Some time ago there was a large tide-power project in the Bay of
Fundy, Nova Scotia, Canada. My understanding was that it worked very
well, but was mostly a "capture the water at high tide, generate 
electricity at
low tide (going out to sea) as well as high tide (coming in from sea)".

I don't know what happened to that project.

--Bob

Mike W wrote:

>this may be an interesting adition to the thread...
>http://news.bbc.co.uk/1/hi/england/cornwall/3477639.stm
>
>On 8 Sep 2005 at 14:30, Gerhard Fiedler wrote:
>
>  
>
>>Olin Lathrop wrote:
>>
>>    
>>
>>>Gerhard Fiedler wrote:
>>>      
>>>
>>>>Not necessarily. It could be that the energy would get transformed from
>>>>kinetic energy into other forms (heat?) anyway -- float or no float. Maybe
>>>>the float just redirects a small part of the energy flow that goes from
>>>>kinetic to thermal into electric instead; in that case, the float wouldn't
>>>>introduce an additional slowing, but would cause a certain ever so slight
>>>>cooling.
>>>>        
>>>>
>>>My point was where the energy was coming from in the first place.  I say it
>>>comes from the kinetic energy stored in the rotation of the planet. You
>>>seemed to disagree so I wanted to hear where you think it does come from. 
>>>      
>>>
>>No, I didn't really disagree with that... Maybe Howard?
>>
>>    
>>
>>>But to address your comment above, you are saying that the energy in
>>>moving the water up and down as tides gets dissipated anyway, therefore
>>>directing it to make electricity doesn't remove any additional energy
>>>from the source. I disagree with this also.  My main argument is that
>>>much of the energy is not dissipated, but returns to the system.  It's
>>>sortof like bouncing a mass at the end of a spring.  Once you get it
>>>going, it take relatively little power to sustain a large oscillation.
>>>That's because little is being dissipated.  The energy just gets sloshed
>>>around between the spring and the mass.  Only the little bit lost to friction
>>>and air resistance must be replaced by the driving mechanism each cycle. 
>>>      
>>>
>>If this is true, then I agree with you.
>>
>>    
>>
>>>Certainly there is energy dissipated by the oceans as they rise and fall due
>>>to tides, but most of it is stored and released as potential energy in the
>>>height of the water column.  Think of a planet that has a uniformly thick
>>>ocean layer over a perfectly smooth solid core.  The tides would be traveling
>>>waves.  They would loose a little energy in the internal friction of the
>>>water due to viscocity, and some more in the friction with the ground, but
>>>most of the energy would be transferred around the globe in a big wave.  The
>>>driving force is essentially in phase with the motion. 
>>>      
>>>
>>Not sure how much the internal friction contributes. Any numbers?
>>
>>    
>>
>>>Now think of a large float used to extract this energy into up/down
>>>motion of a fixed mechanical system.  If there is no force on the
>>>mechanical system (the float just bobs in the water), then no energy is
>>>extraced.  To extract energy, there has to be a force in the direction
>>>of motion.  This means the float must be lagging the wave, causing a
>>>phase shift in the wave itself. Once the wave is lagging its driving
>>>force, the driving force must be imparting more energy to the wave.  The
>>>extra energy has to come from somewhere, which is the kinetic energy stored
>>>in the earth's rotation long ago. 
>>>      
>>>
>>Yes, I agreed already to the source of this energy being the kinetic energy of
>>the rotation. The question is really whether the energy would be conserved as
>>kinetic energy if the float wasn't there, or if it would get lost (as kinetic
>>energy) anyway -- maybe at the coast line. It seems to me that there's quite a
>>bit of kinetic energy that gets lost (as kinetic energy) at the coast lines...
>>
>>Gerhard
>>-- 
>>http://www.piclist.com PIC/SX FAQ & list archive
>>View/change your membership options at
>>http://mailman.mit.edu/mailman/listinfo/piclist
>>
>>    
>>
>
>
>  
>


-- 
Note: To protect our network,
attachments must be sent to
attach@engineer.cotse.net .
1-866-263-5745 USA/Canada
http://beam.to/azengineer

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist