Stockage de l’électricité avec de l’air comprimé

En plus des batteries, de l'hydrogène et des stations de transfert par pompage (STEP), il est possible de stocker l'électricité à l'aide d'air comprimé. Une puissante usine exploitant cette technologie sera bientôt érigée en Californie.

    Avec ses 500 MW et ses 4 à 6 GWh de capacité de stockage prévus, l'usine d'air comprimé de Rosamond (Californie) sera la plus puissante du genre au monde. Pour se faire une idée, cela représente l'équivalent d'environ une heure de consommation électrique en région Provence-Alpes-Côte-d'Azur. Située à une centaine de kilomètres au nord de Los Angeles, sa mission sera de stabiliser le réseau local en proie à des coupures de courant régulières. Mais comment fonctionne ce système ?

    Le principe du stockage d'air comprimé (appelé aussi CAES, pour Compressed Air Energy Storage), est assez simple. En cas de surproduction d'électricité, l'usine comprime l'air ambiant à une pression de 70 à 100 bars. L'air est alors stocké dans de grandes cavités souterraines et la chaleur générée par les compresseurs (jusqu'à 600°C) récupérée via des échangeurs. Ensuite, en fonction des besoins du réseau électrique, l'air et la chaleur (stockés dans la roche, l'huile ou les sels fondus) sont libérés dans une turbine qui entraîne un alternateur.

Stocker de grandes quantités d'énergie

    Ce système est, avec la STEP (station de transfert d'énergie à stockage pompé), l'un des plus efficaces pour l'accumulation d'électricité. Son rendement est d'environ 70 % et il peut stocker de grandes quantités d'énergie pour un investissement des plus faibles (entre 400 € et 1 200 €/kW).

    La société canadienne Hydrostor, à l'origine du projet californien, s'est ainsi associée à l'américain Pattern Energy et au français Meridiam pour exploiter cette technologie. Cependant, contrairement aux centrales CAES conventionnelles qui nécessitent une cavité saline pour stocker l'air comprimé, les centrales Hydrostor peuvent utiliser tout type de sous-sol.

    L'entreprise revendique déjà une première station à Goderich, en Ontario (Canada), d'une capacité modeste de 1,75 MW pour 10 MWh de stockage. Au-delà de son futur gigaoctet, elle envisage un deuxième site californien, dont les caractéristiques n'ont pas encore été dévoilées. Les deux usines devraient être inaugurées entre 2024 et 2026.

 The different types of photovoltaic cells

 What is a photovoltaic cell and its types? | Energy Hamd

1- What is a photovoltaic Cell

    The photovoltaic cell is a semiconductor, used to generate solar energy. Its purpose is to capture the sun's radiation in order to transform it into electricity.
    The solar cell, or photovoltaic, can operate alone, when the needs are lower, for a solar calculator for example. To meet larger needs, it is assembled into photovoltaic solar modules, which we commonly call solar panels.

2- How the photovoltaic cell works

    The photovoltaic cell works thanks to solar radiation. To generate electricity, it uses the photovoltaic effect that is obtained by the impact of photons from sunlight on a semiconductor material. The latter transmits the energy of the photons to the electrons which will then create the electric voltage. Here is the operating principle of a photovoltaic cell.

3- Solar cell composition

a- Amorphous silicon

Amorphous silicon is obtained from silicon gas. This gas is vaporized on a support, made of glass, flexible plastic or metal, using a vacuum spraying process. These photovoltaic cells are dark gray.
 

b- Monocrystalline silicon

Monocrystalline silicon is the result of cooling molten silicon. Once solidified, it turns into a uniform crystal which is cut into thin slices to form the photovoltaic cell. The color of this material is blue, with no trace of crystals or the like.
 

c- Polycrystalline silicon

To obtain polycrystalline silicon, the silicon is melted in a square and elongated metal mold, called an ingot mold. The color of this type of cell is blue and dotted with patterns left by the crystals. This peculiarity allows us to easily recognize this photovoltaic cell.
 

d- Cadmium telluride

Cadmium telluride (CdTe) is another raw material used to design photovoltaic cells. The manufacturing process hermetically traps a layer of cadmium telluride absorption between two glass supports.

4- Types of photovoltaic cells

a- The monocrystalline silicon photovoltaic cell

    This type of photovoltaic cell is one of the most common. It is obtained from monocrystalline silicon, applied in a single wafer. It makes it possible to compose solar panels that will produce electricity used to supply a home or the public network, for example.

b- The polycrystalline silicon photovoltaic cell

    Easily recognizable by its blue crystals, this photovoltaic cell consists of a single wafer of silicon. It is square in shape. It is often found in domestic, agricultural or industrial installations.

c- The amorphous silicon cell

     The amorphous silicon photovoltaic cell is composed of a thin layer of silicon, much thinner than monocrystallines or polycrystallines. It is mainly found to power low-power devices, such as solar watches, garden lights or even solar calculators.

d- The tandem photovoltaic cell

    The tandem photovoltaic cell is designed from two simple semiconductor layers. This can be a layer of amorphous silicon and another of crystalline silicon (mono or poly) for example. It shows all its interest for industrial use.

e- The CIGS photovoltaic cell

    This type of photovoltaic cell uses a semiconductor material made from an alloy of copper, indium, selenium and gallium. This mixture is placed in a very thin layer on a support.

f- The thin-film cell of cadmium telluride

    This model of photovoltaic cell is also made from a material other than silicon. Here, cadmium telluride is used in a single layer sealed between two glass plates.

g- The multi-junction photovoltaic cell

    The multi-junction photovoltaic cell consists of different layers of semiconductor materials that convert every ray of the sun, regardless of exposure. The layers are stacked, forming the multi-junction photovoltaic cell. At the moment, only spacecraft have it.

5- The advantages and disadvantages of each cell

a- The monocrystalline silicon photovoltaic cell

    This photovoltaic cell offers an efficiency of around 25%, one of the best on the market. Solar panels made from monocrystalline silicon cells have a lifespan of around 30 years, which is very cost effective despite the high cost to purchase. The downside of this type of solar cell is that it offers very low efficiency when there is not enough sunlight. It is therefore better suited to the sunniest regions.
 

b- The polycrystalline silicon photovoltaic cell

    The manufacture of this type of photovoltaic cell is simpler than the monocrystalline silicon version. Its cost is therefore lower. On the efficiency side of the solar panel, we can expect between 14 and 18 %, which is significantly lower than monocrystalline cells. However, it has the advantage of being able to be used in cloudy weather, thanks to its irradiation flexibility.
 

c- The amorphous silicon cell

    This solar cell has many advantages. First of all, it is inexpensive to manufacture. It can also be integrated on any type of support, flexible or rigid. Another plus point is that it catches sunlight even on cloudy days. Its main drawback is that it offers low efficiency, around 7% at most. To be profitable, the surface area of ​​the solar panel must therefore be substantial. Likewise, its performance decreases over time.
 

d- The tandem photovoltaic cell

    The efficiency of this type of cell is interesting, but its complex manufacture makes it an expensive photovoltaic cell to produce. As with all other models, the cleaning of the solar panel must be optimal in order to enjoy consistent performance and better longevity.
 

e- The CIGS photovoltaic cell   

    This type of solar cell represents the new generation of photovoltaic cell. First of all, it offers a very interesting return, between 10 and 20%. One of the main advantages is that it is designed with materials other than silicon, which are less toxic. Also, the support used can be flexible, in order to capture a maximum of solar rays. However, to obtain a good yield, it is necessary to provide a larger surface area than for other types of cells.
 

f- The thin-film cell of cadmium telluride

    This type of photovoltaic cell uses a technology set up to develop the efficiency of solar panels. The stake is doubly interesting, because it also makes it possible to reduce costs. Offering a low thermal coefficient, this type of cell is however composed of toxic products, which is a big drawback.
 

g- The multi-junction photovoltaic cell

    The multi-junction photovoltaic cell offers optimum efficiency of around 40%. The only downside is that this type of solar cell is not marketed. Indeed, it is only used in the space environment.