## 3 Methodology
The figure below (Figure 5) shows the impact of PV electricity production on the change in energy production from conventional sources (lignite and hard coal) in the morning power demand peak. For the purposes of describing the phenomenon, four days with the largest and the smallest volume of electricity production (June 2022) from PV were selected. All eight of the selected days were workdays (Monday-Friday). Based on the obtained results, it can be concluded that days with maximum PV production volumes translated into a significant decrease in production in hard-coal power plants (\(-15.5\%\)) and a relatively lower decrease in lignite power plants (\(-10.8\%\)) by comparing the difference in generation between 8 am and 12 pm. In the case of the four days with the lowest PV production, these drops were much smaller and amounted to \(-3.61\%\) for hard coal; for lignite they reached an average of only \(-0.17\%\). On this basis, it can be concluded that the high values of electricity production from PV displace the generation in coal-fired units in the first place, and to a lesser extent in those fired with lignite. This is due to two main factors: first, the problem with lignite storage (work in a continuous system: excavator-conveyor belt-power plant) and management pressure to limit the consumption of hard coal due to the cessation of its import from Russia. To estimate changes in the electricity generation profile in Poland, the data provided by PSE--the transmission system operator--were used. These data are aggregated by types of generating units and, in the case of thermal power plants, for specific blocks of these power plants (Table 2). Figure 5: _Cont_. In the case of renewable sources, the characteristic indicators are the utilization rate of the installed capacity and the self-consumption of the produced energy. In the case of wind energy in Polish conditions, there is practically no self-consumption, which results from its nature and specificity, where large wind turbines are connected to the grid and not to prosumer installations, as in the case of PV. According to data from ARE [58], such pro-consumer photovoltaic installations connected to the grid at the end of May 2022 in Poland were 1,104,597, with an average installed power of 7.4 kWp. The average annual self-consumption coefficient for these prosumers is estimated at the level of approx. 37% of the energy produced in the PV installation. Formula (2) presents the monthly installed capacity utilization ratio for photovoltaic and wind sources. \[PUF(m)=\frac{MP_{n}(m)}{IP_{n}(m)\cdot d(m)\cdot 24} \tag{2}\]  
where:  
_PUF_--monthly power utilization factor, %;  
_m_--month of analyses;  
_MP\({}_{n}\)_--monthly production, based on PSE Data, GWh;  
_IP\({}_{n}\)_--installed power source, based on ARE Data, GWp;  
_n_--technology (PV, HC or L); \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Year (Period)** & **Lignite, GWh** & **Natural Gas, GWh** & **Hard Coal, GWh** & **PV, GWh** & **Wind Onshore, GWh** \\ \hline
**2019** & 37,771 & 11,129 & 76,225 & * & 14,566 \\
**2020** & 34,423 & 12,693 & 70,184 & 1757 & 15,156 \\
**2021** & 41,558 & 12,801 & 80,299 & 4616 & 15,251 \\
**I-VI 2022** & 21,503 & 5334 & 37,084 & 4600 & 10,544 \\ \hline \hline \end{tabular}
* No data for PV.  
\end{table} 
Table 2: Total electricity production by source in Poland. Figure 5: Hourly electricity production from lignite, hard coal and photovoltaics. (**a**) Four days in June 2022 with the highest production of PV energy. (**b**) Four days in June 2022 with the lowest production of PV energy. \(d\)--number of days in the month. Since 1 April 2022, the method of settlement for photovoltaic prosumers has changed in Poland. Until then, the electricity produced by prosumers was settled in the discount system. The prosumer could return a surplus to the grid and, if necessary, collect up to 80% of its volume, so the power grid was de facto for him an energy store [57; 59; 60].