1.5 kW Organic Rankine Cycle (ORC) Power Generator – Compact 28V System for Waste Heat Recovery

Organic Rankine Cycle Silent Power Plant 1.5 kW 28 VDC from 1974 Sunstrand Aviation in Rockford Illinois

1 kW Organic Rankine Cycle (ORC) Power Generator Overview

The 1 kW ORC system represents a breakthrough in compact thermal-to-electric power conversion. Designed to produce 28 volts DC from waste heat sources, it enables direct battery charging or microgrid integration. The system is ideal for small-scale or remote applications where efficiency, reliability, and autonomy are essential.

Purpose and Objectives

• Designed to recover low-grade heat and convert it into usable electrical power.

• Provides a 28V DC output suitable for direct storage or load operation.

• Demonstrates the technical and economic feasibility of micro-ORC systems below 5 kW.

• Targets industrial waste heat, small engines, geothermal, and solar-thermal sources.

System Design and Operation

• Closed-loop Organic Rankine Cycle configuration with evaporator, micro-turbine, condenser, and pump.

• Compact and modular design for easy deployment and scalability.

• Integrated control system for automated startup, operation, and shutdown.

• Rapid startup within approximately 90 seconds.

• Designed for unmanned or remote installations with minimal maintenance.

Operating Conditions

• Heat source temperature: 90 to 130 degrees Celsius.

• Working fluid: primarily R245fa, with R134a and R1233zd(E) evaluated as alternatives.

• Turbine inlet pressure: 10 to 12 bar.

• Turbine outlet pressure: 2 to 3 bar.

• Mass flow rate: approximately 0.06 to 0.1 kilograms per second.

• Condenser temperature: about 60 degrees Celsius.

Turbine and Generator

• Single-stage radial inflow micro-turbine operating at 35,000 to 55,000 RPM.

• Turbine efficiency between 65 and 70 percent.

• Direct-drive permanent magnet generator producing 28 volts DC.

• No gearbox required, minimizing mechanical losses.

• Oil-free bearing design eliminates the need for lubrication systems.

Performance Results

• Net electrical power output: 1.0 to 1.2 kilowatts.

• Thermal input: approximately 15 to 20 kilowatts.

• Overall system efficiency: 6.3 to 7.5 percent.

• Pressure ratio: 4.5 to 5.8 to 1.

• Power stability: voltage fluctuations within ±2 percent.

• Startup time: approximately 90 seconds from cold start.

• CFD and experimental validation show results within ±5 percent accuracy.

Key Discoveries and Innovations

• Proven viability of micro-ORC systems for small-scale waste heat recovery.

• Direct 28V DC output simplifies connection to energy storage and low-voltage systems.

• Stable power generation under fluctuating thermal input conditions.

• Compact oil-free turbine and bearing system reduce maintenance requirements.

• Demonstrated flexibility across multiple working fluids for different temperature ranges.

• Modular configuration allows for parallel operation of multiple units to achieve higher power levels.

• Simple electronic control system allows fully automated operation with minimal human supervision.

Working Fluid Observations

• R245fa achieved the highest output power and system efficiency.

• R1233zd(E) provided environmental benefits with lower global warming potential.

• R134a offered better performance at lower temperature heat sources below 100 degrees Celsius.

Environmental and Economic Benefits

• Converts low-temperature waste heat that would otherwise be lost.

• Offers low maintenance and long operational life due to oil-free and sealed design.

• Enables carbon reduction through renewable or recovered heat utilization.

• Expected payback period estimated at three to five years depending on application.

• Modular architecture supports distributed energy generation and microgrid use.

Limitations and Future Development

• Efficiency limited by condenser performance and turbine clearance losses.

• Research underway to integrate recuperators to improve thermal efficiency.

• Future systems will explore the use of supercritical CO₂ for higher density power generation.

• Planned enhancements include advanced high-speed generators and solar thermal integration.

Conclusion

The 1 kW 28V Organic Rankine Cycle system demonstrates a compact, efficient, and practical solution for converting waste heat into clean electricity. With fast startup, stable operation, and minimal maintenance requirements, it proves that micro-ORC technology can play a vital role in decentralized energy systems. Its direct DC output, modular design, and compatibility with renewable heat sources make it a promising foundation for future small-scale power generation and hybrid renewable applications.

TEL: 1-608-238-6001 Email: greg@infinityturbine.com

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