HOMER Energy Support

Battery Failure Criteria

Last Updated: Jul 25, 2016 03:24PM MDT

In the battery details window to form the lifetime curve „depth of discharge“ and „cycles to failure“ have to be entered.  What is the definition of the batteries failure? Is it for example, when the battery will not reach 80% of its initial capacity?


HOMER does not model the degradation in battery performance with use.  It assumes that the efficiency and capacity of a battery remain constant right up until the time that it fails and needs to be replaced.  HOMER uses the lifetime curve to determine that time of failure.  Manufacturers usually provide a lifetime curve showing cycles to failure versus cycle depth, or at least one or two points on that curve.  In the lifetime tests required to produce such a curve, manufacturers must define the failure of the battery, but I do not know what definition they use.  In the limited amount of lifetime data I have been able to obtain, I don't believe I have ever seen that definition spelled out.

Whenever I create a battery, I simply enter whatever lifetime curve data the manufacturer provides.  If one manufacturer uses a more generous definition of failure than the others, then batteries produced by that manufacturer will appear artificially long-lived in HOMER.

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