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Author Topic: Can someone check this battery calculation is right please?  (Read 2795 times)
beastman
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« on: September 10, 2013, 03:35:30 PM »

My demand load is 29092 watts a day (yes I know its alot)
I am looking at 3 days autonomy and 50% discharge.

I've worked out I'd need 48 6 volt 600 amp batteries - from Navitron these would cost nearly 16K

http://www.navitron.org.uk/product_detail.php?proID=799&catID=157

Does that sound about right? Do I need to size this to a different voltage (related to the PV panels) or does that not matter?

thanks
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Tiff
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« Reply #1 on: September 10, 2013, 03:53:24 PM »

I think you only need half as many batteries:

24 6v batts x 300Ah (50%) = 7,200Ah x 6v = 43,200wh
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beastman
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« Reply #2 on: September 10, 2013, 04:01:56 PM »

thanks Tiff - not sure about all this but this is how I worked it out

I need 29092 watts hours per day x 3 (autonomous days) = 87276 x 2 (50% depth of discharge) = 174552 watts hours needed.

Those batteries are 6 volts @ 600 amps which is 3600 watt hours x 48 of them = 172800 watts hours (close enough)

Does that seem right?
 
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hobbit-express
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« Reply #3 on: September 10, 2013, 04:50:59 PM »

I think your calculation is correct beastman. If you use 29092wh per day and you want 3 days usage to 50%DOD without any input then 29092 x3 = 87276wh x 2= 174552 / 48 = 3636.5Ah@48V DC. Navitron offer a wider range of batteries than are currently on the website. If I were you I would be looking either:
24 x Rolls Solar 5000, 2V, 3426Ah (C100) , 2017Ah (C10) which would roughly be 16570.00 + Vat
48 x Rolls Solar 4000, 2V, 1729Ah (C100) , 1105Ah (C10) which would roughly be 15056.64 + VAt
I hope this helps
Hobbit Express
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Justme
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« Reply #4 on: September 10, 2013, 04:59:14 PM »

Why will all the energy come from the battery?

You could reduce the size if you are prepared for some to come from the secondary recharge source.

IE main recharge source is solar so if you get a run of bad days you need to recharge via a genny.

That same genny will be running for say 4 hours per day. With  good planning the large loads could be run only when the genny is on, plus you save 4/24th's of your back ground load. Could reduce your bank size by 50%.

If your main power source is very large & can recharge your 3 days of usage in one day then a big battery bank is worth while. However its most likely that it will be winter when you need the autonomy & after the 3 days are up you will still need more power as the sun is still not up to it.

But to answer the question.

29.092 kWh per day x 3 days = 87.276kWh

87.276kWh x 2 (for the 50% SOC) = 174.552kWh

174.552kWh / 48v = 3636amph

That is a very large battery.

Can you not reduce the load?

Or think about splitting the load so that during peak times its supplied via a genny?
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30 x 58mm panel 259L TS
1200watts solar 120vdc
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24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
Tiff
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« Reply #5 on: September 10, 2013, 05:47:01 PM »

I think you only need half as many batteries:

24 6v batts x 300Ah (50%) = 7,200Ah x 6v = 43,200wh

I'm a numpty - I missed out that you wanted 3 days worth.  facepalm
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beastman
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« Reply #6 on: September 10, 2013, 05:55:23 PM »

Many thanks gents for the answers.

@ Hobbit - where did you see these: 24 x Rolls Solar 5000, 2V, 3426Ah (C100) , 2017Ah (C10) which would roughly be 16570.00 + Vat

I can't see it on the website.

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martin
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« Reply #7 on: September 10, 2013, 06:16:14 PM »

as Hobbit said "Navitron offer a wider range of batteries than are currently on the website" Wink
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billi
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« Reply #8 on: September 10, 2013, 07:37:26 PM »

....not sure if one still should use this  old /aged rule of 3 days   , with pv prices so low ones far better off with an oversized pv ....my opinon...
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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
camillitech
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« Reply #9 on: September 10, 2013, 08:11:25 PM »

....not sure if one still should use this  old /aged rule of 3 days   , with pv prices so low ones far better off with an oversized pv ....my opinon...

What do you do in the winter if you don't have a '1.1kw hydro turbine as back up generator' then, dunno about in Ireland but here in Scotland there's no sun for three months of the year  Grin

Having said that Billi, you're quite right, I'd half the bank size and increase the PV tenfold, a 2.85kw array is going to do nothing for a 3500ah 48v battery bank.

Good luck, Paul
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'Off grid' since 1985,  Proven 2.5kW, Proven 6kW direct heating, SI6.OH, 800ah Rolls, 4.75kW PV ,4xTS45, Lister HR2 12kW, , Powerspout pelton, Stream Engine turgo, 60 x Navitron toobs and a 1500lt store. Outback VFX3048 and 950ah forklifts for backup,
offthegridandy
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« Reply #10 on: September 10, 2013, 08:41:32 PM »

You're going to need a hell of a big genny and inverter/charger set up as well, me thinks to recharge after 3 days.
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billi
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« Reply #11 on: September 10, 2013, 08:51:28 PM »

 Smiley  i admit . My 40 kwh battery that i bought about 7 years back has that 3 days @ 50 % .....

But , i think i ad more pv that is strong enough to avoid any deep discharge of the battery most of the year ,


If i would take 3 days out of my bartrey  in winter i surely need an alternative generator to fill the batts..  Each place os diffrent....

Best regards and it aint easy to write on a tiny mobile




By the way .....one of the best advice HERE A FEW YEARS BACK was using traction / forklift batteries ( PzS Cells)
One can now get so called SPzS cells in a bigger cell housing......
« Last Edit: September 10, 2013, 08:58:36 PM by billi » Logged

1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
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« Reply #12 on: September 10, 2013, 08:55:46 PM »

"it aint easy to write on a tiny mobile"

 hysteria hysteria hysteria

Nice one billi, I have been giggling to myself at the thought of a tiny mobile.  hysteria

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Everything is possible, just give me TIME.
camillitech
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« Reply #13 on: September 10, 2013, 08:56:22 PM »

You're going to need a hell of a big genny and inverter/charger set up as well, me thinks to recharge after 3 days.



 Cool



 genuflect  genuflect
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http://lifeattheendoftheroad.wordpress.com/

'Off grid' since 1985,  Proven 2.5kW, Proven 6kW direct heating, SI6.OH, 800ah Rolls, 4.75kW PV ,4xTS45, Lister HR2 12kW, , Powerspout pelton, Stream Engine turgo, 60 x Navitron toobs and a 1500lt store. Outback VFX3048 and 950ah forklifts for backup,
clockmanFR
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« Reply #14 on: September 10, 2013, 08:58:48 PM »

Nice Paul,

Love the beer keg, does it run on beer?     hysteria hysteria
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Everything is possible, just give me TIME.
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