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Is the acceptable DOD constant over the battery lifetime? (Decentralized energy system)

Is the acceptable DOD constant over the battery lifetime? (Decentralized energy system)

Is the acceptable DOD constant over the battery lifetime? (Decentralized energy system)

(OP)
Hi all,

I am currently working on a project to include a battery model to a photovoltaic system design simulation tool. We have already included a capacity degradation function to account for the reducing capacity until it reaches the end of lifetime.
However we would like to know from an operator's perspective if you would keep the depth of discharge constant as the capacity sinks (thus the minimum capacity is reduced), or should you rather keep the minimum capacity constant (therefore having a lower DOD).

Thanks!

RE: Is the acceptable DOD constant over the battery lifetime? (Decentralized energy system)

If you're picking a reasonable DOD as specified by studying the battery's data sheet then it likely will not matter which way you lean on this as other things will tend to bring down the pack, lifetime wise, before the nuances between the two modes you describe above will cause much difference.

The data sheets only give a cycle life based on a fixed DOD from Day One. Technically if you slowly reduce the DOD because you're only using 40% of the battery each cycle and the capacity is slowly decaying it would likely give you the longest life. But that may not be as cost effective as getting the most out of every cycle to do whatever you're doing with the battery power.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Is the acceptable DOD constant over the battery lifetime? (Decentralized energy system)

(OP)
thank you for your reply! Since we use the information from the data sheet I think it is then wisely to use a fixed DOD. Besides we want the more cost-efficient option and it seems this is the one.

RE: Is the acceptable DOD constant over the battery lifetime? (Decentralized energy system)

Howdy RC,
Just to confirm; we are talking about a lead-acid battery here, correct?
GG

"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

RE: Is the acceptable DOD constant over the battery lifetime? (Decentralized energy system)

(OP)
GroovyGuy,

The main focus is lead-acid batteries as the allowed DOD is lower than for Li-ion; therefore more uncertainties during planning. Would there be any extra consideration regarding this with Li-ion?

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