## 4 Urban Population and Urban PV Generation vs. Energy Sustainability
### Photovoltaic Generation in Cities and ETI 2017
so to supplement this information in the calculations, the usable area of the rooftops of the city of Barcelona (BCN) was used as a reference. To be able to analyze the useable rooftop area of each of the selected cities, the ratio 0.0512 was used (see Equation (3)). This is the ratio between the usable rooftop area of Barcelona, a figure obtained from the map of Barcelona's renewable resources map [84; 85], and the area of the city. The solar generation capacity data for each of the selected cities were obtained from the global tilted irradiation (GTI) from the Global Solar Atlas of the World Bank Group [86], using a figure of 16% efficiency [87] to calculate the PV generation (see Equation (2)). The equations calculations are the following:  
\[PV\_Urban\_Generation_{(\text{Country})}=\sum_{City}PV\_Generation_{City}, \tag{1}\]  
\[PV\_Generation_{(\text{City})}=\upmu\times GTI_{City}\times Rooftop\_Area_{City}, \tag{2}\]  
\[Rooftop\_Area_{(\text{City})}=Area_{City}\times Rooftop\_Area_{BCN}/Area_{BCN}. \tag{3}\]  
As a result of this selection of countries and cities, 183 cities were identified from 123 countries (Finland and Iceland were not included because there were no results for them in the GTI indicator): Sixty-seven of these countries were represented by means of one city and 59 with two cities. Data from the International Energy Statistics of the U.S. Energy Information Administration (EIA) [88] were used to calculate the distribution of the electricity generation mix of the study countries. In addition, in the calculation of CO\({}_{2}\) emissions, emission factors calculated by [89] (based on data from the International Energy Agency, IEA) were used. Figure 10 presents the distribution of the electricity generation mix and the hypothetical urban PV generation of each segment of the ETI ranking countries. According to these results, in each segment, generation with fossil fuels has a major presence and the first segment has the lowest hypothetical urban PV generation. The 125 ETI 2017 countries would vary, on average, in the concentration (reduced diversity) of electricity generation by \(-\)15.94% due to the hypothetical increase in their urban PV generation. This would have an impact on the reduction of 56.31% of the power electric generation from fossil fuels, and consequently on the reduction of 64% of the CO\({}_{2}\) emissions of these countries. According to these results and based on the hypothesis, the urban PV generation of these countries would allow them to improve their energy sustainability (excluding from this conclusion the countries that worsen their position by the variation to the minimum in the four indicators used of the pathway calculator). Additionally, the use of the local solar resource would allow these countries to improve their sustainability due to the reduction of the dependence on energy imports. Although the diversity  
Figure 10: Share of the electricity generation mix and share with urban PV (Photovoltaic) generation by ETI ranking segments 2017. Note: Renewables—biomass and waste, geothermal, solar, tide, and wave electricity, and wind. (towards concentration) of the primary energy supply would be reduced in some countries, the increase in consumption of renewable resources would allow them to reduce CO\({}_{2}\) emissions. Table 2 summarizes the averages of the results obtained, and Figure 11 presents graphically the results of each segment of countries in the ranking. As indicated in this table, the first segment of the ranking shows the lowest variation of fossil-based electricity generation (\(-30.93\%\)) and the fifth segment the largest variation (\(-91.41\%\)): The first segment is occupied by countries with \(32.35\%\) of the fossil generation, on the other hand the fifth segment only represents \(1.2\%\) of this generation; this indicates that in this segment PV generation has a broader scope to replace fossil-based electricity.