Energy storage: an overview of different technologies in the industrial sector

Especially in the industrial sector, storage solutions play an important role in the context of Europe's energy and thermal transition. An overview of common processes and solutions.

Modern energy storage systems are a key technology for a successful energy transition, especially in energy-intensive industries, which are still largely dependent on fossil fuels. We discussed what types of energy storage systems are available on the market and what applications they are suitable for. Also, let's take a look at the pros and cons of different technologies.

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Why energy storage is important

Different types of energy storage solutions

1. Mechanical energy storage

2. Electrochemical energy storage

3. Thermal energy storage

4. Electrical energy storage

Energy Storage of the Future: Why Energy Storage Matters

The need to limit CO2 emissions and thus drive decarbonization is undeniable. To achieve this, fossil fuels such as natural gas, coal, and oil must be replaced by renewable energy. However, given the weather, day and season related fluctuations of renewable energy sources, as well as the increasing demand for electricity due to the advancement of electrification, the power system must become more flexible in order to be able to guarantee future system and supply security. Energy storage systems are essential for modern energy supply because they decouple generation and consumption over time, allowing for flexible use. This not only benefits consumers, but also increases the stability of the grid.

Different types of energy storage solutions

There are various techniques for storing energy, and they differ in both how they work and the form of energy they store. While some energy storage systems have been successfully used for many years, others are still new to the market.

1. Mechanical energy storage

Mechanical energy storage systems are based on classical Newtonian mechanics. Energy is stored in the form of kinetic or potential energy and in the form of pressure energy. The most well-known mechanical energy storage systems include pumped storage power plants, compressed air energy storage systems, and flywheels.

1.1 Pumped storage power stations: the power of water

Pumped storage power plants are particularly suitable for storing electricity on a large scale. Excess energy is used to pump water from the lower basin to the higher basin (upper basin). According to this principle, electrical energy is stored in the potential energy (positional energy) of water. When needed, the water is released through a turbine into the lower basin and converted back into electricity with the help of a generator. The efficiency of pumped storage power plants is about 75 to 80 percent. Due to its geography, this form of energy storage is only suitable for limited large-scale use in many countries.

1.2 Energy storage by means of compressed air accumulators

Compressed air storage systems store energy by compressing air. The air is enclosed in suitable containers or underground storage tanks under high pressure. The stored mechanical energy can be released as needed by releasing compressed air through a turbine, which is used to drive the generator. Although compressed air storage systems are relatively inefficient, they are suitable for storing electricity generated from renewable energy sources such as wind power.

1.3 Energy storage by flywheel

In the case of the use of flywheels or flywheel mass storage devices, excess electrical energy is stored in the form of kinetic energy. To do this, the flywheel moves with the help of an electric motor. When the stored energy is to be extracted, the rotating mass stops and the rotating energy is recovered by the generator. Due to the high friction losses, this type of storage is often used as short-term storage, such as buffering peak loads.

2. Electrochemical energy storage

Electrochemical energy storage devices store energy in the form of chemical energy. During the discharge process, the latter is converted back into electrical energy. Electrochemical energy storage systems include batteries and accumulators. Especially in the field of small storage capacities, such as automotive batteries, electrochemical storage has long been popular.

2.1 Battery

It is impossible to imagine industrial and private homes without batteries. Depending on its use, different materials are used in the structure. For example, disposable batteries are typically more compact and have a higher energy density than rechargeable batteries. Therefore, the former is used in medical implants or watches, etc. Accumulators are used in the industrial sector.

2.2 Accumulators

Accumulators are a widely used form of electrochemical energy storage that is available in a variety of sizes. Their main advantage is that the process that occurs when the battery is charged is largely reversible. As a result, the energy loss that occurs is very low, usually only a few percent. The degree of self-discharge varies depending on the battery type. However, it is generally considered to be relatively mild. The energy density of batteries is significantly higher than that of other capacitors. However, it is very low compared to the energy density of the fuel – which makes it relatively difficult to design long-range electric vehicles.

3. Thermal energy storage

Especially when it comes to the necessary heat conversion, thermal energy storage solutions are increasingly being discussed in the public debate. The potential is huge, especially in the industrial sector. The most widely used thermal storage systems include sensible heat storage, latent heat storage, and thermochemical heat storage. Different operating principles vary depending on storage time, temperature, and storage principle.

3.1 Sensitive heat storage

In sensitive energy storage systems, thermal energy is stored by raising the temperature of the material. Storage materials used include water, heat transfer oil, concrete, sandstone, bricks, or molten salt. Depending on the material used for storage, the storage duration varies. Sensitive thermal storage, such as ENERGYNEST's ThermalBattery™, is considered to be the most established and cost-effective method of thermal energy storage.

3.2 Latent heat storage

In latent heat storage systems, which are rarely used in industrial settings, thermal energy is stored with the help of phase change materials, including salt or kerosene. During phase changes, such as from solid to liquid, the material absorbs energy and then remains in the material as so-called latent energy. Latent heat storage systems can store energy for a longer period of time without significant losses.

3.3 Storage of Thermal Chemicals

Reversible gas-solid reactions are also used in thermochemical heat storage systems. In this case, the energy is stored as part of the endothermic reaction rather than an increase in temperature. The main advantage is that storage leakage is relatively low.

4. Electrical energy storage

In the context of the energy and thermal transition, electricity from renewable sources is crucial. Various technologies make it possible to store this energy directly in an electrical energy storage system without conversion. However, this is not always economically feasible in practice. In the context of electrical energy storage, there is a difference between capacitors and superconducting energy storage systems.

4.1 Capacitors: Energy storage in an electric field

Capacitors typically utilize electrostatic force. The energy storage in a capacitor is based on the electric field that holds the stored energy. "The key advantage is that with these types of storage, the electrical energy does not have to be converted into other forms of energy, which avoids high conversion losses. However, this advantage is relativized by the extremely low energy density (both in terms of volume and weight) and the disadvantages of high cost. For this reason, their applications are currently more present in niche areas," writes the Center for Energy Networks and Energy Storage Research (FENES).

4.2 Superconducting magnetic energy storage devices

In another type of electrical energy storage, the so-called superconducting magnetic energy storage, a direct current from the rectifier passes through a coil made of superconducting materials such as iron, phosphorus, lanthanum or oxygen. This creates a magnetic field in which energy is stored.

When the battery is loaded, the power supply is interrupted and a switch made of the same superconducting material is activated. This switch is responsible for disconnecting the coil from the inverter. The circuit is then reconnected to the inverter to release the stored energy. In this way, alternating current is generated by direct current.

This energy storage system generates direct current with an efficiency of about 97%. However, considerable cooling requirements need to be considered, which often hinders the economical industrial application of the technology.