Numerical simulation of a hybrid concentrated solar power/biomass mini power plant

Renewable electricity generation systems are increasingly used as a means of reducing harmful emissions and also reducing operational costs, by comparison with the use of fossil fuels. However, renewable energy sources such as solar energy are characterised by a high degree of intermittence, sometimes unpredictable. This constraint leads to inability to meet the demand of a power system. Hybridisation with more stable renewable sources, such as biomass, represents a resourceful way of meeting energy demands uninterruptedly. Besides stability, hybridisation with biomass allows a fully renewable solution, at the same time promoting security of energy supply. In this paper, a hybrid renewable electricity generation system is presented and modelled. The system relies on a combination of concentrating solar energy (CSP) and biomass sources to drive an ORC cycle. The solar field is constituted by 12 parabolic trough collectors with a net aperture area of 984 m². As backup energy, a biogas boiler is used, running on organic food waste. The nominal ORC electrical output is 60 kW. The system was designed and a prototype will be installed in Tunis, in the framework of the REELCOOP project, co-funded by the EU. A computer model was developed with a combination of EBSILON and EES. EBSILON is used for the solar field (SF) and boiler simulations, and EES for the ORC. Annual simulations were carried out for solar-only and hybrid modes. Distinct operation ranges and boiler sizes were analysed. The system annual yield is significantly improved with hybridisation, with enhancement of SF and ORC efficiencies. Electrical generation stabilisation was achieved during the whole year with the fulfilment of ORC minimum requirements. On the other hand, hybridisation promoted energy excess mostly in the summer months, demonstrating that hybridisation significantly reduces, but not eradicates, the need of storage.