system
Given the following post, respond as if you're commenting on Reddit:
human
What happens to electricity pushed onto a grid beyond that grid's capacity to use it?

With the ascendancy of renewable or otherwise privately generated electricity, many electric companies allow electricity produced in excess of private use to be 'pushed' back onto the wider grid, even paying for that generated electricity in many cases.  It makes sense to me that, most connected users being net-electricity-consumers, whatever electricity I push onto the grid is just used by someone else connected to the grid.  

My question is, what happens once private generation exceeds grid usage?  Where does 'unused' electricity go?  What method or mechanism is used to shed excess energy in an electrical grid?
gpt
The grid is composed by several sections that can be opened, closed and rerouted to match supply and demand without putting too much current in the grid. If you put too much current elements of the grid would fail (transformers, breakers, even cables that could melt). 

Depends on where the electricity is coming from you can disconnect that section not to overload the rest of the grid. The same can be done with demand (if an area is pulling too much current it could bring the rest of the grid down). 

Grid management will make sure that excess current is disconnected from sections that can't support it. With power companies those loads are negotiated every morning and planned carefully during the day.

With home generation that production can also be predicted but contrary to the power plants, that current can't be disconnected easily, at least not without causing at least some local issues. 

So there are two methods, either you get power plants to reduce production (which is not that a fast thing to do and after the bidding is done in the morning prices are already set) or you disconnect other big renewable generators (wind, and solar farms). Those can be disconnected from the grid and the energy is just lost to heat.