When my excess electricity goes back into the grid, where does it go after it has passed through my meter? Does it go to the next closest house needing power?
Pretend your panels are a water pump connected from a nearby pond (your roof) to a water tower (the grid).
The grid is a large reservoir that can simultaneously take and provide electricity. This is because there are multiple sources and destinations for the electricity.
If no one else was using electricity when you were providing it, your meter would not register outgoing electricity (credit).
It's not a very meaningful question because the only thing that matters is how much each customer is charged and how much power the utility needs to generate.
However, if you are into tracking electrons, for a copper wire of length 1 meter and diameter 2 millimeters carrying a DC current of 1 Ampere, it takes 12 hours for the electrons to travel the one meter.