Prospects of biomethane production from sunflower residues as the regional substrate (case of Ukraine)

Ukraine's energy sector is currently prioritising diversification through increased local renewable energy production. This study establishes a high-resolution assessment of the biomethane potential of sunflower residues in Ukraine by differentiating the yield dynamics and degradation kinetics of specific morphological fractions (leaves vs. stalks). Unlike the majority of existing literature focused on green silage, this research investigates fully matured, dry post-harvest residues, identifying a consistent empirical leaf-to-stalk mass ratio of 32–35% as a critical coefficient for high-precision regional energy modelling. Batch anaerobic digestion tests were performed according to VDI 4630 and DIN 38414/S8 standards in 2 L reactors at a mesophilic temperature of 37°C using two dominant hybrids, P64LE25 and NK Neoma. Methane production kinetics were quantitatively analysed and validated using the modified Gompertz model. The results demonstrated a 100% difference in yields between fractions. Leaves yielded up to 200 mL CH 4 ·g −1 VS, while stalks, characterised by a recalcitrant lignocellulosic structure, exhibited longer fermentation times of up to 32 days. The Gompertz model showed high accuracy with a relative deviation of δ < 5%. The regional biomethane potential was evaluated considering estimated theoretical biomass potential, leaf-to-stalk mass ratio and experimental productivity data. The case-study identifies five Ukrainian regions with abundant potential for biomethane production from sunflower residues. Annually, these residues offer a theoretical biomethane potential of 2.467 billion m 3 , which represents approximately 13% of Ukraine's total natural gas production. Sunflower waste is a vital, sustainable substrate for strengthening national energy security and supporting sustainable decentralised infrastructure, particularly for sustainable post-war reconstruction.