Re: [RE-wrenches] discharging Rolls batteries

[Bruce Geddes]

Re: [RE-wrenches] discharging Rolls batteriesHi Hugh.

Positive electrode:  PbO2 + 3H +HSO4 + 2e = PbSO4 + 2H2O  (e= electron)

Negative electrode:  Pb + HSO4 = PbSO4 + H +2e

Sorry, I can't insert the superscript symbols to show electrical charge.  If it 
is confusing let me know and I will repost this with the charge in brackets 
following the ion.

In cold conditions the ion transfer rate slows so in effect the internal 
resistance of the cell rises.  It simply can't deliver the electrons under 
load.  If the electrons are taken out at a reduced rate then the Vdrop of the 
"internal resistance" is lowered and the cell terminal voltage stays up for 
longer.

So, to use your analogy of the bank, in cold weather the money counters operate 
more slowly and if the temperature rises they return to normal speed.  The 
money is still there, it is just the rate at which it comes out that varies.  
In cold weather the counters simply won't deliver as much before they say "my 
fingers are too cold, that's all you get today!"

Bruce Geddes
PowerOn
  - Original Message - 
  From: Hugh 
  To: RE-wrenches 
  Sent: Saturday, January 16, 2010 12:25 PM
  Subject: Re: [RE-wrenches] discharging Rolls batteries


  hi


  We know that batteries deliver less amphours at low temperature and at high 
currents.  Volts drop quicker.  That's my starting point.  My question that I 
still do not hear an answer to is this:


  If the battery is a bank account and its harder to get the money out in cold 
weather and when you want to get your hands on a lot at once...  Does this 
actually mean that some of the money gets lost?  What happens to it?  Is it 
perhaps available later when the bank warms up or the demand gets less hectic?  
Is there really less money in there or does it just seem like less due to the 
conditions?


  I notice that Ah capacity is actually defined as how much Amphours you can 
get out before the battery reaches a certain terminal voltage.  I am wondering 
whether it is the ability to maintain voltage that is the limiting factor 
whereas the chemicals in there can still deliver amphours, given  the right 
temperature and time later.  You can certainly see recovery take place when a 
battery warms up and/or operates on lighter loads.


  One last time what happens to the chemicals (lead and lead oxide) that 
represent Amphours of charge in the battery plates?  For me this is a little 
bit like current of 10 amps entering one end of  a piece of wire and only 9 
amps coming out the other end.  I understand that the volts go down due to 
voltage drop (in this analogy) but loss of current is entirely a different 
matter.


  Thanks for any help with this rather obscure question.


  Hugh


A lead-acid battery is an electro-chemical processor (just like you and 
other living things). When you and your battery are cold or hot, performance 
changes because the chemical process is affected by temperature. Cold equals 
sluggish chemical reaction, reduces the capacity to perform work, and affects 
battery performance linearly. Battery chemistry is well understood. When I get 
some time, I'll google for temperature-based formulas and charts unless someone 
else posts the links first.

  - Original Message -
  From: Hugh
  To: RE-wrenches
  Sent: Friday, January 15, 2010 12:02 AM
  Subject: Re: [RE-wrenches] discharging Rolls batteries


  Hi Jamie,




Remember, as batteries cool actual capacity is reduced, so if 200AH is 
50% @ 25C it is significantly more than 50% @ 5C.   Thus, you are discharging 
more deeply.



  But earlier you put it this way:


  Regarding temperature effects on capacity, earlier responses are spot 
on as the lower capacity is totally as a result of slower reaction times as a 
result of lower temperatures.  



  There is an issue here that I need to understand better.  You state that 
a battery has lower capacity in low temperatures.  Suppose you take a fully 
charged, 400 Ah battery and cool it down to -5 degrees C where according to our 
numbers it will only have 80% of its nominal capacity.  You then remove 160 Ah 
(say 10 amps for 16 hours).  It will then be 50% discharged.  Now warm it up 
again to 20 degrees or whatever.  My question is: will you only have 200 
amphours left in it now?  And if so, what happened to the other 40 amphours?  
Does low temperature operation actually lose amphours, or is it just more 
sluggish?  What is the chemical explanation for the lost amphours?


  I understand batteries as a chemical process of converting amphours into 
chemical changes.  I assume that a given amount of electrical charge converts a 
given amount of lead into lead sulphate (and likewise) back again.  I 
understand that cooling will make this process less efficient and thereby 
result in a rise in charging voltage and a drop in discharging voltage.  But 
does a low temperature actually mean that a given amount of lead be

Re: [RE-wrenches] discharging Rolls batteries

[Hugh]

Hi Bruce,

At 22:58 +1300 16/1/10, Bruce Geddes wrote:
in cold weather the money counters operate more slowly and if the 
temperature rises they return to normal speed.  The money is still 
there,



Yes but if that is the case then the actual capacity is not affected 
by temperature - just the ability to deliver.  I would like to think 
it's that simple, but in reality I suspect that there is some loss of 
amphours under these conditions.  I am not yet clear about the 
mechanism, but I suspect that there is more to it than just a 
'volt-drop' style explanation such as you offer below.


As far as I understand it, there are two losses: one of voltage due 
to internal resistance and chemical 'sluggishness' and another actual 
loss of capacity in amphours ( getting less amphours out of the 
battery than you put in).  I am trying to establish what happens to 
those missing amphours, and also to what extent they actually are 
missing and to what extent they are just rendered inaccessible by the 
decision to end the discharge at a certain voltage which in turn is 
affected by the previous 'volt-dop' issues.


If it were really just a case of the bank tellers having cold fingers 
then it would seem reasonable to hammer the battery down to a much 
lower voltage in the confident knowledge that we are still only 
taking out 50% of the capacity as enshrined as 'good practice'. 
however if some of the cash has actually got lost (where to?) then it 
is nt legitimate to hit the battery bank for more cash in this way.


I haven't yet heard from any Wrench what actual voltages they would 
use to set the LBCO or the genstart on an Outback (or an SW), but one 
has told me off-list that it's a negotiation with the client.  Fair 
enough but what are the numbers used in the negotiation, and are they 
temperature dependant?


Thanks, Joel for the reading matter which I am working on!  I hope to 
become wiser in due course.


best

Hugh


At 17:45 -0800 15/1/10, Joel  Davidson wrote:


Some charge energy is lost in heat and some in coulombic efficiency.
There are educational powerpoints, papers and other information 
about batteries on the internet.
See 
http://en.wikipedia.org/wiki/Faraday_efficiency

and http://www.mpoweruk.com/soc.htm
and 
http://web.mit.edu/mit_energy/resources/iap/MatSciOfRenewEnergy_Lecture2_Batteries_2006.pdf
and 
http://ecee.colorado.edu/~ecen4517/materials/Battery.pdf
and 
http://users.ece.utexas.edu/~kwasinski/EE394V_DG_Fall2008_Week5%20part2.ppt#1
and for info about long series strings of batteries see 
http://www.battcon.com/PapersFinal2004/SymonsPaper2004.pdf






Bruce:

Hi Hugh.

Positive electrode:  PbO2 + 3H +HSO4 + 2e = PbSO4 + 2H2O  (e= electron)

Negative electrode:  Pb + HSO4 = PbSO4 + H +2e

Sorry, I can't insert the superscript symbols to show electrical 
charge.  If it is confusing let me know and I will repost this with 
the charge in brackets following the ion.


In cold conditions the ion transfer rate slows so in effect the 
internal resistance of the cell rises.  It simply can't deliver the 
electrons under load.  If the electrons are taken out at a reduced 
rate then the Vdrop of the "internal resistance" is lowered and the 
cell terminal voltage stays up for longer.


So, to use your analogy of the bank, in cold weather the money 
counters operate more slowly and if the temperature rises they 
return to normal speed.  The money is still there, it is just the 
rate at which it comes out that varies.  In cold weather the 
counters simply won't deliver as much before they say "my fingers 
are too cold, that's all you get today!"


Bruce Geddes
PowerOn

- Original Message -
From: Hugh
To: RE-wrenches
Sent: Saturday, January 16, 2010 12:25 PM
Subject: Re: [RE-wrenches] discharging Rolls batteries

hi

We know that batteries deliver less amphours at low temperature and 
at high currents.  Volts drop quicker.  That's my starting point. 
My question that I still do not hear an answer to is this:


If the battery is a bank account and its harder to get the money out 
in cold weather and when you want to get your hands on a lot at 
once...  Does this actually mean that some of the money gets lost? 
What happens to it?  Is it perhaps available later when the bank 
warms up or the demand gets less hectic?  Is there really less money 
in there or does it just seem like less due to the conditions?


I notice that Ah capacity is actually defined as how much Amphours 
you can get out before the battery reaches a certain terminal 
voltage.  I am w

[RE-wrenches] enphase and racks

[North Texas Renewable Energy Inc]

Wrenches,
The front page of the vol 2 #12 issue of Solar Industry magazine is a very
candid article on micro inverters, primarily the Enphase. Enphase input
directed at installers may differ from their peer review simply because
other inverter mfgrs can dissect and test their competitors products to a
much more precise degree than you or I.
Enphase and other mfgrs makes several recommendations that may influence the
installers design/install process, and maybe even the decision whether to
use their product.
regards

Jim Duncan
North Texas Renewable Energy
Since 1993
817.917.0527
ntrei.com






  From: Erika M. Weliczko 
  Subject: [RE-wrenches] enphase and racks
  To: "'RE-wrenches'" 
  Date: Friday, January 15, 2010, 7:03 PM


  Any thoughts on which rack hardware is most and least conducive to hosting
enphase inverters?



  TIA,

  Erika
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Re: [RE-wrenches] Enphase 210s

[Marv Dargatz]

And Sunpower.  But, they're not on the list
http://www.enphaseenergy.com/downloads/Enphase_Module_Compatibility_List.pdf
because Sunpower has not officially endorsed their use with Enphase.

We should probably take any further discussion off list.

See ya!

Marv
707 763-4784  x7016



Marco Mangelsdorf wrote:

  
  
  

  
  Are the Enphase 210s only compatible with the
Sanyo mods?
   
  Thanks,
  marco
   
  
  

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Re: [RE-wrenches] discharging Rolls batteries

[Darryl Thayer]

Hi Hugh I am copying you and wrenches as some of my posts have not shown up.
The way I look at it is:  A charged battery has some number of molecules of 
Ions? each carry 2 electrons.  That is you store of Amp-hours, 6.25x10^18 
electrons make 1 amp-sec.  Now at rest and 25 C the electrons want to excape at 
2.1 volts per cell the voltage times the charge is the energy.  and if you 
charge slowly and discharge slowly one amp hour in should equal 1 amp hour out. 
 If you charge fast the ions cannot line up fastenough to collect their 
electrons and the voltage rises and some of the electrons make H2 and O2, 
causing water loss. You are charging at higher voltage than you will ever get 
out, and wasting both amp-hrs and voltage ie wasting energy. (some electrons 
make H2SO4 and some make H2 and O2) 

Now for Discharge: The way you get amp-hrs is the ions give up theie electrons. 
If the battery is cold the the Ions can not move very fast, and you have to 
force them, by using part of their desire to rid themselves of their electrons 
and the voltage drops.  (Now it also depends upon the distance the Ions have to 
move, so when you first start discharge the voltage is higher and after a while 
the voltage falls do to a lack of Ions near the plates called hysterises) The 
amp-hrs are there but the watt-hrs are not.  The watt-hrs you can get out 
depends upon the voltage and amp-hrs.  The voltage as we see depends upon the 
discharge rate, it also depends upon hysterisis. 

In my solar class I have the students measure hystersis at 25 C and slow rates. 
 

As to your important question can the LVCO be set and what should it be set 
at?. It is to complicated and I think the SOC method should be best.   



--- On Sat, 1/16/10, Hugh  wrote:

> From: Hugh 
> Subject: Re: [RE-wrenches] discharging Rolls batteries
> To: "RE-wrenches" 
> Date: Saturday, January 16, 2010, 7:04 AM
> 
> Re: [RE-wrenches] discharging Rolls
> batteries 
> Hi Bruce,
> 
> 
> At 22:58 +1300 16/1/10, Bruce Geddes wrote:
> in cold
> weather the money counters operate more slowly and if the
> temperature
> rises they return to normal speed.  The money is still
> there,
> 
> 
> 
> 
> Yes but if that is the case then the actual capacity
> is not
> affected by temperature - just the ability to
> deliver.  I would
> like to think it's that simple, but in reality I
> suspect that there is
> some loss of amphours under these conditions.  I am
> not yet clear
> about the mechanism, but I suspect that there is more to it
> than just
> a 'volt-drop' style explanation such as you offer
> below.
> 
> 
> As far as I understand it, there are two losses: one
> of voltage
> due to internal resistance and chemical
> 'sluggishness' and another
> actual loss of capacity in amphours ( getting less amphours
> out of the
> battery than you put in).  I am trying to establish
> what happens
> to those missing amphours, and also to what extent they
> actually are
> missing and to what extent they are just rendered
> inaccessible by the
> decision to end the discharge at a certain voltage which in
> turn is
> affected by the previous 'volt-dop' issues.
> 
> 
> If it were really just a case of the bank tellers
> having cold
> fingers then it would seem reasonable to hammer the battery
> down to a
> much lower voltage in the confident knowledge that we are
> still only
> taking out 50% of the capacity as enshrined as 'good
> practice'. 
> however if some of the cash has actually got lost (where
> to?) then it
> is nt legitimate to hit the battery bank for more cash in
> this
> way.
> 
> 
> I haven't yet heard from any Wrench what actual
> voltages they
> would use to set the LBCO or the genstart on an Outback (or
> an SW),
> but one has told me off-list that it's a negotiation
> with the client. 
> Fair enough but what are the numbers used in the
> negotiation, and are
> they temperature dependant?
> 
> 
> Thanks, Joel for the reading matter which I am working
> on! 
> I hope to become wiser in due course.
> 
> 
> best
> 
> 
> Hugh
> 
> 
> 
> 
> At 17:45 -0800 15/1/10, Joel  Davidson
> wrote:
> 
> 
> Some charge
> energy is lost in heat and some in coulombic
> efficiency.
> There are educational powerpoints,
> papers and
> other information about batteries on the
> internet.
> See http://en.wikipedia.org/wiki/Faraday_efficiency
> 
> and http://www.mpoweruk.com/soc.htm
> and 
> http://web.mit.edu/mit_energy/resources/iap/MatSciOfRenewEnergy_Lecture2_Batteries_2006.pdf
> and http://ecee.colorado.edu/~ecen4517/materials/Battery.pdf
> 
> and 
> http://users.ece.utexas.edu/~kwasinski/EE394V_DG_Fall2008_Week5%20part2.ppt#1
> and for info
> about long series strings of batteries see 
> http://www.battcon.com/PapersFinal2004/SymonsPaper2004.pdf
> 
>  
>  
> 
> 
> 
> 
> Bruce:
> Hi
> Hugh.
>  
> Positive
> electrode:  PbO2 + 3H +HSO4 +
> 2e =
> PbSO4 + 2H2O  (e=
> electron)
>  
> Negative
> electrode:  Pb + HSO4 =
> PbSO4 + H
> +2e
>  
> Sorry, I
> can't insert the superscrip

Re: [RE-wrenches] discharging Rolls batteries

[Joel Davidson]

Re: [RE-wrenches] discharging Rolls batteriesA battery is an open system. Heat 
is lost. 2nd law of themodynamics. See 
http://theory.uwinnipeg.ca/mod_tech/node70.html

  - Original Message - 
  From: Hugh 
  To: RE-wrenches 
  Sent: Saturday, January 16, 2010 5:04 AM
  Subject: Re: [RE-wrenches] discharging Rolls batteries


  Hi Bruce,


  At 22:58 +1300 16/1/10, Bruce Geddes wrote:
in cold weather the money counters operate more slowly and if the 
temperature rises they return to normal speed.  The money is still there,




  Yes but if that is the case then the actual capacity is not affected by 
temperature - just the ability to deliver.  I would like to think it's that 
simple, but in reality I suspect that there is some loss of amphours under 
these conditions.  I am not yet clear about the mechanism, but I suspect that 
there is more to it than just a 'volt-drop' style explanation such as you offer 
below.


  As far as I understand it, there are two losses: one of voltage due to 
internal resistance and chemical 'sluggishness' and another actual loss of 
capacity in amphours ( getting less amphours out of the battery than you put 
in).  I am trying to establish what happens to those missing amphours, and also 
to what extent they actually are missing and to what extent they are just 
rendered inaccessible by the decision to end the discharge at a certain voltage 
which in turn is affected by the previous 'volt-dop' issues.


  If it were really just a case of the bank tellers having cold fingers then it 
would seem reasonable to hammer the battery down to a much lower voltage in the 
confident knowledge that we are still only taking out 50% of the capacity as 
enshrined as 'good practice'.  however if some of the cash has actually got 
lost (where to?) then it is nt legitimate to hit the battery bank for more cash 
in this way.


  I haven't yet heard from any Wrench what actual voltages they would use to 
set the LBCO or the genstart on an Outback (or an SW), but one has told me 
off-list that it's a negotiation with the client.  Fair enough but what are the 
numbers used in the negotiation, and are they temperature dependant?


  Thanks, Joel for the reading matter which I am working on!  I hope to become 
wiser in due course.


  best


  Hugh




  At 17:45 -0800 15/1/10, Joel  Davidson wrote:


Some charge energy is lost in heat and some in coulombic efficiency.
There are educational powerpoints, papers and other information about 
batteries on the internet.
See http://en.wikipedia.org/wiki/Faraday_efficiency
and http://www.mpoweruk.com/soc.htm
and 
http://web.mit.edu/mit_energy/resources/iap/MatSciOfRenewEnergy_Lecture2_Batteries_2006.pdf
and http://ecee.colorado.edu/~ecen4517/materials/Battery.pdf
and 
http://users.ece.utexas.edu/~kwasinski/EE394V_DG_Fall2008_Week5%20part2.ppt#1
and for info about long series strings of batteries see 
http://www.battcon.com/PapersFinal2004/SymonsPaper2004.pdf





  Bruce:
Hi Hugh.

Positive electrode:  PbO2 + 3H +HSO4 + 2e = PbSO4 + 2H2O  (e= electron)

Negative electrode:  Pb + HSO4 = PbSO4 + H +2e

Sorry, I can't insert the superscript symbols to show electrical charge.  
If it is confusing let me know and I will repost this with the charge in 
brackets following the ion.

In cold conditions the ion transfer rate slows so in effect the internal 
resistance of the cell rises.  It simply can't deliver the electrons under 
load.  If the electrons are taken out at a reduced rate then the Vdrop of the 
"internal resistance" is lowered and the cell terminal voltage stays up for 
longer.

So, to use your analogy of the bank, in cold weather the money counters 
operate more slowly and if the temperature rises they return to normal speed.  
The money is still there, it is just the rate at which it comes out that 
varies.  In cold weather the counters simply won't deliver as much before they 
say "my fingers are too cold, that's all you get today!"

Bruce Geddes
PowerOn

  - Original Message -
  From: Hugh
  To: RE-wrenches
  Sent: Saturday, January 16, 2010 12:25 PM
  Subject: Re: [RE-wrenches] discharging Rolls batteries


  hi


  We know that batteries deliver less amphours at low temperature and at 
high currents.  Volts drop quicker.  That's my starting point.  My question 
that I still do not hear an answer to is this:


  If the battery is a bank account and its harder to get the money out in 
cold weather and when you want to get your hands on a lot at once...  Does this 
actually mean that some of the money gets lost?  What happens to it?  Is it 
perhaps available later when the bank warms up or the demand gets less hectic?  
Is there really less money in there or does it just seem like less due to the 
conditions?


  I notice that Ah capacity is actually defined as how much Amphours you 
can get out before the battery reaches a ce

[RE-wrenches] kW/MW v. kWh/MWh

[Marco Mangelsdorf]

I'm reading a piece on energy storage in the latest issue of Distributed
Energy mag.

 

The writer, Lyn Corum, repeatedly refers to the capacity of storage mediums
(thermal, compressed air, flywheel, battery) in kW and MW terms.

 

Heck, even my friends at Beacon Power refer to their flywheel systems in MW
terms.

 

Am I missing something here?  Shouldn't all references to energy storage be
in kWh and MWh terms?

 

Or am I experiencing a d'oh! moment?

 

Marco

ProVision Solar

 

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Re: [RE-wrenches] discharging Rolls batteries

[Hugh]

OK I have been studying the literature list given me by Joel.  I did 
study all of this theory stuff back in the 1970s when I first got 
into this stand-alone windpower stuff, but it was good to go over it 
again, especially with my new enquiry.


I also have three fairly clear personal answers to my question "Is 
there an actual loss of amphours in cold weather or is the battery 
just not so good at delivering?"  The following answers indicate that 
the amphours are still there, but the loss of performance results in 
a loss of voltage that makes the battery appear to be discharged 
prematurely.



At 15:12 -0400 14/1/10, James Surrette wrote:


Regarding temperature effects on capacity, earlier responses are 
spot on as the lower capacity is totally as a result of slower 
reaction times as a result of lower temperatures.  



At 22:58 +1300 16/1/10, Bruce Geddes wrote:
 to use your analogy of the bank, in cold weather the money counters 
operate more slowly and if the temperature rises they return to 
normal speed.  The money is still there, it is just the rate at 
which it comes out that varies.


At 09:46 -0800 16/1/10, Darryl Thayer wrote:

Now for Discharge: .  The amp-hrs are there but the watt-hrs are not.



OK so if the battery is not actually discharged but is operating at a 
lower voltage due to lower temperature, then it seems to make sense 
to use a lower cut-off voltage.  And people who fly their systems by 
the SOC meter alone will not even be aware of the voltage, and will 
not care that it drops below the normal range.  So I think I now have 
the answer I was looking for there.  Low battery threshold voltages 
should be temperature compensated (although in the opposite direction 
to charging 'bulk' or 'absorption' set-points).


I don't know if anyone is in the mood to take this battery study 
further?  I'd like to talk about Peukert's Law next.  It has some 
similarities.


According to Peukert's law (and manufacturers' data bears this out 
well) the capacity of a battery depends on the rate of discharge. 
Everyone who knows anything about batteries knows that the capacity 
is specified at a certain rate whether it be C20 for a 20 hour 
discharge or whatever.  And the capacity at 100 hours (C100) is about 
33% higher than the capacity at the 20 hour rate.  If you look at the 
way this is measured though, it is based on running the battery down 
to a chosen 'discharge limit' voltage.  And I have not heard anything 
from Wrenches nor seen anything in the literature to suggest that the 
battery discharged in 20 hours has actually lost any amphours 
compared to the 100 hours one.  So it appears to me that if you give 
it a rest and then start discharging it again, but now at the 100 
hour rate you could still get another 33% extra capacity.


Well now.  I don't expect to get away with saying that.  But why not? 
I can't find any evidence that it is not true.


That's probably enough for now, if anyone has bothered to read this 
far.  Thanks for any reactions.

--
Hugh Piggott

Scoraig Wind Electric
Scotland
http://www.scoraigwind.co.uk___
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Re: [RE-wrenches] kW/MW v. kWh/MWh

[Marv Dargatz]

Marco,

You are right on with your observation.  It is extremely frustrating
when "industry experts" in a technical industry use the wrong technical
terms.

rant ON

Another example; the improper use of "panel" when the intended meaning
is "module".  Check 690.2 for the definitions.  Just wait 'til ac
modules are a reality.  

"Hey, take a look at the ac panel, maybe that's the issue".  

"Oh, you mean the load center?" 

"No, the panel".
 
"Oh, you're talking about the ac module."

"Yah, that's what I meant."

"Why didn't you say so in the first place?"

By the way, you can also take your car to a mechanic and he might say,
"Raise the hood.  Let's take a look at the motor."

To which you could reply, "I'm not having a problem with the heater,
air conditioner, or electric windows.  The ENGINE is running rough,
though."

rant OFF

Phew.  Do I ever feel better!



See ya!

Marv
707 763-4784  x7016



Marco Mangelsdorf wrote:

  
  
  

  
  I’m reading a piece on energy storage in the
latest
issue of Distributed Energy mag.
   
  The writer, Lyn Corum, repeatedly refers to the
capacity of
storage mediums (thermal, compressed air, flywheel, battery) in kW and
MW
terms.
   
  Heck, even my friends at Beacon Power refer to
their flywheel
systems in MW terms.
   
  Am I missing something here?  Shouldn’t all
references
to energy storage be in kWh and MWh terms?
   
  Or am I experiencing a d’oh! moment?
   
  Marco
  ProVision Solar
   
  
  

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[RE-wrenches] EnPhase/Racking Best Fit

[solarepiphany]

grees C where according to our 
numbers it will only have 80% of its nominal capacity.  You then remove 160 Ah 
(say 10 amps for 16 hours).  It will then be 50% discharged.  Now warm it up 
again to 20 degrees or whatever.  My question is: will you only have 200 
amphours left in it now?  And if so, what happened to the other 40 amphours?  
Does low temperature operation actually lose amphours, or is it just more 
sluggish?  What is the chemical explanation for the lost amphours?


  I understand batteries as a chemical process of converting amphours into 
chemical changes.  I assume that a given amount of electrical charge converts a 
given amount of lead into lead sulphate (and likewise) back again.  I 
understand that cooling will make this process less efficient and thereby 
result in a rise in charging voltage and a drop in discharging voltage.  But 
does a low temperature actually mean that a given amount of lead being 
converted to sulphate actually give you less amphours electrically?


  (I have similar questions in relation to Peukert's equation where high 
discharge rates impact on the amphour capacity.  The capacity apparently 
'recovers' when the discharge rate is reduced.  To what extent is the capacity 
actually lost by using high discharge rates and to what extent is it just a 
voltage effect that impacts on the terminal voltage, rather than the actual 
chemical state of the battery?)


  I hope you can follow my descriptions.
  --
  Hugh Piggott

  Scoraig Wind Electric
  Scotland
  http://www.scoraigwind.co.uk


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-- 
Hugh Piggott

  Scoraig Wind Electric
  Scotland
  http://www.scoraigwind.co.uk


--


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End of RE-wrenches Digest, Vol 3, Issue 63
**
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Re: [RE-wrenches] kW/MW v. kWh/MWh

[Darryl Thayer]

H Marco
Yes both terms are important, but most of the time they are looking for power 
during the time it takes to fire a peaking plant generator.  It may take 10 to 
15 seconds, Also one of the big uses of storage for utilities is frequency 
stabilization, it is desirable to supply and absorb great quanities of power, 
in very short times.  Therefore they talk of kW and MW instead of kWh and MWh.

A local facility which uses batteries is 10 MW and 1 MWh 


Darryl

--- On Sat, 1/16/10, Marco Mangelsdorf  wrote:

> From: Marco Mangelsdorf 
> Subject: [RE-wrenches] kW/MW v. kWh/MWh
> To: "'RE-wrenches'" 
> Date: Saturday, January 16, 2010, 4:35 PM
> 
> 
> 
>  
>  
> 
> 
> 
> 
> 
> 
>  
> 
> 
> 
> I’m reading a piece on energy
> storage in the latest
> issue of Distributed Energy mag. 
> 
>    
> 
> The writer, Lyn Corum, repeatedly
> refers to the capacity of
> storage mediums (thermal, compressed air, flywheel,
> battery) in kW and MW
> terms. 
> 
>    
> 
> Heck, even my friends at Beacon Power
> refer to their flywheel
> systems in MW terms. 
> 
>    
> 
> Am I missing something here? 
> Shouldn’t all references
> to energy storage be in kWh and MWh terms? 
> 
>    
> 
> Or am I experiencing a d’oh!
> moment? 
> 
>    
> 
> Marco 
> 
> ProVision Solar 
> 
>    
> 
> 
> 
>  
> 
> 
> 
> -Inline Attachment Follows-
> 
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> 
> 


  
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Re: [RE-wrenches] kW/MW v. kWh/MWh

[Dan Fink]

Hello Marco.
No d'oh!
Your assessment is correct; you can't store kilowatts of power, you 
*can* store kilowatt hours of energy.
Author Lyn Corum might have slipped up a couple times in there and 
dropped an 'h' from the kw, but maybe not -- because when storing energy 
on a utility scale, the engineers are greatly concerned with how fast 
the energy can come in, and how fast they can send it out. So when they 
refer to a '50 kw flywheel storage unit,' that often means the max power 
coming in or out at any given instant.
In our (comparatively) puny end of the energy storage business, 
batteries, we rarely have to deal with the issue. Assuming our battery 
bank is big enough to keep the charge or discharge rate below C10, or 
even C1, we just stack more inverters.

DAN FINK



Marco Mangelsdorf wrote:
I’m reading a piece on energy storage in the latest issue of Distributed 
Energy mag.


 

The writer, Lyn Corum, repeatedly refers to the capacity of storage 
mediums (thermal, compressed air, flywheel, battery) in kW and MW terms.


 

Heck, even my friends at Beacon Power refer to their flywheel systems in 
MW terms.


 

Am I missing something here?  Shouldn’t all references to energy storage 
be in kWh and MWh terms?


 


Or am I experiencing a d’oh! moment?

 


Marco

ProVision Solar

 





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