This work focuses attention on the evaluation of global energy balances of an agro-energy system based on a diesel engine fuelled with rapeseed oil integrated with a steam plant fuelled with the residues of rape cultivation. The agro-energy system has been separated into the stages of in-the-field cultivation, transport of products to the industrial plant, and conversion into electric power. For each stage, inputs (fuels, electric power, fertilizers, and so on) and energy outputs (oil, electricity, residues, and by-products) are evaluated. Integration between the engine and the steam plant is implemented through thermal recovery of the engine exhaust gases and cooling fluids (supercharging air, lubricating oil, engine jacket cooling water) to preheat the boiler feed water. The results of the study show that the recovery of thermal energy made available by the diesel engine leads to an increase in steam plant conversion efficiency of more than three per cent (from 25.1 per cent to 28.4 per cent). In other words, energy recovery leads to an equivalent efficiency of the engine over 56 per cent, which is more than nine points above the efficiency of the diesel engine alone. In addition to the sole use of vegetable oil for energy production, the use of straw makes it possible to double net energy production per unit of cultivated area. Implementation of this agro-energy chain provides a net energy production of 55–60 GJ/ha, an energy output—input ratio around 3.0–3.3, and a primary energy saving of about 65–70 per cent compared to the use of fossil fuels.
Energy System Design to Maximize Net Energy Production Considering Uncertainty in Scale-up: A Case Study in Artificial Photosynthesis
