Is there a formula over time to show loss of MPG over time in Hybrids?

[darrellpruden]

Like the title says, is there a formula showing the loss of MPG in a hybrid car over time due to a loss in battery retention? Some colleagues and I were discussing this the other afternoon, when contemplating the purchase of a new hybrid vehicle. We all agreed that since a battery eventually becomes less and less retentive of its charge, the fuel consumption should go up over time. I do not know if the cars have been out long enough for anyone to have any data, but if they do, that would be greatly appreciated.

Darrell Pruden
Missle Division

 

[j2bprometheus]

No formula that I am aware of.

I recall seeing an article in WARD's that the batteries had proven more durable than Toyota had expected.

Did your collegues use total cost of ownership as a criteria? If so, then I think that a conventional small car or a car with a diesel engine might end up with the lowest total cost.

 

[dgallup]

Check out this link for an analysis of the total energy cost of many different vehicles. It doesn't directly address your question but it goes into complete life cycle energy cost. You won't be buying a hybrid after you read it.

http://cnwmr.com/nss-folder/automotiveenergy/

 

[darrellpruden]

Thanks for the info. My colleagues and I did do the research on total cost of ownership, and figured to wait a few years before buying, until then I guess we'll all have to stomach the $3.25+ till then.

 

[crysta1c1ear]

OK
I took this as an engineering question and didn't feel qualified to give a technical answer. If the question is more to do with buying a vehicle, it might be worth me noting that I read an article where an owner claimed his wife's MPG was improving with her Prius as the years went by. This was possibly attributed to instruments giving enough efficiency feedback to enable the driver to improve their driving style.
Of course a single example isn't reprsentative: she may have started ignoring stop signs and not slowing down for schools.
If I rediscover the article, I will post a link, but it is unlikely.

Even if a battery's charge capacity reduces over its life, does the charging and discharging efficiency reduce? I was wondering if something inside the battery with a flat surface at manufacture might more resemble a pumice stone (porous lava rock) after frequent use, have a larger surface area, and work better.

(Sorry, I should learn about batteries rather than drag the thread off topic!)

 

[GregLocock]

Chargeing effcnecy is composed of 2 parts.

The first is the excess voltage required to charge the battery, compared with its discharge value.

This doesn't seem to vary much with PbH+ batteries at least.

The second is the Coulombic efficiency, ie Amp Hours out over Amp Hours in.

My only experience with this is with gel cell PbH+ batteries, and that does not seem to change much over time, either.

Prius uses a very small proportion of the total capacity of its batteries, I think it tends to keep them at 50%+/- 10% charge - this is why it gets such a long chronological life out of them. Since defective cells can be replaced it seems to me that the effective life may be a lot longer than 8 years.




Cheers

Greg Locock

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