Towards a novel holistic design of organic Rankine cycle (ORC) systems operating under heat source fluctuations and intermittency

Organic Rankine cycle (ORC) has been considered as a promising technology in energy conversion from both renewable and industrial waste heat. However, the inherent fluctuating and intermittent characteristics of heat sources challenge ORC systems due to its negative effects on the operation and economic feasibility. Such thermal energy fluctuations are weakly considered at ORC system design and planning phase. Hence, current paper provides a comprehensive overview of heat source fluctuation characteristics, the associated inefficiency and safety issues in ORC systems in terms of working fluids and components, and current solutions to mitigate such variations. Although thermal energy storage and stream control have the potential to ensure an optimal operation close to design-point conditions, the determination of the design-point of ORC systems still remains unclear. Integrated design has been investigated to search the optimal design-point, which is reviewed in-depth from the perspectives of working fluid, cycle configuration, component design, dynamic performance and control design. Based on which, a 1-stage 5-level whole-system holistic design framework is innovatively proposed to enable the integration of ORC with other technologies and achieve simultaneous optimization of molecular, process, components, operation and control. ORC-based systems are considered as a whole to achieve tailored, fluctuation-friendly and cost-effective design, which are expected to maximize the power recovery over its lifespan period while reducing the exergy losses and carbon footprint. In addition, such framework is likely to motivate the adoption of advanced techniques in power system design, such as artificial intelligence.