Thermal storage works nicely with solar thermal plants. Not so good for direct electricity storage though.
But if the other choice is "throttle down the wind farm, because the grid doesn't need that much power" - then a really cheap/simple/safe (but inefficient) storage tech could prove pretty useful.
For limited & short-term use, the plant with vastly-more-expensive storage masses might make sense.
But as soon as you were faced with NIMBYs or environmentalists (hexane's MSDS is far closer to hydrogen fluoride's MSDS than it is to sand's), or if you are working in a less-prosperous part of the world...sand is great stuff.
- High temperatures - Intermittent solar input not a problem - tall central structure (?? maybe a plus given the paper's tall storage vessels)
But high temperature air receivers have their own problems, mostly around receiver material properties (thermal cycling / stress) and heat loss. It's really hard to focus a lot of light from the sun into a tiny aperture, because the sun isn't really a point source, and no mirror is perfectly shaped.