Quote:
Originally Posted by mnmarcus
If I close the valve on a hydraulic accumulator I could come back a year later and the psi(energy) would be nearly the same.
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You are forgetting heat. When the hydraulic system is fully charged it will have converted some energy to heat due to compressing the fluid. If you throw that heat away it is lost efficiency. If you store the heat and use the pressurized fluid soon, (like regenerative braking and then accelerating from a stop) you won't waste the heat. If you brake down a grade and park you may lose it all. For mineral oil like fluids the heat of compression is about .01 K per psi. At full charge the tank will be at 5000psi and about 345K. But when it cools to room temperature the pressure drops to about 4200psi. The residual 85% is there forever. A storage battery has more like a logarithmic self discharge, like a couple percent or remaining capacity per day.
Quote:
Originally Posted by mnmarcus
Estimates for electric hybrids capture more like 20 to 25 percent, because their batteries have comparatively poor power density.
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Ford claims nearly 94%
-mort