When talking about ecological transition, we mean that the world we live in cannot be split into parts to be managed separately without having any environmental consequences. Energy, mobility, waste, logistic, industry, infrastructures (green, blue and grey), tourism, society, wild life, etc. are all parts of the same system and we do need a holistic approach to manage them together. We shall, thus, move toward a new model based on the laws of ecology, that are, according to Barry Commoner: (i) everything is connected to everything else, (ii) everything must go somewhere, (iii) nature knows best, (iv) there is no such thing as a free lunch.
A large part of this transition revolves around energy. This includes the way we transform, distribute, store, use, and redistribute it in our environment. Energy transition means shifting from a linear (forward-oriented) model, based on the massive exploitation of fossil fuels, to a circular (cradle-to-cradle) model, based on the massive exploitation of renewable energy. Since a large proportion of this energy exploitation takes place in cities or is meant to enable activities happening in cities and among cities, actions on urban environments should be at the top of the priority list of decision-makers leading the transition.
The inception of any possible energy transition in urban environments includes the inevitable step of reducing the energy demand by lowering the operational energy use of buildings and by reducing new embodied energy, since, even in cities, “there is no such thing as a free lunch”. To do so it is necessary to maximise the energy retrofit of the existing stock. Renovating buildings means reusing materials and structures and enhancing recycling, with a consequent lower extraction of new raw materials. To decrease operational energy, a minimum amount of new materials and construction activities is nevertheless required (e.g., for thermal insulation).To this purpose we should maximise the use of regionally produced components with a high recycled content, as well as rapidly renewable materials with a certified management of the natural resource.
This is not an approach that will undermine the economy: on the contrary, it requires a complete rethinking of the technologies we use to build our environment and to track the impact within our cities, and it is therefore capable of renovating and restarting the whole architecture, engineering, and construction industry sectors.
Once the demand is reduced we need to supply generation, distribution, and control systems with the highest level of efficiency. The so-called smart grids are energy networks enabling a high degree of control of electric flows, necessary to balance instabilities generated by the massive use of renewable energy sources, such as solar and wind. Smart grids allow the transmission of energy and data, and may go beyond electric power, becoming multi-carrier grids. Although the electrification of many final energy uses is an ongoing process following the diffusion of renewable energy, it will take a long while, if ever possible, before the whole final energy use of a city will be based on electricity only. In the meanwhile, we may promote smart district heating and cooling systems, that, enabled by remote control may substantially contribute to the decarbonisation of our cities by exploiting renewable energy and waste heat.
Stockholm is leading the way in this sector, with a district heating system powered by excess heat by data centres and from purified wastewater.
Hydrogen networks, although still to be considered at an early stage around technology, may also contribute to improving the efficiency of the energy distribution system, but only if hydrogen is produced via the exploitation of renewable energy (green hydrogen). Many technical and economic issues are, nevertheless, yet to be addressed before adoption at the city level is feasible.
In general, a further exploitation of renewable energy sources should be pursued in cities, as envisaged by the EU. To this purpose, it is necessary to maximise local generation and use on-site, that, typically, in cities means exploiting photovoltaic panels, geothermal networks and micro-wind power. Smart grids, empowered by technologies such as block chain, may enable the exchange of locally generated renewable energy as a commodity among peers (consumers and prosumers), helping the diffusion of these technologies. Following directives such as the European Renewable Energy Directive Recast and the Internal Electricity Market Directive, new models of collective self-consumption and energy community are rising in EU, and have already proved viable outside of the EU (e.g., in New York, Brooklyn). However, it is in less developed countries where these schemes may reach their maximum effect in terms of social benefits and decarbonisation, especially where solar energy production is high and no or low-heritage constraints exist for existing architecture. A multidimensional approach to the building envelope may also help, which means starting to consider the envelope of buildings as an active, though architecturally beautiful, building system. Building integrated photovoltaic may represent a game-changer that enables the diffusion of energy communities both in urban and rural environments; however, a lot of research is still required in order to overcome technical and aesthetic limitations of current solutions, promoting deeper coordination among heritage authorities, professionals and manufacturers.
To make the overall system stable, without recurring to combined cycle power plants or nuclear power plants, energy storage needs to be deployed either at the building, neighbourhood or district level. Electrochemical storage is not the only option, as thermal storage may prove to be a viable solution too, especially in the case of geothermal networks. Thermal storage may also rely on the use of phase change materials, although early applications concern only the building scale. The grid itself still represents a form of storage, and interconnected macro-cells of energy communities, in the form of local micro-grids, will allow, in the near future, to improve the grid balance, limiting the dimension and spread of power batteries that represent an environmental challenge yet to be solved. Cities might thus play a crucial role in the stability and management of the national power grid, operating as cells aggregating many important neighbourhood energy communities.
Since no building and city actually use energy, but humans who live in them do, people’s engagement is the cornerstone of energy transition. Badly operated low-energy buildings may indeed use more energy than fairly operated low-performance buildings. Technology, and in particular artificial intelligence, may help improving buildings and cities control, but it cannot totally substitute humans. A deep understanding of the crucial role that our everyday actions have on the health of our environment is the fundamental basis for any transition to a better environment. The transition is first of all human, and although technology may help it, education and information are the essential pillars that will sustain it.