This article was originally posted on RealClearScience.
Desert dwellers are familiar with “dust devils,” tornado-like phenomena that range in size from cute to terrifying. When the sun beats down on dry earth, the ground becomes hot. The surface air warms and rises, leaving behind an area of low pressure that draws in more air. Eventually, a circulating vortex of upwelling hot air forms, and the dust devil is born. Because they are fleeting and haphazard, they cannot be harnessed for energy. Instead, scientists have proposed creating their own dust devils.
In the journal Scientific Reports, researchers propose the construction of a circular shed with solar thermal collectors on its roof. These would absorb sunlight and transfer the heat to air being sucked into the shed. The inrushing air would be trained in a circular direction using “pre-rotation vanes”, i.e., raised spiral lips on the floor of the shed. Just like a dust devil, the circulating wind would create a swirling jet of air that would shoot out the top of the shed. This jet could then be harvested by a wind turbine and converted into electricity. (See images.)
The authors constructed a small model to determine how the shed should be built. Then, using theoretical calculations, they showed that sheds ranging in size from 80 to 440 meters in diameter would be adequate to generate a jet of air with a velocity of 3 m/s (6.71 mph) or greater, which is the minimum velocity necessary to harvest whirlwind energy.
The authors did not discuss the theoretical efficiency of their system. They propose to use the shed as an extension of a conventional solar array, making use of the heat generated from the sun’s rays that are not converted to electricity. However, they would need to find a way to quickly transfer the heat into the inrushing air, as heat decreases the efficiency of solar cells. Therefore, it may turn out that traditional solar or solar thermal power would be more efficient. But, this is certainly an intriguing idea.
Source: Mingxu Zhang, Xilian Luo, Tianyu Li, Liyuan Zhang, Xiangzhao Meng, Kiwamu Kase, Satoshi Wada, Chuck Wah Yu & Zhaolin Gu. “From Dust Devil to Sustainable Swirling Wind Energy.” Scientific Reports 5, Article number: 8322. Published: 09-Feb-2015. doi: 10.1038/srep08322
(Photo: Coal devil in Mongolia by Texasbob/Wikimedia Commons)