3.4.3. Stage "2"

Finally, the degree of self-consumption of electricity produced in potential photovoltaic sources was determined and the averaged values of the degree of auto-consumption in individual enterprises were presented.

Based on hourly historical data:


$$Ep\_{PV} = \frac{Y\_{EC}}{1000} \ast H I\_h \ast \eta \ast \frac{1}{1000} \tag{1}$$

where:

*EpPV*—electricity produced by the *PV* installation on an hourly basis, kWh

*YEC*—*PV* installation power, kWp (average annual electricity demand, kWh)

*HIh*—horizontal insolation on an hourly basis, kWh/m2/year

*η*—efficiency factor of the components of the *PV* installation, assumed *η* = 0.9

The value of the self-consumption electricity was estimated on an hourly basis based on Equation (2). These values were determined for the period from 5 March to 31 May of the following year (10,872 h).

$$\text{Esc}\_{PV} = \begin{cases} \begin{array}{l} H\_{\text{EC}} \text{ if } : H\_{\text{EC}} < Ep\_{PV} \\ \begin{array}{l} Ep\_{PV} \text{ if } : H\_{\text{EC}} \ge Ep\_{PV} \end{array} \end{cases} \tag{2}$$

where:

*EscPV*—hourly consumption of *PV* produced electricity, kWh *EpPV*—hourly *PV* electricity production, kWh

*HEC*—hourly electricity consumption, kWh

The averaged value of the self-consumption coefficient was determined (Equation (3)) as the quotient of the sums of self-consumed and potentially produced electricity in 8760 consecutive hours (Equation (4)).

$$HSCc = \frac{Esc\_{PV}}{Ep\_{PV}} \ast 100\% \tag{3}$$

where:

*HscPV*—hourly *PV* electricity self-consumption coefficient, %

$$\text{SCc} = \frac{\sum\_{1}^{8760} Esc\_{PV}}{\sum\_{1}^{8760} Ep\_{PV}} \ast 100\% \tag{4}$$

where:

*SCc*—annual average *PV* electricity self-consumtion coefficient, %

The specified research sub-periods covered the period from 5 March 2020 to 31 May 2021 (10,872 h) and the corresponding period in 2018/2019. In order not to disturb the analysis on an annual basis, due to the two-stage occurrence of the spring season in the analyzed sub-periods (2112 h), averaged values of the self-consumption coefficient were determined for the next 2112 observations of moving average values from the previous 8760 h. This shift removes the impact of seasonal variability while using the full knowledge of the analyzed sub-periods. The course of the variability of the coefficient is shown in the Section 4.5.

With a low power of the installation, the self-consumption of the produced energy will occur practically always [54] while with the rescaling of the installation, the degree of self-consumption of electricity decreases and, at the same time, the self-sufficiency increases [18,55]. Apart from the power of the installation, the very degree of correlation of the profile course, while maintaining the conditions for which they were determined, remains approximately constant.

## **4. Results of Numerical Analysis of Research Objects**
