Li vs Lead: Cost Debate.
by mattW Livs Lead-Cost Debate
I've decided to try and work out the cost comparisons for a Lithiumpack vs a Lead pack for a set range and a set number of years. IsLead 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 ofusable energy, I’ll try to get that with Lead and with Lithium andsee what we find is cheaper in the long run. Assuming an efficiencyof 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’vealready researched them, but the comparison is probably close inother countries too.
The first step is to source a lithium pack with 10kWh of usableenergy. 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% oftheir rated energy due to the Peukert’seffect. So to give our total energy we multiply ourusable energy by 1.35 meaning we need 13.5kWh to get out 40 milerange with lithium batteries. If we assume a 120V conversion thismeans we need 112.5Ah. The cheapest Lithium batteries I have seenin Australia are $2.50 per 3.2V per Ah. So our 13.5kW pack would take 38 3.2Vcells at ~110Ah and would cost $10450 at normal prices (no groupdiscount), without shipping or BMS.
For a Lead Acid pack we also need to keep the batteries at lessthan 80% DoD and at the 1hr rate we can only expect to get 55% ofthe rated energy of the pack back due to the Peukert’seffect. That means we need to multiply the usable energyby 2.25 to get our total energy, in this case its 22.5kWh. A leadpack could make up a 22.5kWh pack with 18 batteries (108V, 210Ah)at $225 each or $4050, it didn’t say let’s guess the cycle lifearound 650 to 80%. That means we’ll need to replace our lead Acidpack around three times for every lithium pack we buy, meaning ourtotal cost for the lead packs goes up by a factor of 3 to $12150over 2000 cycles.
Lithium’s greater efficiency and cycle life makes up for itshigher initial cost. I didn’t know what the results would be likebefore I started. The10kWh number was chosen just to make it easyto calculate, it has little influence on the result one way or theother. 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/ 130000km = 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 slightlywhen factoring in tire and brake wear. Just for comparison a thecost 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 (therest 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 EVhave a price advantage over ICE’s especially now that normalunleaded is averaging $1.48/L.
In summary, while Lead Acid may be cheaper up front new lithiumpacks are more cost effective in the long run as well as beinglighter, smaller and maintenance free. Obviously battery choicesare highly dependant on individual conversions and budgets but itshould not be assumed that Lead is the budget option, since it’sjust not true anymore.