Posted by *angus.berry* on January 28, 2009, 5:58 am

I wonder if someone could help me with a battery sizing system

calculation to help me get a better understanding.

This is an idea conditions calculation!

Lets say a 150w, 12VDC appliance needs to run 24/7.

I have PV cells that produce 500W x 8 hours a day (every day of the

year :-)

What would the AH rating of battery bank need to be to fall to an

acceptable level overnight without damaging the batteries and sustain

this 'ideal' system, running 24/7

Thanks for any help getting me started in understanding this!

Posted by *drcsolar@gmail.com* on January 28, 2009, 9:13 am

On Jan 28, 12:58am, angus.be...@gmail.com wrote:

*> I wonder if someone could help me with a battery sizing system*

*> calculation to help me get a better understanding.*

*> This is an idea conditions calculation!*

*> Lets say a 150w, 12VDC appliance needs to run 24/7.*

*> I have PV cells that produce 500W x 8 hours a day (every day of the*

*> year :-)*

*> What would the AH rating of battery bank need to be to fall to an*

*> acceptable level overnight without damaging the batteries and sustain*

*> this 'ideal' system, running 24/7*

*> Thanks for any help getting me started in understanding this!*

Watts/Wolts=Amps thats how many Amps your drawing during useage.

150W/

12V=12.5Amps run that for one hour you get 12.5 Ah per hour, now

mulitple that by 24 you get 300 Ah during a 24 hour period.

300 Ah and you want your battery discharge to not exceed 50% SOC so

you would need about 600 Ah of capacity.

And my personal preference would be to go with Trojan but you can use

what ever ones you want being pricing may be an issue.

Posted by *Russ in San Diego* on January 28, 2009, 4:51 pm

*> On Jan 28, 12:58am, angus.be...@gmail.com wrote:*

*> > I wonder if someone could help me with a battery sizing system*

*> > calculation to help me get a better understanding.*

*> > This is an idea conditions calculation!*

*> > Lets say a 150w, 12VDC appliance needs to run 24/7.*

*> > I have PV cells that produce 500W x 8 hours a day (every day of the*

*> > year :-)*

*> > What would the AH rating of battery bank need to be to fall to an*

*> > acceptable level overnight without damaging the batteries and sustain*

*> > this 'ideal' system, running 24/7*

*> > Thanks for any help getting me started in understanding this!*

*> Watts/Wolts=Amps thats how many Amps your drawing during useage.*

*> 150W/*

*> 12V=12.5Amps run that for one hour you get 12.5 Ah per hour, now*

*> mulitple that by 24 you get 300 Ah during a 24 hour period.*

*> 300 Ah and you want your battery discharge to not exceed 50% SOC so*

*> you would need about 600 Ah of capacity.*

*> And my personal preference would be to go with Trojan but you can use*

*> what ever ones you want being pricing may be an issue.*

That workup assumes every day will be sunny. If there's one day with

full cloud cover, the batteries will be drawn down to 0 and their

lifetime will be shot.

You should probably triple (at least) that capacity, depending on the

typical weather patterns for the installation. (How often do you

encounter multiple cloudy days in a row?)

Your panels are also inadequate. If you really get 500W x 8H, they

can produce up to 4kWH/day. Assuming no losses, your load is pulling

3.6 kWH/day. That leaves a scant 0.4 kWH/day for restoring a charge

on the batteries after a cloudy day. You should probably double the

capacity of the panels so that batteries can be fully recharged in one

day.

Posted by *angus.berry* on January 30, 2009, 4:31 am

*> On Jan 28, 12:58am, angus.be...@gmail.com wrote:*

*> > I wonder if someone could help me with a battery sizing system*

*> > calculation to help me get a better understanding.*

*> > This is an idea conditions calculation!*

*> > Lets say a 150w, 12VDC appliance needs to run 24/7.*

*> > I have PV cells that produce 500W x 8 hours a day (every day of the*

*> > year :-)*

*> > What would the AH rating of battery bank need to be to fall to an*

*> > acceptable level overnight without damaging the batteries and sustain*

*> > this 'ideal' system, running 24/7*

*> > Thanks for any help getting me started in understanding this!*

*> Watts/Wolts=Amps thats how many Amps your drawing during useage.*

*> 150W/*

*> 12V=12.5Amps run that for one hour you get 12.5 Ah per hour, now*

*> mulitple that by 24 you get 300 Ah during a 24 hour period.*

*> 300 Ah and you want your battery discharge to not exceed 50% SOC so*

*> you would need about 600 Ah of capacity.*

*> And my personal preference would be to go with Trojan but you can use*

*> what ever ones you want being pricing may be an issue.*

Thank you for your response drcsolar. This is exactly the kind of help

I was looking for based on 'ideal conditions', to get a clear example

of calculations. Now I can consider a 'real world' scenario.

Posted by *drcsolar@gmail.com* on January 30, 2009, 10:26 am

On Jan 29, 11:31pm, angus.be...@gmail.com wrote:

*> > On Jan 28, 12:58am, angus.be...@gmail.com wrote:*

*> > > I wonder if someone could help me with a battery sizing system*

*> > > calculation to help me get a better understanding.*

*> > > This is an idea conditions calculation!*

*> > > Lets say a 150w, 12VDC appliance needs to run 24/7.*

*> > > I have PV cells that produce 500W x 8 hours a day (every day of the*

*> > > year :-)*

*> > > What would the AH rating of battery bank need to be to fall to an*

*> > > acceptable level overnight without damaging the batteries and sustain*

*> > > this 'ideal' system, running 24/7*

*> > > Thanks for any help getting me started in understanding this!*

*> > Watts/Wolts=Amps thats how many Amps your drawing during useage.*

*> > 150W/*

*> > 12V=12.5Amps run that for one hour you get 12.5 Ah per hour, now*

*> > mulitple that by 24 you get 300 Ah during a 24 hour period.*

*> > 300 Ah and you want your battery discharge to not exceed 50% SOC so*

*> > you would need about 600 Ah of capacity.*

*> > And my personal preference would be to go with Trojan but you can use*

*> > what ever ones you want being pricing may be an issue.*

*> Thank you for your response drcsolar. This is exactly the kind of help*

*> I was looking for based on 'ideal conditions', to get a clear example*

*> of calculations. Now I can consider a 'real world' scenario.*

Yeah truely Ideal, I am an over estimater so i would go three times to

normal within means that is......

Good luck with your project.

> I wonder if someone could help me with a battery sizing system> calculation to help me get a better understanding.> This is an idea conditions calculation!> Lets say a 150w, 12VDC appliance needs to run 24/7.> I have PV cells that produce 500W x 8 hours a day (every day of the> year :-)> What would the AH rating of battery bank need to be to fall to an> acceptable level overnight without damaging the batteries and sustain> this 'ideal' system, running 24/7> Thanks for any help getting me started in understanding this!