{ "id": "epbbb2ykjz", "slug": "organic-rankine-cycle", "title": "Organic Rankine cycle", "updated": "2026-10-15", "topic_path": [ { "id": "technology", "label": "Technology and the built world", "api_url": "https://www.edgepedia.org/api/v1/topics/technology" }, { "id": "technology.energy", "label": "Energy technology", "api_url": "https://www.edgepedia.org/api/v1/topics/technology.energy" }, { "id": "technology.energy.energy.fuels", "label": "Fuels and conversion technology", "api_url": "https://www.edgepedia.org/api/v1/topics/technology.energy.energy.fuels" }, { "id": "technology.energy.energy.fuels.alpha-in-to-w", "label": "Titles In to W", "api_url": "https://www.edgepedia.org/api/v1/topics/technology.energy.energy.fuels.alpha-in-to-w" }, { "id": "technology.energy.energy.fuels.alpha-in-to-w.alpha-i-to-re", "label": "Titles I to Re", "api_url": "https://www.edgepedia.org/api/v1/topics/technology.energy.energy.fuels.alpha-in-to-w.alpha-i-to-re" } ], "geo": [ { "id": "geo.nongeo.t1800.technology", "label": "Non-geographic · 1800 to 1945: Technology and the built world", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1800.technology", "path": [ { "id": "geo.nongeo", "label": "Non-geographic", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo" }, { "id": "geo.nongeo.t1800", "label": "Non-geographic · 1800 to 1945", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1800" }, { "id": "geo.nongeo.t1800.technology", "label": "Technology and the built world", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1800.technology" } ] }, { "id": "geo.nongeo.t1946.technology.energy", "label": "Non-geographic · 1946 to 2000: Energy technology", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.technology.energy", "path": [ { "id": "geo.nongeo", "label": "Non-geographic", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo" }, { "id": "geo.nongeo.t1946", "label": "Non-geographic · 1946 to 2000", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946" }, { "id": "geo.nongeo.t1946.technology", "label": "Technology and the built world", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.technology" }, { "id": "geo.nongeo.t1946.technology.energy", "label": "Energy technology", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.technology.energy" } ] } ], "excerpt": "The Organic Rankine cycle (ORC) converts heat into power using an organic fluid with a lower boiling point than water, suited to sources from 80 to 300 °C.", "snippet": "The Organic Rankine cycle (ORC) converts heat into power using an organic fluid with a lower boiling point than water, suited to sources from 80 to 300 °C.", "node": "technology.energy.energy.fuels.alpha-in-to-w.alpha-i-to-re", "markdown": "# Organic Rankine cycle\n\nThe Organic Rankine cycle (ORC) is a thermodynamic cycle that converts heat into mechanical power using an organic working fluid with a lower boiling point than water, suited to heat sources from roughly 80 °C to above 300 °C.[1](https://kcorc.org/technology/history/) • [2](https://www.mdpi.com/1996-1073/18/24/6561) It fills the range of a few kilowatts to a few megawatts where steam turbines perform poorly.[3](https://pure.tudelft.nl/ws/portalfiles/portal/45279342/ORC_PowerSystems_past_and_future.pdf)\n\n| Key fact | Value |\n|---|---|\n| Typical heat-source temperatures | About 80 °C (geothermal water) to above 300 °C[1](https://kcorc.org/technology/history/) • [2](https://www.mdpi.com/1996-1073/18/24/6561) |\n| Demonstrated performance | 301 kW electric output at 121 °C source; 9.4% gross efficiency, about 40% of Carnot[4](https://www.mdpi.com/1099-4300/21/6/619) |\n| Turbine isentropic efficiency | Up to 88.6% measured on a 300 kW radial-turbine unit[4](https://www.mdpi.com/1099-4300/21/6/619) |\n| Common working fluids | R245fa, R123, R134a, toluene, and newer HFO blends, though R245fa and R134a are being phased down under the EU F-gas Regulation, so new ORC systems increasingly use low-GWP fluids such as R1233zd(E), R1234ze(Z), R1224yd(Z), and R1336mzz(Z) or zeotropic HFO/HCFO mixtures[4](https://www.mdpi.com/1099-4300/21/6/619) • [3](https://pure.tudelft.nl/ws/portalfiles/portal/45279342/ORC_PowerSystems_past_and_future.pdf) • [5](https://link.springer.com/article/10.1007/s10973-025-15230-4) • [6](https://portal.fis.tum.de/en/publications/r1224ydz-r1233zde-and-r1336mzzz-as-replacements-for-r245fa-experi/) |\n| Expander power ranges | Scroll 0.35–7.5 kW; screw 7–50 kW; turbines from kW to MW[4](https://www.mdpi.com/1099-4300/21/6/619) |\n| Recuperator benefit | Roughly 10–15% thermal-efficiency gain with dry fluids[2](https://www.mdpi.com/1996-1073/18/24/6561) |\n| Pump burden in supercritical ORC | Up to 20–30% of gross power output[2](https://www.mdpi.com/1996-1073/18/24/6561) |\n\n## How it works\n\nThe ORC is a [Rankine cycle](https://www.edgepedia.org/rankine-cycle) in which the boiler working fluid is an organic compound rather than water. A pump raises liquid fluid to high pressure; the evaporator exposes it to the heat source, where it absorbs heat and transitions from liquid to vapor; the high-pressure vapor expands in an expander, producing shaft power; and the condenser returns it to liquid at low pressure.[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC11625998/) In many designs the fluid passes successively through a preheater, evaporator, and superheater before expansion.[8](https://www.sciencedirect.com/science/article/pii/S0196890422011797)\n\nThe organic fluid matters for three reasons. First, its large molecular weight yields a smaller enthalpy drop across the expander, so the volumetric expansion ratio and acoustic speed are lower, allowing lower rotational speeds or single-stage turbines.[3](https://pure.tudelft.nl/ws/portalfiles/portal/45279342/ORC_PowerSystems_past_and_future.pdf) • [2](https://www.mdpi.com/1996-1073/18/24/6561) Second, for most ORC fluids the expansion is completely dry, avoiding blade erosion and the condensation losses that wet steam expansion causes.[3](https://pure.tudelft.nl/ws/portalfiles/portal/45279342/ORC_PowerSystems_past_and_future.pdf) Third, at the few-kW-to-few-MW scale the steam mass flow would be extremely small and the expansion ratio large, making a simple axial or radial steam turbine problematic and inefficient; water also cannot effectively lubricate contact surfaces inside a positive-displacement expander.[3](https://pure.tudelft.nl/ws/portalfiles/portal/45279342/ORC_PowerSystems_past_and_future.pdf)\n\n## How it is done\n\nA practical ORC unit consists of four main components: the feed pump, the evaporator (often preceded by a preheater and followed by a superheater), the expander coupled to a generator, and the condenser with a cooling-water or air-cooled loop.[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC11625998/) • [8](https://www.sciencedirect.com/science/article/pii/S0196890422011797) Working-fluid selection weighs thermodynamic properties, environmental impact, safety, and cost.[2](https://www.mdpi.com/1996-1073/18/24/6561) Fluids are classified by the slope of the vapor saturation curve in the temperature–entropy diagram as wet (negative slope), isentropic (nearly infinite slope), or dry (positive slope); isentropic and dry fluids are preferred because they avoid liquid droplets during expansion and eliminate the need for superheating.[4](https://www.mdpi.com/1099-4300/21/6/619) • [9](https://www.intechopen.com/chapters/89154)\n\nExpander choice follows the power scale. Scroll expanders cover 0.35–7.5 kW, screw expanders 7–50 kW, and turbines operate from the kilowatt to the megawatt scale.[4](https://www.mdpi.com/1099-4300/21/6/619) Medium- to large-scale units use radial-inflow or axial turbines with isentropic efficiencies above 80% under design conditions, while small units below 50 kW use volumetric expanders at roughly 60–70% efficiency but with simpler design and lower cost.[2](https://www.mdpi.com/1996-1073/18/24/6561) For dry fluids that leave the expander as superheated vapor, an internal heat exchanger (recuperator) can preheat the liquid and raise thermal efficiency by roughly 10–15%.[2](https://www.mdpi.com/1996-1073/18/24/6561)\n\n## Origin\n\nA patent covered an engine concept using ether as the working fluid.[3](https://pure.tudelft.nl/ws/portalfiles/portal/45279342/ORC_PowerSystems_past_and_future.pdf) ORC engines with a reciprocating expander fed by a naphtha vaporizer powered launches; the Gas Engine & Power Company of New York claimed in 1890 to have sold five hundred engines of this design.[3](https://pure.tudelft.nl/ws/portalfiles/portal/45279342/ORC_PowerSystems_past_and_future.pdf) One review credits Charles Tellier in 1885 with the earliest solar ORC system, and the two accounts have not been reconciled.[3](https://pure.tudelft.nl/ws/portalfiles/portal/45279342/ORC_PowerSystems_past_and_future.pdf)\n\nA solar irrigation plant using monochloroethane was built, winning a 10,000 Lire prize with an estimated thermal conversion efficiency of about 3.6%; his ideas were implemented in a 2.6 kW geothermal prototype at the University of Naples in 1939, an 11 kW pilot plant on Ischia in 1940, and a 250 kW plant built in 1943 that was never operated.[3](https://pure.tudelft.nl/ws/portalfiles/portal/45279342/ORC_PowerSystems_past_and_future.pdf) Rankine engines using monochlorobenzene at 140–150 °C with 2–10 kW capacity were built, and a 3 kWe solar ORC demonstrated to the United Nations led to the formation of Ormat.[1](https://kcorc.org/technology/history/) • [10](https://orbi.uliege.be/bitstream/2268/191115/1/chap%2016%20%E2%80%93%20Solar%20thermal%20powered%20Organic%20Rankine%20Cycles.pdf)\n\n## Variants\n\nThree cycle configurations are distinguished by the pressure regime at the evaporator. Subcritical cycles, the simplest and most common, suit low-temperature sources below 150 °C with low-boiling-point fluids. Transcritical cycles heat the fluid at a pressure above the critical pressure while rejecting heat below it, so classic evaporation does not take place, achieving a better thermal match with the heat source and reducing exergy losses in heat exchange; one published analysis reported a 31.5% improvement in net power output for a transcritical ORC, though with worse economics.[11](https://www.frontiersin.org/journals/energy-research/articles/10.3389/fenrg.2020.00006/full) High-temperature sources above 300 °C justify reheated two-stage-turbine or supercritical configurations.[2](https://www.mdpi.com/1996-1073/18/24/6561) Zeotropic-mixture cycles use fluid blends; a published comparison found the zeotropic-mixture ORC a practical solution between 200 and 250 °C, offering balanced performance with lower investment costs.[12](https://ideas.repec.org/a/eee/energy/v324y2025ics0360544225017724.html) Zeotropic mixtures R1233zd/R123, R245fa/R123 (an HFC/HCFC blend, not HFO-based), and R245fa/R1233zd have been selected for hybrid renewable ORC systems on the basis of critical temperature and pressure, environmental performance, and thermodynamic suitability.[5](https://link.springer.com/article/10.1007/s10973-025-15230-4)\n\n## Applications\n\nGeothermal binary plants are the longest-standing application. One review records the first commercially operated geothermal ORC plant at Kiabukwa, Democratic Republic of Congo, in 1952 at 200 kWe,[3](https://pure.tudelft.nl/ws/portalfiles/portal/45279342/ORC_PowerSystems_past_and_future.pdf) while another dates the first geothermal binary ORC plant to 1967 in [Kamchatka](https://www.edgepedia.org/kamchatka), Soviet Union, using refrigerant 12 with 680 kW gross output from 80 °C geothermal water; the two accounts conflict and remain unresolved.[1](https://kcorc.org/technology/history/) In solar power, a grid-connected 1 MWe plant (\"Saguaro\") was commissioned in Red Rock, Arizona, in 2006 by [Arizona Public Service](https://www.edgepedia.org/arizona-public-service).[10](https://orbi.uliege.be/bitstream/2268/191115/1/chap%2016%20%E2%80%93%20Solar%20thermal%20powered%20Organic%20Rankine%20Cycles.pdf) Waste heat recovery is a major growth area, including marine diesel engine exhaust gas.[13](https://journal.hep.com.cn/jomsaa/EN/10.1007/s11804-026-00859-w)\n\n## Limitations and alternatives\n\nQuantified performance illustrates the ceiling: a 300 kW prototype with R245fa and a single-stage radial turbine reached 301 kW electric output at a 121 °C heat source, with turbine isentropic efficiency up to 88.6% and gross generating efficiency up to 9.4%, about 40% of the Carnot limit.[4](https://www.mdpi.com/1099-4300/21/6/619) Loss mechanisms include expander inefficiency, especially in small volumetric machines,[2](https://www.mdpi.com/1996-1073/18/24/6561) and pump work: in high-pressure supercritical designs the feed pump can absorb 20–30% of gross output with high-critical-pressure fluids.[2](https://www.mdpi.com/1996-1073/18/24/6561) Fluid requirements compound the problem: the ideal fluid is non-toxic, non-flammable, non-corrosive, cost-effective, with low or zero GWP and ODP, and thermally stable to the cycle maximum temperature.[3](https://pure.tudelft.nl/ws/portalfiles/portal/45279342/ORC_PowerSystems_past_and_future.pdf) R245fa, widely used in commercial plants, has a GWP of 930 but was retained for material compatibility and thermal stability up to 250 °C.[14](https://link.springer.com/article/10.1007/s43937-024-00053-5) For wet fluids, superheating is needed to prevent turbine erosion, at the expense of efficiency and cost, while for dry fluids superheat can inversely affect efficiency.[9](https://www.intechopen.com/chapters/89154) Because system performance depends strongly on the working fluid, computer-aided molecular design (CAMD) is being applied to select and design novel low-GWP fluids.[15](https://biblio.ugent.be/publication/01JJ24PKC9R6M9GNC1DYH05AB6)\n\nAgainst alternatives, ORC is described as more practical and more widely used among waste-heat-to-power options, with simplicity its main advantage.[16](https://www.sciencedirect.com/science/article/abs/pii/S1364032115009302) A 2025 comparison of subcritical ORC, supercritical ORC, trilateral cycle, zeotropic-mixture ORC, and [Kalina cycle](https://www.edgepedia.org/kalina-cycle) for 100–300 °C sources found the trilateral cycle achieved the highest power output (7.96–212.95 kW) and lowest LCOE (0.09–0.83 USD/kWh) but requires specialized equipment; the Kalina cycle showed superior efficiency at moderate temperatures with zero GWP but demands complex safety protocols; and the zeotropic-mixture ORC was a practical solution between 200 and 250 °C with lower investment costs.[12](https://ideas.repec.org/a/eee/energy/v324y2025ics0360544225017724.html) Published comparisons of ORC, Kalina cycle, and thermoelectric generator configurations for waste heat recovery exist on energy, exergy, economic, and environmental criteria.[8](https://www.sciencedirect.com/science/article/pii/S0196890422011797)\n\n## References\n\n1. [History | KCORC (Knowledge Centre on Organic Rankine Cycle technology)](https://kcorc.org/technology/history/)\n2. [Organic Rankine Cycle System Review: Thermodynamic Configurations, Working Fluids, and Future Challenges in Low-Temperature Power Generation](https://www.mdpi.com/1996-1073/18/24/6561)\n3. [Organic Rankine Cycle Power Systems: From the Concept to Current Technology, Applications, and an Outlook to the Future (Colonna et al., ASME J. Eng. Gas Turbines Power, GTP-14-1658)](https://pure.tudelft.nl/ws/portalfiles/portal/45279342/ORC_PowerSystems_past_and_future.pdf)\n4. [Experimental Investigation of a 300 kW Organic Rankine Cycle Unit with Radial Turbine for Low-Grade Waste Heat Recovery](https://www.mdpi.com/1099-4300/21/6/619)\n5. [Thermodynamic exploration of hybrid renewable ORC systems using HFO-based nanofluid zeotropic mixtures](https://link.springer.com/article/10.1007/s10973-025-15230-4)\n6. [R1224yd(Z), R1233zd(E) and R1336mzz(Z) as replacements for R245fa: Experimental performance, interaction with lubricants and environmental impact - Technical University of Munich](https://portal.fis.tum.de/en/publications/r1224ydz-r1233zde-and-r1336mzzz-as-replacements-for-r245fa-experi/)\n7. [A comparative review of ORC and R-ORC technologies in terms of energy, exergy, and economic performance](https://pmc.ncbi.nlm.nih.gov/articles/PMC11625998/)\n8. [Comparative analysis of organic rankine cycle, Kalina cycle and thermoelectric generator to recover waste heat based on energy, exergy, economic and environmental analysis method](https://www.sciencedirect.com/science/article/pii/S0196890422011797)\n9. [Utilizing Computational Methods to Identify Low GWP Working Fluids for ORC Systems](https://www.intechopen.com/chapters/89154)\n10. [Solar thermal powered Organic Rankine Cycles (book chapter, ORBi)](https://orbi.uliege.be/bitstream/2268/191115/1/chap%2016%20%E2%80%93%20Solar%20thermal%20powered%20Organic%20Rankine%20Cycles.pdf)\n11. [Thermo-Economic Optimization of Organic Rankine Cycle (ORC) Systems for Geothermal Power Generation: A Comparative Study of System Configurations](https://www.frontiersin.org/journals/energy-research/articles/10.3389/fenrg.2020.00006/full)\n12. [Resolving performance contradictions in ORC and alternative power cycles: Systematic analysis of five technologies with time-adjusted economic insights (Energy, 2025)](https://ideas.repec.org/a/eee/energy/v324y2025ics0360544225017724.html)\n13. [Environmental-Based Working Fluid Selection for Organic Rankine Cycle for Waste Heat Recovery in Marine Diesel Engines](https://journal.hep.com.cn/jomsaa/EN/10.1007/s11804-026-00859-w)\n14. [Optimizing Organic Rankine Cycle (ORC) configurations integrated with transient industrial waste heat: a multi-objective approach](https://link.springer.com/article/10.1007/s43937-024-00053-5)\n15. [Working fluid and system optimisation of organic Rankine cycles via computer-aided molecular design: a review](https://biblio.ugent.be/publication/01JJ24PKC9R6M9GNC1DYH05AB6)\n16. [Organic Rankine cycle performance evaluation and thermoeconomic assessment with various applications part I: Energy and exergy performance evaluation](https://www.sciencedirect.com/science/article/abs/pii/S1364032115009302)\n\n---\n*Topic: Encyclopedia › Technology and the built world › Energy technology › Fuels and conversion technology › Titles In to W › Titles I to Re*\n\n*Initially written Sep 29, 2026 · Edited: Oct 15, 2026*\n\n*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*\n\nLicense: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license\n", "same_as": [], "url": "https://www.edgepedia.org/organic-rankine-cycle", "markdown_url": "https://www.edgepedia.org/organic-rankine-cycle.md", "license": { "name": "Edgepedia Community License 1.0", "url": "https://www.edgepedia.org/edgepedia/license", "summary": "Free with credit, commercial use included. AI training is open to everyone. For other uses, organizations over USD 100M in revenue or 100M monthly users license separately.", "spdx": "LicenseRef-Edgepedia-Community-1.0" }, "credit": "\"Organic Rankine cycle\", Edgepedia (EdgeChat), https://www.edgepedia.org/organic-rankine-cycle. Edgepedia Community License 1.0.", "credit_md": "\"[Organic Rankine cycle](https://www.edgepedia.org/organic-rankine-cycle)\", Edgepedia (EdgeChat), [https://www.edgepedia.org/organic-rankine-cycle](https://www.edgepedia.org/organic-rankine-cycle). [Edgepedia Community License 1.0](https://www.edgepedia.org/edgepedia/license).", "credit_html": "\"Organic Rankine cycle\", Edgepedia (EdgeChat), https://www.edgepedia.org/organic-rankine-cycle. Edgepedia Community License 1.0.", "speakable": "The Organic Rankine cycle converts heat into power using an organic fluid with a lower boiling point than water, suited to sources from 80 to 300 °C." }