Techno-economic investigation of integrated biodiesel internal combustion engines and transcritical organic Rankine cycles for small-scale combined heat and power generation

The work presents an integrated system for combined heat and power generation based on a topping biodiesel internal combustion engine (ICE) and a bottoming transcritical organic Rankine cycle (TORC). A 0D/1D mathematical model is developed to evaluate the performance of the innovative biodiesel system in design and off-design conditions for a wide range of rated power and organic fluids. The analysis highlights that the TORC integration improves the total full load electric power by more than 12%, and the engine size significantly influences the integrated system performance. The total electric efficiency increases from 35.0% to 47.9%, whereas the thermal efficiency decreases from 27.2% to 19.8% when the ICE's nominal power moves from 10 kWel to 500 kWel.Afterward, a multi-objective investigation is carried out to define the most suitable power of the proposed biodiesel system and its capability to satisfy the energy request of specific users. A thermal self-consumption equal to 100%, an electric self-consumption larger than 94%, and a payback time of 5.2 years are found. Lastly, a sensitivity analysis demonstrates the economic feasibility of the proposed biodiesel integrated system for a wide range of prices of energy vectors and system components.