Le stockage d’électricité : une nécessité pour répondre aux enjeux de la transition énergétique


Because it lacks flexibility, the classic model of production-distribution-consumption of electricity no longer responds to new uses and the French network must very quickly find solutions enabling it to ensure the supply-demand balance. Energy storage thus appears to be a solution for the future, capable of both solving the problems of intermittency of renewable energy and responding to new uses such as the charging of electric vehicles. Jean-Marc Guillou, technical director at Socomec for energy storage systems, answered our questions.

Jean-Marc Guillou, technical director of the Socomec group for energy storage systems
Jean-Marc Guillou is technical director of the Socomec group for energy storage systems (Credit: Socomec)

Socomec is an industrial group created in 1922, which brings together more than 3,600 experts around the world.

Socomec’s specialty can be summed up in three words: availability, control and security of low-voltage electrical networks.

For several years, the group has offered energy storage systems based entirely on electrochemical technologies.

Jean-Marc Guillou is in charge of technical activities from product and project development to the operation and maintenance monitoring phases.

The objective of the European Union is to reduce net greenhouse gas emissions by at least 55% (FIT for 55) by 2030, in particular by reducing exhaust emissions from new cars, vans and trucks. To achieve this goal, the European Commission has strengthened its renewable energy directive and set a target for the European energy mix to reach 42.5% renewable production by 2030, more than double the 2021 production The major constraint of this approach is that this production ofso-called renewable electricity is intermittent.

Engineering techniques: What needs does energy storage meet?

Jean-Marc Guillou: The needs are numerous but, whatever the intended application, the key word in energy storage is “flexibility”. Notable applications are the integration of renewable energy, with the adaptation between production and consumption of green energy, the reduction of energy consumption costs, the smoothing of consumption peaks, the reduction of installation costs (by optimizing the sizing) as well as the strengthening of the current electricity network which is constrained by new uses around electric mobility. Storage can also play a role in helping energy distributors meet their availability commitments.

Could you specify the uses concerning the integration of renewable energies?

The energies mainly concerned here are wind power and photovoltaics. Other energies, notably tidal energy, are also discussed, but for the moment present a lesser constraint on the electricity network. These renewable energies are, of course, virtuous, but they are no less problematic for electricity networks. There are two reasons for this.

As I said previously, the first point concerns their intermittent nature: the period of electricity production does not correspond perfectly to the need for consumption on the electricity network. In this case, the integration of elements of battery storage allows the energy produced by these installations to be moved in order to consume it over a more appropriate period, for example in the evening.

The second point concerns the insufficient capacity of the electricity network to transport the electricity produced by large solar and/or wind installations. Indeed, these new production sites are generally relatively far from the points of consumption, which involves transporting this energy via the historic electricity network, to the points of consumption/distribution.

As the network is not robust or structured enough for this, heavy investments in electrical infrastructure are, in fact, necessary in order to limit congestion phenomena. The addition of energy storage means then makes it possible to relieve constraints on certain network connection points, which avoids investing in new costly power lines that have a significant impact on the environment.

This has been the subject of several demonstrators, notably the RINGO project led by RTE, responsible for transport and the balance of the electricity network in France.

What are the uses of electric mobility?

Electricity storage will also make it possible to develop new uses such as electric mobility, because it must be remembered that the French electric transport network is currently not structured to accommodate the expected transformations. We know that Europe plans to install 5.2 million non-residential charging stations by 2030 and today, it only has 500,000. To achieve these objectives, several European programs exist, such as the “Infrastructure for Alternative Fuels” (AFIR) project which allows players in these infrastructures to invest with the support of governments.

However, the forecasting models used to build current infrastructure had indeed anticipated the increase in the volume of electricity consumed, but not its acceleration.

In fact, low-power chargers, between 3 and 22 kW, installed in private homes are suitable for slow recharging of electric vehicle batteries, most often at night. With the help of intelligent load management software, it is therefore easy to control these installations and limit the impact on the electricity network.

In the case of charging stations located in public places (motorways, supermarkets, etc.), fast charging is required, which involves the use of high-power direct current chargers, up to 350 kW per charger (a station can be equipped with several chargers). These new consumption points cause strong constraints on the French and European electricity network, a problem which will be further amplified in the case of bus and truck charging, because power levels could rise up to 3 MW per point.

Battery storage is a response to this problem, because it acts as an energy tank capable of limiting the power demands induced by the charging of electric vehicles.

Can energy storage also interest manufacturers?

Of course, the rules here are different in all European countries, but industrial energy supply contracts are based, in general, on power peaks reached. If this peak occurs infrequently, the financial consequences for the manufacturer can then be significant. Energy storage here presents the opportunity to limit these power demands and smooth the injection or withdrawal curve from the electrical network, thus making it possible to reduce the connection power and optimize the sizing of the installations. And when coupled with renewable energy production solutions, this system also allows manufacturers to reduce their environmental impact.

Furthermore, for manufacturers with strong process continuity constraints, the addition of battery storage also limits dependence on the electricity network, particularly during power grid outages or breakdowns.

Finally, the increase in electricity costs that has been observed in recent years has also highlighted the interest for aggregators in managing storage installations among manufacturers.

Does energy storage reduce CO emissions2 ?

As mentioned earlier, photovoltaics (PV) do not produce electricity at the right time. The current solution consists of shaving, that is to say, limiting production on the electricity network. However, if it is not possible to use this electricity to its full potential, this means that the figures announced in terms of reduction of CO emissions2 are not accurate!

For manufacturers wishing to move towards reducing their carbon footprint, the installation of a storage system is therefore particularly useful.

From a technological point of view, how does a storage system work?

An energy storage system consists of two major elements: a conversion part and an energy storage part, i.e. batteries.

Socomec offers different energy storage solutions. Take the example of the SUNSYS HES L (Hybrid Energy Storage) range of converters. These solutions are an assembly of modular 50 kVA converters that can be paralleled to meet needs up to 600 kW and 186 kWh energy storage cabinets that can reach several megawatts in parallel.

As its name suggests, the role of the converter is to convert the direct current coming from the batteries into alternating current synchronous with the electrical network. These intelligent systems manage network support and communication with different network operators, allowing for “optimal” integration.

Concerning the design of these converters, we use SiC technologies which allow us to achieve the best results in terms of output and efficiency.

Batteries (or accumulators) are electrochemical systems, the objective of which is to store energy in chemical form and release it in electrical form. We use lithium-iron-phosphate (LFP) technology for several reasons.

The main one concerns the safety aspect, because the risk of thermal runaway is lower with this technology, the Thermal Runaway trigger point being higher, in comparison with Nickel Manganese Cobalt (NMC) technology.

In addition, the batteries are placed in a special cabinet, equipped with glycol water cooling, to maintain an optimal operating temperature in the batteries. In the event of a failure, the cabinet also has an inert gas fire extinguishing system, which avoids any risk of propagation.

This technology also offers longer lifespans at lower cost, compared to NMC technology. In return, the energy density and power capacities (c-rate) are however reduced, but for our so-called “stationary” applications, the advantages are clearly greater than the constraints.

Finally, we are also studying the integration of new energy storage solutions that are both safer and cleaner.


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