Energy source

Engineering

Solar mirror

Solar energy

Mechanical engineering

Thermodynamics

Physics

Photovoltaic thermal hybrid solar collector

Nuclear engineering

Renewable energy

Environmental science

Thermal energy

Stirling engine

Electrical engineering

Renewable Energy

The paper addresses the assessment of the Stirling engine performance by comparing biomass and solar energy as external renewable energy sources. A program-code was developed in the MatLab® to solve the thermal model of an alpha-Stirling engine, accounting for the limitations in the heat transfer processes in the regenerator and the losses due to pumping effects. The solar energy source was modelled as a concentric solar dish collector, considering a receiver located at the focal point and designed to absorb the maximum possible of the solar radiation. Regarding the biomass system, the temperature of the flue gases leaving the bed is computed through an energy balance, considering the fuel energy introduced into the bed, the energy that is provided by the bed and the incident radiation in the bed. The simulation results show that the biomass-fuelled Stirling engine provided 87.5% more power output than the solar energy source, with an efficiency of 46.67%. Also, the average receiver temperature from the solar source is about 775 K, whereas, in the boiler bed, the temperature reaches the value of 1288 K. In the solar-dish modelling, the reflected radiation that passes into the cavity receiver depends on the aperture ratio and rim angle. It was proved that a rim angle of at least 45° is required to ensure lower focal distances. Otherwise, the Stirling receiver needs to be far from the surface of the dish, resulting in higher thermal losses and lower temperature inside the receiver cavity. In biomass-fuelled system, it was shown that the temperature of the flue gases increases with the increasing the radiation flux, and decreases for higher split percentages between the primary and secondary air. The study also revealed the need to investigate the combustion stability regarding the particle emission in the flue gas, which can reduce the temperature close to the hot cylinder of the Stirling engine. The LCoE for the solar-power system is of about 1658 €/kWh, which is 52% higher when compared with the biomass-fuelled system (0.109 €/kWh). In conclusion, biomass-fuelled Stirling engines are able to provide a higher power output with higher thermal efficiency, avoiding the problems usually related to solar energy intermittency.

Assessment of the Stirling engine performance comparing two renewable energy sources: Solar energy and biomass