How is electricity from a power station added to the grid?
I have a solar installation on my roof that produces up to 4kW.

It's connected to the grid through an imaginitively-named device called a "grid tie inverter". This does two things:


it detects the phase of the existing grid supply and refuses to turn on otherwise ("anti islanding"). This allows sections of the grid to be turned off safely and is a regulatory requirement.
it supplies AC power to its terminals (converted from the ~320VDC of the panels) in phase with the grid supply. Necessarily this is at a voltage fractionally higher than the grid supply, enough to overcome the voltage drop on the wires between the substation and my house.


Because I got the system supplied through an approved installer, I'm eligible for feed-in tariffs and have a second electricity meter which pays me £0.13 for every kWh of energy generated.