Techno-economic assessment of a biomass-based combined power and cooling plant for rural application

This paper presents techno-economic assessment of a biomass-based combined power and cooling plant suitable for off-grid rural areas. The proposed plant employs an indirectly heated air turbine cycle drawing heat from combustion of biomass-derived producer gas. The installation capacity of 50 kW is determined based on the present electricity demand and taking into account the possible demand growth over next 10 years. The gas turbine operating condition is optimized at pressure ratio 10 and turbine inlet temperature 1100 °C, where it shows maximum efficiency. Waste heat of the power generation unit is utilized by a 120 metric ton (MT) cold storage facility that runs on NH₃–water vapour absorption refrigeration cycle. Both electrical and thermal storage units are included in the plant to cater to the hourly variations in power and heat demands. Lithium-ion battery is chosen for electrical storage, and Hitec salt-based phase change material is chosen for thermal storage, their storage capacities being estimated at 250 kWh and 220 kWh, respectively. The paper proposes a new method of determining effective cost of electricity, taking into account the avoided electricity for conventional cooling. The effective price of electricity is found to be 0.08 USD/kWh. Estimated payback period of the plant, without subsidy, is 14.4 years, and with 50% capital subsidy this is reduced to 6.6 years. Cost of storage as well as the discount rate is seen to influence the plant economy and payback period considerably. Based on the analysis, a policy recommendation has also been outlined in the paper.