This is basically a kinetic storage battery? I'm not sure about the  
storage system mentioned here but wouldn't you need to raise 36,000  
kg 10 meters to get 1 kwh? Is there some trick to the hydraulic  
system that would let it work with less mass?


On Aug 6, 2006, at 3:13 PM, Howard Winter wrote:

> On Sun, 6 Aug 2006 14:18:38 -0700, William "Chops" Westfield wrote:
>
>>
>> On Aug 6, 2006, at 2:44 AM, Vitaliy wrote:
>>
>>> I remember a while back one of the presenters at the local SAE  
>>> chapter
>>> meeting mentioned that storing the braking energy as
>>> compressed air achieves up to 70% efficiency, compared to
>>> only 20% for batteries.
>>
>> I find both figures hard to believe.  70% is about the number
>> I see quoted for high efficiency gas turbines (which do NOT
>> operate on compressed gas; efficiency is dependent on gas input
>> temperature.)  I'm pretty sure compression is nowhere near that
>> efficiency.  And battery charging is more than 20% efficient
>> as well.  They might be comparing an overall cycle efficiency
>> for electric to a hypothetical compressed gas motor efficiency,
>> or they might just be wrong...
>
> Nobody has mentioned hydraulic storage - a hydraulic accumulator  
> consists of a piston in a vertical cylinder on top of a column of
> hydraulic fluid, with a heavy weight resting on it.  Hydraulic  
> pumps pump fluid into the system, and any energy that isn't used  
> raises the
> weighted piston.  When the energy needs to be retrieved the piston  
> descends, giving back the stored energy.  It's very efficient because
> unlike compressed air there's no heat-loss associated with it -  
> only the friction of the piston and the fluid.  If there are no  
> leaks, the
> stored energy doesn't degrade over time, like most other storage  
> systems.
>
> Back when there was a "London Hydraulic Power Company" there were  
> hydraulic accumulator towers in a number of places on the system,  
> and at
> least one still exists (at Limehouse, although it is no longer  
> functional - they've built a staircase through the weight-case so  
> visitors
> can climb to the top!).  Tower Bridge had six of them, four of  
> which were housed in the rounded brickwork bases of the towers.
>
> I don't know how efficient the whole hydraulic pump/accumulator/ 
> motor system would be, but it could be worth considering.
>
> Cheers,
>
>
> Howard Winter
> St.Albans, England
>
>
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