This kind of computation is very difficult, let's take the aluminum frame of the panels or the steel structure to fix them, they need a lot of energy to extract and to produce them, but then , you can recycle aluminum and steel for ever (almost)
Also you have to compare with other uses. Of course the most stupid construction to day is a tank, but men still build and destroy tanks. For the price of the war in Irak, we could have installed 100 % solar for the whole humanity.