€ for a Homemade Solar Cell Installation?

[Lord of nothing]

Hi
We have a Garage (Red) next to our Neighbour (Green) and Cyan is our Roof.
[ Attachment Invalid Or Does Not Exist ]

Orange mean "good" Sunligt and Red mean "much more" Sunlight.
My idea is to put Solar Cells on the Garage in some degree angle.
I am quite optimistic because its marked Orange. One small downer the Light  could only come from South and West because East is the Wall from our Neighbour. I read here some Solar Cell cost ~150€ who sound reasonable.
What does a Inverter cost? Sorry for that stupid question is possible to use at the same time both Source Mains + Solar? School was so long ago... 
Thanks