LiFePO4 - The future for off-grid battery banks?

[Ampster]

Thanks for the update and for bumping this thread. It is interesting to reflect how the technology has evolved. I have not stayed with the same LFP cells in 12 years but have continued to believe it provides the best long term value for energy storage despite the continued scepticism. The EV conversion community saw this value equation twelve years ago.

[plateauhops]

Hi All,

Well it's almost been 12 years now - thought I'd update in my System and the LiFePO4 cells.

So our original solar panels were getting old so I sold them locally , and used the cash to offset new set of panels - so now have 6200W. Got an extra 60A MPPT regulator, so I have 2 banks of solar with a regulator on each in parallel charging batteries. Haven't used the generator in ages for charge as I now charge when I need to from my Leaf - I can give details if you are interested, but suffice to say the 12V battery in the car is in parallel with a DC-DC converter with the main traction cells and you can draw1700W ish out if you want to.

Still same LiFePO4 cells so the lifetime is great - IO remember folks had said it was untested technology etc but honestly the data at the beginning spoke for itself as being superior in every way to PbA.

Anyways - I hope all is well out there to anyone still watching this thread!

Regards,

Steve.

Hi Steve,

I just logged in for the first time in around a year, but I recall LifePO4 being next- gen back in 2010. I still think they are a lot "greener" than Lead-acid, but recently my local utility company co-op sent me in their newsletter an article about "iron-air batteries". Some major companies like Amazon are investing in this. The idea of batteries being 10x as dense as they are seems like a game changer. While I think there are benefits to buying LifePO4 battery banks (if the budget can allow it), there are a lot of reasons where it may not yet be economically feasible, nor able to store enough power to run certain things like heating and AC. But what if energy storage could be so dense as to be able to accomplish full home heating and cooling? Some homes are relatively energy efficient, but in northern climates they still require a lot of energy to heat via electric (oil/space heaters) (or heat pumps which have a co-efficiency of performance of 3x the former). It would be nice to have an energy storage medium capable of converting both solar thermal panels water- and photovoltaic into usable heat- but storing it may not be necessarily more efficient by converting it into a battery than a water heater using sunlight to warm water- to an extent. I am thinking https://en.wikipedia.org/wiki/Thermal_energy_storage may have some residential applications, perhaps hybridizing both solar thermal and solar photovolatics into some usable energy that is not just heat. for example, if warm weather causes an excess of heat, that heat could be stored and converted into electric power using a tubine. But in colder weather, having only sunlight might limit the amount of power a thermal energy storage system could provide, thus a PV system would need to be quite adequate. Maybe PVs already do this, but may need 60 panels to product 20kwh in northern climates.

[steveg]

Hi All,

Well it's almost been 12 years now - thought I'd update in my System and the LiFePO4 cells.

So our original solar panels were getting old so I sold them locally , and used the cash to offset new set of panels - so now have 6200W. Got an extra 60A MPPT regulator, so I have 2 banks of solar with a regulator on each in parallel charging batteries. Haven't used the generator in ages for charge as I now charge when I need to from my Leaf - I can give details if you are interested, but suffice to say the 12V battery in the car is in parallel with a DC-DC converter with the main traction cells and you can draw1700W ish out if you want to.

Still same LiFePO4 cells so the lifetime is great - IO remember folks had said it was untested technology etc but honestly the data at the beginning spoke for itself as being superior in every way to PbA.

Anyways - I hope all is well out there to anyone still watching this thread!

Regards,

Steve.

[miahallen]

steveg, thank you for staying active in this thread

[steveg]

I saw the Latronics inverter in your picture and thought, here is yet another system in Australia or New Zealand.
As PNJunction said, thanks for the update. Your system is the oldest that I have seen an update on.


Looks like a perfectly sized LFP battery if you are running a generator with just over one days storage capacity (~15kWh). I would be interested to know how often you have to run your generator.

We have a smaller system and requirements, we have 1140W of solar panels, 360Ah@24volts LFP battery(~9kWh around three days storage capacity) installed in April 2013, 4kW inverter and no generator. Our winter requirements are ~2.5-3kWh and summer ~5-6kWh. Like you, cooking is done on induction hotplate and electric oven in summer and wood stove in winter.

If one didn't want to run a generator, now that solar panels are so cheap I would look at oversizing the solar array and decreasing the battery to maybe two days storage capacity.

If the battery lasts ten years I have calculated that the cost of storing power in our battery will be ~$0.40-$0.50/kWh, for your system I calculate around $0.30/kWh assuming you are storing around half you daily consumption.

Simon

Hi Simon,

Yeah system works well still - 6+ years in. Generator runs are only really in winter, and not every day. On a nice crisp day in winter we still get 12-14kWh power - anything less than around 7kwh the day previous then we would start the generator the next day. So in summer : we would only run generator say 2-3 times on horrible cloudy days - most cloudy days give us 8-12kWh ('summer' starting late August through early May) 8 months of the year.

Batteries have only been deep cycled (power dropped out) a handful of times say 20? maybe - otherwise everything well.

Our 'otherwise' cost would be NZ$0.30/kWh + NZ$1.00 per day connection fee - 10yrs 13kWh/day = NZ$3650 connection fee + NZ$14235 power ... nice.

So far it's been 6 (and a bit) years...

[karrak]

Hi All - Well, we're almost at 6 years for install from my original message - batteries seem as fresh as the day we put them in - LiFePO4 so far seems quite superior to PbA. We still use an induction cooktop and dishwasher and oven when we have power for them... Generator runs are in winter months or more than 2 days rain/dark days. Approx 90hours generator total run time each winter season ~ approx 135Ltrs gasoline. haven't had to replace an LED lightbulb.

We went from aging NiCd batteries (ex railway locomotive batteries that I got for free) that you never knew how much energy they had stored in them with woeful efficiency to the LFP battery. The change in performance is hard to believe!

Thanks for the information on generator run time.

I would be interested to know what voltage and cut off current you charge your battery to and if you float the battery.

I used to think that floating LFP batteries could be bad for them, but am now of the view that charging to 3.45 V/cell and floating at around 3.35 V/cell will not decrease the lifespan of them and will give you a battery that is close to 100% full at the end of the day if there has been enough sun.

Thanks
Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger
Latronics 4kW Inverter, homemade MPPT controller

[solar pete]

Howdy steveg, thanks for popping in with that info, very good to see 6 years on the same set of batteries and all is well, good stuff, well done sir

[steveg]

Hi All - Well, we're almost at 6 years for install from my original message - batteries seem as fresh as the day we put them in - LiFePO4 so far seems quite superior to PbA. We still use an induction cooktop and dishwasher and oven when we have power for them... Generator runs are in winter months or more than 2 days rain/dark days. Approx 90hours generator total run time each winter season ~ approx 135Ltrs gasoline. haven't had to replace an LED lightbulb.

[PNjunction]

If the battery lasts ten years I have calculated that the cost of storing power in our battery will be ~$0.40-$0.50/kWh, for your system I calculate around $0.30/kWh assuming you are storing around half you daily consumption.

Kind of a side note about costs vs Pb ... maybe it's been hammered to death, but most cycle-life comparisons and so forth don't take into account that most people murder their Pb batteries long before the lab-rated performance data is reached! Ie, sulfation, no eq for flooded, undercharging agm, etc in a typical solar setup.

For LFP, once you get it under control, be it a commercial system, or a diy version for a battery geek, the chances of murdering cells in OUR application can be remote. Not impossible surely, but the chances of meeting lab specs, even half-way, is probably greater in probability than lead acid in the real world. That real-world maintenance issue (with QUALITY lfp cells, not counterfeits or used hacks) vs lab-specs can make it less costly than marketing charts make it out to be.

[karrak]

Hi Everyone - well another post on the progress of my LiFePO4 batteries - you may have seen my initial post to this thread 5yrs ago?

I saw the Latronics inverter in your picture and thought, here is yet another system in Australia or New Zealand.
As PNJunction said, thanks for the update. Your system is the oldest that I have seen an update on.

Our home is off-grid and has been for approx 5.5yrs now – we have 4kw solar – we have LiFePO4 and *not* lead acid (PbA). We use no gas to cook or heat our water and our *annual average* consumption is 12kWh per day – our highest peak is 29kWh consumed in 24 hrs. In summer we easily generate 20kWh per day and in the middle of winter (on a sunny day) we generate 12kWh (my guess) per day. We get snow, but not as much as some I guess...

(late addition – I got off my arse and got the numbers - We have generated a total of 25.984MWh in 5yrs 148days (my meter tells me) so there’s the average – 25984kWh / 1974 days = 13kWh/day)

Looks like a perfectly sized LFP battery if you are running a generator with just over one days storage capacity (~15kWh). I would be interested to know how often you have to run your generator.

We have a smaller system and requirements, we have 1140W of solar panels, 360Ah@24volts LFP battery(~9kWh around three days storage capacity) installed in April 2013, 4kW inverter and no generator. Our winter requirements are ~2.5-3kWh and summer ~5-6kWh. Like you, cooking is done on induction hotplate and electric oven in summer and wood stove in winter.

If one didn't want to run a generator, now that solar panels are so cheap I would look at oversizing the solar array and decreasing the battery to maybe two days storage capacity.

If the battery lasts ten years I have calculated that the cost of storing power in our battery will be ~$0.40-$0.50/kWh, for your system I calculate around $0.30/kWh assuming you are storing around half you daily consumption.

Simon

[PNjunction]

Wow - pretty clean. From the looks of it, I see no physical issues with what appears to be the older Hi-Power white cells, which EV'ers used to trash pretty often.

Kind of a testament to our "sub-c" application where even the lower cost cells, if taken care of, can provide good service for at least what - 7 years now?

Have you done any preventative maintenance since then - like checking cell voltages with your own multimeter just to make sure the bms is still playing nice? Are those cell bolts snug? (careful here!!).

Thanks for the update. That's rare on most forums.

[steveg]

Hi Everyone - well another post on the progress of my LiFePO4 batteries - you may have seen my initial post to this thread 5yrs ago?

Our home is off-grid and has been for approx 5.5yrs now – we have 4kw solar – we have LiFePO4 and *not* lead acid (PbA). We use no gas to cook or heat our water and our *annual average* consumption is 12kWh per day – our highest peak is 29kWh consumed in 24 hrs. In summer we easily generate 20kWh per day and in the middle of winter (on a sunny day) we generate 12kWh (my guess) per day. We get snow, but not as much as some I guess...

(late addition – I got off my arse and got the numbers - We have generated a total of 25.984MWh in 5yrs 148days (my meter tells me) so there’s the average – 25984kWh / 1974 days = 13kWh/day)

I encourage you to look into Lithium Iron cells – on paper my calculation (electronics engineer by trade) says they will have a lifetime of 15->20+ years – remember a PbA battery you can only use 1/3 of its capacity, you can’t take large prolonged loads from the cell, it doesn’t like uneven charging/discharging (i.e. clouds go in front of sun) and it doesn’t like temperature variation in order to get your 10yr lifetime. PbA also has much lower charge efficiency averaged over its lifetime so your PV panels will charge the cells less and less over time.

To illustrate - We cook on an induction cooktop, our water is heated by the excess power (along with solar hot water tubes) – we have a 320m^2 5 bedroom + study home with triple garage (3445 sq ft) – So that’s 240M^2 living space (2580sq.ft)

Our battery pack is 300Ah at 48V and weighs 160kg and fit in the back of my car (not pickup/truck) to bring it home – it is the equivalent in *usable* energy to a 1000Ah 48V PbA bank – it has a lid too of course - it cost me $7000USD in 2009 (purchased before be built house)

We have a 7kW sine inverter and a 2kw Honda petrol generator which takes 4litres to fill and can run for 3.5hrs to charge for the day when sun is hiding.

I haven't noticed any life degradation in the battery at all so far ... but I guess I cant make a strong claim on capacity claim unless I put an amp-hour meter on it and cycle it.

Steve...

[Sunking]

Out of curiosity, would there be any way to charge cells in parallel, but discharge them in series? That way you wouldn't have to worry about them getting out of balance, right? Or would the added complexity not be worth it? (Well, that and the amperages would be so much higher too; a miniscule 200w solar array would work down to roughly 60 amps at 3v5...)

To complex, but not nessecary. When you recieve new Lithium batteries, .all manufactures instruct you to connect all the cells in PARALLEL. From there either Bottom Balance or Top Balance. You cannot take new cells with a BMS and Top Balance. It could take years to do that. You need something like a Powerlab 8 to do this. With a Powerlab 8 you can discharge at 40 amps, or charge at 100 amps.

As for getting depends on how you use them. If you are using a BMS with Shunt Boards or Cell Monitor you will go out of Balance. In other words if you Top Balance they do go out of Balance. If you Bottom Balance and do not connect Monitors, Shunts, or BMS they rarely ever ever go out of Balance.

[Living Large]

(Well, that and the amperages would be so much higher too; a miniscule 200w solar array would work down to roughly 60 amps at 3v5...)

I know that most (all?) off-the-shelf charge controllers wouldn't be able to output voltages that low, but just being a curious noob

You answered your own question, both on voltage and current. Nothing will work with that low a voltage, and a moderate size system would require several hundred amps of current. And how would such a system be automatically "reconfigured"? You'd end up with something on a par with the Space Shuttle - they don't fly those anymore.

[organic farmer]

... Out of curiosity, would there be any way to charge cells in parallel, but discharge them in series? That way you wouldn't have to worry about them getting out of balance, right? Or would the added complexity not be worth it?

You guessed it. The added complexity would be horrible.