150–200 (150–200 m³/tonne)

150–200 normal cubic metres of biogas per tonne of fresh crop residue is the canonical planning range for biogas yield from typical Indian agricultural residues. The range covers the practically achievable specific yield from feedstocks like paddy straw, wheat straw, cotton stalks, and sugarcane tops under well-managed mesophilic anaerobic digestion, expressed on a fresh-weight basis. It is a working benchmark used in pre-feasibility studies, SATAT plant sizing, and rapid sanity checks of project capex against expected gas output, rather than a guaranteed yield.

The range arises from variation in feedstock composition and process performance. On a volatile solids (VS) basis, methane yields for these residues sit at 180–300 Nm3 CH4 per tonne VS, but the fresh-weight conversion is moderated by three factors: total solids content (typically 85–92% for air-dried residues), VS fraction (75–85% of TS, the rest is ash), and actual conversion efficiency in the digester (60–80% of theoretical maximum). Multiplying these out — for example, paddy straw at 88% TS x 78% VS/TS x 70% conversion x 280 Nm3 CH4/t VS — gives approximately 135 Nm3 biogas per tonne fresh, sitting at the lower end of the 150–200 band. Better residues like sugarcane tops, fresh maize stover, or chopped Napier grass reach the upper end and beyond.

Indian CBG operators planning around this range must also account for the methane fraction of biogas. Raw biogas at 60% CH4 means that 150–200 Nm3 biogas equates to 90–120 Nm3 of methane per tonne fresh feedstock. After upgrading losses of 2–4% methane slip and compression duty, dispensable bio-CNG is approximately 65–85 kg per tonne fresh residue. At SATAT notified prices of Rs 54 per kg, this is roughly Rs 3,500–4,500 of CBG revenue per tonne of feedstock — against feedstock procurement and pre-processing costs of Rs 1,800–2,800 per tonne for residues in north India. The narrow margin explains why Indian CBG economics is so sensitive to feedstock cost, pre-treatment energy, and digester conversion efficiency — and why operators continuously experiment with co-digestion, enzymatic pre-treatment, and process control to push specific yields toward the upper end of the planning range.