Model-based optimisation of solar-assisted ORC-based power unit for domestic micro-cogeneration

Integrating flat solar thermal collectors and organic Rankine cycle (ORC)-based power units in microcogeneration systems ensures a reduction in CO2 emissions in domestic applications. The key component of these systems is the expander, which must withstand frequent off-design operating conditions owing to the intermittent nature of the solar source. Despite being in the first stage of technological development, scroll expanders are widely adopted in small-scale applications owing to their operating flexibility and robustness. In this study, a domestic micro-cogeneration unit equipped with a scroll expander is characterised experimentally. The experimental data are used to calibrate the expander and ORC unit models. The models are used to evaluate the operating limits of the units as functions of the main operating parameters. The maximum power and efficiency are obtained as 300 W and 3 %, respectively, for hot water temperatures between 90 degrees C and 100 degrees C, close to the rated performances. Finally, the effect of adopting a dual-intake port on the expander and unit performance is assessed. The technology facilitates the widening of the operating range (20-140 g/s mass flow rate of WF) and a peak power production of 1.2 kW.