Some basic battery bank calculations

[terryc]

On Wed, 25 Mar 2009 01:09:07 +1100, Sylvia Else wrote:

- if you
can find an economic way of doing it. However, even running the
numbers on the back of an envelope will quickly show that it's not
just uneconomic - it's hugely uneconomic.

Care to share them?

I lost the envelope. But calculate the cost of the batteries you'd need
to support your day-time load. Then calculate the amount the interest
you'd earn on the money if you didn't buy batteries. Then calculate the
diffence in cost of the electricity you achieve through changing the
times you draw power from the grid.

Finally, take into account the very limited life of batteries.

The numbers show that it's a no-brainer.

Which is why the power generation industry isn't doing it already.

Power industry isn't doing it because their size in batteries can not be
purchased at the local garage.

Okay, taking my fileserver, which requires 96 watts max and my LG995E CRT
monitor which requires 72 watts max, that means 168 watts I need out of
the battery bank, or 14 amps @ 12Volt.

So, to cover 7am to 10pm, I need to store 15x14 = 210 amp hours. In lead
acid, this means 420amps hours.

Practically, that equates to 5x100AmpHr batteriess hour at $200 (old
price), or $1,000. 10 year life span means costs 28c per day in
depreciation. Loan costs is 6% atm or 20c per day.

Electricity savings are 15(0.1575-0.0554) =$1.53c. Net savings are $1.07c
per day. <BLINK> or $3,905.50c over ten years.

 

[Alan Rutlidge]

"terryc" <newssevenspam-spam@woa.com.au> wrote in message
news:49c9b7a4$0$26373$c30e37c6@pit-reader.telstra.net...

On Wed, 25 Mar 2009 01:09:07 +1100, Sylvia Else wrote:


- if you
can find an economic way of doing it. However, even running the
numbers on the back of an envelope will quickly show that it's not
just uneconomic - it's hugely uneconomic.

Care to share them?

I lost the envelope. But calculate the cost of the batteries you'd need
to support your day-time load. Then calculate the amount the interest
you'd earn on the money if you didn't buy batteries. Then calculate the
diffence in cost of the electricity you achieve through changing the
times you draw power from the grid.

Finally, take into account the very limited life of batteries.

The numbers show that it's a no-brainer.

Which is why the power generation industry isn't doing it already.

Power industry isn't doing it because their size in batteries can not be
purchased at the local garage.

Okay, taking my fileserver, which requires 96 watts max and my LG995E CRT
monitor which requires 72 watts max, that means 168 watts I need out of
the battery bank, or 14 amps @ 12Volt.

So, to cover 7am to 10pm, I need to store 15x14 = 210 amp hours. In lead
acid, this means 420amps hours.

Practically, that equates to 5x100AmpHr batteriess hour at $200 (old
price), or $1,000. 10 year life span means costs 28c per day in
depreciation. Loan costs is 6% atm or 20c per day.

Electricity savings are 15(0.1575-0.0554) =$1.53c. Net savings are $1.07c
per day. <BLINK> or $3,905.50c over ten years.

Okay, so now your batteries are flat and need recharging.
I assume you are going to solar or wind turbine recharge these batteries, or
are you intending running an extension lead over the fence and stealing your
neighbour's power to recharge the batteries?

 

[Sylvia Else]

terryc wrote:

On Wed, 25 Mar 2009 01:09:07 +1100, Sylvia Else wrote:


- if you
can find an economic way of doing it. However, even running the
numbers on the back of an envelope will quickly show that it's not
just uneconomic - it's hugely uneconomic.
Care to share them?
I lost the envelope. But calculate the cost of the batteries you'd need
to support your day-time load. Then calculate the amount the interest
you'd earn on the money if you didn't buy batteries. Then calculate the
diffence in cost of the electricity you achieve through changing the
times you draw power from the grid.

Finally, take into account the very limited life of batteries.

The numbers show that it's a no-brainer.

Which is why the power generation industry isn't doing it already.

Power industry isn't doing it because their size in batteries can not be
purchased at the local garage.

Okay, taking my fileserver, which requires 96 watts max and my LG995E CRT
monitor which requires 72 watts max, that means 168 watts I need out of
the battery bank, or 14 amps @ 12Volt.

So, to cover 7am to 10pm, I need to store 15x14 = 210 amp hours. In lead
acid, this means 420amps hours.

Practically, that equates to 5x100AmpHr batteriess hour at $200 (old
price), or $1,000. 10 year life span means costs 28c per day in
depreciation. Loan costs is 6% atm or 20c per day.

Electricity savings are 15(0.1575-0.0554) =$1.53c. Net savings are $1.07c
per day. <BLINK> or $3,905.50c over ten years.

I think you lost a factor of 100 there. It's 3905.5 cents, or just over $39.

10 year life with a 15 hour discharge to 50% capacity and 9 hour charge
back to 100% on a daily cycle?

What about the charger, the inverter, and the timer? They cost money too.

Sylvia.

 

[terryc]

On Wed, 25 Mar 2009 14:49:21 +0900, Alan Rutlidge wrote:

"terryc" <newssevenspam-spam@woa.com.au> wrote in message
news:49c9b7a4$0$26373$c30e37c6@pit-reader.telstra.net...
On Wed, 25 Mar 2009 01:09:07 +1100, Sylvia Else wrote:


- if you
can find an economic way of doing it. However, even running the
numbers on the back of an envelope will quickly show that it's not
just uneconomic - it's hugely uneconomic.

Care to share them?

I lost the envelope. But calculate the cost of the batteries you'd
need to support your day-time load. Then calculate the amount the
interest you'd earn on the money if you didn't buy batteries. Then
calculate the diffence in cost of the electricity you achieve through
changing the times you draw power from the grid.

Finally, take into account the very limited life of batteries.

The numbers show that it's a no-brainer.

Which is why the power generation industry isn't doing it already.

Power industry isn't doing it because their size in batteries can not
be purchased at the local garage.

Okay, taking my fileserver, which requires 96 watts max and my LG995E
CRT monitor which requires 72 watts max, that means 168 watts I need
out of the battery bank, or 14 amps @ 12Volt.

So, to cover 7am to 10pm, I need to store 15x14 = 210 amp hours. In
lead acid, this means 420amps hours.

Practically, that equates to 5x100AmpHr batteriess hour at $200 (old
price), or $1,000. 10 year life span means costs 28c per day in
depreciation. Loan costs is 6% atm or 20c per day.

Electricity savings are 15(0.1575-0.0554) =$1.53c. Net savings are
$1.07c per day. <BLINK> or $3,905.50c over ten years.


Okay, so now your batteries are flat and need recharging.

This was drafted out from the thread about solar power installers (my
newsagent sulked). It is to do with battery banking off peak power and
using it during the peak/shoulder periods o run equipment. The batteries
are recharged as off peak equipment.

 

[Mark Harriss]

terryc wrote:

This was drafted out from the thread about solar power installers (my
newsagent sulked). It is to do with battery banking off peak power and
using it during the peak/shoulder periods o run equipment. The batteries
are recharged as off peak equipment.

Don't forget the battery charging losses too, lithiums would be
perfect in that respect only with nearly 100% charge efficiency.

 

[terryc]

On Wed, 25 Mar 2009 17:39:40 +1100, Sylvia Else wrote:

terryc wrote:
On Wed, 25 Mar 2009 01:09:07 +1100, Sylvia Else wrote:


- if you
can find an economic way of doing it. However, even running the
numbers on the back of an envelope will quickly show that it's not
just uneconomic - it's hugely uneconomic.
Care to share them?
I lost the envelope. But calculate the cost of the batteries you'd
need to support your day-time load. Then calculate the amount the
interest you'd earn on the money if you didn't buy batteries. Then
calculate the diffence in cost of the electricity you achieve through
changing the times you draw power from the grid.

Finally, take into account the very limited life of batteries.

The numbers show that it's a no-brainer.

Which is why the power generation industry isn't doing it already.

Power industry isn't doing it because their size in batteries can not
be purchased at the local garage.

Okay, taking my fileserver, which requires 96 watts max and my LG995E
CRT monitor which requires 72 watts max, that means 168 watts I need
out of the battery bank, or 14 amps @ 12Volt.

So, to cover 7am to 10pm, I need to store 15x14 = 210 amp hours. In
lead acid, this means 420amps hours.

Practically, that equates to 5x100AmpHr batteriess hour at $200 (old
price), or $1,000. 10 year life span means costs 28c per day in
depreciation. Loan costs is 6% atm or 20c per day.

Electricity savings are 15(0.1575-0.0554) =$1.53c. Net savings are
$1.07c per day. <BLINK> or $3,905.50c over ten years.


I think you lost a factor of 100 there. It's 3905.5 cents, or just over
$39.

Nope, but I think it proves that you didn't do any back of envelope
calculations as you completely missed my senior moment that left out the
correct factor and used elapsed time.

In any case, it is currently break even if you can get 15.75c/kwh as your
max power cost.

What about the charger, the inverter, and the timer? They cost money
too.

A charger is the only other piece of equipment you need and a good one

lasts for decades. Computers can run directly off 12v these days. The
time is the off peak switch.

 

[Sylvia Else]

terryc wrote:

On Wed, 25 Mar 2009 17:39:40 +1100, Sylvia Else wrote:

terryc wrote:
On Wed, 25 Mar 2009 01:09:07 +1100, Sylvia Else wrote:


- if you
can find an economic way of doing it. However, even running the
numbers on the back of an envelope will quickly show that it's not
just uneconomic - it's hugely uneconomic.
Care to share them?
I lost the envelope. But calculate the cost of the batteries you'd
need to support your day-time load. Then calculate the amount the
interest you'd earn on the money if you didn't buy batteries. Then
calculate the diffence in cost of the electricity you achieve through
changing the times you draw power from the grid.

Finally, take into account the very limited life of batteries.

The numbers show that it's a no-brainer.

Which is why the power generation industry isn't doing it already.
Power industry isn't doing it because their size in batteries can not
be purchased at the local garage.

Okay, taking my fileserver, which requires 96 watts max and my LG995E
CRT monitor which requires 72 watts max, that means 168 watts I need
out of the battery bank, or 14 amps @ 12Volt.

So, to cover 7am to 10pm, I need to store 15x14 = 210 amp hours. In
lead acid, this means 420amps hours.


Practically, that equates to 5x100AmpHr batteriess hour at $200 (old
price), or $1,000. 10 year life span means costs 28c per day in
depreciation. Loan costs is 6% atm or 20c per day.

Electricity savings are 15(0.1575-0.0554) =$1.53c. Net savings are
$1.07c per day. <BLINK> or $3,905.50c over ten years.


I think you lost a factor of 100 there. It's 3905.5 cents, or just over
$39.

Nope, but I think it proves that you didn't do any back of envelope
calculations as you completely missed my senior moment that left out the
correct factor and used elapsed time.

I didn't go through your calculations with a fine toothcomb. I don't
know what you meant by "nope". 1.07cents per day is 390.55 cents per
year, or 3905.5 cents in ten years = about $39.

In any case, it is currently break even if you can get 15.75c/kwh as your
max power cost.

And subject to getting a ten year life out of lead-acid batteries used
in this regime. Where are these 100 Amp-Hour batteries for $200 that
will last 3650 cycles?

BTW, what about the efficiency? The charge discharge cycle of a battery
loses quite a lot of energy.

What about the charger, the inverter, and the timer? They cost money
too.

A charger is the only other piece of equipment you need and a good one
lasts for decades.

How must does it cost?

Computers can run directly off 12v these days.

Mine can't.

The time is the off peak switch.

Did you include the cost of the switch? Is that a practical solution?

Sylvia.

 

[terryc]

On Wed, 25 Mar 2009 20:24:08 +1000, Mark Harriss wrote:

Don't forget the battery charging losses too, lithiums would be
perfect in that respect only with nearly 100% charge efficiency.

Only on that aspect. Otherwise, they are exceedingly expensive. Lithium
is ideal in instantaneous high pulse power situations, or as a very
expensive weight saving device.

 

[terryc]

On Wed, 25 Mar 2009 22:54:14 +1100, Sylvia Else wrote:

Electricity savings are 15(0.1575-0.0554) =$1.53c. Net savings are
$1.07c per day. <BLINK> or $3,905.50c over ten years.


I think you lost a factor of 100 there. It's 3905.5 cents, or just
over $39.

Nope, but I think it proves that you didn't do any back of envelope
calculations as you completely missed my senior moment that left out
the correct factor and used elapsed time.

I didn't go through your calculations with a fine toothcomb.

You didn't go through anything. You have consistently displayed a lack of
understanding of some basic facts. Hint have a look at your last
electricity bill and you will realise where you made your mistake.

1.07cents per day
is not my figure.

 

[Sylvia Else]

terryc wrote:

On Wed, 25 Mar 2009 22:54:14 +1100, Sylvia Else wrote:

Electricity savings are 15(0.1575-0.0554) =$1.53c. Net savings are
$1.07c per day. <BLINK> or $3,905.50c over ten years.


I think you lost a factor of 100 there. It's 3905.5 cents, or just
over $39.
Nope, but I think it proves that you didn't do any back of envelope
calculations as you completely missed my senior moment that left out
the correct factor and used elapsed time.
I didn't go through your calculations with a fine toothcomb.

You didn't go through anything. You have consistently displayed a lack of
understanding of some basic facts. Hint have a look at your last
electricity bill and you will realise where you made your mistake.


1.07cents per day
is not my figure.

You ignored all the rest.

Where are these batteries?

Sylvia.

 

[Sylvia Else]

terryc wrote:

On Wed, 25 Mar 2009 01:09:07 +1100, Sylvia Else wrote:


- if you
can find an economic way of doing it. However, even running the
numbers on the back of an envelope will quickly show that it's not
just uneconomic - it's hugely uneconomic.
Care to share them?
I lost the envelope. But calculate the cost of the batteries you'd need
to support your day-time load. Then calculate the amount the interest
you'd earn on the money if you didn't buy batteries. Then calculate the
diffence in cost of the electricity you achieve through changing the
times you draw power from the grid.

Finally, take into account the very limited life of batteries.

The numbers show that it's a no-brainer.

Which is why the power generation industry isn't doing it already.

Power industry isn't doing it because their size in batteries can not be
purchased at the local garage.

Okay, taking my fileserver, which requires 96 watts max and my LG995E CRT
monitor which requires 72 watts max, that means 168 watts I need out of
the battery bank, or 14 amps @ 12Volt.

So, to cover 7am to 10pm, I need to store 15x14 = 210 amp hours. In lead
acid, this means 420amps hours.

Practically, that equates to 5x100AmpHr batteriess hour at $200 (old
price), or $1,000. 10 year life span means costs 28c per day in
depreciation. Loan costs is 6% atm or 20c per day.

Electricity savings are 15(0.1575-0.0554) =$1.53c. Net savings are $1.07c
per day. <BLINK> or $3,905.50c over ten years.

As you pointed out, you've omitted the factor of 0.168, reducing the
gross saving to $0.257, and meaning your net saving is negative.

If you're going to do this properly, then you should assume that you're
paying back the loan from the electricity cost savings. You should also
factor in inflation. In practice, as long as both interest rates and
inflation rates are reasonably small, you can subtract the inflation
rate from the interest rate to give a "real interest rate", and then
treat the inflation rate as zero.

The daily saving is 0.168kW * 15 hours * $0.1021/kWh = $0.257 per day.
Treated as 12 equal length months per year, that's $7.83 per month
that's available to pay off the loan.

Run the numbers on that with 6% interest and 3% inflation, and monthly
repayments, and after 10 years, you still owe $289 (in present day dollars).

To break even, you'd need to get the batteries and other equipment for
$791. And this is still assuming that batteries will last for 10 years,
that nothing simply breaks and has to be replaced, and ignoring any
losses in the charge-discharge cycle.

Sylvia.

 

[terryc]

On Thu, 26 Mar 2009 13:53:25 +1100, Sylvia Else wrote:

The daily saving is 0.168kW * 15 hours * $0.1021/kWh = $0.257 per day.
Treated as 12 equal length months per year, that's $7.83 per month
that's available to pay off the loan.

Err, that was the figure after the loan was paid.

Run the numbers on that with 6% interest and 3% inflation, and monthly
repayments, and after 10 years, you still owe $289 (in present day
dollars).

Who gives a stuff. I'm only interested in the loan interest rates.

 

[Sylvia Else]

terryc wrote:

On Thu, 26 Mar 2009 13:53:25 +1100, Sylvia Else wrote:

The daily saving is 0.168kW * 15 hours * $0.1021/kWh = $0.257 per day.
Treated as 12 equal length months per year, that's $7.83 per month
that's available to pay off the loan.

Err, that was the figure after the loan was paid.
Run the numbers on that with 6% interest and 3% inflation, and monthly
repayments, and after 10 years, you still owe $289 (in present day
dollars).

Who gives a stuff. I'm only interested in the loan interest rates.

Why? The whole point of the exercise is to increase one's future wealth.
As far as possible you want to factor in all the relevant variables.
Doing otherwise can present the illusion that the path taken is optimum,
when it's not.

Sylvia.

 

[terryc]

On Thu, 26 Mar 2009 16:46:45 +1100, Sylvia Else wrote:

Why? The whole point of the exercise is to increase one's future wealth.

Yep, and if I'm not paying for electricity, that is doing it. You
obviously missed that point.

 

[Alan Rutlidge]

"terryc" <newssevenspam-spam@woa.com.au> wrote in message
news:49cadeb9$0$26362$c30e37c6@pit-reader.telstra.net...

On Wed, 25 Mar 2009 20:24:08 +1000, Mark Harriss wrote:

Don't forget the battery charging losses too, lithiums would be
perfect in that respect only with nearly 100% charge efficiency.

Only on that aspect. Otherwise, they are exceedingly expensive. Lithium
is ideal in instantaneous high pulse power situations, or as a very
expensive weight saving device.

Also they deteriorate rapidly if any air gets into them. :-(

 

[Sylvia Else]

terryc wrote:

On Thu, 26 Mar 2009 16:46:45 +1100, Sylvia Else wrote:

Why? The whole point of the exercise is to increase one's future wealth.

Yep, and if I'm not paying for electricity, that is doing it. You
obviously missed that point.

If you're not paying for (or rather in the battery bank case, paying
less for) electricity but are paying more for the equipment required
than you are saving, then your future wealth is reduced.

I'd still like to have a link for these alleged 3650 cycle batteries.

Sylvia.

 

[terryc]

On Fri, 27 Mar 2009 11:47:14 +1100, Sylvia Else wrote:

terryc wrote:
On Thu, 26 Mar 2009 16:46:45 +1100, Sylvia Else wrote:

Why? The whole point of the exercise is to increase one's future
wealth.

Yep, and if I'm not paying for electricity, that is doing it. You
obviously missed that point.

If you're not paying for (or rather in the battery bank case, paying
less for) electricity but are paying more for the equipment required
than you are saving, then your future wealth is reduced.

But I'm not, for which i produced figures to show this. If you want to
discuss this further, then produce your own set of figures.

I'd still like to have a link for these alleged 3650 cycle batteries.

Do you have trouble using a search engine for basic searches?
Read here, then progress.

http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

Basically, if you do not see the benefit, then don't do it.

 

[Sylvia Else]

terryc wrote:

On Fri, 27 Mar 2009 11:47:14 +1100, Sylvia Else wrote:

terryc wrote:
On Thu, 26 Mar 2009 16:46:45 +1100, Sylvia Else wrote:

Why? The whole point of the exercise is to increase one's future
wealth.
Yep, and if I'm not paying for electricity, that is doing it. You
obviously missed that point.
If you're not paying for (or rather in the battery bank case, paying
less for) electricity but are paying more for the equipment required
than you are saving, then your future wealth is reduced.

But I'm not, for which i produced figures to show this. If you want to
discuss this further, then produce your own set of figures.

Your electricity savings were $0.25 per day, not $1.53 per day, as I
thought you'd realised, because you're drawing 0.168 kW, not 1kW. That
saving is completely wiped out by your own estimation of interest and
depreciation.

The true situation is not so bad, as I indicated, because the interest
drops as you pay back the loan. But there's still a net loss over 10 years.

I'd still like to have a link for these alleged 3650 cycle batteries.

Do you have trouble using a search engine for basic searches?
Read here, then progress.

http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

And the place where you intend to source the 10 year life batteries at
the prices you stated?

Sylvia.

 

[terryc]

On Fri, 27 Mar 2009 12:20:14 +1100, Sylvia Else wrote:

But I'm not, for which i produced figures to show this. If you want to
discuss this further, then produce your own set of figures.

Your electricity savings were $0.25 per day, not $1.53 per day, as I
thought you'd realised, because you're drawing 0.168 kW, not 1kW. That
saving is completely wiped out by your own estimation of interest and
depreciation.

These are not your figures, but a deliberately misinterpreted set of mine.
Do your own calculations and stop digging yourself deeper into the hole
you've already started.

 

[Sylvia Else]

terryc wrote:

On Fri, 27 Mar 2009 12:20:14 +1100, Sylvia Else wrote:


But I'm not, for which i produced figures to show this. If you want to
discuss this further, then produce your own set of figures.
Your electricity savings were $0.25 per day, not $1.53 per day, as I
thought you'd realised, because you're drawing 0.168 kW, not 1kW. That
saving is completely wiped out by your own estimation of interest and
depreciation.

These are not your figures, but a deliberately misinterpreted set of mine.
Do your own calculations and stop digging yourself deeper into the hole
you've already started.

Explain how your figures should be interpreted then.

Sylvia.