Batteries: an important energy storage solution

How it works

Batteries are indispensable for our daily lives.  We need them to power our smart phones and notebooks, and they make sure our electric vehicle gets from A to B. They have also become a key for maintaining a stable power grid. 

Large-scale battery storage systems help balance out fluctuations in the power grid. They can rapidly store electricity and make it available quickly in order to keep production and consumption in balance in the power network.

Be it in a smart phone or an electric vehicle, or as a large-scale battery storage system: Batteries use electrochemical cells that chemically store energy that can be converted into electricity.

Lithium-ion batteries are the most commonly used electrochemical batteries. The advantage: They have a high energy density. Lots of energy can be stored in a minimal space.

As the term “lithium-ion” suggests, lithium is an important battery component. According to the globally identified reserves, lithium occurs most frequently in Chile, followed by Australia, Argentina and China. 

A lithium-ion battery consists of two electrodes, the cathode and the anode. They are separated by an electrolyte, a conductive material. While the cathode comprises storage material like lithium-nickel-manganese-cobalt-oxide, the anode is normally made of graphite.  

When the battery is discharged, the lithium ions – ions are positively charged load carriers – migrate from the anode to the cathode through the electrolytes. At the same time, the anode releases electrons that flow to the cathode by means of an external power circuit, and supply our smart phone or other devices with power. The lithium ions from the anode travel through the electrolytes to the cathode where they accumulate. In contrast, when charging, i.e. when the battery is supplied with power from an outside source, the electric energy is transformed into chemical energy. The lithium ions and the electrons flow in the reverse direction.

When cells are connected in series, also known as serial connection, operating voltage increases. If a higher storage capacity is required, the cells are connected in parallel. These two systems can also be combined.  

The most important parameters of a battery are the output (measured in kilowatts, kW, or megawatts, MW), and the energy that can be stored (measured in kilowatt-hours, kWh, or megawatt-hours, MWh).  

Axpo works with large-scale battery storage systems. The output and storage capacity of these batteries is in the megawatt or megawatt-hour range.

Batteries from A to Z

Large battery energy storage systems (BESS) are designed for high output and large storage capacity. A system consists of a battery system, the battery cell, and an integrated cooling and energy management system (EMS), as well as an energy conversion system comprising inverters and transformers.

The most important answers on the topic of batteries

Construction of a BESS takes about one year and, as a rule, the system can be operated for 20 years. Environmental impact is minimal in construction and system operation is environmentally friendly.

The majority of battery cells are produced in Asia. The most critical battery component of LFP batteries is lithium. The majority of the global mining of lithium is conducted in South America, Australia and China.

Battery storage capacity decreases over time and through use. One charging cycle per day results in a capacity reduction of about 2% per year.

Batteries contain critical raw materials, which are difficult to mine in Europe. Once the battery has reached its service life, the raw materials can be extracted and recycled.


It is expected that the investment costs for battery systems will decrease in the long term because the efficiency in implementing projects will increase, and more and more scaling effects will be generated. However, lithium shortages can result in a temporary price increase as was seen at the beginning of 2022.

Regulatory framework conditions

Battery storage systems are used in multiple markets and are both power consumers and power generators. It is therefore important that the regulatory authorities set a clear framework for the construction and operation of such systems.

Grid conditions

Historically seen, the transmission and distribution grids in most countries were designed with centralised production in mind. The battery capacity that can be installed is dependent on the feed-in point and the network topology at that specific location.

  • Battery storage capacity indicates the energy volume that can be stored (measured in megawatt-hours, MWh).
  • Output indicates the energy per time unit that can be charged or discharged (measured in megawatt-hours, MWh).
  • The C-Rate indicates how quickly a battery can be charged or discharged. C-Rate = output divided by storage capacity.
  • State-of-Health (SoH) describes the relationship between the storage capacity of a used battery and a new battery: Initially the SoH is 100%.
  • The State-of-Charge  (SoC) indicates the charging state of a battery: at 0% the battery is empty and at 100% SoC it is fully charged.
  • The number of cycles indicate how many equal, full charging and discharging cycles a battery carries out over a specific time period. As a rule, batteries carry out 1 to 2 equivalent full load cycles per day.
  • Round trip efficiency measures the energy that can be recovered in comparison to the energy stored (output divided by input). Round-trip efficiency is normally 85% or higher.
  • Battery service life depends on its operation. Frequent charging and discharging, as well as extreme charging states, decrease the service life of a battery.


Large battery energy storage systems (BESS) perform the following tasks:

  • Energy shifting: For example, power that was generated during the day from photovoltaic can be stored and fed into the grid at night
  • Peak shaving: Peak shaving refers to lowering and smoothing peaks in the power grid in order to save grid costs
  • Imbalance: The difference between the effective, generated energy in relation to traded energy
  • Day-ahead and intraday trading
  • Ancillary services: Primary and secondary control capacity
  • Reserve energy
  • Alleviating grid bottlenecks and postponing grid investments through peak energy flow management

In addition, battery storage systems contribute to ensuring reliable energy supply. Making capacities available can be remunerated.  

BESS can be connected in front-of-the-meter (FTM) or behind-the-meter (BTM). As a rule, large-scale battery storage system to support the grid are connected in front-of-the-meter (FTM).

A battery can be operated independently or together with photovoltaic or wind energy systems. The advantage of the second option is that infrastructure can be jointly used (land, grid connection). Operational restrictions are the disadvantage.

Verwandte Magazinartikel

All magazine articles


Was hinter den Strompreiserhöhungen steckt

Die Strompreise in der Grundversorgung steigen an

Read more


Alp da Schnaus vielfältig genutzt

Vereinbarkeit von Freizeitaktivitäten, Natur und Energieerzeugung in Ilanz/Glion

Read more


Premiere im Kanton Schwyz

Axpo und EWS setzen mit erster alpiner Solaranlage im Kanton Schwyz neuen Impuls

Read more


Reservekraftwerke als Teil des Schweizer Stromsystems

Abruf nur im Notfall

Read more


Wasserstoff aus dem Rhein - ein Puzzleteil der Schweizer Energiezukunft

Axpo produziert 350 Tonnen Wasserstoff aus Rheinwasser

Read more


Grüner Wasserstoff einfach erklärt

Axpo setzt auf den Energieträger H2

Read more

Verwandte Medienmitteilungen

All media releases


ENERPARC-Tochter Sunnic Lighthouse und Axpo schliessen zweites grünes PPA

Read more


Axpo, Nobian und WIRCON unterzeichnen langfristigen Solarstromabnahmevertrag in den Niederlanden

Read more


Axpo plant weitere alpine Solaranlage in Ilanz/Glion

Read more

More energy knowledge

See all

Limmern pumped storage plant: Battery in the mountains

A pumped storage plant functions like a large battery. You can find out exactly how it works and what it has to with the security of electricity supply in Switzerland here.

Read more

Grids: For a secure supply of electricity

Electricity comes out of the socket, of course! But how does it get there, what do Axpo’s networks have to do with it, and why do we use drones?

Read more

Renewable energies: Strong in Switzerland and internationally

Axpo is the largest producer of renewable energies. We know our way around hydroelectric power, wind power, solar energy and biomass. Click here for the details.

Read more