HOMER Energy Support

Battery capacity curve data

Last Updated: Jul 25, 2016 03:46PM MDT

When defining a battery’s capacity curve, we need to specify multiple points on the capacity-versus-discharge-current graph, and each of those capacity values must be measured using the same cutoff voltage (voltage per cell).  Here’s an example:


That’s what I call a ‘capacity curve’: multiple capacity-current points, with each capacity value defined using the same cutoff voltage. 

Some product brochures provide a single capacity curve, as on page 2 of the attached Deka brochure.  Some actually provide multiple capacity curves, each for a different cutoff voltage, as on pages 8 & 9 of the Exide brochure.  (In a case like that, we would have to choose a cutoff voltage and use only that capacity curve.)

In some cases, brochures specify only one point on the capacity curve, and that’s clearly not enough for us.  But in some unfortunate cases, brochures misleadingly specify multiple capacity-versus-current points where each capacity value is measured using a different cutoff voltage.  This looks like a capacity curve, but it isn’t.  We can’t use this kind of data in HOMER.  The EcoSafe brochure is one example:


The Hoppecke OPzS brochure does the same thing:


We need to be careful about this when creating a battery in HOMER using data from a brochure.

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