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Do ultracaps have a future in stationary power storage?

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Posted by John Ladasky on October 17, 2006, 7:39 pm
 


Ultracaps are getting a lot of attention lately.  But I'm not sure why
everyone is leaping to use them in electric automobiles.  They are
still quite heavy, for the amount of power that they store.  And they
still cost quite a bit.  In a recent post, I did some math and
concluded that the storage density of present-day commercial ultracaps
was 1.2 watt-hours/kg, and cost $.56 per Wh.

http://groups.google.com/group/alt.energy.renewable/msg/4d23b7acc945c27d

But while people talk about using ultracaps in cars, I think that
another energy-storage application has been overlooked.  Today,
off-grid renewable energy systems and backup power systems use
lead-acid batteries for storage.  Lead-acid batteries store energy at a
much higher density than ultracaps (~30 Wh/kg) and are cheaper, at
about $.20 per Wh.

BUT lead-acid batteries have a finite lifetime, often needing
replacement in under 5 years.  Meanwhile, there are the environmental
costs of handling all of that lead.  Ultracaps can, theoretically, last
forever?  I attach a value to things that you don't have to throw away,
and perhaps you do as well.

Right now, expressed strictly in terms of costs to consumers at the
point of sale, it looks like you would have to require stationary power
storage for somewhat over a century, in order to justify choosing
ultracaps over lead-acid batteries.  What are the prospects for
ultracap costs coming down (and, hopefully, charge storage densities
going up)?  How might that change the ultracap market?


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Posted by T.Keating on October 19, 2006, 1:34 am
 


wrote:


1. They have very low energy density when compare to conventional
battery tech..
   http://www.thomas-distributing.com/cta-d-rechargeable-batteries.php

NiMh $9 == (2 x 1.2 * 12 * 3600) == 103,680 joules of storage.

  NiMH bat lifespan can be vastly extended if charge state is kept
within 50% of middle of its operating range.      So chop in half.. $9
== 51,840 joules good for ten years and 50,000 cycles or more.


2. Significant Losses incured in charging and recapturing stored
energy.(20 to 25% in each direction).   Voltage is not a  constant thus
requiring somewhat lossy setup/stepdown switching power supplies in
order to match impedence of load/production to caps current charge
state.

3.  Accumulated leakage imbalances between caps.
  (Requires bleeding charge in order to rebalance.)

4.  Note: Wiring 2 Caps in series.. (Doubles voltage rating, but halves
available capacitance.)    see
http://en.wikipedia.org/wiki/Series_and_parallel_circuits


Thus the module cited (via google links).
http://www.ferret.com.au/articles/55/0c035255.asp

Has effective capacitance rating of 1 / ((1 / 2600)*6)  == 433 farads @
16v and a cost of  $40 dollars for 55,424 joules of storage.

http://www.signonsandiego.com/news/business/20060608-9999-1b8maxwell.html

Note pictures in this cited article and the size of the super caps..
It takes 6 of them wired in series to match 54% of the energy capacity
in a pair of D-cell NiMH bats.


That price point doesn't exist..
   its around $6 per Wh.. while NiMh bats are $.66 per Wh..


They like to talk without doing the math or science.


Forever.. no way..  physics and material fatigue dictates otherwise.

As you apply charge to a capacitor internal mechanical stresses
increase  as squared function..  (Just like energy capacity. W =
1/2C*V^2)

Where internal Force == 333 *(Q1) *(Q2) / (D * r)

in which
   Q1 is total charge on negative plate.  (CV)
   Q2 is total charge on positive plate.   (CV)
  D is dielectric constant
  r is distance seperating surfaces..

Cycling large caps thru it's entire charge state is going to fatigue
plates, dielectrics significantly.    Any design that significantly
increases C or V  capability is going to increase internal forces
(squared).


Posted by T.Keating on October 19, 2006, 1:40 am
 

wrote:


They like to talk without doing the math or science.


Ultra caps have very low energy density when compare to conventional
battery tech.

http://www.thomas-distributing.com/cta-d-rechargeable-batteries.php
$9 == (2 x 1.2 * 12 * 3600) == 103,680 joules of energy storage.

  Note: NiMH bat lifespan can be vastly extended if charge state is
kept within 50% of middle of its operating range.      So chop in
half.. $9 == 51,840 joules good for 50,000 cycles or more.



Significant Losses incurred in charging and recapturing stored
energy.(20 to 25% in each direction).   Voltage is not a constant thus
requiring somewhat lossy setup/stepdown switching power supplies to
match impedance of load/production to current charge state.

Accumulated leakage imbalances between caps.
  (Requires bleeding charge in order to rebalance charge state.)

Note: Wiring 2 Caps in series.. (Doubles voltage rating, but halves
available capacitance.)
http://en.wikipedia.org/wiki/Series_and_parallel_circuits


Thus the module cited .
http://www.ferret.com.au/articles/55/0c035255.asp

Has effective capacitance rating of 1 / ((1 / 2600)*6)  == 433 farads @
16v. and has a cost of  $40 dollars for 55,424 joules of storage.

http://www.signonsandiego.com/news/business/20060608-9999-1b8maxwell.html

Note the pictures in this cited article and the size of the super
caps..  It takes 6 of them wired in series to match 54% of the energy
capacity in a pair of D-cell NiMH bats.


That price point doesn't exist..
   its around $6 per Wh, while NiMh bats are $.66 per Wh.


Forever.. no way..  physics and material fatigue dictates otherwise.

As you apply charge to a capacitor internal mechanical stresses
increase  as squared function..  (Just like energy capacity. W =
1/2C*V^2)

Where internal Force == 333 *(Q1) *(Q2) / (D * r)

in which
   Q1 is total charge on negative plate.  (CV)
   Q2 is total charge on positive plate.   (CV)
  D is dielectric constant
  r is distance separating surfaces..

Cycling large caps thru it's entire charge state is going to fatigue
plates, dielectrics significantly.    Any design that significantly
increases C or V  capability is going to increase internal forces
(squared).


Posted by danny burstein on October 19, 2006, 5:53 am
 

[ lots of good stuff snipped ]

I've been trying to figure out a way of reducing
the starting and initial torque demands on
elevator motors. They're a pretty uniqe load, and
they massively distort the power needs in a modest
sized apartment building - thus driving us crazy
when plotting out emergency power.

Ignoring (yes, I know....) the cost issues, would
they be plausably practical for this purpose?

Let's say, using the back of an envelope, that
the motor is a 10 kw job, pulling 50 kw for
the first 1/4 second, 20 kw the next two seconds, then
floating at 5 or so during the trip.

( 3 phase AC )

If we could use them to provide the starting
surge, it would dramatically simplify the system.

Any thoughts?

thanks.
--
_____________________________________________________
Knowledge may be power, but communications is the key
             dannyb@panix.com
[to foil spammers, my address has been double rot-13 encoded]

Posted by T.Keating on October 19, 2006, 10:59 am
 

On Thu, 19 Oct 2006 05:53:57 +0000 (UTC), danny burstein


You'll need either a Phase converter..
  (motor generator that spins up when the call button is depressed.)

http://www.kayind.com/products_application/MA.htm


or a soft start controller..

google
"soft start for 3 phase motors elevators"

http://www.mceinc.com/Products/Components/smartstart.html



See above..
   The application doesn't really call for all that current..
  So get rid of it and extend the motor life.


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