## 3 Methodology  
The purpose of creating the methodology is to determine how the development of renewable energy sources in Poland (in this case PV sources, which are more predictable than wind sources on the whole-region scale) influences the change in the energy generation profile and thus (with a large reduction in the share of carbon sources) on the reduction of CO2 emissions. The conducted analysis is based on the historical similarity of the replacement of conventional (carbon) sources by PV by determining in how many cases (%) a specific carbon source will be replaced (Figure 4). It will also allow determination of the reduction of CO2 emissions within the National Power System (NPS) and the demand for hard coal. In the case of demand exceeding the domestic production, the analysis will allow determination of the volume of imports. The universal access to electricity requires efficient operation of an extensive system for its generation, transmission and distribution. In Poland, over 80% of electricity is generated in thermal power plants (mainly lignite or hard coal), with an increasing share of generation from renewable energy sources. It is still not possible to store a large volume of electricity (excluding pumped storage power plants), which in practice means that at any time the amount of energy produced in power plants must be equal to the energy consumed by consumers. In Polish conditions, this translates into a reduction in electricity production in thermal power plants on sunny and windy days (hours) by replacing their production potentials with RES. Analogically, it works also in opposite conditions: during windless and cloudy days (nights), almost all of the demand is covered by coal power plants (with a small share of hydropower plants, flow and pumped storage, and natural gas and biomass thermal power plants). For individual energy sources (hard coal, lignite, photovoltaics), important for the analysis, the average emissivity was determined according to Formula (1) as the following:  
\[SE=\frac{PPSE}{EPCP} \tag{1}\]  
where:  
\(SE\)--source emissivity, millions of tonnes CO\({}_{2}\)/TWh;  
\(PPSE\)--power plants source emission, based on EU ETS Data, millions of tonnes CO\({}_{2}\);  
\(EPCP\)--energy production on coal power plants, based on ARE Data [53], TWh. Domestic electricity consumption in 2021 increased by 5.36% per annum and amounted to 174.4 TWh. In the same period, total electricity production increased by 13.97% year on year to 173.58 TWh. Thus, the balance of international exchange amounted to 0.82 TWh (the majority of imports). In 2021, 93.04 TWh of electricity was produced from hard coal (an increase by 30% year on year), 45.37 TWh from lignite (an increase by 19.5% year on year), 13.37 TWh in gas power plants (decrease by 4%), and in wind farms14.23 TWh (increase by 0.4% year on year). According to EU ETS data, in 2021 the production of electricity from hard coal resulted in the emission of 82 million tons of CO\({}_{2}\) (which, with the production reported by Polskie Sieci Elektroenergetyczne S.A. (PSE) [54,55], gives an average emission of SE at the level of 880 kg CO\({}_{2}\)/MWh), from lignite 50 million tons of CO\({}_{2}\) (SE value 1100 kg CO\({}_{2}\)/MWh) and emissions caused by electricity production from natural gas 7 million tons of CO\({}_{2}\) (525 kg CO\({}_{2}\)/MWh). On the other hand, according to the Intergovernmental Panel on Climate Change (IPCC) report from 2014 [56], the average equivalent of renewable energy sources (mainly related to their production and maintenance) is 11 kg CO\({}_{2}\)/MWh for wind  
Figure 4: Simplified algorithm of the proposed methodology. turbines and 44 kg CO\({}_{2}\)/MWh for photovoltaic panels. This value may be slightly different for specific installations, which results, among others, from their productivity, location or investment scale [57].