. Recent outdoor tests of a meter-scale prototype coupled with a simple vertical axis turbine and placed on a surface that is directly heated by solar radiation have demonstrated continuous rotation of the turbine with significant extraction of kinetic energy from the columnar vortex in the absence and presence of cross wind.