Dear Dominik,
NREL made a brief foray into the certification business back in the 1990s. Included in that effort were reports for design guidelines. I didn’t think the DGs were ever completed or published, but I see now that DG03 was. I do know that DG01 was never completed because I was one of the authors. We actually use the IEC 61400-x and the Germanischer Lloyd standards here at NREL and I would recommend you use them. Unfortunately, they are not free.
Marshall