No Partition to install Yosemite to
This post is for a different problem, but contains the same solution:

How do I fix my SSD after installing Yosemite and Enabling TRIM? No boot &amp; can&#39;t erase

I had to go to the terminal (it is available in the installation tool) and do as described in the link:

Use diskutil list
and check which volume/partition you want to delete (for me the clue was the size corresponding to my hard drive).

Then type diskutil eraseDisk JHFS+ name disk0.
"name " will be the name of the volume you create.

Close the terminal, go back to the installation tool and install as you would expect.