I love this concept for the same reason I like gravity batteries: the physics are dead simple, require nothing exotic (what could be more common than sand?), and can operate virtually anywhere on Earth: sand batteries that can hold energy (heat) for weeks or months at a time: https://www.msn.com/en-us/money/markets/could-sand-be-the-next-lithium/ar-AA1fIlmY
@darkuncle
So - if you want to store heat, absolutely - there's a good reason this is popular in places that want it for heating. Steam is another variant of this form of power. If you want to convert solar energy to heat, store it, then convert it back to electricity - you end up with conversion losses, often significant. Between that and density issues - hot sand isn't a super general-purpose solution. Having said that, molten sodium is fairly efficient and shows some promise. It's all about trade-offs. The reality is that batteries today are *really good* at storing and releasing electricity, and that tends to be more useful/useable than energy in other forms.
@Biggles good at storing and releasing on short timescales, less so at seasonal timescales