## HOMER Energy Support

### Minimum SOC in HOMER

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

As we saw in some articles the minimum SOC has an important effect in optimization of renewable energy systems. If we want to consider different minimum SOC in our project, how we can carry out this? In battery input windows of HOMER it is an icon (NEW) that when we click it, a new window is opened with the specifications of a type of battery (for example Hoppecke 24 OPzS 3000) which we can change these specifications. So, the question is that, if we change the minimum SOC of the battery, how we should take this change in battery costs. For example, if the initial cost of a type of battery with a minimum SOC of 40% is \$1100, how this value should be taken for a minimum SOC of 20% or 50%?

In HOMER, the minimum SOC is a property of the battery, so to model a battery with two different values of minimum SOC, you will need to create two different battery types, which differ in the value of the minimum SOC.

The cost of a particular battery does not depend on how you decide to operate that battery.  So I think you should use the same initial cost regardless of the minimum SOC you assume.  But the minimum SOC may affect the battery lifetime, so you might want to change the lifetime throughput as you change the minimum SOC.

Presumably the lifetime throughput decreases as the minimum SOC decreases, but I have no way of knowing how.  My guess is that the lifetime throughput falls off a cliff as the minimum SOC gets low enough to permit physical damage to the battery such as sulfation:

That graph is imaginary.  I have never seen a graph like this, so it’s just my guess.  If this graph is roughly correct, then HOMER’s approach, where the minimum SOC is a property of the battery and you set it as low as you think is safe, is the correct approach.  There would be no point in optimizing the choice of minimum SOC.

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