Thermal Efficiency Analysis of a 1 kW Organic Rankine Cycle System with Solar Collection Using R-245fa
Thermal Efficiency Analysis of a 1 kW ORC System with a Solar Collection Stage and R-245fa Working Fluid: A Case Study
OverviewResearchers from the Universidad Autónoma de Querétaro (Mexico) and collaborating institutions conducted a detailed thermal efficiency analysis of a 1 kW Organic Rankine Cycle (ORC) system that includes a solar collection stage. The study focused on how adding a regeneration stage and using R-245fa as the working fluid could enhance system performance.Objectives• To measure and compare system efficiency between simple and regenerative ORC modes.• To evaluate the influence of a solar collector on thermal performance.• To demonstrate low-temperature solar energy integration into small-scale ORC systems.• To identify operational parameters improving performance for renewable and waste-heat applications.System Description• The ORC unit consisted of a boiler (CAL-800), scroll expander (ESG-400), heat exchangers, cooling tower, and solar collector.• The working fluid R-245fa circulated through the evaporator, expander, condenser, and regeneration heat exchanger.• A solar thermal collector preheated the regeneration water circuit to around 180 °C at peak solar hours.• The expander speed was controlled near 3,600 RPM to maintain 1 kW electrical generation at 115 V and 60 Hz output.Experimental Setup• Location: Technological Liaison Center for Sustainability (CETESU), Querétaro, Mexico.• Heat source temperature: 80 °C to 95 °C.• Cooling water outlet temperature: around 23 °C.• Working fluid flow rate: approximately 0.08 kg/s.• The system was tested in both simple and regeneration + solar modes for comparison.Key Results• Thermal efficiency (simple mode): 35.27%.• Thermal efficiency (regeneration + solar mode): 51.30%.• Carnot theoretical limit: 66.7%.• Efficiency gain: roughly +30% due to solar regeneration.• The solar collector provided sufficient thermal input to reduce boiler LP-gas use and overall system fuel consumption.• The working fluid reached evaporation at 110 °C and pressure at 11.8 bar, while the condenser operated at 30 °C and 1.8 bar.Insights and Discoveries• Adding a solar regeneration loop preheats the R-245fa before the main evaporator, significantly improving thermal efficiency.• The mass and energy balance equations confirmed consistency between measured and theoretical performance.• The solar stage reduced fossil fuel dependency by partially substituting boiler energy with renewable heat.• When operating in regeneration mode, the ORC achieved lower input energy demand for the same output power.• The working fluid inlet temperature to the primary exchanger is a critical parameter for maximizing performance.• The findings validated the integration of renewable energy with waste-heat systems for distributed generation.Environmental and Operational Benefits• Solar-assisted regeneration decreased CO₂ emissions and fossil fuel consumption.• The ORC system’s use of organic fluids allows efficient power generation from low• and medium-temperature heat sources.• Potential for application in industrial waste-heat recovery, solar hybrid systems, and off-grid micro-generation.• Projected reduction in CO₂ emissions: up to 1,226 tons avoided annually when scaled to industrial systems.Conclusions• Integrating a solar collection stage into a 1 kW ORC system significantly increases efficiency.• Regeneration improved overall performance by approximately 30%.• The experiment confirms that solar-enhanced ORC systems can operate effectively at small scale.• The setup provides a practical model for industries seeking low-cost, renewable-integrated power generation.Future Recommendations• Investigate alternative low-GWP refrigerants (R134a, R600a, R290) to replace R-245fa.• Conduct a cost-benefit analysis of multistage regeneration systems.• Develop scalable modular ORC units for distributed renewable installations.• Combine with energy storage or photovoltaic systems to maximize solar utilization.SummaryThe study proves that a 1 kW ORC system with R-245fa can reach over 50% thermal efficiency when enhanced with solar-driven regeneration. This hybrid configuration bridges renewable solar heat with thermodynamic recovery technology, enabling efficient, low-emission, small-scale power generation for industrial and distributed energy systems.
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