Guide to thermal batteries: how they work and their advantages

Thermal batteries: how they work and what advantages they offer

Thermal batteries, also called thermal accumulators, represent an innovative technology in the panorama modern energy since they emerge as a promising solution to the – increasingly complex – challenges of energy production and storage. In recent decades, the increase in energy needs, combined with the increasingly urgent need to contain CO2 emissions, has led to an increasing use of technologies aimed at energy saving and, in general, the production of energy from renewable sources. In this context, solutions for the accumulation of thermal energy, or thermal batteries, are finding particular interest due to their characteristics of versatility, economic feasibility and possibility of integration with already existing energy production systems, ranging from the industrial sector to the civil and residential one, as well as the creation from scratch.

In this guide we will provide an overview of the existing types of thermal batteries, we will explore their functioning and list the most significant advantages they offer.

What is a thermal battery?

We can define a thermal battery as an energy storage system coming from a source that generates it (for example a heat pump) for subsequent use. The accumulated heat - also called thermal storage or thermal energy (from the English TES, Thermal Energy Storage) - can be recovered when necessary and released again when the user requests it to meet a series of energy needs.

How do thermal batteries work?

Thermal batteries exploit the physical principle of change of state to store energy in the form of heat. When energy is available, it is transferred into the battery, triggering the phase change of the PCM  material (Phase Change Material) which is able, in this way, to retain heat for a long time (several hours or even days) with low dissipation levels. 

When it is necessary to recover energy, the previously accumulated heat is used to heat a heat transfer fluid, generally water, which in turn returns the heat to the user.

Through thermal energy storage systems, therefore, heat is transferred to the storage medium during the charging period, is stored and released when necessary, during the so-called discharge process.

The types of thermal batteries

In today's panorama there are three main types of technologies that can be used for the accumulation of thermal energy, and they are:

• sensible heat accumulation
• the accumulation of latent heat
• the thermochemical accumulation

Let's start from the first. Sensible thermal energy storage is one of the most popular options for reducing energy consumption and lowering CO2 emissions. This technology uses water, or solid materials (e.g. sand, rock, cement) as a means to store and reuse thermal energy. Water storage systems represent the most widespread technology due to its low cost, but due to its low energy density, for the same amount of energy stored, it takes up large spaces. Furthermore, if for healthcare use, it requires regular and continuous maintenance of the systems to avoid the emergence of legionella. Furthermore, this type of thermal storage is the least efficient because it is affected by greater thermal dispersion and above all the release of heat corresponds to a degradation of the useful energy (exergy) supplied to the user due to the continuous lowering of the temperature, specific to the heat sensitive.

We then have latent heat accumulation systems, which accumulate energy without altering the temperature of the material, but modifying its state. This process is made possible by the so-called phase change materials or PCMs (Phase Change Materials), which have the specificity of storing energy in their mass in the form of latent heat when they pass from one physical state to another. In the past, these materials have been used mainly in construction and for solar applications, since they work by accumulating and storing excess heat, but they are finding more and more interest as a replacement for water storage tanks given that they have an energy density of three to five times greater than water (smaller storage volumes) and essentially eliminate the legionella problem (they do not contain water).

Finally, thermochemical storage systems are based on chemical reactions that they allow thermal energy to be stored in the form of chemical energy: in addition to having a high storage density and an almost zero heat dispersion effect over time, they are suitable for long-term applications.

Advantages of thermal batteries

The choice of one heat storage system rather than another depends mainly on factors such as the required storage period, economic feasibility, operating conditions and environmental constraints. This will be a topic we will explore further in the near future. For the moment it is enough to know that the advantages of the main thermal storage systems, or thermal batteries, are numerous and different:

1. Energy efficiency: Thermal batteries offer high energy efficiency , as they can store large amounts of energy with minimal losses during the storage and recovery process, as well as maintaining constant temperature during the discharge phase.
2. Flexibility: These batteries can be easily integrated with photovoltaic systems, heat pumps, cogeneration and other renewable energy sources, allowing greater flexibility in the use of available energy resources.
3. Long life: thermal batteries do not deteriorate over time and have a longer life to 20 years, thus reducing long-term maintenance and replacement costs.
4. Scalability: Thermal batteries can be custom sized to meet the specific needs of a given plant or energy system, making them highly scalable and suitable for a wide range of applications.
5. Sustainability: By using environmentally friendly materials and exploiting renewable energy sources to charge the batteries, this system contributes to reduce greenhouse gas emissions and the overall environmental impact of energy.
6. Reliability: Thanks to their robustness and minimal maintenance required, thermal batteries offer high operational reliability, reducing costs to a minimum downtime and ensuring constant and stable energy.

Do you want to learn more about the specific advantages of i-TES thermal batteries? Let's talk about it Here.

The present and future of thermal batteries

Thermal batteries represent an innovative and promising solution for energy storage, offering numerous advantages compared to conventional technologies. With the growing demand for sustainable energy and the need to address the issues related to the intermittency of renewable sources, these batteries will play a fundamental role in shaping the future of the energy sector and transition 5.0. By exploring their functioning and benefits, their significant potential in improving the efficiency, flexibility and sustainability of modern energy systems emerges.

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