When we announced our plans to add a biomass filter to the Clean Power Index in January, we knew we needed to get the distinction between biomass and biogas right first. These two generator types sound similar but are polar opposites in emissions terms, and the filter needed to reflect that. Today, the biomass filter is live.
Biogas is not biomass
Biomass power - principally wood-burning at industrial scale - is the UK power sector's second largest source of carbon emissions after fossil gas, exceeding even coal. Biogas from anaerobic digestion is fundamentally different: it captures methane from organic waste that would otherwise decompose and release greenhouse gases. Most emissions experts treat it as near-zero-carbon.
The biomass filter strips out biomass while correctly retaining biogas, so suppliers using genuine low-carbon anaerobic digestion aren't unfairly penalised. We described the preliminary work required to make this distinction correctly in this blog.
What the filter reveals
The filter identifies significant differences between suppliers. The score for Good Energy barely changes with biomass excluded because their supply is dominated by wind, solar, and biogas rather than wood burning.
Compare that with Drax Energy Solutions, whose score drops from 77% to 17% with the biomass filter on. That's because their supply genuinely is dominated by biomass - specifically, wood-burning at industrial scale.
The filter makes this difference visible for the first time.
Why these filters matter
The word "renewable" doesn't always mean what consumers expect. Biomass is technically classed as renewable by Ofgem, the regulator, but many energy consumers prefer to avoid it because of its significant carbon emissions. Conversely, though nuclear power isn't classed as renewable, it is zero-carbon - and many consumers are happy to receive clean, firm power from it.
The Clean Power Index now offers three filters so users can define "clean" on their own terms:
- All renewables - the standard, regulated view
- Renewables excluding biomass - for consumers who want renewables without high-emission wood-burning, while correctly retaining biogas
- Clean power including nuclear - all low-carbon sources, for consumers who care about carbon rather than the renewable label. Added in December 2025
Together, these give consumers and businesses the most complete picture available of what "clean power" actually means for each supplier.
Data submissions
So Energy and Good Energy responded to our call for data and their submissions are here. If suppliers believe their generator classifications need correcting, please get in touch.