system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 : How does the power grid differentiate what customer is using what suppliers power, when it's all going through the same transmission lines?
gpt
It does not.  
All of the producers submit power to the same grid, and all of the customers get power form the same grid.
Even in countries where the power production market is a free market, the distribution grid is managed by a single company as it is considered a natural monopoly.  
Every producer sells power to the grid at a certain price, then the grid sells that power to the customers. The thing is that in the case of little private customers, instead of buying from the grid they have a contract with an wholesale company that buys power from the grid and ensures the power supply for its customers.