*3.2. Evaluations about the Safety Factor SF*

Figure 5 represents the hourly gas flowrates from the 6:00 of the analysed day to the 6:00 of the following day for the 2019. Different values of MNG are obtained depending on the days, i.e., the lowest flowrate is calculated during the weekends and during public holidays.

**Figure 5.** Hourly gas delivery for the 17 days analyzed in August 2019. Data from [45].

Figure 5 seems to show similar values for the lower flowrates. This trend has been further investigated. The results of the statistical data analysis for the three years are summarized in Table 6. As shown, the maximum and average flowrates are almost the same for the three years, while a difference occurs for the minimum value that in 2018 reached the smallest value, i.e., 16,965,404 kWh/h in the time period 02:00–03:00 of the 15th of August 2018. However, it should be noted that, considering a Gaussian statistical distribution for 2018 data, from a probabilistic approach the 99.7% of the values should be within the range [19,750,649 kWh, 93,321,690] (=μ − 3σ). Applying the Le Chauvenet's criterion the minimum natural gas flowrate calculated in August 2018 was discarded resulting as a statistical outlier. This value, in fact, could be justified by different reasons, such as for example a maintenance activity. Based on remaining data, the MNG was assumed equal to 30,000,000 kWh/h, i.e., an hourly natural gas flowrate of 2,529,511 Sm3/h based on the LHV reported in Table 4.


**Table 6.** Results from the data analysis performed concerning hourly gas flowrate in August 2017, 2018 and 2019.

(\*) The minimum value calculated in the 15th of August can be considered as an outliner and not considered for the analysis. Applying the Chauvenet's criterion a minimum value equal to 30,442,626 kWh/h results for 2018.

Due to the assumptions and simplifications performed for the calculation of the MNG, a safety factor SF equal to 0.9 was considered appropriate for the hydrogen threshold calculation.

#### *3.3. Computation of the Hydrogen Blending Threshold*

Applying Equation (12) and the values reported in Table 7 a corrected blending threshold equal to 27,293.4 Sm3/h, that are equivalent to 2326 kg/h of hydrogen, can be computed. Based on an annual timeframe of 3500 h/year, typical for a P2H plant for electric grid stability service [52], a total hydrogen production up to 8141 ton/year can be estimated. In Table 8 the results of the preliminary assessment are summarized.


**Table 7.** Parameters used in the calculation of corrected hydrogen blending threshold.


