“Lack of demand” and “already distributed” is relative to the proximity between you shoving power into the local grid and the closest user who can take advantage of it simultaneously.
You can pick any point on the grid from the power station to the fusebox. There are losses due to transmission and there are losses due to transforming. The closer the two points are, the lower the losses, but they exist.
Unless we’re talking a high density area, even just going to the next house is going to require transforming up to line voltage and back down. That’s the best case, and it assumes that the neighbor actually needs the power at the time. The farther away that power has to go before someone uses it when it’s being produced determines how much would otherwise be used and how much of the total distance is already transmitted.
I can’t even get power 1000’ across my property without a transformer. It’s 1/2 a mile to my closest neighbor and another mile to the neighbor after that.
If thousands of people in area start shoving power back in, then none of them need it when it’s being produced by definition, and it has to go even further to where it can be used. More people on solar actually makes the problem worse.
“Unless we’re talking a high density area... It’s 1/2 a mile to my closest neighbor and another mile to the neighbor after that.”
That is quite rural. Most of America’s population doesn’t not fall into a category even close to that. The 220V fed back through the meter would be used instantly be the next house. I wonder who paid for the power lines to come to all those houses a half a mile apart? It sounds like it would be thousands of dollars per house.
” it assumes that the neighbor actually needs the power at the time”
How many houses do you know of that have a meter that stops turning, EVER?