Energy Transition in Metropolises, Rural Areas, and Deserts. Louis Boisgibault

scale. They affect the energy sector in many ways, for example, in the manufacturing of photovoltaic cells. They are based on monocrystalline silicon, polycrystalline silicon, thin films and organic substances. For crystalline silicon, the silicon is melted and then gently cooled to obtain a single homogeneous crystal (monocrystalline) or more quickly to obtain multiple crystals (polycrystalline).

      The crystal is cut into ingots to work at a scale of 200 µm and form photovoltaic cells. For thin films, silicon is fixed in thin layers of only a few micrometers on a glass or plastic support.

      Other rare materials such as copper, indium, gallium, selenium and cadmium telluride can be used. For organic photovoltaic cells, an active layer is made up of organic molecules. Nanotechnologies miniaturize equipment and increase its performance at a lower cost.

      Biotechnology is defined by the OECD as “the application of science and technology to living organisms, as well as its components, products and modeling, to modify living or non-living materials for the production of knowledge, goods and services”. They make it possible, for example, to produce biofuels, organic products alternative to oil and gas from raw materials, plant sugars and algae, which are transformed into finished products and biogas using microorganisms. They also allow the treatment and elimination of pollution.

      New generation computing impacts data processing capacity, production systems, microelectronics, energy system components, smart grids, data transmission and blockchain.

      Finally, the cognitive sciences aim to describe, explain and simulate the mechanisms of animal and human thought. They model complex information processing systems capable of acquiring, storing, using and transmitting knowledge. This artificial intelligence helps to consume less energy, to better appreciate local consumption to adjust production and to preserve the planet’s limited and non-renewable hydrocarbon resources.

These NBICs are currently transforming the exploitation of stock energy (hydrocarbon and nuclear), with their associated networks, and will allow flow energy to become more competitive for the production of electricity, heat, fuel and fuel.

      Table 1.1. Properties of renewable energies

Sectors	Electricity	Heat	Combustible	Fuel
Biofuel				X
Biomass	X	X	X	X
Biomethane	X	X	X	X
Marine energies	X
Wind turbine	X
Geothermal energy	X	X
Hydropower	X
Solar photovoltaic	X
Thermal solar energy		X
Thermodynamic solar energy	X	X

      Biofuel is an agrofuel produced from non-fossil organic materials, vegetable oil (rapeseed, algae) or alcohol (sugar, starch). It is important for metropolises and rural areas to reduce dependence on fossil fuels.

      Biomass comes from organic matter of plant or animal origin in solid/liquid form that can be used as an energy source. Its direct combustion produces heat which, through cogeneration, can also produce electricity. The fermentation of organic matter can produce biogas or biomethane (CH₄). Its chemical transformation by pyrolysis can produce fuel and biofuel. Wood fire, which is the combustion of solid biomass, is the traditional means of heating in all spaces. In metropolitan areas and rural areas, the challenge of collecting, sorting, incinerating and recycling household waste is important for producing recovered heat and electricity. A collective heating system can be powered by organic waste and pallets, shreds and wood pellets, i.e. biomass fuel of various kinds. Methanization units require more space and in rural areas allow the use of manure and agricultural waste by fermentation to produce biogas.

Marine energies are made up of six sectors, namely tidal energy, wave energy, current energy, ocean thermal energy, osmotic energy and wind energy (large offshore wind). The use of algae to produce biofuels that can be used to power the internal combustion engine of vehicles is currently being studied. These energies are still marginal in the global energy mix. Their potential should not be underestimated as they can benefit coastal areas. Do they benefit metropolitan areas, rural areas or deserts? We can have metropolises, rural areas and deserts by the sea that benefit from this electricity, which is repatriated to land by cable, and then fed into the grid or possibly self-consumed.

      Wind turbines convert the kinetic energy of the wind into mechanical energy, which is then most often transformed into electricity. This mechanical energy has been used for centuries to grind grain in traditional mills. It is transformed into electricity by modern horizontal and vertical axis wind turbines. These wind turbines can be small for urban and rural buildings. Others are very large, with a mast longer than 150 m, a nacelle for mechanical components and a rotor to receive the blades. They can only be installed in parks located far from residential areas.

      Geothermal energy consists of exploiting the energy from the earth, which is recovered by geothermal collectors, in the form of usable heat that can potentially be converted into electricity. At low energy, the heat comes from shallow depths and its temperature is not sufficient (5–10°C) to be used directly for heating. A heat pump must be added to increase the temperature, a popular feature in single-family homes in urban and rural areas. At medium and high energy, heat drawn at a high temperature (from 50°C to over 150°C) or at high depth (from 600 m to over 2,000 m), can be used directly. It is suitable for certain urban areas, both for collective and tertiary buildings, which are then supplied by a heating network. For higher temperatures, often in volcanic areas, when the flow rate is sufficient, the heat can be converted into electricity.

      Hydraulics converts the movement of water into kinetic energy, which is then most often transformed into electricity. This kinetic energy has been used for centuries to grind grain in traditional water mills. It is located in rural areas for small and large hydropower, although the electricity produced by the turbines of the dams can then supply the cities.

Solar energy can take many forms. The French physicist Edmond Becquerel discovered the photovoltaic effect in 1839. This is one of the effects that is implemented in photovoltaic cells from solar radiation. It is used to produce electricity. Solar thermal energy makes it possible to produce heat and hot water from solar collectors. Concentrated thermodynamic solar energy converts solar