This paper presents a unique flywheel-based regenerative energy recovery, storage and release system developed at the author’s laboratory. It can recover and store regenerative energy produced by braking a motion generator with intermittent rotary velocity such as the rotor of a wind turbogenerator subject to intermittent intake wind and the axels of electric and hybrid gas-electric vehicles during frequent coasting and braking. Releasing of the stored regenerative energy in the flywheel is converted to electricity by the attached alternator. A proof-of-concept prototype called the SJSU-RBS was designed, built and tested by author’s students with able assistance of a technical staff in his school.

Keywords – regenerative energy recovery; flywheel; energy storage; kinetic energy


The present research involves the design, construction and testing of a flywheel-based regenerative braking system (RBS), the SJSU-RBS. This particular RBS can store the kinetic energy produced by intermittent energy sources otherwise would be lost because the recovered regenerative energy by these sources is often too small to be saved. This unique regenerative braking system (RBS) allows the recovered regenerative energy to be converted into electric energy by an integrated flywheel/alternator unit. Major components in the SJSU-RBS is presented in Figure 1,


in which the “rotary motion generator” may be the spinning axel of an electric vehicle during coasting and braking, or an electric motor driven by the power generated by solar photovoltaic cells with fluctuating solar energy intensity, or a wind turbine rotor rotating at variable speeds by intermittent intake wind. The inertia clutch in the system engages the flywheel/alternator unit to the input shaft at a constant or accelerated rotary speed of the motion generator. The same clutch disengages the same unit from the input shaft of the motion generator at a reduced speed or after complete stop turning of this shaft. The disengaged flywheel/alternator unit, though spins at reduced speed, can continue to produce electricity. A “speed boosting” device such as an epicyclic gear train with a combination of “sun,” “satellite” and “rim” gears is introduced in the RBS to boost the spinning speed of the flywheel for maximum storage of the kinetic energy. A unique electric charging system has been developed and it is attached to the SJSU-RBS for “electric energy storage, distribution, and management system” as shown in Figure 1. This system can save any level of electricity generated by the recovered regenerative energy by the RBS using a trickle charge controller and a bank of ultracapacitors. It accumulates the input energy to a level that is high enough to be charged to the principal energy storage of the power plants, or to the batteries of an electric vehicle.


A new regenerative braking system, the SJSU-RBS was developed with the design, construction and testing of a proof-of-concept prototype. It involves a fast spinning flywheel/alternator unit with a uniquely designed progressive braking system and an epicyclic gear train. This new SJSU-RBS can be readily adapted to power plants driven by renewable energies from intermittent sources such as solar, wind and braking of electric and hybrid gas-electric vehicles during coasting and braking. The SJSU-RBS was proof-tested for its feasibility and practicality for the intended applications. Despite the success in the preliminary bench-top testing of the prototype of the SJSU-RBS as presented in the paper, a few key technical issues remain unsolved. Issues such as the optimal design of flywheel for maximum net recovery and storage of regenerative energies; quantification of aerodynamic and electromechanical resistance to the free spinning of the flywheel, and the effective and optimal control of the motion of the flywheel and the driving shafts, etc. will have significant effects on the performance of the SJSU-RBS or similar regenerative braking system for maximal recovery of regenerative energies in reality. Further research on the detailed design and integration of the SJSU-RBS to wind power generating plants and EVs and HEVs for performance enhancements is desirable. The success of such integration will result in great economical returns to the renewable power generation industry. Efficient power generations by renewable energy sources by RBS will make significant contributions to the sustainable development of global economy and well-being of all humankind.

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