That book[1] speaks of the Andasol Solar Power Station, and makes several dubious statements about it. The one being cited is:
> The well-insulated tanks where molten salt is stored contain enough thermal energy for up to a week
A false claim. It has enough energy for 7.5 hours. (149.7MW/1123MWh)
In any case, is says nothing about duration. The wiki writer may have just mistaken capacity for duration. I couldn't find any evidence of this power station storing energy for any amount of time. It's used on the night immediately after the day that charged it.