How is Switching between standard electricity and solar/other electricity achieved?
On sites with permanent power grid connection, the usual way to go is to not balance at all, regardless of consumption or production, but rather transfer all produced power into the grid, and draw all consumed directly from the grid. 

You just measure production, consumption and the difference, and display that. 

Because produced power is either DC or out of sync with the grid, you have to convert it to grid phase anyway. Then why switch, balance, and all that? Just put it on the grid, provided you have a contract for that. As far as I am aware, this is the usual situation for houses with production and all production sites, like small watermills or so. 

On sites without permanent power grid connection, or without contract to supply power, things are of course more difficult. Sometimes, say in yachts or campers, you find two separate installations for DC and AC. Using DC to balance makes things manageable, especially if you also have batteries to buffer the energy. In this situation, most devices will be DC driven, with a few DC/AC convertes to drive systems which require AC. 

If you want to balance with AC grid online, things become more difficult. For one part, the security aspects: You dont want to supply 230V to a line that is supposed to be switched off for repairs, for instance. The supply has to be aware of line being switched off and stop supplying power, etc. Personally, I would avoid this situation, because of danger and effort.