Thanks for all your replies.
When I started this topic, I didn't know at all, that mining altcoins with graphic card, to get BTC, was profitable.

At home, in my personal computer I already have a GTX 1060.
I tested out and I get 0.008 to 0.009 BTC (~1.43€) per day with a total consumption of 153watts (0.58€ per day) at the wall.
Even at home, where I pay my electricity bill, it is still profitable to use my GTX 1060.

At the location where I have 400watts of free power, I decided I will use a RX480.
I bought one at 200€.
With the rest of the computer it should consume 240 watts at the wall and is similar to an GTX 1060. So I'm thinking I could "mine" 0.008 to 0.009 BTC per day also.
If I went for my initial plan, and bought an Antminer S7 (~350€) and underclocked it, I could of mined 0.00072117 BTC per day (1.6Th/s @ 400 watts).

I ended up paying less, using less power and mining more.
Thanks !