Hot Rock Energy Storage

Here’s a piece on “hot rock” energy storage, where tanks of tiny stones, the size of peas, are heated to as much as 600 degrees C when energy from intermittent sources like solar and wind exceeds demand.

How this could possibly be more efficient or less expensive than molten salt, I have no idea.  The idea of using a solid rather than a liquid (that can be pumped) makes no sense to me, but this, apparently, is a “thing” in today’s energy world.