Batteries for completely off grid solar

We have lived off grid for ten years and I am always keeping an eye on the latest battery technology and talking to our local solar company.
Unfortunately ,at this stage of the technology it seems the best choice for completely off grid battery storage are lead acid gel batteries.
I won’t go into all the whys and wherefore but this is the consensus from people who should know.
Lithium etc may be suitable for on grid supplementation but as yet they cannot do the job completely off grid.
Go solar and save your grandchildren!


I’ll have to disagree with your buddytess. I’ve lived off-grid since 1991, and am really glad to have ditched Lead-acid batteries in 2012, and installed a LiFePO4 battery. I’ve done all my own ELV off-grid work, and the efficiency of the LiFePO4 battery is way, way ahead of any Lead-acid battery. I monitor my system with a high accuracy data logger with 1 and 5 sec sampling and Lithium chemistry just blows Lead-acid out of the water with performance and efficiency.


Hello Gordon
Thanks for your feedback.
I am very interested to know more about the LiFe batteries.
What capacity a/hrs do you have and what wattage panels do you match them with?I presently run a 12volt/1200 amphour system.
What draw down can you comfortably/long term expect?
Price? Where did you buy them?
Fire hazard?
Size?Weight?Installation requirements?
Thank you

My LiFePO4 battery is 400AH @52V nominal (21kWh), and I currently have about 7kW of PV panels connected. 12V systems are generally reserved for small camping/portable systems these days, due to their inefficiencies at high load.

Over summer I often use 40-50kWh per day, mainly due to running a large water chiller for Rainbow Trout in an aquaponics system. Current use is averaging around 25kWh per day. Overnight depth of discharge is generally around 40-50%, although I’ve been below 80% occasionally. I do a reasonable amount of MIG welding, and run washing machine, toaster, dishwasher, microwave/oven (I bake bread a few times per week), induction hob, 2 freezers and a fridge, 5 water pumps for house and AP, air pumps for AP, computers etc.

Before I installed the large AP system, I ran the house and a smaller AP system for over 2 years with about 4kW of PV and no generator use at all, which was a big change from using Lead-acids, due to their inefficiency- they needed frequent generator use in cloudy weather, as they shouldn’t be discharged very deeply at all if you want them to last.

I bought the Lithium cells from an EV place in WA, although they no longer stock that size in CALB cells. The 16 cells were about $10000.

There is no fire hazard with LiFePO4 chemistry, nor any acid fumes. They weigh 228kg, hugely less than an equivalent usable capacity of Lead-acid battery.


Hello Gordon
Thank you for your speedy response…
We got "stuck"with the old 12volt system when we bought the place and I realise it is inefficient but a big job to completely rewire etc.
You have double the panels(about 3.5 kw) we have and about 1/3 more equivalent battery capacity.
I am thinking about 1200 ahrs @12volts would do us as we do not have the load you are carrying.
I echo your negative comments about lead acids recharge/discharge etc but did not realise these LiFeSO4 batteries were commercially available in the sizes I needed.
The only negative I can see re these c/w lead acid is they appear to be about double the price. Any ideas?
Thanks for your advise.

Double the upfront price, yes, but the long term cost of energy delivered is significantly less than a decent quality Lead-acid battery. Keep in mind that you only need about 50-60% of the nameplate capacity of a Lead-acid battery, as you can safely discharge them much more deeply. You can also safely discharge them at a much higher rate, and without losing significant capacity due to the Peukert Effect.

With daily discharging of a Lead-acid battery to 50% DOD, most would be lucky to last a year or 2.

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All good points ,Gordon . . .
I understand there are some specific requirements for charging/discharging?
Low voltage cutoff>2.5 volts , high voltage cutoff 3.2volts/cell or 12.6volts for a 12volt system?
Could I use my existing Plasmatronics PLC reprogrammed or would I need a new PLC?
To keep all cells balanced a “battery management system” is coupled to each cell as there is no equivalent charging procedure using over voltage as per lead-acid?
Any other points that one should know about with LiFeSO4 batteries?
What brand are yours?You are obviously happy with them. . . .
Once again thanks for your advice and time

Yes, there are requirements, just as there are for Lead-acid batteries, although some types of Lead-acid can take more abuse and survive.
Low Voltage Disconnect of 2.5V (for high discharge rate), or above that for non EV use. I have my inverter set to turn off at 48V, which is an average cell voltage of 3V. If you go to 2.5V under low discharge rates, you may well wreck a cell, as it will be completely discharged.
I’m currently charging to 3.44V/cell (but have it set a bit lower in summer). I’m not sure where your 3.2V/cell comes from, but if it were true, you couldn’t charge your battery!
A Plasmatronics regulator could do the job if you can correctly set the charging voltage set points and absorb time.

It is recommended that you use a BMS, but I haven’t run one for 3 years myself, as I keep a close eye on the battery via my data logger. If you have a ‘hands off’ approach, then you’d definitely want to use one. I do run cell balancers, that supposedly help keep the cell voltages close, but I notice they still diverge a bit at low states of charge, and at the very top of end of charging.

No, you cant do an equivalent of an high voltage equalise charge for a Pb-acid with any Lithium battery.

Other points: there is no Sulphur in LiFePO4 - Lithium ferrous phosphate :wink:

My cells are CALB, but I have replaced one with a Winston cell last year, as its capacity was a bit down on the others, and CALB 400AH cells were not available then, supposedly not being made according to the importer, but I have seen them for sale in the US.

A friend of mine is looking into solar with battery storage but apparently you need at least 20 solar panels for the system to operate properly, is this correct?
Like all new technologies, there are many pitfalls and opinions.

The panels generate the power and the number required depends on what the power requirements are over what time span. .
More power needed more panels required. . .
Best to start with working out what electrical items you need to power and work backwards.

Impossible to say, without a lot more information

For my boat I did a quick search for “LiFePO4 battery” and found on ebay they started at around $550 for a 620CCA with many being over a $1,000. They would need to three times better than lead to justify the cost.

Hello jeoffer
I am starting to come round to Gordon’s point of view . …
For my situation I need about 1200 amp hours of lead-acid batteries for a draw down of about 240amp hours I.e about a 20 % draw down.
The latest lead acid gels would cost me about $4500.
I would require about 500 amp hours of the LiFePO4 s to provide the same draw down at a 50% discharge rate.
I have had a look on the net and I can get 600 amp hours of LiFePO4 for just over $5000 so it is line ball on cost and I believe the technology is superior to lead acid . . .

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Interesting topic. I’ve often thought about storage on my place, which is quite small and has a lot less fish than yours @gordon ! but we do get a lot of sun - an annual daily average close to 22 Mj/m^2. Looking to get 4.5kw of panels soon …

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22.5MJ/m^2/day sounds quite sunny, here it is a bit over 18, or 5kWh/m^2/day, which is about what it has averaged so far this year, although 10 days of June so far have been mostly overcast/foggy all day. The generator has been getting some use.
If you can keep your daily usage to 10-12kWh on average through winter, and cut back in cloudy weather, then with ~20kWh of LiFePO4 battery, you could probably get through winter without the need to use a generator, with 4.5kW of PV.


We had some clouds the other day … it’s sometimes a little surreal when there are clouds and the remote prospect of rain, we had 4.4mm of rain in February, nothing since. January on the other hand was ‘swimming month’ but still much sun :slight_smile:

Based on my last power bill, I use about 22kWh per day - but a little over a week ago I turned off the hot water (we have solar minus the boost button, so it was going by thermostat rather than human intervention) last place I had I probably used the boost button a couple of times in 6 years so I reckon this will be the same - that should reduce usage a little. I recently optimised a lot of lighting so that should trim it further.

A friend currently has 18 panels (256w each I reckon) and says he does 20kWh at the moment - summer is better, 32kWh or thereabouts …

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Hello Gordon
I have been following up re purchase of LiFePO4 batteries and I am looking at 700 ahrs @12V ie about 8 kwatts which should be fine for our usage of about 4kwatts given a 50 % DOD.
Ev Products seem to be the most competitive but difficult to contact/follow up .
Is this" company" run out of someone’s garage in Perth?
Also they say a bms is not required as they balance the batteries before despatch and as long as correct high and low voltages are maintained then the batteries will stay balanced.
EV company on the other hand have manufactured their own bms for maintaining equivalence between cells and bring up the point of runaway cells causing a fire.
As these batteries are going to be under our house I am thinking I better get the bms as “a belts and braces” approach.
Could I please have your thoughts re the above?
Thank you

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Hi Buddytess, firstly, I’d recommend going for a nominal 24V (in Lead-acid parlance, 26V for LiFePO4), rather than 12V system, due to greater efficiency and ability to handle higher loads without having to go to ridiculously large cable size. 12V systems are generally only used for camping or portable systems these days.

I suspect most of the purveyors of Lithium batteries for the DIY market are sole traders with ‘out of the garage/shed’ type operations, as the market is so small, and getting a response from them can be difficult at times.

A Battery Management System is generally used to protect the battery from single cell and overall battery high and low voltage excursions, disconnecting it if any voltage strays out of the safe zone. However, a BMS should only be the protection of last resort. Your inverter should have a suitable low voltage disconnect for the battery, which stops them from being discharged too deeply. You should use a good quality MPPT charge controller to charge the battery from PV panels, and with suitable settings it should keep the top end voltage in a safe range.
Cell balancing may not be required initially in the “balanced cells” 12V batteries, but I think in time the state of charge will drift apart, so, having some sort of cell balancer is a good idea. The ones sold by EVPower only bleed off a bit of charging current (2A, not enough in my experience) at high voltage (3.65V/cell) - too high a voltage for long battery life in the opinion of many, myself included.
I’ve bought a balancer from the US that (supposedly) actively balances the cells across the whole operating voltage range, and it does a reasonable job most of the time, except near full charge and at low states of charge. There are a number of different brands of this type of balancer available if you do an internet search. IMO they are far superior to the ones that only bleed off charge at the top.
I’ve operated my 16 cell LiFePO4 without a BMS for a few years now, but trust my inverter to disconnect at the correct low voltage, and keep an eye on the battery with a data logger, so I have a pretty good idea of how it is going, and if I need to run a generator to stop the state of charge going too low. One of these days I’ll probably put together a BMS of sorts for disconnecting some PV panels if the voltage goes too high, and disconnecting the loads if it goes too low, using a relay driver.


Another article on Renew Economy about the biggest threat to domestic battery storage, on or off-grid, in Australia. Standards gone mad!


Thanks @gordon

It seems like a policy written by power industry representatives.

What happened to the slow, methodical, world’s best practice approach Standards Australia used to follow?

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