In the UK (and Europe) there are incentives for people to do it. My sister gets paid a fixed 69 p per unit produced irrespective of whether she uses it or not. That rate was fixed when she installe the panels and at that time the cost to buy 1kWh was about 11p so the government pay her 5 times more for the electricity than she can buy it for.

There were some ever inventive Greeks prosecuted for selling the electricity to the grid but also taking it form the grid, their field full of panels was never wired up. They came unstuck when someone noticed they were generating in the middle of the night.

The payment tariffs only apply to a maximum 4kWh in Europe. After that you are considered commercial so the rate drops.

The distributed generation phenomenon is causing real problems for the utilities because they can no longer assume a network to be dead once it is disconnected from the grid. I offer solutions for utilities in this field, utility technology / communications / sensors is what I do if I am doing anything.