In the latest report by Irena, the International Renewable Energy Agency (IRENA), entitled "Rise of renewables in cities: Energy solutions for the urban future", it is clear that large urban centres are responsible for 70% of the world's climate-altering emissions linked to energy production. According to Irena, the city of the future must pay more attention to urban planning and energy systems, so large cities (cities with a population of between 5 and 10 million inhabitants) must implement long-term programmes to increase the development of smart green cities, also encouraging the use of electric vehicles, energy efficiency in buildings, the implementation of storage systems and the adoption of intelligent energy management systems for the integration of high volumes of energy produced from renewable sources. The declared objective is to achieve the year 2050 with greater production of renewable energy in urban centres, only in this way can we hope to significantly reduce CO2 emissions and create more liveable cities. Of the 671 cities that have decarbonisation programmes, few metropolises aim to have 100% renewable energy. On the other hand, smaller towns and cities, with between 50,000 and 100,000 inhabitants, often promote ambitious plans to build urban networks powered entirely by green energy. Unfortunately, most of these cities are located in Europe and North America, leaving the question as to what the energy fate of southern countries such as Asia and Africa will be.
As far as the sources and technologies used are concerned, the use of solar thermal and geothermal energy in cities is increasing, although their potential remains virtually untapped, while the possibility of including wind energy in city contexts remains an open question that clashes with legislative, regulatory, financial and aesthetic limits. The real potential of photovoltaics remains to be discovered, once substantial shares of installed systems in urban centres are reached. A special focus should also be given to waste management which, especially in developing countries, should be integrated with energy management. It is estimated that 60-80% of the waste produced in these countries is organic and could represent an excellent resource to be converted into biogas.
