I was wondering if it would be possible, perhaps, instead of using cranes to stack blocks of stones, to elevate an entire building by some small amount every day when there is enough excess energy. Lowering the building in the night to recover some of the stored energy. This would definitely be a very challenging engineering problem but the thought of transforming each house in a city into a battery using only its own potential energy without being dependent on chemical means of storage is intriguing to me.