Not next door no, but they are going to have to be in roughly the same region, because power losses over long distance transmission become significant in pretty short order.
I think you put the batteries near the load point. Transmission losses are more painful for higher cost energy (battery storage), than low cost (excess wind power).
For maintenance free batteries, coupled with an intermittent power source and an intelligent controller, the whole system coukd act as a constant power source.
I think the point is, from the perspective of electricity grid maintenance, it doesn't matter much (given sufficient transport capabilities) if you stuff all the wind turbines on one end, and all the redox batteries on the other end of the country.
No need to integrate the production and storage solutionss at all.
There's no reason you couldn't have region-local storage locations underground. There are lots of huge natural and artificial cave systems that would be perfect for temperature control of even enormous batteries. I don't think transmission losses to a regional underground storage facility will be a huge concern.
