Not only allowed: it is obligatory (vis-a-vis distributors). It is for all types of regenerative energy if network specifications are fulfilled, but with different feed-in tariffs for different types. (For example, for geothermal, it is between 15 and 7.16 c/kWh depending on size; for wind, it is currently at least 5.39 c/kWh, upped to 8.53 for a limited time for units exceeding predictions by 50%, and 9.1 c/kWh for off-shore units.)

BTW, while I was speaking about Germany, my own country (Hungary) has a rather crappy version of feed-in tariffs (tailor-made for the large electricity companies, consequently with almost no usage). However, the German system is now copied in many European countries in some form.

_{*Lunatic*, n.
One whose delusions are out of fashion.}