Researchers from China's Harbin Institute of Technology proposed to combine pumped hydro storage systems with compressed air energy storage (CAES) technology in an attempt to address a well-known issue of pumped hydro schemes – dealing with large head variations in hydraulic machinery.
[pdf] A decentralized variable electric motor and fixed pump (VMFP) system with a four-chamber cylinder is proposed for mobile machinery, such that the energy efficiency can be improved by hydro-pneumatic energ.
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