Comment by petronio
Interestingly, just yesterday I found out 4 already exists, but it's inverse of what you're thinking: top up excess battery capacity overnight, when grid prices are low, and then resell during the day when purchase prices are high.
I think the economic problem is that while there /may/ be overproduction during the day, the day is the only time other than early-mid evening when there is significant demand.
You would effectively be targeting the early-mid evening demand, assuming there was overproduction during the day, and with the current cost of batteries, their installation, and their replacement, I can't see the numbers working out.
I would love for battery prices to come down enough to make something like this possible though.
Yes, item 4 does exist. Tesla and Sunrun both have virtual power plants. Tesla operates as a peaker plant, while Sunrun is a base-load plant.
What I want is different in terms of its organization. The intention is to establish a local community microgrid that anyone with the necessary equipment can participate in. I think the biggest problem will be the accounting, but that's my blind spot