Building Code §35 - Building in the Outer Area

Can someone help me, I don't understand (1) 8:

"(1) In the outer area, a project is only permissible if public interests do not oppose it, sufficient development is ensured, and if
(...)
8. it serves the use of solar radiation energy on, at, and in roof and exterior wall surfaces of buildings used permissibly, provided that the system is structurally subordinate to the building."

Does that mean I could build a little house and put a photovoltaic system on it and use it? Is that allowed?

In outdoor areas, only so-called privileged projects may be realized. These include, for example, agricultural, energy generation, industrial, nuclear, and military uses that have no place in cities or villages.

So a 20 MW solar field would be OK, and then you could also possibly justify a company apartment for the service employee next to it. Because of your 10 KW photovoltaic system, however, the official in the building authority will only chuckle tiredly at you...

What specific use are you aiming for?

I want to build a small holiday home – really just a small wooden cabin – and over the years add a few things: a toilet shed ([Trockentoilette]), sauna, shower, etc. (All in a self-contained system without connection to public utilities)

Does that mean that I could build a little house

No, because your little house would not be used in an authorized manner.

He could possibly build a garden house without a permit. This varies in each federal state. Where do you want to build?

That is different in every federal state.

I wouldn't know in which federal state it is exempt from approval, but even if it is, that doesn't mean it is allowed.