I cannot recall any of the supermarkets having any sort of lot in the area at all, although as noted I don't recall a Penny Markt. As a pedestrian one doesn't always take note of the parking signage but there is a road just behind the Courtyard between the hotel and Axel Springer buildings which may have some parking. There is also a side street with a Chinese restaurant which may have some. To be frank, I don't hold out much hope for easily finding a spot and in those cases I usually find that the parking charge is actually a value considering time spent and chances of a free spot being available.