Lithium vs Lead; the Great Cost Debate.
Posted 02-03-2009 at 01:21 PM by mattW
Tags lead, lithium, thundersky, trojan
I've decided to try and work out the cost comparisons for a Lithium pack vs a Lead pack for a set range and a set number of years. Is Lead Acid actually cheaper or does is just seem that way up front? This article aims to find that out. The method is to get 10kWh of usable energy, I’ll try to get that with Lead and with Lithium and see what we find is cheaper in the long run. Assuming an efficiency of 250Wh per mile (a compact car) we should get a range of 40 miles (65km) with either pack. I’ll be using Australian prices since I’ve already researched them, but the comparison is probably close in other countries too.
The first step is to source a lithium pack with 10kWh of usable energy. The Lithium batteries I have chosen get 2000 cycles to 80% DoD and I estimate that at the 1 hr rate they will deliver 95% of their rated energy due to the Peukert’s effect. So to give our total energy we multiply our usable energy by 1.35 meaning we need 13.5kWh to get out 40 mile range with lithium batteries. If we assume a 120V conversion this means we need 112.5Ah. The cheapest Lithium batteries I have seen in Australia are Thundersky LiFePo4 LFP prismatic cells $2.50 per 3.2V per Ah. So our 13.5kW pack would take 38 3.2V cells at ~110Ah and would cost $10450 at normal prices (no group discount), without shipping or BMS.
For a Lead Acid pack we also need to keep the batteries at less than 80% DoD and at the 1hr rate we can only expect to get 55% of the rated energy of the pack back due to the Peukert’s effect. That means we need to multiply the usable energy by 2.25 to get our total energy, in this case its 22.5kWh. Trojan T605 batteries could make up a 22.5kWh pack with 18 batteries (108V, 210Ah) at $225 each or $4050, it didn’t say how many cycles it would take on the website but let’s guess around 650 to 80%. That means we’ll need to replace our lead Acid pack around three times for every lithium pack we buy, meaning our total cost for the lead packs goes up by a factor of 3 to $12150 over 2000 cycles.
Now I must admit that I didn’t look very hard for the cheapest batteries and I am only guessing the cycle life of the Trojans but even if it’s not precisely accurate it does show that the myth that Lead is clearly cheaper than lithium is not well founded. Lithium’s greater efficiency and cycle life makes up for its higher initial cost. I didn’t know what the results would be like before I started. The10kWh number was chosen just to make it easy to calculate, it has little influence on the result one way or the other. I thought the results would be close but not this close. Please note that the Lithium pack would require a BMS, which would cost $1270 but that still means you are going to pay around $12k whether you go with Lithium or Lead. It would also be worth mentioning that you would be paying for more electricity over that time with Lead; 36MWh costing $3600 compared to 21.6MWh $2160 @ $0.10 per kWh and recharging 80% of capacity. You would also need to water the batteries if you went with the Trojans, while the lithium’s would be maintenance free. It’s also worth mentioning that there are apparently disputed copyright issues with the thundersky cells and their previous record with customer support apparently not good, but this was just a cost comparison and the number look pretty convincing.
The total cost per km for the 2000 cycles is $15 750/ 130 000km = 12.1c per Km (19.7c/mile) for Lead Acid and $13888/ 130 000km = 10.7c per km (17.4c/mile) for the LiFePO4. These would obviously increase slightly when factoring in tire and brake wear. Just for comparison a the cost per km of a bunch of small ICE cars are listed here the cheapest being 41.44c/km but only 33.5% of that cost was for fuel and servicing (the rest being common cost for EVs as well) so that’s 13.9c/km for the cheapest ICE using fuel at $1.25/L. Clearly then EV have a price advantage over ICE’s especially now that normal unleaded is averaging $1.48/L.
In summary, while Lead Acid may be cheaper up front new lithium packs are more cost effective in the long run as well as being lighter, smaller and maintenance free. Obviously battery choices are highly dependant on individual conversions and budgets but it should not be assumed that Lead is the budget option, since it’s just not true anymore.
The first step is to source a lithium pack with 10kWh of usable energy. The Lithium batteries I have chosen get 2000 cycles to 80% DoD and I estimate that at the 1 hr rate they will deliver 95% of their rated energy due to the Peukert’s effect. So to give our total energy we multiply our usable energy by 1.35 meaning we need 13.5kWh to get out 40 mile range with lithium batteries. If we assume a 120V conversion this means we need 112.5Ah. The cheapest Lithium batteries I have seen in Australia are Thundersky LiFePo4 LFP prismatic cells $2.50 per 3.2V per Ah. So our 13.5kW pack would take 38 3.2V cells at ~110Ah and would cost $10450 at normal prices (no group discount), without shipping or BMS.
For a Lead Acid pack we also need to keep the batteries at less than 80% DoD and at the 1hr rate we can only expect to get 55% of the rated energy of the pack back due to the Peukert’s effect. That means we need to multiply the usable energy by 2.25 to get our total energy, in this case its 22.5kWh. Trojan T605 batteries could make up a 22.5kWh pack with 18 batteries (108V, 210Ah) at $225 each or $4050, it didn’t say how many cycles it would take on the website but let’s guess around 650 to 80%. That means we’ll need to replace our lead Acid pack around three times for every lithium pack we buy, meaning our total cost for the lead packs goes up by a factor of 3 to $12150 over 2000 cycles.
Now I must admit that I didn’t look very hard for the cheapest batteries and I am only guessing the cycle life of the Trojans but even if it’s not precisely accurate it does show that the myth that Lead is clearly cheaper than lithium is not well founded. Lithium’s greater efficiency and cycle life makes up for its higher initial cost. I didn’t know what the results would be like before I started. The10kWh number was chosen just to make it easy to calculate, it has little influence on the result one way or the other. I thought the results would be close but not this close. Please note that the Lithium pack would require a BMS, which would cost $1270 but that still means you are going to pay around $12k whether you go with Lithium or Lead. It would also be worth mentioning that you would be paying for more electricity over that time with Lead; 36MWh costing $3600 compared to 21.6MWh $2160 @ $0.10 per kWh and recharging 80% of capacity. You would also need to water the batteries if you went with the Trojans, while the lithium’s would be maintenance free. It’s also worth mentioning that there are apparently disputed copyright issues with the thundersky cells and their previous record with customer support apparently not good, but this was just a cost comparison and the number look pretty convincing.
The total cost per km for the 2000 cycles is $15 750/ 130 000km = 12.1c per Km (19.7c/mile) for Lead Acid and $13888/ 130 000km = 10.7c per km (17.4c/mile) for the LiFePO4. These would obviously increase slightly when factoring in tire and brake wear. Just for comparison a the cost per km of a bunch of small ICE cars are listed here the cheapest being 41.44c/km but only 33.5% of that cost was for fuel and servicing (the rest being common cost for EVs as well) so that’s 13.9c/km for the cheapest ICE using fuel at $1.25/L. Clearly then EV have a price advantage over ICE’s especially now that normal unleaded is averaging $1.48/L.
In summary, while Lead Acid may be cheaper up front new lithium packs are more cost effective in the long run as well as being lighter, smaller and maintenance free. Obviously battery choices are highly dependant on individual conversions and budgets but it should not be assumed that Lead is the budget option, since it’s just not true anymore.
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Total Comments 154
Comments
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Firstly, let me say that I am new to this forum, and this is my first post. I have spent some time wading through some of the topics, and the 15 pages of this topic! BTW, this should be a sticky if it isn't already.
I am currently in the process of researching building an EV, to replace one of my cars as a town runabout.
Having said that, I have been using electric assist on my bikes for the last year or so. I ended up building a recumbent trike with a hub motor, to use as my commuter vehicle, in lieu of building a full size EV.
I soon ditched the lead, mainly due to the weight and the crap performance from the lead batteries.
I went with a 36v/10AHr 'duct tape' LiFePo4 battery pack from China. Came with its own BMS and charger.
The pack only weighs 3.5 kg, and I can get the full 10 AHr from the battery. The discharge curve is fairly flat, and even though the voltage sags a bit, it is nowhere as bad as lead. Good for at least 30k's, and possibly closer to 40 k's. Don't really know as I haven't run the pack down to LVC.
These packs wouldn't be of any use in EV's though, as they are really only rated at 1C discharge, and I run mine at between 1 and 1.5C discharge.
Having said that, there are LiFePo4 packs that are rated at higher C ratings that would suitable for EV's.
Even though I cannot comment on the peformance difference between lead and LiFePo4 in an EV, I can certainly comment on their differences on an e-bike! And for me, its like chalk and cheese, and the LiFePo4 is the cheese!
Will I get my 1000 min cycles? I don't know.
What I do know, is that if/when I build an EV, I would prefer to use a LiFePo4 pack based on my e-bike experience. As long as I could get a high enough C rating! But that would depend on the setup that I will be aiming for for my purposes, but that would be a topic for another thread!Posted 10-10-2008 at 11:11 AM by freddyflatfoot 
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To start,
Tesla Motor and other ev start ups are using the small lithum battery packs in groups and then adding super caps and electronic controls, The prius PHEV use both lead acid or lithum. Johnson controls (Interstate Battery)has not geared up to mass produce lithum battery for automotive industry sector. Continential has justed started in Germany to manufacture lithum battery to be put in Mercedes. The cost of lithum battery for automotive application in the US is too high currentlyPosted 10-10-2008 at 04:11 PM by TexasCotton
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You can factor into the cost of lithium batteries that they can be sold for stationary off-grid solar PV systems use.They still have enough storage capacity for this application.
You can't build an ultrlight EV car with lead,only a lead sled.Posted 10-11-2008 at 11:32 AM by sunworksco
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You mean after their rated cycle life?Quote:Originally Posted by sunworksco
You can factor into the cost of lithium batteries that they can be sold for stationary off-grid solar PV systems use.They still have enough storage capacity for this application.
That's one thing I've been wondering. If a LiFePO4 battery is rated 2000 cycles at 80% discharge, what happens after 2000 cycles? Does it just have reduced capacity? On the LionEV 'upgrade to Lithium' page it refers to an 80% reduced capacity after the rated cycle life. I don't know how reliable that is, or how fast the capacity falls with each additional cycle, but even at reduced capacity the EV would still be useful for a while. I've kinda guestimated that my pack (whenever I may get it) will hopefully give me 68 miles at 80% DOD. I'd probably be able to use the car until the capacity was all the way down to 60% of the rated capacity before I wouldn't be able to make it to and from work.Posted 10-12-2008 at 08:57 PM by mark1030
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I've read that when it degrades not only is the capacity less but the power is also going down and the heat during discharge is going up. So it might work OK to retire a battery pack to off-grid backup if you don't have spikey loads but really, the batteries are starting to tell you that they are dying. It might not be safe to keep pushing them much longer. I wish it weren't so.Quote:Originally Posted by mark1030
That's one thing I've been wondering. If a LiFePO4 battery is rated 2000 cycles at 80% discharge, what happens after 2000 cycles? Does it just have reduced capacity?Posted 10-13-2008 at 01:17 AM by saab96
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The general rule seems to be that storage capacity is reduced to between 80% and 90% in all of the cycle life charts that I've seen (after 2000 cycles). I've been told by sales reps (so take this with grain of salt) that DOD of only 10-20% produces so little capacity loss that its hard to even measure after 2000 or more cycles.Posted 10-13-2008 at 01:48 AM by david85
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To rekindle more of the Lithium vs Lead debate, David85's pricing for Li-prismatics is working down to $.50/WattHour, of which it is ALL usable.
Lead packs have a characterisc such that you have a lot of power, but you can't use it all on each charge cycle or suffer from premature pack death at only a few hundred cycles. EV owners like to only use 50% of pack capacity to help save their packs.
A typical EV truck battery pack is 24 x Trojan T-125 providing 200*24*6 = 28880 Watt Hours. Price for Trojan is about $140 * 24 = $3360.
Lead acid total pack is ($3360/28880) = $.11/WattHour.
If you factor in that you can only use 50% of the available power in a lead-acid pack, the price for lead goes up to $.22/WattHour. So, Lithium is now only about twice the price of lead, but gives you 4 times the number of charge cycles at 1/4 the weight.
To fan the flames... I have unsubstantiated rumors that there are other large purchases at the $.30/Wh for the thunderskys. Over the next several months I hope to be reporting more of this, if and when the orders are filled. Let's keep our fingers crossed.
Mark.Posted 11-09-2008 at 08:04 AM by hardym
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You really need to add in the cost of a fully functioning BMS with lithiums, which can be substantial.Posted 11-09-2008 at 08:39 AM by JRP3
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Assuming you stay with the same battery type with each replacement pack or the BMS is particularly versatile, that's a one time cost just like any other fixed part of the EV (motor, controller, charger, etc...)Quote:Originally Posted by JRP3
You really need to add in the cost of a fully functioning BMS with lithiums, which can be substantial.
Posted 11-09-2008 at 08:56 AM by saab96
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That's a good point but it still needs to be paid for upfront if choosing lithium batteries over lead and should be added to the cost. You can eliminate it from the equation if it's your second lithium pack.
Posted 11-09-2008 at 09:23 AM by JRP3
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the lithium batteries are lighter per amp hour and this relates to less amp hours used per mile
so a true comparison would have to be in total kilometers driven by each pack.
this would take into account where a stuffed pack was just able to do the local commute befor replacment.Posted 01-15-2009 at 01:46 PM by piersdad
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Still no comparison. 72 volts and 225 amp hours of Trojan j186a hc batteries cost about 1500 dollars. Thundersky batteries that run the same voltage and amp hours cost 9 to 10,000 dollars.
Why buy lithium when lead is so much cheaper. If I could afford that much lithium I would be building a custom starship cruiser with an AC Propulsion drivetrain.Posted 01-16-2009 at 11:34 AM by Jason Lattimer
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Actually you can get a little cheaper than that since lithiums have more usable ah than lead. So a 72 volt 200ah pack will cost around $8000, take you farther, last longer, and be about one third the weight of the lead pack, which will improve drive ability all around. Yes it costs a lot more but it's not a straight comparison.
Posted 01-16-2009 at 11:44 AM by JRP3
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Thanks Freddy, exactly what i was thinkingQuote:Originally Posted by freddyflatfoot
I went with a 36v/10AHr 'duct tape' LiFePo4 battery pack from China. Came with its own BMS and charger.
The pack only weighs 3.5 kg, and I can get the full 10 AHr from the battery. The discharge curve is fairly flat, and even though the voltage sags a bit, it is nowhere as bad as lead. Good for at least 30k's, and possibly closer to 40 k's. Don't really know as I haven't run the pack down to LVC...What I do know, is that if/when I build an EV, I would prefer to use a LiFePo4 pack based on my e-bike experience. As long as I could get a high enough C rating!
I source 36v 15Ah packs from Hong Kong for electric skateboards. The performance of the LiFePO4 compared to the SLA they replace is nothing short of amazing! Running an 800watt motor the LiFePO4 pack will happily discharge at 30Amps (2C) for up to 70mins and provide peaks of 46Amps for extended hill climbs. Range of the boards has gone from 20kms (SLA) to well over 30kms (LiFeP04). Also, because of the flat discharge curve - you can ride at top speed (30km/hr) constantly...whereas with the SLA you would be down to 20-25 km/hr after only 10mins! Cheers, NigelPosted 05-09-2009 at 04:59 PM by kiwi_nigel
