So after having some looks at bitcoin mining and setting up nicehash on my pc (single gtx 970) to have a look at how it works (ofcourse I won't be able to make any profit because of power consumption), I wondered if buying an Antminer S9 and starting to mine at home with a powercost of 0,26$/KwH would be profitable or will I just lose my investment.
The Asic technology help a lot in mining but, if there is the possibility you should try with some free green energy, then the profits will be bigger.
How are you going to get "free" energy? If you're referring to solar, that's quite a pricey investment that doesn't break even for years.