The Solar Vortex
The Fluid Mechanics Research Laboratory at Georgia Tech and its partners are developing technology to generate scalable, low-cost electric power from "anchored" columnar vortices that can be controllably formed in areas with high surface heating rates. Such vortices entrain the ground-heated air layer in regions with high surface solar heating rates, and convert the (gravitational) potential energy into “solar-induced wind” with significant kinetic energy. "Dust devils” that occur in nature are driven by the same physics, but their lack of an anchor causes them to "wander" and ultimately dissipate. Each vortex is sustained by continuous entrainment of ground-heated air through an azimuthal array of stationary ground-mounted vertical vanes. Electric power is generated by using the air motions within the columnar vortex to drive a vertical-axis turbine. Meter-scale laboratory experiments at Georgia Tech have demonstrated formation and sustainment of a buoyancy-driven vortex that was investigated in some detail. The investigation has focused 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 assessment of the available mechanical energy for the prediction of energy extraction from large-scale vortices. Scaled‑prototypes (1.5 and 5 m) tested in summer 2014 demonstrated successful initiation and sustainment of a buoyancy-induced vortex using only solar radiation.
Power Generation Concept
The Georgia Tech-led team uses a set of vanes to force the buoyant, ground-heated air layer (warmer than the air above) to rotate as it rises, forming a columnar vortex that can be anchored and which draws in additional hot air to sustain itself to provide a new thermomechanical link between solar energy and electrical energy. Georgia Tech’s technology uses a vertical-axis rotor and a generator to produce power from this rising, rotating flow, similar to a conventional wind turbine. This solar-heated air is broadly available, especially in the southern U.S. “sunbelt” yet has not been utilized. The turbine can be specifically designed (and vertically placed) to maximize power extraction from the tangential and axial momenta of the vortex-induced flow. Simple calculations show that for a vortex 5 meters in diameter with nominal tangential and axial wind speeds of 8 m/s and 11 m/s coupled to a 10 m diameter vertical-axis turbine, 50 kWe could be extracted, in principle. An estimate for the cost of energy of the technology, $0.09 per kWh, is competitive with current renewable energy technologies.
Supported by ARPA-E and GT