## 4 Urban Population and Urban PV Generation vs. Energy Sustainability
### Photovoltaic Generation in Cities and ETI 2017  
As mentioned above, cities are at the center of the energy transition due to their high electricity consumption and the high energy saving capacity of buildings. Additionally, given the uniformity of the distribution of the solar resource on a global scale [75], cities have the capacity to generate electricity near the same consumption points. By deploying PV systems in urbanized areas, cities can cover part of their electricity demand and contribute to the use of local energy resources in their countries. Thus, PV generation is the main technology to move towards the energy sustainability of cities. PV is the fastest growing renewable energy technology in the last decade. Its generation capacity has grown from 2026 MW in 2009 to 480,357 MW in 2018 [76]. [77] estimates that by 2023 this growth path will double, with a significant acceleration in the growth of distributed generation. Beyond the environmental benefits and energy independence of many regions, the deployment of PV technology could generate EUR 6.67 billion gross value added to Europe and 9 million jobs to 2050 worldwide [78]. The use of solar energy in cities is an objective already underway ([79] reports the commitment of 100 cities in the United States to cover 100% of their energy consumed with renewable energies. [80] reports the same objective for cities of the United Kingdom. [81, 82] study the feasibility of this possibility for the entire planet). On a voluntary basis, 65 cities from 56 countries in the world have reported, in 2018 to the CDP (CDP is a not-for-profit charity that runs a disclosure system on environmental data [83]) organization, their objectives for the use of renewable energies to be met in the next 30 years. Thirty-one of these cities include the use of solar energy, and 21 aim to reach 100%. Based on the great importance of PV generation in the energy transition, this section presents an analysis of the urban PV generation contribution to the energy sustainability of the ETI 2017 countries. The specific objective was to study the effect of the increase of this generation in the indicators \"concentration (reduced diversity) of electricity generation\", \"concentration (reduced diversity) of total PE supply\" (PE, primary energy), \"import dependence\", and \"GHG emissions from energy sector\" of the pathway calculator (WEC). The hypothesis followed for this analysis is that the use of the urban PV would allow these countries to obtain a better energy sustainability. Before addressing the description of the calculation and analysis procedure followed, the results obtained in the manipulation of the four pathway calculator indicators from which this hypothesis was raised are described below. Table 1 shows these results. Reducing the concentration of electricity generation would allow 113 of the 125 countries to obtain a better position in the ETI and; therefore, better energy sustainability. The reduction of the concentration in the total supply of primary energy would allow 106 countries to obtain a better position in the ranking. The reduction of the dependence on energy imports would also allow the 125 countries to obtain a better position in the ranking (only Denmark would retain the same position as in the other three indicators, because this country already has the number 1 position in the ETI ranking). For the last, the reduction of GHG emissions in the energy sector would allow all these countries to obtain a better position in the ranking. The empirical procedure followed to calculate the contribution of the urban PV generation to the sustainability of countries was the following.