Expanders for micro-CHP systems with organic Rankine cycle

The continual increases in global energy demand and greenhouse gas emissions call for more and more utilisation of sustainable energy sources, such as solar energy, biomass energy, and waste heat. Solar thermal energy, the heat of biomass combustion and waste heat may be used to drive a combined heat and power (CHP) system. In recent years, several micro-CHP systems with organic Rankine cycle (ORC) suitable for domestic applications (1–10 kW e) driven by solar thermal, biomass-fired boilers and waste heat resources have been investigated. These ORC-based micro-CHP systems have lower operation pressures and temperatures compared to conventional steam-Rankine cycle CHP systems and hence safer for household applications. However, the lack of commercially available expanders applicable to ORC-based micro-CHP systems has hindered the development of these novel CHP systems. This paper summarizes the findings of the market research for the expanders and discusses the selection and choices of the expanders for ORC-based micro-CHP systems. The working principles and the characteristics of several kinds of expanders, including turbine expanders (i.e., turboexpander), screw expanders, scroll expanders and vane expanders, are introduced and evaluated. ► Expanders are vital to ORC-based micro-CHP but not yet commercially available. ► Selection and choices of the expanders for 1–10 kWe micro-CHP are discussed. ► Vane expanders modified from vane-type air motors have been applied by the authors. ► Scroll expanders and vane expanders are likely the good choices for 1–10 kWe micro-CHP.