Some research and industrial trends in ORC power systems
The rising industrial interest and the growing and lively international scientific community researching the ORC technologies are opening up new possibilities for the future ORC power systems. The figure below shows the traditional range in which ORC power systems are the most suitable technology from a techno-economic point of view. It is worthwhile to not that the boundaries of this operating map are expanding. On one side, larger installations in term of power production are already feasible and competitive from an industrial point of view. On the other side the research is very lively in the field of small scale ORC (<100kW). The low-capacity market has large potential, especially for mass-production units. Possible applications include heat recovery for automotive engines, domestic CHP or distributed cogenerating solar power plant.
Very low capacity ORC systems have not reached yet the commercial maturity yet; several technical challenges are being faced to make them feasible and lower the costs. Some of the key aspects being investigated include: methods to select and design the expanders; holistic multi-objective optimization strategies; dynamic modelling to characterize the system under transient conditions; effective control system designs.
Low-capacity ORC systems are also often used in combination with non-steady heat sources (e.g. in the case of waste heat recovery on an internal combustion engine). Thus, innovative optimization strategies, capable of taking in to account transients, can bring to more efficient configurations and research efforts are going in this direction.
Another hot topic is the exploitation of new fluids. This can have a large impact on the system, for example by overcoming the current thermal-stability limit, or by reducing the Global Warming Potential of the installation. Theoretical studies on mixtures have been performed but, despite promising results, more efforts are required to acquire the lacking knowledge for the widespread adoption of mixtures as working fluid.
Quite a lot of efforts are also being put in carrying on experimental campaigns in order to obtain data both at the system and at the component level. These data are necessary to validate and improve the models used in the design and optimisation processes.
The exploitation of supercritical cycle configurations is another important topic requiring further research; for example on the design of trans-critical heat exchanger and of suitable expanders. Similarly, supercritical CO2 power cycles are a promising solution to exploit high temperature heat sources. These cycles share many features and also some technological challenges with the ORC cycles. Several test loops are being constructed and multiple researches are going on to upgrade the technology readiness level, (http://sco2symposium.com/www2/sco2/default.htm).
 Sylvain Quoilin, Martijn Van Den Broek, Sébastien Declaye, Pierre Dewallef, Vincent Lemort; Techno-economic survey of Organic Rankine Cycle (ORC) systems; Renewable and Sustainable Energy Reviews 22 (2013) 168-186,
 Lorenzo Tocci, Tamas Pal, Ioannis Pesmazoglou, Benjamin Franchetti; Small Scale Organic Rankine Cycle (ORC): A Techno_Economic Review; Energies 2017, 10, 413; doi:10.3390/en10040413