3.2.2. Battery Energy Storage System

The storage system is composed of a 10 MWh/2.5 MW lithium iron phosphate (LFP) battery, whose round-trip efficiency is assumed to be constant at 90%, as in [18]. A cycling degradation model, based on depth of discharge (DOD) is implemented, sourced from a finalization of the degradation curve presented in [19]. The model calculates degradation by using rainflow counting of the cycles performed during the day and determines the State of Health (SOH) lost based on the DOD of these cycles, in accordance with the curve shown in Figure 4.

**Figure 4.** Cycling degradation model.

A calendar degradation model, sourced from [20], is incorporated into the plant model. This model is based on tests conducted on different LFP batteries over 899 days, where they were maintained at various SOCs and temperatures. The test results for 25 ◦C were selected and are presented in Table 2.

**Table 2.** Calendar degradation results at 25 ◦C [20].


As depicted in Table 2, daily calendar degradation can be represented as a linear function of SOC. Since it is also considered linear with respect to time, the following expression has been obtained from the table:

$$\text{Deg}\_{cal}(h) = \text{SOC}(h) \times \frac{1.2 \times 10^{-4}}{24} \tag{7}$$

where the following apply:

