After a while I was a bit unhappy with the reliability of the FS20 <-> io-homecontrol® system I had created. I was looking for alternatives and found it in the HM-LC-SW4-PCB, which is a HomeMatic 4 channel switch. If you buy it as a kit it is available for 29,95 € per unit. The soldering was no problem at all with the included instructions. The principle is quite the same as with the F20 switches, I always connected two Velux remotes to one HomeMatic switch.
As HomeMatic is using a bi-directional protocol the reliability of the whole system increased significantly.
Now the shutters are being closed automatically at sun-set and are opened up at sun-rise. If the sun rises before 07:00 CE(S)T the shutters will stay closed until 07:00, this helps getting enough sleep during the summer period.
IMPORTANT NOTE: do not open the shutters in the bedroom on weekends automatically, trust me!