Principle of Hybrid Energy Storage Systems based on Hydro-pneumatics and Supercapacitors for Distributed Generation and Renewable Energy Sources Support
This paper presents hybrid energy storage systems based on hydro-pneumatics and Supercapacitors with high potentials regarding life cycle and impacts on environment. These so called “Batteries with Oil-hydraulics and Pneumatics (BOP)” systems exploit the high performances of oil-hydraulics machines to store energy into compressed air. In the first system, the BOP-A, compression and expansion of a trapped volume gas take place in the storage vessel. A Maximum Efficient Point Tracking algorithm is used to optimise the efficiency of the oil-hydraulic machine. As the maximum efficiency conditions impose the level of the converted power, an intermittent time-modulated operation is applied to the pneumatic-to-electric conversion subsystem to obtain a variable mean power. A smoothly variable output power is achieved with the help of a supercapacitive auxiliary storage device used as a filter. The paper describes the concept of the system, the principle of the Maximum Efficiency Point Tracking (MEPT) algorithm and the strategy used to vary the output power. Practical results are reported, that have been recorded from a first prototype of BOP-A. In addition, the paper introduces the second and more promising system, the BOP-B, where compression and expansion of fresh air are done in liquid-piston work-chambers with integrated heat exchangers. This leads to an almost isothermal process and therefore to high efficiency and high energy density. Finally, some economical considerations are made, in the context of a stand alone photovoltaic home supply, through a comparative cost evaluation of the presented hydro-pneumatic systems and a lead acid batteries system. This evaluation confirms the cost effectiveness of the studied hybrid storage systems.
Record created on 2006-07-10, modified on 2016-08-08