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Redox batteries
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Jean-Marc Delaplace
science forum beginner


Joined: 11 Apr 2006
Posts: 5

PostPosted: Fri Jun 16, 2006 8:46 pm    Post subject: Redox batteries Reply with quote

I am currently trying to define what the appropriate battery would be
for a hybrid boat. I found information on Vanadium batteries, that
apparently are close to commercialization. Their biggest drawback is
apparently the low specific energy, but this is not very critical on a
boat. I also read about Cerium that could provide a higher energy density.
Does someone know about these? What is their future? Are the claimed
advantages of Vanadium batteries true?
In short, I would like to discuss the topic in all its aspects,
including hazard and ecologic risk.
For those who have no documentation but are chemists - which i am not -
I can supply them with information I got by writing to a company that is
currently developing a vanadium battery.
Jean-Marc
Back to top
Evgenij Barsukov
science forum Guru Wannabe


Joined: 09 May 2005
Posts: 137

PostPosted: Mon Jun 19, 2006 1:23 pm    Post subject: Re: Redox batteries Reply with quote

Jean-Marc Delaplace wrote:
Quote:
I am currently trying to define what the appropriate battery would be
for a hybrid boat. I found information on Vanadium batteries, that
apparently are close to commercialization. Their biggest drawback is
apparently the low specific energy, but this is not very critical on a
boat. I also read about Cerium that could provide a higher energy density.
Does someone know about these? What is their future? Are the claimed
advantages of Vanadium batteries true?
In short, I would like to discuss the topic in all its aspects,
including hazard and ecologic risk.
For those who have no documentation but are chemists - which i am not -
I can supply them with information I got by writing to a company that is
currently developing a vanadium battery.
Jean-Marc

From the technical point of view using vanadium battery on the boat
appear to be a good idea as specific energy is basically irrelevant.
But than why not use deep-cycle lead acid cells, as same argument
applies there.

Main issue with using vanadium flow battery in a boat is the possibility
of a leak. Soluble vanadium salts are toxic and the chance of damping a
ton of this solution into a picturesque bay killing all forms of life
for years to come appears scary.

Regards,
Evgenij
Back to top
Jean-Marc Delaplace
science forum beginner


Joined: 11 Apr 2006
Posts: 5

PostPosted: Mon Jun 19, 2006 4:52 pm    Post subject: Re: Redox batteries Reply with quote

You are right about the concern with the leaks. However, I still do not
know how toxic vanadium is for the environment. Of course, containment
measures should be taken in the design so as to avoid any spillage.

I want to answer your question about not using lead acid batteries. I
hope this will raise an interesting debate.

First, let me recall that my purpose is to build a hybrid propulsion
house boat. That is, a boat that will sometimes ride at top speed (15
km/h), sometimes at half speed (most canals are limited to 6 km/h) and
sometimes it will stay at a mooring for days.

The objective is to be energy-efficient. The energy source will be one
or more of the following:
-a diesel generator: 20 kW;
-photovoltaic cells: at most 1 kW peak;
-wind turbine: at most 500 W peak.

To achieve optimum fuel efficiency, the generator must be used near full
power exclusively. Then, the role of the battery is to buffer this
pulsed power source to deliver just as much power as needed when needed.

To save energy, using the generator should, as much as possible, be
avoided and power should come preferably from the sun and/or the wind.

This is where the lead-acid battery has two major drawbacks:

1) A lead-acid battery should always be fully charged, i.e. it should be
partially discharged for the shortest period of time possible, to
avoid the degradation process to come to play. This is not compatible
with waiting until sun or wind are available.

2) A lead acid battery must be charged using precise current rates
according to the state of charge. This is incompatible with the idea of
accumulating all and as much energy is available at a time, i.e. always
using the generator at nominal power.

3) Everyone knows that event with the utmost care, a lead acid battery
shall not withstand more than say 1,500 equivalent full-discharge cycles.

I think that vanadium batteries completely address these three points,
which make me hope they become available - and affordable - within a few
years.

Sorry to be lengthy but I would be very pleased to discuss these
arguments with as many people as possible.

Jean-Marc

Evgenij Barsukov wrote:
Quote:
Jean-Marc Delaplace wrote:

I am currently trying to define what the appropriate battery would be
for a hybrid boat. I found information on Vanadium batteries, that
apparently are close to commercialization. Their biggest drawback is
apparently the low specific energy, but this is not very critical on a
boat. I also read about Cerium that could provide a higher energy
density.
Does someone know about these? What is their future? Are the claimed
advantages of Vanadium batteries true?
In short, I would like to discuss the topic in all its aspects,
including hazard and ecologic risk.
For those who have no documentation but are chemists - which i am not
- I can supply them with information I got by writing to a company
that is currently developing a vanadium battery.
Jean-Marc


From the technical point of view using vanadium battery on the boat
appear to be a good idea as specific energy is basically irrelevant.
But than why not use deep-cycle lead acid cells, as same argument
applies there.

Main issue with using vanadium flow battery in a boat is the possibility
of a leak. Soluble vanadium salts are toxic and the chance of damping a
ton of this solution into a picturesque bay killing all forms of life
for years to come appears scary.

Regards,
Evgenij
Back to top
Roy Lewallen
science forum addict


Joined: 06 May 2005
Posts: 58

PostPosted: Mon Jun 19, 2006 7:11 pm    Post subject: Re: Redox batteries Reply with quote

Jean-Marc Delaplace wrote:
Quote:
. . .
I think that vanadium batteries completely address these three points,
which make me hope they become available - and affordable - within a few
years.

Sorry to be lengthy but I would be very pleased to discuss these
arguments with as many people as possible.

Without knowing anything at all about vanadium batteries, I can make the
following general observations:

1. Purveyors of new technologies are nearly always overoptimistic. This
improves their ability to attract investors and enhances stock price.

2. Nearly always, when a technology is introduced which solves the
problems in an older technology, it has has its own, new, problems and
limitations. They may not be apparent at first, but are discovered as
time goes by. This is why there's not just one kind of battery, and why
lead-acid batteries are still in very wide use more than 100 years after
their invention and in spite of the many, many other types which have
been developed since.

This new battery technology might prove to be the ideal solution to all
your problems. But I wouldn't bet on it, and I wouldn't put much time or
money into designing a system to accommodating them until they actually
exist and their real properties are known. And I wouldn't delay
launching my boat until they appear.

Roy Lewallen
Back to top
mumuusa@gmail.com
science forum beginner


Joined: 19 Sep 2005
Posts: 14

PostPosted: Tue Jun 20, 2006 12:50 pm    Post subject: Re: Redox batteries Reply with quote

Eventhough lot of battery technologies are poping up the current
established proven technology for Hybrid systems is NiMH. I recommend
NiMH.

M Moorthi
www.battery-consulting.com

Roy Lewallen wrote:
Quote:
Jean-Marc Delaplace wrote:
. . .
I think that vanadium batteries completely address these three points,
which make me hope they become available - and affordable - within a few
years.

Sorry to be lengthy but I would be very pleased to discuss these
arguments with as many people as possible.

Without knowing anything at all about vanadium batteries, I can make the
following general observations:

1. Purveyors of new technologies are nearly always overoptimistic. This
improves their ability to attract investors and enhances stock price.

2. Nearly always, when a technology is introduced which solves the
problems in an older technology, it has has its own, new, problems and
limitations. They may not be apparent at first, but are discovered as
time goes by. This is why there's not just one kind of battery, and why
lead-acid batteries are still in very wide use more than 100 years after
their invention and in spite of the many, many other types which have
been developed since.

This new battery technology might prove to be the ideal solution to all
your problems. But I wouldn't bet on it, and I wouldn't put much time or
money into designing a system to accommodating them until they actually
exist and their real properties are known. And I wouldn't delay
launching my boat until they appear.

Roy Lewallen
Back to top
Evgenij Barsukov
science forum Guru Wannabe


Joined: 09 May 2005
Posts: 137

PostPosted: Tue Jun 20, 2006 2:15 pm    Post subject: Re: Redox batteries Reply with quote

Jean-Marc Delaplace wrote:
Quote:
You are right about the concern with the leaks. However, I still do not
know how toxic vanadium is for the environment. Of course, containment
measures should be taken in the design so as to avoid any spillage.

I want to answer your question about not using lead acid batteries. I
hope this will raise an interesting debate.

First, let me recall that my purpose is to build a hybrid propulsion
house boat. That is, a boat that will sometimes ride at top speed (15
km/h), sometimes at half speed (most canals are limited to 6 km/h) and
sometimes it will stay at a mooring for days.

The objective is to be energy-efficient. The energy source will be one
or more of the following:
-a diesel generator: 20 kW;
-photovoltaic cells: at most 1 kW peak;
-wind turbine: at most 500 W peak.

To achieve optimum fuel efficiency, the generator must be used near full
power exclusively. Then, the role of the battery is to buffer this
pulsed power source to deliver just as much power as needed when needed.

To save energy, using the generator should, as much as possible, be
avoided and power should come preferably from the sun and/or the wind.

This is where the lead-acid battery has two major drawbacks:

1) A lead-acid battery should always be fully charged, i.e. it should be
partially discharged for the shortest period of time possible, to avoid
the degradation process to come to play. This is not compatible with
waiting until sun or wind are available.

This is true. However, once your boat is moored, what prevents you from
connecting a charger to it and charging the batteries to full?
Deep cycle batteries can tolerate even full discharge, as long as
they are recharged soon to prevent crystallization of PbSO4.

Quote:
2) A lead acid battery must be charged using precise current rates
according to the state of charge. This is incompatible with the idea of
accumulating all and as much energy is available at a time, i.e. always
using the generator at nominal power.

Lead Acid battery is one of the least sensitive to charging rates
(probably only cylindrical NiCd beats it in this respect, but they
are not available in right sizes). If you take the Lind book on
batteries, there are over 10 different charging methods described for
lead-acide, which have little in common. Which basically means, it does
not matter how to charge it as long as you do not cause
1) persistent extensive gasing
2) persistent undercharged condition (unsufficient voltage)

Occasional gasing is not harmful, and even good for the battery
(equalizes, mixes the electrolyte). So if you have short spikes
of charging, it is no problem.
More of a problem can be persistently low voltage (or current so low
that it is below self-discharge rate). But it is the matter of designing
your charger properly (e.g. having bust converter if voltage from
your generator/solar cells etc is not enough, and provide sufficient
power capability of your power generating equipment.

In fact I can turn the table here - vanadium flow battery is bound to
have low power capability/capacity ratio, because its electrode surface
is much smaller than any conventional battery. Low power applies both
for charging and discharging - so at high charging spikes it might
overvoltage and you would have to stop charging. At high load spikes it
might not be able to provide sufficient power, and your equipment will
shut-down.

Quote:
3) Everyone knows that event with the utmost care, a lead acid battery
shall not withstand more than say 1,500 equivalent full-discharge cycles.

Here vanadium flow might have advantages, but this is a big "might" as
this is a completely unproven technology.

Btw if we are talking graphite-foam electrodes that vanadium batteries
needs to employ to achieve high surface area electrodes and therefor
acceptable power capability, there have been a recent development in
lead-acid cells that also use carbon-foam electrodes to greatly increase
its longevity:
http://www.powermanagementdesignline.com/news/177101291
In both cases, the problem with graphite-foam being brittle would have
to be addressed.

Quote:

I think that vanadium batteries completely address these three points,
which make me hope they become available - and affordable - within a few
years.

My main concern (in addition to environmental) is power capability, that
I pointed out in the paragraph 2).

Regards,
Evgenij


Quote:

Sorry to be lengthy but I would be very pleased to discuss these
arguments with as many people as possible.

Jean-Marc

Evgenij Barsukov wrote:
Jean-Marc Delaplace wrote:

I am currently trying to define what the appropriate battery would be
for a hybrid boat. I found information on Vanadium batteries, that
apparently are close to commercialization. Their biggest drawback is
apparently the low specific energy, but this is not very critical on
a boat. I also read about Cerium that could provide a higher energy
density.
Does someone know about these? What is their future? Are the claimed
advantages of Vanadium batteries true?
In short, I would like to discuss the topic in all its aspects,
including hazard and ecologic risk.
For those who have no documentation but are chemists - which i am not
- I can supply them with information I got by writing to a company
that is currently developing a vanadium battery.
Jean-Marc


From the technical point of view using vanadium battery on the boat
appear to be a good idea as specific energy is basically irrelevant.
But than why not use deep-cycle lead acid cells, as same argument
applies there.

Main issue with using vanadium flow battery in a boat is the
possibility of a leak. Soluble vanadium salts are toxic and the chance
of damping a ton of this solution into a picturesque bay killing all
forms of life for years to come appears scary.

Regards,
Evgenij
Back to top
Jean-Marc Delaplace
science forum beginner


Joined: 11 Apr 2006
Posts: 5

PostPosted: Thu Jun 22, 2006 5:27 pm    Post subject: Re: Redox batteries Reply with quote

Evgenij Barsukov wrote:
Quote:
Jean-Marc Delaplace wrote:

You are right about the concern with the leaks. However, I still do
not know how toxic vanadium is for the environment. Of course,
containment measures should be taken in the design so as to avoid any
spillage.

I want to answer your question about not using lead acid batteries. I
hope this will raise an interesting debate.

First, let me recall that my purpose is to build a hybrid propulsion
house boat. That is, a boat that will sometimes ride at top speed (15
km/h), sometimes at half speed (most canals are limited to 6 km/h) and
sometimes it will stay at a mooring for days.

The objective is to be energy-efficient. The energy source will be one
or more of the following:
-a diesel generator: 20 kW;
-photovoltaic cells: at most 1 kW peak;
-wind turbine: at most 500 W peak.

To achieve optimum fuel efficiency, the generator must be used near
full power exclusively. Then, the role of the battery is to buffer
this pulsed power source to deliver just as much power as needed when
needed.

To save energy, using the generator should, as much as possible, be
avoided and power should come preferably from the sun and/or the wind.

This is where the lead-acid battery has two major drawbacks:

1) A lead-acid battery should always be fully charged, i.e. it should
be partially discharged for the shortest period of time possible, to
avoid the degradation process to come to play. This is not compatible
with waiting until sun or wind are available.


This is true. However, once your boat is moored, what prevents you from
connecting a charger to it and charging the batteries to full?
Deep cycle batteries can tolerate even full discharge, as long as
they are recharged soon to prevent crystallization of PbSO4.

2) A lead acid battery must be charged using precise current rates
according to the state of charge. This is incompatible with the idea
of accumulating all and as much energy is available at a time, i.e.
always using the generator at nominal power.


Lead Acid battery is one of the least sensitive to charging rates
(probably only cylindrical NiCd beats it in this respect, but they
are not available in right sizes). If you take the Lind book on
batteries, there are over 10 different charging methods described for
lead-acide, which have little in common. Which basically means, it does
not matter how to charge it as long as you do not cause
1) persistent extensive gasing
2) persistent undercharged condition (unsufficient voltage)


What do you mean with being little sensitive to charging rate?
Apparently you can charge a LA battery at C rate until 80% SOC, but the
remaining has to be charged at about C/10 ("finishing and equalizing").
This is where the benefit of hybrid propulsion is lost: whereas I could
charge 80% at full power of my generator, that is 0.8 h, to charge the
remaining 20% at C/10 would require running the generator at 1/10 its
power for 2 hours ! I would then spoil the efficiency advantage i was
planning stating that the generator need be used at full power only for
the best efficiency. If you consider that friction consumes more than
10% of the total engine torque, when you run an engine at 10% load it
consumes two times more oil than required, which mean half the expected
engine efficiency. In addition, you come into problems such as cylinder
glazing, etc.
In short, I think the constraint of slow charging over 80% ruins the
advantage of using a hybrid propulsion chain. This i why I think lead
acid is just not adequate for hybrid propulsion.


Quote:
Occasional gasing is not harmful, and even good for the battery
(equalizes, mixes the electrolyte). So if you have short spikes
of charging, it is no problem.
More of a problem can be persistently low voltage (or current so low
that it is below self-discharge rate). But it is the matter of designing
your charger properly (e.g. having bust converter if voltage from
your generator/solar cells etc is not enough, and provide sufficient
power capability of your power generating equipment.

In fact I can turn the table here - vanadium flow battery is bound to
have low power capability/capacity ratio, because its electrode surface
is much smaller than any conventional battery. Low power applies both
for charging and discharging - so at high charging spikes it might
overvoltage and you would have to stop charging. At high load spikes it
might not be able to provide sufficient power, and your equipment will
shut-down.

3) Everyone knows that event with the utmost care, a lead acid battery
shall not withstand more than say 1,500 equivalent full-discharge cycles.


Here vanadium flow might have advantages, but this is a big "might" as
this is a completely unproven technology.

Btw if we are talking graphite-foam electrodes that vanadium batteries
needs to employ to achieve high surface area electrodes and therefor
acceptable power capability, there have been a recent development in
lead-acid cells that also use carbon-foam electrodes to greatly increase
its longevity:
http://www.powermanagementdesignline.com/news/177101291
In both cases, the problem with graphite-foam being brittle would have
to be addressed.


I think that vanadium batteries completely address these three points,
which make me hope they become available - and affordable - within a
few years.


My main concern (in addition to environmental) is power capability, that
I pointed out in the paragraph 2).

Regards,
Evgenij



Sorry to be lengthy but I would be very pleased to discuss these
arguments with as many people as possible.

Jean-Marc

Evgenij Barsukov wrote:

Jean-Marc Delaplace wrote:

I am currently trying to define what the appropriate battery would
be for a hybrid boat. I found information on Vanadium batteries,
that apparently are close to commercialization. Their biggest
drawback is apparently the low specific energy, but this is not very
critical on a boat. I also read about Cerium that could provide a
higher energy density.
Does someone know about these? What is their future? Are the claimed
advantages of Vanadium batteries true?
In short, I would like to discuss the topic in all its aspects,
including hazard and ecologic risk.
For those who have no documentation but are chemists - which i am
not - I can supply them with information I got by writing to a
company that is currently developing a vanadium battery.
Jean-Marc



From the technical point of view using vanadium battery on the boat
appear to be a good idea as specific energy is basically irrelevant.
But than why not use deep-cycle lead acid cells, as same argument
applies there.

Main issue with using vanadium flow battery in a boat is the
possibility of a leak. Soluble vanadium salts are toxic and the
chance of damping a ton of this solution into a picturesque bay
killing all forms of life for years to come appears scary.

Regards,
Evgenij
Back to top
Evgenij Barsukov
science forum Guru Wannabe


Joined: 09 May 2005
Posts: 137

PostPosted: Thu Jun 22, 2006 8:37 pm    Post subject: Re: Redox batteries Reply with quote

Jean-Marc Delaplace wrote:
Quote:
Evgenij Barsukov wrote:
Jean-Marc Delaplace wrote:

You are right about the concern with the leaks. However, I still do
not know how toxic vanadium is for the environment. Of course,
containment measures should be taken in the design so as to avoid any
spillage.

I want to answer your question about not using lead acid batteries. I
hope this will raise an interesting debate.

First, let me recall that my purpose is to build a hybrid propulsion
house boat. That is, a boat that will sometimes ride at top speed (15
km/h), sometimes at half speed (most canals are limited to 6 km/h)
and sometimes it will stay at a mooring for days.

The objective is to be energy-efficient. The energy source will be
one or more of the following:
-a diesel generator: 20 kW;
-photovoltaic cells: at most 1 kW peak;
-wind turbine: at most 500 W peak.

To achieve optimum fuel efficiency, the generator must be used near
full power exclusively. Then, the role of the battery is to buffer
this pulsed power source to deliver just as much power as needed when
needed.

To save energy, using the generator should, as much as possible, be
avoided and power should come preferably from the sun and/or the wind.

This is where the lead-acid battery has two major drawbacks:

1) A lead-acid battery should always be fully charged, i.e. it should
be partially discharged for the shortest period of time possible, to
avoid the degradation process to come to play. This is not compatible
with waiting until sun or wind are available.


This is true. However, once your boat is moored, what prevents you from
connecting a charger to it and charging the batteries to full?
Deep cycle batteries can tolerate even full discharge, as long as
they are recharged soon to prevent crystallization of PbSO4.

2) A lead acid battery must be charged using precise current rates
according to the state of charge. This is incompatible with the idea
of accumulating all and as much energy is available at a time, i.e.
always using the generator at nominal power.


Lead Acid battery is one of the least sensitive to charging rates
(probably only cylindrical NiCd beats it in this respect, but they
are not available in right sizes). If you take the Lind book on
batteries, there are over 10 different charging methods described for
lead-acide, which have little in common. Which basically means, it
does not matter how to charge it as long as you do not cause
1) persistent extensive gasing
2) persistent undercharged condition (unsufficient voltage)


What do you mean with being little sensitive to charging rate?
Apparently you can charge a LA battery at C rate until 80% SOC, but the
remaining has to be charged at about C/10 ("finishing and equalizing").
This is where the benefit of hybrid propulsion is lost: whereas I could
charge 80% at full power of my generator, that is 0.8 h, to charge the
remaining 20% at C/10 would require running the generator at 1/10 its
power for 2 hours !

You are applying this formula too formally. The reason for the waiting
period during last 20% SOC has really nothing to do with SOC itself,
it has to do with waiting for diffusion to equalize concentrations
and therefore it only applies to the case of continuous charge.

In hybrid application most of the charging is done opportunistically,
e.g. when primary energy generator has some extra energy not used for
propulsion. So first of all charging would be way below 1C rate
(most likely ~C/10), second it would not be continuous, which eliminates
the need for any waiting period to reach 100% SOC. If you charge bursts
from 1C to C/100, that average to C/10 over time, you do not need to
do any waiting at the end, you will end up with 100% charged battery.

Same applies also to continuous charge at low rate.

Lead acid batteries have been used in hybrid applications (e.g. diesel
submarines) for almost a century and are still being used.


Quote:
I would then spoil the efficiency advantage i was
planning stating that the generator need be used at full power only for
the best efficiency. If you consider that friction consumes more than
10% of the total engine torque, when you run an engine at 10% load it
consumes two times more oil than required, which mean half the expected
engine efficiency. In addition, you come into problems such as cylinder
glazing, etc.

Even if charging is not opportunistic but continuous, problem of
efficiency can be easily taken care of by switching off the generator
completely to give time for concentration equalization, and than turning
it back ON periodically.

Speaking about 1C rate (either charge or discharge), vanadium flow
battery would require gigantic electrodes and flow rate to come anywhere
close to this rate. All present implementations that I have seen are
working in C/10 to C/100 rates.

Quote:
In short, I think the constraint of slow charging over 80% ruins the
advantage of using a hybrid propulsion chain. This i why I think lead
acid is just not adequate for hybrid propulsion.

As shown before, this constraint appears only on paper. Correct
understanding of the reasons of this charging recommendation shows that
it does not apply to this application.

Regards,
Evgenij
Back to top
Jean-Marc Delaplace
science forum beginner


Joined: 11 Apr 2006
Posts: 5

PostPosted: Thu Jun 22, 2006 9:31 pm    Post subject: Re: Redox batteries Reply with quote

Evgenij,

thank you for your documented and patient answer.
I would like to discuss specifically an operating mode that is probably
not used in sea boats, but that is so likely in river boats that I am
very concerned with it.
When you say that charging will use a fraction of the power of the
generator because most of it is used by the propulsion, you are right
when you consider riding at nominal (=full) speed.
For a river and canal boat, this corresponds to about 15 km/h. However,
on many canals, the speed limit is 6 km/h. If you consider that the
required power is proportional to the cube of the speed, this means
using (6/15)^3 = 0.064 of the nominal power. Let's say 10%.
In this case, what I need is having the generator run for one hour at
full power, then quietly ride using the batteries only for ten hours.
This is where I see a problem with the charging rate of the top of the
SOC. Do you have a proposal?

Next, as far as vanadium batteries, you know that being flow cells, the
battery capacity and the battery power are totally decoupled. So you can
have a cell stack tailored for a certain power (in my case 20 kW), and
have the tanks sized for a certain energy (in my case 20 kWh).
I have discussed the features of vanadium batteries with
Rob Blackwell
Business Development Manager
Pinnacle VRB Limited
and he gave me figures that apparently make sense. Of course, as you
emphasize, my guess is that most of what they boast of is true, but they
keep discreet on possible serious drawbacks that maybe they already know
- and maybe they do not even suspect yet !

best regards,
Jean-Marc

Evgenij Barsukov wrote:
Quote:
Jean-Marc Delaplace wrote:

Evgenij Barsukov wrote:

Jean-Marc Delaplace wrote:

You are right about the concern with the leaks. However, I still do
not know how toxic vanadium is for the environment. Of course,
containment measures should be taken in the design so as to avoid
any spillage.

I want to answer your question about not using lead acid batteries.
I hope this will raise an interesting debate.

First, let me recall that my purpose is to build a hybrid propulsion
house boat. That is, a boat that will sometimes ride at top speed
(15 km/h), sometimes at half speed (most canals are limited to 6
km/h) and sometimes it will stay at a mooring for days.

The objective is to be energy-efficient. The energy source will be
one or more of the following:
-a diesel generator: 20 kW;
-photovoltaic cells: at most 1 kW peak;
-wind turbine: at most 500 W peak.

To achieve optimum fuel efficiency, the generator must be used near
full power exclusively. Then, the role of the battery is to buffer
this pulsed power source to deliver just as much power as needed
when needed.

To save energy, using the generator should, as much as possible, be
avoided and power should come preferably from the sun and/or the wind.

This is where the lead-acid battery has two major drawbacks:

1) A lead-acid battery should always be fully charged, i.e. it
should be partially discharged for the shortest period of time
possible, to avoid the degradation process to come to play. This is
not compatible with waiting until sun or wind are available.



This is true. However, once your boat is moored, what prevents you from
connecting a charger to it and charging the batteries to full?
Deep cycle batteries can tolerate even full discharge, as long as
they are recharged soon to prevent crystallization of PbSO4.

2) A lead acid battery must be charged using precise current rates
according to the state of charge. This is incompatible with the idea
of accumulating all and as much energy is available at a time, i.e.
always using the generator at nominal power.



Lead Acid battery is one of the least sensitive to charging rates
(probably only cylindrical NiCd beats it in this respect, but they
are not available in right sizes). If you take the Lind book on
batteries, there are over 10 different charging methods described for
lead-acide, which have little in common. Which basically means, it
does not matter how to charge it as long as you do not cause
1) persistent extensive gasing
2) persistent undercharged condition (unsufficient voltage)


What do you mean with being little sensitive to charging rate?
Apparently you can charge a LA battery at C rate until 80% SOC, but
the remaining has to be charged at about C/10 ("finishing and
equalizing"). This is where the benefit of hybrid propulsion is lost:
whereas I could charge 80% at full power of my generator, that is 0.8
h, to charge the remaining 20% at C/10 would require running the
generator at 1/10 its power for 2 hours !


You are applying this formula too formally. The reason for the waiting
period during last 20% SOC has really nothing to do with SOC itself,
it has to do with waiting for diffusion to equalize concentrations
and therefore it only applies to the case of continuous charge.

In hybrid application most of the charging is done opportunistically,
e.g. when primary energy generator has some extra energy not used for
propulsion. So first of all charging would be way below 1C rate
(most likely ~C/10), second it would not be continuous, which eliminates
the need for any waiting period to reach 100% SOC. If you charge bursts
from 1C to C/100, that average to C/10 over time, you do not need to
do any waiting at the end, you will end up with 100% charged battery.

Same applies also to continuous charge at low rate.

Lead acid batteries have been used in hybrid applications (e.g. diesel
submarines) for almost a century and are still being used.


I would then spoil the efficiency advantage i was planning stating
that the generator need be used at full power only for the best
efficiency. If you consider that friction consumes more than 10% of
the total engine torque, when you run an engine at 10% load it
consumes two times more oil than required, which mean half the
expected engine efficiency. In addition, you come into problems such
as cylinder glazing, etc.


Even if charging is not opportunistic but continuous, problem of
efficiency can be easily taken care of by switching off the generator
completely to give time for concentration equalization, and than turning
it back ON periodically.

Speaking about 1C rate (either charge or discharge), vanadium flow
battery would require gigantic electrodes and flow rate to come anywhere
close to this rate. All present implementations that I have seen are
working in C/10 to C/100 rates.

In short, I think the constraint of slow charging over 80% ruins the
advantage of using a hybrid propulsion chain. This i why I think lead
acid is just not adequate for hybrid propulsion.


As shown before, this constraint appears only on paper. Correct
understanding of the reasons of this charging recommendation shows that
it does not apply to this application.

Regards,
Evgenij
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Evgenij Barsukov
science forum Guru Wannabe


Joined: 09 May 2005
Posts: 137

PostPosted: Fri Jun 23, 2006 2:37 pm    Post subject: Re: Redox batteries Reply with quote

Jean-Marc Delaplace wrote:
Quote:
Evgenij,

thank you for your documented and patient answer.
I would like to discuss specifically an operating mode that is probably
not used in sea boats, but that is so likely in river boats that I am
very concerned with it.
When you say that charging will use a fraction of the power of the
generator because most of it is used by the propulsion, you are right
when you consider riding at nominal (=full) speed.
For a river and canal boat, this corresponds to about 15 km/h. However,
on many canals, the speed limit is 6 km/h. If you consider that the
required power is proportional to the cube of the speed, this means
using (6/15)^3 = 0.064 of the nominal power. Let's say 10%.
In this case, what I need is having the generator run for one hour at
full power, then quietly ride using the batteries only for ten hours.
This is where I see a problem with the charging rate of the top of the
SOC. Do you have a proposal?

Yes, I would suggest to split the generator runs into 3-4, so you give
battery enough time to relax (about half-hour) which will avoid the need
for lower charging rate at the end.
You do not need to modify the charger itself - it bases lowering the
current on voltage only, and "relaxing" will make sure that battery
voltage will not go high enough to start throttling down the current.

You can still allow some throttling down (say 20-30%), until you reach
the generator speed where efficiency takes a hit. This is to minimize
number of generator runs.

Quote:
Next, as far as vanadium batteries, you know that being flow cells, the
battery capacity and the battery power are totally decoupled. So you can
have a cell stack tailored for a certain power (in my case 20 kW), and
have the tanks sized for a certain energy (in my case 20 kWh).

This is true, but higher power stack will mean larger size/weight/price.
Ask them about all these parameters for the power that you need.
They might have quoted your the price for their standard (low power
stack) and told you that they can tailor to different power, but did
they tell you how the price scales?
In my estimation price of the stack and the pump
(and the battery overall, as otherwise there is only a cheap tank) will
scale proportionally to power.

One problem of large stack is replacement cost if some subunit fails.
If that happens with battery, it can be replaced. Would this be
the case with electrode stack - are they modular? You need to
find out.

Quote:
I have discussed the features of vanadium batteries with
Rob Blackwell
Business Development Manager
Pinnacle VRB Limited
and he gave me figures that apparently make sense. Of course, as you
emphasize, my guess is that most of what they boast of is true, but they
keep discreet on possible serious drawbacks that maybe they already know
- and maybe they do not even suspect yet !

I don't disagree that it can be technically done, but just check that
size/weight/price will be suitable.

Regards,
Yevgen

Quote:

best regards,
Jean-Marc

Evgenij Barsukov wrote:
Jean-Marc Delaplace wrote:

Evgenij Barsukov wrote:

Jean-Marc Delaplace wrote:

You are right about the concern with the leaks. However, I still do
not know how toxic vanadium is for the environment. Of course,
containment measures should be taken in the design so as to avoid
any spillage.

I want to answer your question about not using lead acid batteries.
I hope this will raise an interesting debate.

First, let me recall that my purpose is to build a hybrid
propulsion house boat. That is, a boat that will sometimes ride at
top speed (15 km/h), sometimes at half speed (most canals are
limited to 6 km/h) and sometimes it will stay at a mooring for days.

The objective is to be energy-efficient. The energy source will be
one or more of the following:
-a diesel generator: 20 kW;
-photovoltaic cells: at most 1 kW peak;
-wind turbine: at most 500 W peak.

To achieve optimum fuel efficiency, the generator must be used near
full power exclusively. Then, the role of the battery is to buffer
this pulsed power source to deliver just as much power as needed
when needed.

To save energy, using the generator should, as much as possible, be
avoided and power should come preferably from the sun and/or the wind.

This is where the lead-acid battery has two major drawbacks:

1) A lead-acid battery should always be fully charged, i.e. it
should be partially discharged for the shortest period of time
possible, to avoid the degradation process to come to play. This is
not compatible with waiting until sun or wind are available.



This is true. However, once your boat is moored, what prevents you from
connecting a charger to it and charging the batteries to full?
Deep cycle batteries can tolerate even full discharge, as long as
they are recharged soon to prevent crystallization of PbSO4.

2) A lead acid battery must be charged using precise current rates
according to the state of charge. This is incompatible with the
idea of accumulating all and as much energy is available at a time,
i.e. always using the generator at nominal power.



Lead Acid battery is one of the least sensitive to charging rates
(probably only cylindrical NiCd beats it in this respect, but they
are not available in right sizes). If you take the Lind book on
batteries, there are over 10 different charging methods described
for lead-acide, which have little in common. Which basically means,
it does not matter how to charge it as long as you do not cause
1) persistent extensive gasing
2) persistent undercharged condition (unsufficient voltage)


What do you mean with being little sensitive to charging rate?
Apparently you can charge a LA battery at C rate until 80% SOC, but
the remaining has to be charged at about C/10 ("finishing and
equalizing"). This is where the benefit of hybrid propulsion is lost:
whereas I could charge 80% at full power of my generator, that is 0.8
h, to charge the remaining 20% at C/10 would require running the
generator at 1/10 its power for 2 hours !


You are applying this formula too formally. The reason for the waiting
period during last 20% SOC has really nothing to do with SOC itself,
it has to do with waiting for diffusion to equalize concentrations
and therefore it only applies to the case of continuous charge.

In hybrid application most of the charging is done opportunistically,
e.g. when primary energy generator has some extra energy not used for
propulsion. So first of all charging would be way below 1C rate
(most likely ~C/10), second it would not be continuous, which eliminates
the need for any waiting period to reach 100% SOC. If you charge bursts
from 1C to C/100, that average to C/10 over time, you do not need to
do any waiting at the end, you will end up with 100% charged battery.

Same applies also to continuous charge at low rate.

Lead acid batteries have been used in hybrid applications (e.g. diesel
submarines) for almost a century and are still being used.


I would then spoil the efficiency advantage i was planning stating
that the generator need be used at full power only for the best
efficiency. If you consider that friction consumes more than 10% of
the total engine torque, when you run an engine at 10% load it
consumes two times more oil than required, which mean half the
expected engine efficiency. In addition, you come into problems such
as cylinder glazing, etc.


Even if charging is not opportunistic but continuous, problem of
efficiency can be easily taken care of by switching off the generator
completely to give time for concentration equalization, and than
turning it back ON periodically.

Speaking about 1C rate (either charge or discharge), vanadium flow
battery would require gigantic electrodes and flow rate to come
anywhere close to this rate. All present implementations that I have
seen are working in C/10 to C/100 rates.

In short, I think the constraint of slow charging over 80% ruins the
advantage of using a hybrid propulsion chain. This i why I think lead
acid is just not adequate for hybrid propulsion.


As shown before, this constraint appears only on paper. Correct
understanding of the reasons of this charging recommendation shows that
it does not apply to this application.

Regards,
Evgenij
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