Techno-economic and environmental assessment of photobioreactors coupled with solar power for Chlorella vulgaris cultivation

Biological carbon dioxide (CO₂) sequestration via microalgae has garnered significant attention as a promising strategy for mitigating climate change. However, its commercial deployment is hindered by high capital investment and substantial energy requirements. This study assesses the techno-economic and environmental feasibility of CO₂ sequestration through the cultivation of Chlorella vulgaris in a proposed solar photovoltaic (PV)-integrated tubular photobioreactor (TPBR) system. To achieve an annual bio-fixation of 20,000 kg CO₂, a 15.56 m3 TPBR with an energy demand of 19,208 kWh/year was modelled, yielding a projected annual algal biomass production of 10,782 kg. The electricity sourcing was compared between natural gas-based grid supply and on-site solar PV, with the SAM NREL used to simulate an annual PV generation of 26,146 kWh. PV integration eliminated CO₂ emissions and, when combined with the nutrient recycling and the use of CO₂ from local bio-treatment facilities, reduced operating expenditure by 2.90% and increased net cash returns by 4.96%. Four operational cases (grid-only, PV with net metering, PV with battery storage, and PV-battery with circular bioeconomy integration) were evaluated. The most sustainable configuration was identified as the off-grid PV-battery system with circular bioeconomy integration, which achieved a breakeven price of $48.46 per kg of biomass. The system demonstrated a potential CO₂ sequestration efficiency of 91%. Sensitivity analysis identified selling price, specific growth rate, and culture volume as key factors influencing economic profitability. The results indicate that combining renewable energy with circular bioeconomy principles can significantly improve the sustainability and economic viability of microalgal-based CO₂ sequestration systems.