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Last Updated: Jul 25, 2016 03:44PM MDT

What capacity are the Depth of Discharge inputs for the Lifetime curve?

 

HOMER assumes that the battery needs replacement after a certain kWh throughput, which it calls the ‘lifetime throughput’.  It assumes this lifetime throughput is a constant, independent of depth of discharge, rate of discharge, time spent at low state of charge, and every other factor.
 
When you create a new battery in HOMER, HOMER calculates the suggested value of the lifetime throughput from the lifetime curve, but the lifetime throughput is actually an input that you can change.  The lifetime curve itself has no direct effect; it exists in HOMER only as a means of estimating the lifetime throughput.
 
That’s my indirect answer to your question.  My direct answer is I don’t know whether you should use the C20 numbers or the C100 numbers or some other numbers for the lifetime curve.  You should use whichever numbers you think will lead to the best estimate of the lifetime throughput.
 
That probably means that if you expect the battery will typically experience charge and discharge rates in the range of the C20 rate, then the C20 rate lifetime numbers are probably the right ones to enter.  But of course that is a tough call to make a priori, and in the end I suspect that the uncertainties in the estimation of the battery lifetime overwhelm any difference that would result from using the C20 lifetime numbers versus the C100 lifetime numbers.

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