Just because you choose "green" electricity doesnt mean you'll see green sparks coming from you're power plug!
The reliability of your electricity supply will not be affected because you are still attached to the same energy grid. When you choose a renewable electricity plan an equal amount of green electricity is added to the grid so that you are really choosing what kind of energy that is added to the grid on your behalf.
Furthermore, the supply of green energy is not limited to a particular project - so there is always a constant and uninterrupted supply of renewable energy from a number of different sources that are added into the grid shared with conventional energy supplies.