Recently, various interventions and reports have been published presenting biogas as a renewable and circular energy source. These are messages that hide the complexity of this technology. To begin with, the projected biogas plants are refineries that produce a non-renewable fuel that needs to be processed. Furthermore, the energy balance of the entire process for biogas production, from cradle to grave, is negative: more energy is consumed than is ultimately produced.The internal operation of the biogas plants themselves can absorb nearly 30% of the energy obtained. To this, approximately an additional 16% must be added for the transport of slurry, manure, and animal waste that feed the plants, as well as the resulting digestate to the farms that will accept it. However, the largest – and often ignored – energy cost is associated with the generation of slurry and manure. These materials are not free; they require a significant energy expenditure in feed, climate control, and farm operations. The meat obtained only recovers approximately 50%-60% of the energy contained in the feed, and the energy invested in producing slurry can be equivalent to 80% of the energy that the biogas plant ultimately generates.And what do these feeds contain? Primarily, soy and cereals. Soy mostly comes from America, transported by ships that consume large quantities of diesel. Both soy and cereals are produced using agricultural machinery – again, diesel – and to make them grow, chemical fertilizers and pesticides are needed. The production of these fertilizers depends on fossil fuels and minerals from mines in the Sahara, Canada, and other distant locations, all of which are finite and non-renewable resources. The expansion of these crops also entails other problems, such as deforestation in the countries where they are produced, contributing directly to climate change.To all this, we must add the industrial inputs that these plants require. The project planned in La Sentiu de Sió (Noguera), the largest currently in Catalonia, would annually require thousands of tons of nitric acid, potassium carbonate, ferric chloride, or methanol, in addition to tens of thousands of tons of water. The associated waste is also considerable: ferrous metals, plastics, and contaminated filters, among others.