I don't think that the sand units you can install in your home have the ability to store energy across seasons. They are more like hot water heaters; heat when you have solar, but you can use some hot water at night when electricity is more expensive.
So this would be like, in a mild climate, the sun is going to keep your house warm during the day and you are generating some solar. You use the solar to heat up the sand, and then overnight, you recover some of that energy to use for heat. (I think you can get electricity back out of the heated sand as well, but it's like 70% efficient compared to >90% for a lithium battery. So I think the big application is in heating, less for charging your car after you get home from work.)
So this would be like, in a mild climate, the sun is going to keep your house warm during the day and you are generating some solar. You use the solar to heat up the sand, and then overnight, you recover some of that energy to use for heat. (I think you can get electricity back out of the heated sand as well, but it's like 70% efficient compared to >90% for a lithium battery. So I think the big application is in heating, less for charging your car after you get home from work.)