score:9
According to Timatic (the system used by most airlines, and generally the best source for such things), a passport is NOT required for Germany citizens that have a national ID card.
Passport required.
Passport Exemptions:
Nationals of Germany with a national ID card.
Nationals of Germany with a Travel Permit in Lieu of Passport (Reiseausweis als Passersatz) accompanied by an expired German passport, an expired German national ID card or a valid identification document.
Nationals of Germany with a temporary passport.
Note that the layout of Timatic can be a little confusing - it states that a passport IS required, but then states exceptions that override the previous requirement. Thus the "national ID card" exception means that the previous "passport required" rule does not apply. The visa section is the same - it states a visa is required, but then states the exceptions where one is not.
In my experience, VisaHQ is generally not a reliable source for such rules. In this case their statement that a "passport AND ID card" is required simply makes no sense - even if a passport was required, there would be no need for both that and an ID card to be shown.