Not just racks..Those are king sized battery back ups.
Maybe overkill to store electricity to run household appliances but the people my acquaintance bought his house from did just that and he got them with the house.
of course there are more pedestrian ways to save solar energy at reduced cost.
Absolutely, battery storage is the essential factor - and it is a perilous path to enter for length of service and reliability. UPS systems are available, but using them for household needs ... well, I wonder. I have no experience with such installations.