Biochar production from pruning biomass as a carbon removal strategy in isolated island systems: integrated techno-economic assessment for the Canary Islands

Decarbonizing isolated island energy systems remains particularly challenging due to structural dependence on imported fossil fuels, fragmented infrastructure, and limited availability of dispatchable renewable resources. In parallel, these territories generate substantial quantities of residual lignocellulosic biomass that often remain underutilized despite their potential for carbon-negative valorization. This study evaluates the technical, environmental and techno-economic potential of biochar production from pruning biomass in isolated island systems, using the Canary Islands as a representative case study. Based on a previously quantified regional biomass resource exceeding 650,000 t/year of dry biomass, dominated by Pinus canariensis residues, an integrated assessment framework was developed combining conceptual slow pyrolysis modelling, carbon balance analysis, techno-economic evaluation and sensitivity assessment. Under the base-case scenario, 1 t of dry biomass produced approximately 350 kg of biochar, 300 kg of bio-oil and 350 kg of syngas. Net carbon removal reached approximately 0.66 t CO2eq/t biomass, equivalent to 9885 t CO2eq/year for a modular 15,000 t/year facility and up to 428,350 t CO2eq/year under a theoretical regional deployment scenario. The estimated gross production cost reached approximately €374/t biochar, with CAPEX, carbon credit price and biochar market value identified as the most influential economic variables. The results suggest that biochar deployment could represent a complementary negative-emission pathway for geographically constrained energy systems by integrating biomass valorization, carbon dioxide removal and territorial decarbonization strategies. Beyond the specific case analysed, the proposed framework offers a replicable methodology for evaluating biomass-based carbon removal systems in structurally constrained territories.