Use 24kWh Nissan Leaf Battery as powerbank for nightrate electricity

isnottheword

As per the thread title, could an end of life Nissan Leaf battery be used as a powerbank - to store cheaper off-peak nightrate electricity and 'spend' it domestically during peak/daytime hours?


Is there any financial or technical merit in that idea?

Joe1919

Hi. Just accept this below as a rough calculation.
I am assuming night rate at 10c per kwhr, day rate at 20 c per kwhr and the efficiency of your used battery at 70%.

It will cost 24 X 10c = 2.40 to charge battery at night.

The potential value of this energy during the day is 24 X 70% X 20c =3.36.

Your potential gross profit is 96c /day at 70% efficiency.

At 90% efficiency, this figure would be Euro 1.86/day

If your used battery efficiency is below 50%, you will actually make a loss.

PS What I mean by efficiency is power OUT divided by power IN as a %.

Your used battery may also have a lower efficiency in terms of reducing the kwhr capacity.

I have not taken into account other inefficiencies and costs.

air

Good post by Joe, he's spot on.
Also the batteries are hard enough to come by in the first place.

gctest50

plus the burning :

isnottheword

yup - thanks both. No harm in asking - if it's a non-runner, then perhaps I'll find a different use.


You're quite right - batteries are hard to come by. However, I'm driving a Leaf - but kind of set apart from other leaf drivers as I'll be clocking up serious mileage on it. Just thinking ahead. There may also be the opportunity to swap out the battery for a higher capacity battery as we move forward (already possible with the latest battery) - so if I was to find a good use for the original, might be able to justify.

Some folks using older batteries for solar - but again, not sure how the economics of that stacks up....

Speedwell

The idea might be useful to develop for emergency power in case of outages. Call me paranoid; I used to live on the Texas Gulf Coast and three hurricanes went directly over my apartment; I could have used a half-day or more of usable power just for the lights and a few fans. A gas-powered generator wasn't an option since it would have to be set in a shared area where it would certainly have been stolen.

isnottheword

gctest50 wrote: »

plus the burning :

I'd imagine it depends upon how the battery is used. Nissan don't have a cooling system for the Leaf battery but they did introduce this for the e-nv200 which effectively uses the same battery..

air

The cooling is only to improve charge rates and increase long term lifespan, it has nothing to do with fire prevention.
Fire is only caused by over charging or mechanical damage. The leaf has individul cell monitoring to prevent the former and excellent packaging to prevent the latter.

isnottheword

air wrote: »

The cooling is only to improve charge rates and increase long term lifespan, it has nothing to do with fire prevention.
Fire is only caused by over charging or mechanical damage. The leaf has individul cell monitoring to prevent the former and excellent packaging to prevent the latter.

Yeah, I thought as much - as never heard of it being an issue. Tesla had a problem on that front at one stage but I believe they sorted it out.

air

Telsa's batteries use thousands of 18650 style tiny cells, there are large numbers of individual cells in parallel so the potential for imbalance between parallel cells is quite large. I believe the indidvidual cells are fused but it's still not a great design IMHO, granted their execution is excellent but it's far from an ideal starting point. They only went with the cylindrical cells to take advantage of existing manufacting processes and availability.

The leaf battery only has 96 cells by comparison and they are only paralleled in pairs - so 48 pairs of cells in series.
Every 4 cells is packaged within an individual module container - like a sardine can, and these in turn are packaged within the overall outer container. It's relatively easy to replace individual modules within a few hours, there are a few specialists in the UK offering this service already for about £1000 IIRC.

isnottheword

air wrote: »

It's relatively easy to replace individual modules within a few hours, there are a few specialists in the UK offering this service already for about £1000 IIRC.

Only aware of one - Indra/Mike Schooling. Are there others you are aware of?
Id be hopeful that more third party service providers get involved with this - and that the cost of same comes down...

air

I think there's another guy on SpeakEV doing it as well as Mike Schooling.
The cost is pretty reasonable as is, there's a few hours work involved and they have to buy the modules also, balance all the cells and code them in I believe.

Nothing wrong with lead acid. Cheaper per kWh, less volatile, readily available components.

air

Lead acid produces hydrogen when charged and this needs to be piped outdoors to avoid the risk of explosion. It's also far more complex to charge than lithium and requires a lot more maintenance (for flooded cells - which are the only long lived ones).

Indeed. The paltry about of hydrogen they produce which is explosive at 3% to air can be recombined with hydrocaps, vented with a piece of fish tank tubing, sealed in a box with active ventilation, put in a shed with a draught or just compromise on performance and get VRLA.


They are nowhere near as complicated as lithium ion to charge. Maybe more hands on because there's no BMS but all you need is a good charge controller (which are rare) and occasional watering.

air

Far far far simpler than lead acid to charge.
Apply 4.2V per cell, limit current to relevant value - usually irrelevant if charger capacity is reasonable.
BMS just has to monitor cells and halt charging if any cell exceeds 4.2v.

It's easy charge li-ion cells with rudimentary temperature monitoring but batteries are another matter.
A lithium ion BMS is far more sophisticated than you are giving it credit for, it watchdogs individual cell voltage, temperature, balancing, coolant deployment (if there is any).
Of course you don't need one...a car engine runs fine without oil.

You'd get thousands of cycles from a li-ion instead of hundreds if you terminated charge at 4.05V instead of 4.2V.

What happens a li-ion battery if you tether it to a wind turbine and the dump load fails open circuit? FLA will gas using the electrolyte as coolant.

For FLA all you need is constant current to 2.47v per cell, constant voltage thereafter reducing current until the specific gravity reads 1.275 per cell, temperature compensating + 5mV per cell per °C below 25°C or minus 5mV per degree above.
A programmable 3 stage charger with a single external thermistor sensor can be automated to do this.
Do this once a week and otherwise keep them below 50% discharge they are as good as any other.

I get it, a 150 year old proven technology, 99% recyclable should make way for a new lightweight wall mountable technology that hasn't matured yet to prove if it's longevity claims are true or not. Regardless of the bottom line; price per watt-hour. I am reminded of this again and again and have to acknowledge the sensibility of the argument. I merely stated that there is nothing wrong with lead acid if you like to keep it simple and want a non-proprietary, durable, cost effective and less hazardous alternative with readily available off the shelf components and electronics.

The biggest problem I have charging FLA is finding a charger without ludicrously over-zealous end of charge safety margins that leave the battery at 10% DOD.

Tesla addressed the cell imbalance problem by using fuse tabs between cells, soon as one of the 444 cells per module pulls too much current it becomes redundant in the battery.

air

I know all about lithium ion batteries and have been working with them for over 12 years in high discharge environments. In my experience good quality lithium batteries rarely go out of balance if they are well protected mechanically and not over charged or discharged.
I directly manage millions of euro worth of batteries and spend several hundred thousand on them each year.

I don't think the dump load / wind turbine argument is a valid one, you could use a redundant dump load and any lithium battery should have an under / over voltage disconnect contactor on it in any case.
In the unlikely event of all dump loads failing you lose your wind turbine.

I mentioned the fusible links in the Tesla battery in post 10.

The only thing maintaining demand for lead acid batteries at the moment is cost and the costs of lithium ion batteries will continue to drop.
Once it drops a little more nobody will want to deal with lead acid any more.
They have already been displaced by lithium in virtually all mobile applications and many stationary ones.

Another great advantage of lithium is being able to read the state of charge accurately and repeatedly simply by measuring the resting voltage.
I use a small bank of 4 Nissan Leaf modules and it is ultra convenient, safe, light weight and I always know where it's at with regard to state of charge simply by looking at the voltage output.
I cycle it within 25 to 90% capacity with a balancing charger but it has never needed balancing.
Using a battery like the leaf one in a stationary environment makes for a very easy retirement, the charge and discharge rates are nothing like those experienced in a car and the temperatures are far more stable.

air

Pardon me, I find it strange then with such experience that you say lead acid charging is more complex.
For most people they turn on a charger once a day and turn it off when the green led blinks.

air wrote: »

I don't think the dump load / wind turbine argument is a valid one, you could use a redundant dump load and any lithium battery should have an under / over voltage disconnect contactor on it in any case.
In the unlikely event of all dump loads failing you lose your wind turbine.

True I intended it as an example of inherent redundancy.

air wrote: »

Another great advantage of lithium is being able to read the state of charge accurately and repeatedly simply by measuring the resting voltage.

So you have to disconnect all loads before you can ascertain the capacity? Why not just Coulomb count? Li -ion coulombic efficiency is good enough to do this reliably.



Really the best solution is drive the Leaf to a free charge point then power your house from that...

air

It's a matter of fact, not opinion, the lithium charge profile is far simpler.

Lead acid has 3 discrete charging phases, plus as you point out it requires temperature compensation of charge voltage set points.
Lithium has a single charge profile - apply 4.2V per cell, that's it, no temperature compensation, no different charge stages, end of story.
Lithium is less tolerant of severe over and under charge, but lead acid banks suffer from imbalance failures also and series strings fail in exactly the same manner.
The lead acid BMS systems I use all monitor individual blocks - they would monitor cells only that LA is such antiquated technology that there is no standard for cell taps in multi cell blocks. They fail in exactly the same manner as series lithium strings from a cell perspective.

You don't have to disconnect all loads, you can measure discharged also and it is a lot easier to do than LA, no fancy algorithms needed as the state of charge can be continually recalibrated any time the load is low.
Thee ability to simply check voltage at low or no load and get a 99% accurate estimation of state of charge with nothing more than a voltmeter is highly convenient.

air

Lithium Ion charge profile & clicky




Lead acid charge profile

Both are CC / CV and LA chargers are being adapted to charge Li-Ion because they are similar. Sure there's an extra float stage for those who don't use the lead battery, and an EQ stage for those how don't charge them fully.
You could charge either with constant voltage. Car alternators have been doing it successfully for a century.

Lithium Ion can't charge below 0°C

Tell me how do you limit charge to 4.2V and 90% SOC?

So lithium ion does not need a temperature sensor to compensate charge for ambient temp. but it does require a sensor on every cell for safety...complicated I guess is relative.

How does lithium perform at charging under load?

I don't believe it is the battery that is antiquated. They are also available in 2V cells and can be monitored any way you wish.
Balancing lead acid is a matter of charging until the specific gravity is 1.275 per cell, if this is not attained; charge until specific gravity is 1.275 per cell. Failures are rare once this is maintained.

Balancing lithium (which you do not advocate) requires either discharging the cells individually, charging the cells individually or floating a trickle current.

When a lead acid fails it's far less violent.

air wrote: »

no fancy algorithms needed

(Charged current)time - (load current)time = SOC.


All that aside the relevant detail that seems to be missed (bar post 2) is the cost per kWh to make a concession by using night-rate electricity during the day.

Neither FLA or Li-Ion have met a price point to be viable for this.
One is far, far closer than the other but you can work that one out yerselves.



Convert battery cycles over lifetime to kiloWatt-hours. (see manufacturer data if it is available...if it is not available treat with suspicion)
Add system costs.
Add solar PV.
Convert cost of system to price per kWh.


Subtract night-rate cost per kWh from day-rate cost per kWh.
Add ~15% installation losses to import.
Multiply answer by annual load minus annual PV input
Multiply answer by expected battery lifetime.
Factor inverter and battery replacement cost every 10-15 years.

Delta answers.

air

Charging under load?
It's simple arithmetic, if the charge current exceeds the load current the battery charges, if it's less the battery discharges, that's it.

Of course the lithium cells have a charge profile but the only important thing is how it affects the charger design, and it doesn't.
The charger only has to limit maximum ouput voltage, the variation in actual cell voltage is irrelevant.

On top of that, the lithium batteries require no maintenance charging, it's the same charge profile every cycle. No equalisation charging, no boost charging.

The state of charge calculation for lead acid is not a simple as you propose, if it was there wouldn't be a market for the likes of the smart gauge etc. Peukert effect and battery health all complicate matters and even with a fully featured management system it's difficult to estimate sate of charge to better than 10% accuracy.

Anyway that's all I have to say on it.

Sir Liamalot

I don't care to kick this around all day either air.

Sir Liamalot wrote: »

(Charged current)time - (load current)time = SOC.

I meant that as a Li-ion formula.

Yes FLA SOC is intricately complicated for deep cycles over 4 days. Not an issue if charged every day as meters can auto reset the drift at 100% SOC.
I can get my Ah meter ± 5% after a 3 week deep cycle with extensive micro-cycling...


By discharging under charge performance I was querying how they handle sustained high voltage & heat or are load compensating chargers available?

air

They age faster if stored at high state of charge for long periods, the same goes for temperature.
Heat is not likely to be an issue in this country.

I mean if you apply a load to a charging Li-Ion battery are there chargers designed to discriminate between charge power and load power to prevent overheating of the battery? This is a feature of the higher end FLA chargers but the basic ones will just see the total load as the battery SOC and cook the battery which would be more detrimental to a Li-Ion than a FLA...but undesirable in both cases.

air

The LiIon charger doesn't care about the battery capacity and will just supply current to the load until the battery reaches the set point, or indefinitely if it doesn't.
Say you were charging a 10Ah battery from empty with a 1A charger, after 5 hours you turn on a 1A load. The charger will supply all the load and the battery sits there oblivious. There is no heating of the battery as no current is flowing through it.

This is actually a big advantage of lithium as a standby pack for a renewables based energy system, it's ideal for being left mid range indefinitely. There is no need to cycle it fully, or to ever charge it to 100%. Far greater usable range of state of charge than LA too while retaining cycle life, so you can use a smaller Ah capacity pack for an equivalent storage requirement.

air

air wrote: »

The LiIon charger doesn't care about the battery capacity and will just supply current to the load until the battery reaches the set point, or indefinitely if it doesn't.
Say you were charging a 10Ah battery from empty with a 1A charger, after 5 hours you turn on a 1A load. The charger will supply all the load and the battery sits there oblivious. There is no heating of the battery as no current is flowing through it.

This is normal of a CV supply and electrical theory.

Let's take it further say the load is 500mA for 11 hours, does the charger hold the charge voltage of 4.2V heating the battery to the 11th hour or does it complete charge of the battery after 10 hours and then load supply at a more battery friendly terminal voltage?

The ability to not deteriorate without a periodic full charge and without entering the >95% SOC which is the most inefficient for a FLA is as far as I can see the only advantage the chemistry has other than weight for mobile applications, it's a big one but not a deal maker for me. Most of the year reaching a full charge every week isn't an issue. I'm usually out and about long enough to arrive home to a full battery, it's definitely not an issue to an installation with a grid supply other than an efficiency hit.

The usable range is 10% extra; FLA 100% - 50%, L-Ion 80% - 20% I factor this into kWh lifetime/ cost calculations. It's a lot cheaper buy 20% more lead.
The peukert exponent is actually a capacity advantage with FLA if you overspec. and work at >C50.

It occurred to me that charging with only CV the system is reliant on the charger ampacity to battery capacity relationship in that with too large a charger without current limiting the battery will be harmed (I appreciate you have mentioned this air although somewhat dismissively)
This is another benefit of li-ion the C0.5 charge rate, in that I wouldn't go past C2 charging with FLA and even then only under 85% SOC.

air

If the charger is connected it will try to hold the battery at the full terminal voltage indefinitely, regardless of load or state of charge.
If it's configured for 4.2V, then it will maintain 4.2V per cell indefinitely.
If the load exceeds the capacity of the charger then the battery will begin to discharge and supply some of the load current, and it's voltage will drop.
There is no heating in a Li Ion voltage that is being held at 4.2V as there will be no current through it.

Many people that live off grid will suggest that the usable range for lead acid is a lot narrower than that.
Working at C50 discharge rates on the other hand is never going to be economic.
Batteries have a calendar lifetime as well as a cycle lifetime. Far better to use the correct sized bank and replace it when required with one that's brand new.
Also saves you having to accommodate a huge bank, get it delivered and dispose of it.

The battery will be heated as it has an internal resistance. You can observe it experimentally if you have any doubts. I would call that method sustained overcharge. Why do you choose 4.2V and not a 20% larger battery charged to 4.05V that will last 5 times longer?

The usable range of LA is 50% you can compare the cost per kWh from 5% to 50% DOD and you will net the same result. Most people off grid want a big battery with ample reserve that lasts a long time hence the reduced discharge. Much like people with Ferraris don't drive to work every day at 200kmph.

I work at C50 - C75 it is a correct sized battery and entirely economic compared to replacing it every 4 years from over-discharge fatigue. Please don't tell me you have disposed of a lead acid that died of old age and not abuse....I have yet to meet one that has ever come to a natural end, giving me an example of a starter battery in a car isn't going to hold any water unless you can prove somehow that it was being correctly maintained.
In my experience either their carers kill them or they are running for decades.
People off grid need a battery that lasts a week not an overnight special. Which given a 12hour day discharge would be C170.
My battery is 100% efficient between 60% an 95% due to the reduced peukert exponent.

air

There is zero heating because there is zero current through the battery. LiIon has virtually zero self discharge so there is no trickle charging or anything else required. The internal resistance is irrelevant if it's neither charging or discharging.
There seems to be a fundamental gap in your understanding somewhere.

embedded clicky

I believe the gap is in taking what I'm told by manufacturers and salespersons and verifying or disproving it experimentally in real world conditions.
You could prove me wrong with an adjustable PSU and a thermometer or an ammeter.

embedded clicky wrote:

Permanent capacity loss is greatest at
elevated temperatures with the battery voltage
maintained at 4.2 V (fully charged).

****

Applying a continuous voltage to a battery after it is fully
charged is not recommended, as it will accelerate permanent
capacity loss and may cause internal lithium metal plating.
This plating can develop into an internal short circuit,
resulting in overheating and making the battery thermally
unstable. The length of time required is months.

air wrote: »

There is zero heating because there is zero current through the battery.

It is a parallel load of a given resistance in circuit.




My understanding comes from seeing starter batterys boiled dry across split charge relays from holding a 14.4V charge voltage at "no amps" while traction batteries with an order of magnitude greater capacity are being charged the other side of the relay.
It's a highly documented problem to which end there's chargers designed to prevent it.
Another common example I see is boiling electrolyte at charge voltages due to primitive chargers without load discrimination.