Storage of energy

The storage of energy is the action which consists in placing a quantity of energy in a place given to allow its later use.

From a strategic and economic point of view, the storage of energy to large scales is of great interest for the States. Indeed, it contributes to the Energy independence of the State, i.e. with its capacity to satisfy interior its energy needs in real-time, but also to prevent the cuts in the provisioning. So the storage of energy is often the object of an special attention on behalf of the political powers, especially in the States strongly dependant from abroad for their energy supply.

By extension, the " term; storage of énergie" is often employed to indicate the storage of the matter which contains this energy.

Output of a storage of energy

The operation of storage of energy is always associated with the opposite operation consisting in recovering stored energy (the destocking ). These two operations of storage/destocking constitute a cycle of storage. At the end of a cycle, the storage system finds its initial state (ideally " vide"). There is then regenerated storage. The output of a cycle corresponds to the relationship between the quantity of energy recovered on the quantity of energy which one initially sought to store. Indeed, each of the two operations of storage and destocking invariably induces losses of energy or matter: part of initial energy is not really stored and part of stored energy is not really récupée.

The output of a cycle of storage of energy depends enormously on the nature of storage and the physical systems implemented to ensure the operations of storage and destocking.

Storage of the mechanical energy

Storage in the form of potential energy

Hydraulic storage

The hydraulic stoppings constitute water reserves which, while falling, makes turn of the generating turbines of electricity.

An optimization of the system consists in re-using the water which was released. Storage by pumping is used by places to equalize the daily load (i.e. the requirement in electricity): water is pumped and re-installed towards Barrage S of altitude when the demand on the network is low (during the Off-peak hours and the Week-end for example), by using the over-production of the nonadjustable devices (Nucléaire, Solaire, wind,…) ; during the peaks of consumption, this water goes down again and produces again electricity.

It is the same electromechanical device reversible, which produces electricity or goes up water by pumping. The output is excellent (more than 90%). However, relatively few places have the place for the stoppings of storage per pumping with a Ligne with high voltage in the vicinity.

One uses also this type of device in the tidal central of the Rance (in France): with high tide, one is not satisfied to passively store water, one also pumps to increase the reserve, water which will be slackened advantageously with low tide (one assembles the water of a few meters, on the other hand one uses his potential of fall on ten meters moreover ).

Compressed air

a method is to employ electricity to compress air. This one is usually stored in an old mine or another closed geological device. When the electricity demand is important, one uses the air thus compressed to make turn a Turbine coupled to a producing alternator of electricity. Projects of this type were conclusive in Alabama and Germany, although the output is poor (40%).
Second method under development: oil and air batteries, (technique containing compressed air and of oil) will in the long term allow the storage of electricity the local scales, regional, even international, at a competitive cost.

Storage in the form of energy kinetic

Storage by wheel of inertia

Energy is stored in the form of kinetic energy on a heavy disc. To accumulate energy, an engine accelerates the disc. To use energy, an electric generator is connected; in practice, the generator can be the engine (the same electric machine can act of engine or generating brake/).

A heavy disc turning is actuated by an electrical motor, which acts as a generator when one has energy requirement, slowing down the disc and producing electricity.

Friction must be minimum to avoid the losses. It is possible while placing the wheel in the vacuum and on stages with magnetic levitation, systems making the method expensive. Moreover high speeds of wheel allow a greater storage capacity but require resistant ultra materials to resist the bursting and to avoid the explosive effects of a breakdown of the system, during which the kinetic energy of rotation would be converted into kinetic energy of translation (in other words, the disc would be transformed into Projectile…).

In practice, this type of storage is of a use very running but it is practically limited to the “wheels of inertia” within the apparatuses of energy production, which very operate a smoothing with short term to regularize the supply. It is in particular the case of all the thermal engines, especially of the turbo engines Diesel whose jolts are important.

It has been already several decades that urban buses functioned with a wheel of inertia laid out flat under the floor. This system makes it possible to make several kilometers without pollution and in silence before a " recharge" , which is carried out at the time of the prolonged stops of a few minutes in the stations equipped for this purpose. At the time, the revival of single the large disc was done by a pneumatic system or an electrical motor laid out in the roadway. The technical complexity of this solution (size, the weight of the equipment, the complexity of use and the gyroscopic effect which unbalanced the vehicles) associated with a weak economic interest (comparison between the cost and that of the use of other energies) stopped its use.

The technical evolution gives this system to the last style. The use of two lighter contrarotating discs but turning at very high speed, thanks to new materials more resistant, and launched by an integrated electrical motor, allows a clear improvement of the tare weight report/ratio/payload. This also allows a use in the inclined cities, where the weight is even more penalizing.

To note that the output of this system, called " sometimes; battery mécanique" , is higher than the use of chemical accumulators.

Applications in the railway field were also tried.

This technology is also used in food without static interruptions (ASI) and dynamic (ADI) ( Uninterruptible Power Supply in English) allowing to mitigate the rupture of the power supply during several seconds and to allow the starting of an emergency power unit.

Chemical and biological storage

Electrochemical potential: Electric fencer

The storage of great quantities of electricity with giant electrochemical accumulators forever be carried out. The electrochemical accumulators are generally heavy, expensive, have one limited lifespan and pose problems of Pollution (acid and heavy metals) at the time of their end-of-life.

On the other hand, of many systems Domestique S disconnected from the Distribution network of electricity are based on the use of Accumulator battery or of pile S. In practice, they are useful for the small apparatuses electric household appliances S; recently an renewed interest for the vehicles producing little or not polluting gas started again the creation of vehicles Automobile S completely functioning thanks to this type of energy or a hybrid way (electricity in complement of fossil energy).

The Condensing S of average and large capacity, known as condensing chemical are another use of the electrochemical couples to store energy. Their use is very current in the Appareil S and Machine S electric S with or without electronic embarked.

Pile
Electric fencer
Chemical Accumulator battery
Condensing
Supercondensateur S

Alive photosynthesis and other systems

The production of molecules rich in energy and easily usable to release this energy is at the base of the life.

Fuel

Gas

Energy to be stored can in theory be used to produce, (then to store and transport), of gaseous fuels of synthesis, (such as the Méthane or the Hydrogène), or even an intermediate product like the Ammoniac. (It is besides the solution adopted in the projects aiming at benefitting from the largest reserve of solar energy available, namely the tropical ocean)

Hydrogen

The Hydrogen as fuel was proposed as solution in the problems of energy. Storage can be carried out in several forms:

Storage of hydrogen gas:

This mode of storage is simplest technologically, but it presents disadvantages. The majority of materials are indeed porous lived hydrogen, which generates losses during a storage of long life. Moreover, this mode of storage requires a large volume.

liquid Storage of hydrogen:

The liquefaction of hydrogen makes it possible to mitigate the problem of volume of gas storage, but however requires to cool hydrogen and to preserve it at very low temperature, which returns storage over one long life more complicated and not very advantageous.

Storage in solid form:

The solid and stable storage of hydrogen in the form of amino pastilles makes it possible to solve at the same time the problems of volume and duration. However, this mode of storage presents disadvantages relating to the transport of this energy.

Antimatter

Although the storage of energy by Antimatière is for the moment only theoretical and seems difficult extrèmement has réalister, it is advisable to speak about it.

the phase " stockage" could be realized by concentrating a very energy Photon in a precise point, which would cause to produce two particles (one of matter, the other of antimatter).
the phase " déstockage" would be realized by putting in contact these two particles, which while meeting would produce a formidable discharge of energy (Certain researchers estimated that 1g Matière combined has 1g Antimatière would produce as much energy than at the time of the atomic explosion of Hiroshima)

If this possibility of storage of energy is not used, it is that it seems for the moment impossible to store antimatter for the transport of energy without it being in contact with our matter.

Storage of heat

The storage of heat can be carried out through two different phenomena associate with the materials who ensures storage. One speaks then about storage by significant heat and storage by latent heat.

storage by significant heat

In storage by significant heat, energy is stored in the form of a rise in temperature of material of storage. The quantity of stored energy is then directly proportional to volume, the rise in temperature and the Heat-storage capacity of material of storage. This type of storage is limited only by the difference in temperature available, the thermal losses of storage (related to its thermal insulation) and possible the Changement of state which can have to undergo material of storage (Fusion or Vaporisation).

storage by latent heat

In storage by latent heat, energy is stored in the form of a change of state of material of storage (Fusion or Vaporisation). Stored energy depends then on the latent heat and the quantity of material of storage which changes state. Contrary to significant storage, this type of storage can be effective for differences in temperatures very weak. In the case phase shift solid/liquid, and a quantity of stored energy and a given material of storage, latent storage requires less volume than storage by significant heat owing to the fact that the latent heat is generally much higher than the heat-storage capacity.

Note : These two types of storage can be used to store cold.

Some examples of storage of heat:

In the domestic heating systems, one uses sometimes large the thermal Inertia of certain materials brick S, Huile to slowly restore the heat accumulated during periods when heat was produced or collected. But generally, storage is ensured by an isolated warm water balloon.
In the furnaces with wood fire, out of brick and Refractory ground , the capacity of the arch of the furnace to store heat is used for the cooking of objects (pottery, enamels, etc) or of dishes (bread, pizza pie, etc).
Of the materials to phase shift (MCP) is currently studied to improve thermal inertia of the walls of the buildings.

Storage of electricity

The electricity is a derived energy, i.e. it results from the transformation of primary energy. Another characteristic: this energy is not storable: produced electricity is instantaneously consumed or lost. The problem to store this type of energy is in fact that of the to quickly produce on autonomous systems (not connected to a network of production). It is what one obtains for example by using the principle of the pile or the battery, based on a chemical reaction: a pile stores chemicals which will react and produce electricity with the request. These technologies present major disadvantages which limit their use: their weight, their cost, their low productivity and, in certain cases, dangerosity of the components or their aspect polluting (acid, lead).

Condensing
magnetic Storage with superconductive (SMES)

See too

Food without interruption

External bonds

is Some figures according to the mode of storage easy to store energy? by Jean-Marc Jancovici

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