10-12 power cuts a year is a substantial amount of power interruptions... I can see why you are so motivated to complete such a project.
Where I live power is so cheap and reliable that I am fighting with myself because as much as I enjoy batteries as a hobby, I will literally never receive an ROI on such a project. I would be building because I like it, not because I need it. To make matters worse, I am in an HOA and can't have solar panels. I am almost to the point I feel like giving up on such a project because I truly can't take advantage of it but it's still fun.
Moving back onto the point of this thread... I think it's a smart idea, but I have concerns about the wear and tear on the battery pack. Perhaps the extra cycles don't really pay off in the long terms, perhaps its a raw deal if the packs life is degraded to the point where it barely offsets the cost of a replacement, or reduced life on the car.
i think its a bigger issue on cars like the Nissan Leaf than cars like my Mercedes which is actually a Tesla, as Tesla manage the thermals so much better than any other manufacturer out there.
there are Teslas out there with over a 50,000charge cycles and they still have 85%+ original range left. Comparatively there are Nissan and Renault packs now with less than half their original range.
no Tesla packs in existence have gone below 75% original capacity yet, which is testimony to the incredible job Tesla do managing their packs.
also power walk type application is childs play for a Tesla pack that can supply 200a at 460v peak to a pair of 450whp motors!