Technical Guideline Part 6 (TR 6) describes procedures for determining wind potential and energy yields at wind turbine (WT) sites. In Germany in particular, this Technical Guideline is the definitive standard for the preparation of yield assessments. It is considered necessary by many investors, banks and project developers that yield reports must be prepared on the basis of TR 6. Accreditations for determining wind potential and energy yields are based on TR 6. Furthermore, the EEG 2017 refers to TR 6 when proving the site quality before commissioning. Appendix C of TR 6 describes this verification. Here, the site yield before commissioning is determined from the gross electricity yield minus the loss factors defined in the EEG 2017 Annex 2.