Here on Belgium at least 10% of the houses do have solar panels. Most of the were installed 10 to 12 years ago when the government handed out some rewards for installing them. But because it is a free economy the prices of the channels where very expensive, because people got a lot funded by the government.
Now these rewards are dropped for new installations, but the prices of the installations also have dropped immensely !

For the grid controllers, solar panels are a real nightmare. It will make their work a lot harder. When there are only nuclear power station of others, it is much easier to predict how much energy will be produced and how much they need to buy in. With the private solar paneling it is much harder from them to predict at what capacity they should run the power plants. And don't forget that too much energy on the grid is as bad as too low energy!

In Belgium, when you do have solar panel you do have to pay an extra grid fee to donate the not consumed power to the grid. As a reward the personal counter will runs backwards. But it won't go negative.

In some cases it isn't a good investment but at least these people are doing something for the environment!

Cheers,
Peter