One rule is missing: multi-fuel generation units in European electricity transparency reporting

Commission Regulation (EU) No 543/2013 requires transmission system operators to publish generation per unit on the ENTSO-E Transparency Platform, and each unit is reported with one production type. This preprint examines how units that burn two fuels at once are recorded, and proposes one addition to ENTSO-E's Manual of Procedures that requires no schema change. Across 2 191 documents covering 199 generation units in three bidding zones (Finland, Poland, the Netherlands) where biomass co-firing is documented in a dated primary source for 2021–2024, no unit carries two production types in the same document. Three operators handle multi-fuel plants in three different single-valued ways. Moving the biomass electricity that Statistics Netherlands documents out of the Dutch coal column changes the zone's 2023 annual carbon intensity by −34.53 gCO2eq/kWh (−6.26 %), on the codecarbon 3.2.8 factor set with biomass counted as zero. An annual fuel share corrects the annual mean and leaves an hourly timing error, which the paper quantifies per zone. The two datasets and the measurement method are described in arXiv:2609.16152. The upload contains the PDF and its LaTeX source (pdflatex). v1.1 archives the script and output behind the percentage factors in the provenance appendix; no figures changed.