I was surprised when I read about it too, but it's true, they quite literally just plug them right into the normal plugs.
It works because there's a certain tolerance on the German breakers that allow for power to reverse. The balcony panels take advantage of this. However this also limits the possible output to whatever the tolerance is, otherwise it would overload and shut off or worse.
Actually, they don't.
When Denmark sold the Danish West Indies to USA in 1916-1917, part of that deal was to ratify that USA accepted the full Danish ownership of Greenland.
At the time, this was done to keep Norway from making claims to Greenland.
But anyway, we quite literally have a document written by USA and signed by USA stating that Denmark alone owns Greenland.
Edit: Took some time to find, but here it is signed by U.S Secretary of State Robert Lansing who made the deal under President Woodrow Wilson.