Rechargeable Battery Efficiency

[owg]

Does anyone have any data on the efficiency of rechargeable batteries. Something like (useable energy out)/(energy in) times 100, for one cycle. I could not find anything on this on Google. I am thinking of batteries of the type that can be found in a modern hybrid car.

HAZOP at

http://www.curryhydrocarbons.ca

 

[jmw]

visit thread769-167782 and follow the link to see what this company claims for its battery technology.

JMW

http://www.ViscoAnalyser.com

 

[GregLocock]

Roughly speaking there are two simple forms of losses. Coulombic efficiency, that is amp hours out is less than amp hours in, and resisteive, that is that you have to charge at a higher voltage than you'll get back.

Used over less than their full range lead acids are pretty much 100% for coulombic, and around 90% for resistive. If you try to deep discharge them, and fully recharge them, the overall efficiency rapidly drops to 75% or worse. Also, the coulombic efficiency drops rapidly as you increase the current, this is called Peukert's effect. Energy density is say 30 Wh/kg

Early Priuss used NiMH, 60 Wh/kg, see

http://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_NiMH_Overview.pdf

for efficiencies. That article also has NiCd batteries, which would need very careful management in a hybrid.

Actually that's a good document, as it makes clear there is no such thing as one efficiency number for a given battery. say 1.0/1.2 coulombic, and 1.27/1.4 resistive, ie 75% overall

The next step in hybrid batteries is some sort of Lithium Ion based system. 86% resistive, very non linear coulombic efficiency. If you can figure out how to use them these are the best bet.






Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[owg]

Thanks for that very good answer. The efficiency is not bad. I recalled learning in an economics course that power purchased in the form of non rechargeable batteries cost about 250 times that purchased from the local utility. I am glad that rechargeables are substantially better.

HAZOP at

http://www.curryhydrocarbons.ca

 

[Dinosaur]

Don't get too carried away. While the 250x value is extremely poor ( 0.4% eff ), you are measuring $ there and not energy. To get a proper understanding of the $ effeciency of rechargable batteries in this application you have to do a life cycle cost analysis of the rechargable which will be much less that 75%.