Andreas,
I never expected you to go for the Orbitz thing. I just sort of wanted to stir the pot so to speak. Since you mentioned Quake Catcher, I'll give you an idea along those lines.

Solar@home
Using a small solar panel like the ones that come with the solar powered yard lights, create a module to be mounted outside the house. It could be simple and connect by USB or complex and connect by Bluetooth. It could then be used to collect information about the intensity and duration of sunlight received from all over the world. Would this information be useful? Maybe if you were planning solar power installations or growing crops or doing research into solar energy.

It's about a two hour drive from here on s good day. Twenty years ago I was stationed at Panzer Kaserne in Böblingen.

Since you liked the smilie here is another one