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Author Topic: Battery help  (Read 5494 times)
DaveB275
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« on: April 28, 2010, 10:24:10 AM »

Reading lots and (slowly) learning.

If you were starting from scratch with a new build, to be off grid, with an estimated 9kWh daily requirement, and 2.1kW peak load, what battery size/configuration might be best?

Have tried to start from the energy requirements and work back to sizing batteries. If I've understood other posts, consensus seems to be 48V system, made up from 2V or 6V cells? I confess this is not my strong point and the choices of batteries seem bewildering. Any guidance would be appreciated.

Have been recommended 3.5kW PV array + plan to have diesel generator backup & small wind. May be able to add some form of hydro later.
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Billy
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« Reply #1 on: April 28, 2010, 10:56:43 AM »

Welcome Dave,

I guess it all depends on how long you may be without power coming in as to the size of you bank.  If you have access to multiple top ups then in theory the bank can be smaller.  If the peak load will be around 2-3kw (how long for) then the bank should be capable of running this without seriously loosing capacity.  I would reckon the bank to be around 700ah@C20 minimum to cope with that load for an hour or two without killing them.

As to the voltage, 24/48 is good and will allow for smaller cable sizes especially with 48v.  Availability of equipment at your voltage will perhaps be the main factor.  If you want to run stuff directly off the batteries then 24v will give you a better choice.

You want your battery bank to have the best chance if you are off grid and rely on them.  My Rolls batteries come with a ten year guarantee and an expected life of at least 15 if they are looked after but they are not cheap.  Others seem quite happy with ex-forklift sets and get good results for far less.

9kwhr a day is a bit steep, we have managed to get ours nearer 5 even with all the normal household stuff.  Yours is nearer the national average, you should be able to reduce it unless you have some power hungry stuff.

hth

 Grin Grin
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martin
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« Reply #2 on: April 28, 2010, 11:01:17 AM »

Billy's right - that's one heck of a lot of power to try to provide using batteries - firstly go through everything with the proverbial fine-tooth comb*, and wherever possible, use an alternative power source - fridges, freezers and cooking, use gas (bottled if off mains) and make sure you only use electricity for things that cannot be powered any other way - it's expensive stuff to make and store...............

*In a scheme of this sort, always "start at the other end" first, minimise your requirements, THEN look to provide them........ Wink
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Justme
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« Reply #3 on: April 28, 2010, 11:23:43 AM »

We use 2 to 3 kWh per day, more in winter than summer. Our bank is 12v & 1550ah (but uprating it soon to 12v x 2800ah, but when the inverter need changing it will be 48v x 700ah). We have 1.2kWp array that provide every thing from April to August ish baring periods of weather that last more than 3 days in a row or a string of bad weather over a few more days.

We have a similar peak load via our 3000kva inverter. When running at full load the bat V does fall to the low bat warning (but not shut down)level so could do with being bigger or newer but it does recover the instant the load is removed.


We can go for 3 to 4 days with little of no charge & still not go below 50% SOC.

You really need to reduce that 9kWh per day demand first. It will save you big .

For your 9kWh demand I would spec a 48v bank at 1500-2000ah for 3 to 4 days use. Thats a big bank & I would not want to buy a new one at the price it would be.
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
2 x Victron Multiplus II 48/5000/70
Cerbo GX & GX 50 touch
BMV 700
6kva genny
48v 1000ah
Grid Possibly coming soon
dhaslam
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« Reply #4 on: April 28, 2010, 11:50:42 AM »

Have been recommended 3.5kW PV array + plan to have diesel generator backup & small wind. May be able to add some form of hydro later.

If you have a suitable source for hydro you should do that first before investing in  solar or batteries. 
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EccentricAnomaly
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« Reply #5 on: April 28, 2010, 12:28:52 PM »

... - fridges, freezers and cooking, use gas (bottled if off mains) ...

But that's not really off grid, is it?  It seems to me, though, that lots of off-grid people use electricity for these purposes quite sensibly.
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martin
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« Reply #6 on: April 28, 2010, 01:52:19 PM »

I'd agree about hydro - look at that first! Wink
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Justme
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« Reply #7 on: April 28, 2010, 02:27:49 PM »

Yep to use hydro you would only need a 4-500watt turbine running at full power 24/7.
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
2 x Victron Multiplus II 48/5000/70
Cerbo GX & GX 50 touch
BMV 700
6kva genny
48v 1000ah
Grid Possibly coming soon
DaveB275
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« Reply #8 on: April 28, 2010, 04:48:41 PM »

Great - thanks everybody. Just the sort of feedback I need, especially hearing from those who are doing it already.

Agree my figures seem high, but as I was having to estimate just about everything, I erred on the pessimistic side, then allowed even a bit more. (Actually worked it out at 7.6kWh). Biggest problems seem to be Borehole pump for water, and the Sewage treatment system the architect has shown (Bio-pure running 24/7). Was keen on non-electric unit (Biorock), but kept being told to avoid it.

Hydro seems inviting but presents several problems initially, which is why I was thinking to add this in later.

Plenty more to think about/learn yet, but finding this forum helps.
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Justme
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« Reply #9 on: April 28, 2010, 09:33:33 PM »

How much water are you using per week?

We use less than 0.5kWh per week to run our borehole pump.

Its 30m down (can go as deep as 50m) & will fill a 1000l container in about 20 ish mins. The container lasts us (3 adults & 1 child) over a week. Its rated at 1000watts but I have not tested the actual draw yet as I cant find the plug in meter. In summer I try to fill it when the bat is full but its still sunny as other wise the PV power would have been waisted. Eventually I will automate the process.
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
2 x Victron Multiplus II 48/5000/70
Cerbo GX & GX 50 touch
BMV 700
6kva genny
48v 1000ah
Grid Possibly coming soon
DaveB275
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« Reply #10 on: June 20, 2010, 08:37:35 PM »

Just an update.   Current wishlist is to have:

   6 x 4V  1104 ah  Rolls batteries RB4KS21P
   1 x Victron Phoenix MultiPlus 24V 3000VA Inverter
   12 x Kyocera KD210GH-2P 210Wp panels
   1 x Outback Flexmax 80 MPPT controller (Is this ok for the PV, or would splitting it over 2 be better?)
   1 x Miniwind 2200-24 (possibly?) - Charge controller needed?
   1 x diesel generator (yet to be defined)

Have re-assessed our power needs to a slightly more realistic 3kWh per day (summer) an 6.5kWh (winter), but as this is all still theory, its hard to be sure.

Have discussed hydro option with BabyHydro, but they think its not worth it.  Sad

As always, would welcome any comments or suggestions on the above.
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billi
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« Reply #11 on: June 20, 2010, 09:46:28 PM »

Sorry  first  and do not take this too seriously  Tongue

Go for 48 Volt System  (one outback FM 80 for upto 5 kw PV then )
Buy a cheaper battery with more AH  like a fork lift one,  instead of cycling an expensive smaller  one deeper )
Get double the amount of PV for the money you saved already  to avoid deep discharge and lesser diesel generator run-time  and even save more in shopping around for a "deal of good panels " and they are available  Grin


The days are over that PV is expensive compared to Battery storage , so invest in more PV ...

Perhaps get the 5 kw Victron quattro  as well

 whistlie Billi
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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
Justme
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« Reply #12 on: June 20, 2010, 09:53:29 PM »

You have over 100amps of PV but the controller can only use 80amps.
It will work but you will loose top end power (but get better bottom end performance).

I to run the FM80 with 100amps of PV but on a 12v system.

As has been said 48v might be better for you.
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
2 x Victron Multiplus II 48/5000/70
Cerbo GX & GX 50 touch
BMV 700
6kva genny
48v 1000ah
Grid Possibly coming soon
Outtasight
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« Reply #13 on: June 22, 2010, 11:23:27 PM »

I've got a 60A MPPT controller and 1458Wp attached to it.  At very low battery times (24V) that maxes it out at 60A but at absorption (28.2V) it's only about 52A.  On partially cloudy cool days I've seen the array surge to 109% of nominal output and that caused the controller to register an overload in its log (battery current was capped at 60A).

If you go 48V you can pick up old UPS inverters in the 3kW to 5kW range dirt cheap.
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http://solarbodge.blogspot.com/
3.58kWp & 800Ah LiFeYPO4 off-grid(ish). See 'Cobbled together PV in W.Sussex' (in "Show Us Yours")
Justme
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« Reply #14 on: June 24, 2010, 09:42:06 PM »


If you go 48V you can pick up old UPS inverters in the 3kW to 5kW range dirt cheap.

Just dont try to use the charger to charge you bank. They are sized to recharge an occasional use over a long period connected to the mains.
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
2 x Victron Multiplus II 48/5000/70
Cerbo GX & GX 50 touch
BMV 700
6kva genny
48v 1000ah
Grid Possibly coming soon
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