Economic Feasibility of Small - Scale Organic Rankine Cycle Driven by Solar Energy and Biomass

The current thesis provides energy and economic analyses for Organic Rankine Cycle (ORC) power plants driven by solar and bioenergy. The system comprises of an ORC power unit, an auxiliary gas heater with evacuated tube collectors or biomass-fired boiler. Electric power capacity range tested is between 35 kW and 110 kW. An optimisation process was conducted using SAM software to determine the optimal size of the solar ORC components. The result showed that the optimal size of the evacuated tube collector area, tilt angle, storage tank volume and the energy needed from the auxiliary unit for 35 kW system are 100 m2, 45°, 4 m3 and 1636 kWh/year respectively. The simulation result of the solar part shows that the temperature of the hot water never falls below 100 °C which is above the temperature determined by the ORC manufacturer to get the maximum power. Also, the solar fraction of the solar water heating is calculated to be 0.98. The proposed system of biomass-fired ORC power plant assumes that the hot water goes directly to the ORC evaporator. The biomass boiler size determined based on manufacturers information to match the operating temperature. The economic calculation results showed that solar ORC power plant is economically feasible while Biomass is not feasible under same operating conditions. Saving to Investment Ratio (SIR), Internal Rate of Return (IRR), Simple Payback Period (SPP) and Levelized Cost of Energy (LCOE) for 35 kW ORC power plants are 1.3, 9%, 5.9 years and 0.12 $/kWh respectively for solar ORC, and those values increase as the power capacity increase. For 35 kW biomass-fired ORC power plant the values are 0.9, 0%, 6.4 years and 0.19 $/kWh respectively and becomes slightly high for higher capacities. Furthermore, the sensitivity analysis results showed that Solar Organic Rankine Cycle (SORC) Power plant is not feasible when the operation hours become less than 5000 hours and the system becomes more feasible as the power plant capacity increase while the biomass-fired ORC becomes feasible when the capacity is more than 40 kW.