Fuel Savings post 1-tonne weight reduction (if any)!

We are considering use of Lithium batteries as alternative to the lead acid batteries, there are various reasons for it. I note that the Lithium batteries are around 7 times lighter in weight for the same output. This equates to roughly a metric tonne reduction in weight. Would there be any fuel savings from such weight reduction, lets say for an SD70ACe locomotive. I just cant get my head around the Hp-Hr/gallon values that usually are quoted for freight locomotives. I was hoping it would be a simple mpg calculation that we are accustomed to, when quoting car fuel efficiencies!

Not really remember in railroads tonnage on the axles on the locomotives determines the tractive effort which means how much cargo you can pull. Now in air cargo or space lifting you pull a ton out of the carrier the plane or rocket they literally will give you the money in kind back.

i knew that the answer to this is far from simple.
I was thinking of ways how a one-tonne reduction in loco weight can be realised e.g. for a given number of trips a locomotive makes per year, an additonal tonne can be pulled. If we times that to the size of the locomotive fleet, you get a few loaded wagons’ worth of extra tonnage every year. Then you times that by lifecycle of locomotive etc. etc. etc.

Lithium ion batteries would be a bad idea on a locomotive, as their lifetime gets dramatically shorter when hot (above 100ºF) and don’t work at very cold temperatures. Other battery technologies may work better, but lead-acid batteries are a known quantity in RR work.

The weight savings from a lighter battery may be best used by increasing fuel capacity.

Anyone who owns a car knows that lead acid batteries don’t work very well either in sub zero F. A WAG in my mind is that the percent decline is probably similar for both batts.

I looked into temperature ranges for Li-ion batteries after seeing your post. The gist was the Li-ion performance drops off rapidly below 32F and lifetime starts dropping off above 100F and gets really bad above 140F. Based on that, I would say that lead acid batteries have a somewhat wider usable temperature range than Li-ion batteries. LFP batteries have a bit wider temp range than Li-ion.

Remember CSX created their ‘Heavy’ locomotives. Adding an additional 20 tons of weigh to the standard AC traction GE locomotives in concert with some software changes to the fuel mapping. Prior to the Heavies, normal was two units on 80 cars of coal. Once the Heavies were introduced, two heavies were good for 90 cars of coal.

Thanks all for comments so far. We operate in desert environment in the Middle East (i should have mentioned in my OP). Lead-acid battery are maintenance hungry (servicing locations for topups are limited on our 1500 KM long network) and prone to overheat (especially during summer months where mercury consistently tops 50 degrees C). They’ve struggle to last beyond 3 years. We also have NiCd batteries on few locomotives, they have survived better (5 years plus) with very little maintenance but are six times as expensive in comparison to lead-acid. The Li-Ion costs only 3 times as much as lead-acid and can be considered maintenance free for the proposed life of 8 years (or more). So, it is worth considering for us, considering the circumstances.
Back to the original question, a tonne of weight reduction on locomotive equates to WHAT if anything, saving of fuel or being able to haul an additional tonne of cargo per trip or …

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The physics that benefit race cars does not benefit rail transportation. Weight on rail is a big part of being able to move large loads on rail. CSX added 20 tons of weight to their ‘heavy’ locomotives and is able to haul roughly 715 tons of additional freight on their routes.

Lithium batteries have an abysmal fire safety record - in your 50C environment I suspect lithium to be even more suspect. I am nowhere near an expert in battery technology and the consequences of each variety.

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Lithium batteries literally if overheating will self ignite and then burn even underwater as they provide their own oxygen. The risks aren’t worth it in my opinion. You’re saving some weight but risking a fire that could consume an entire locomotive and the environmental damages from the diesel fuel leaking from that. Not worth it stick with the lead acid or look into AGM batteries they seem to last longer.

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If ambient temperatures exceed 50C, the you will need to limit charge of Li-ion battery to 80% to prevent rapid deterioration of the battery. I’m pretty sure that a Li-ion battery will need an active cooling system for that application.

It is a consideration at this stage, however the said batteries have been in use for nearly 5 years with some freight operators in Australia (with similar temperatures).
It does have internal cooling, trip mechanisms and fire suppression so the design seems to be mindful of risks such batteries present.