Sand Thermal Storage: Operation, Limitations, and Benefits

Sand thermal storage is a technology gaining attention in the thermal energy sector, particularly in district heating plants. This system allows for storing thermal energy at high temperatures and gradually releasing it for industrial and civil applications.

However, despite its advantages, sand storage has some limitations that make it less versatile than other thermal energy storage solutions. In particular, the use of large centralized systems can be less efficient compared to modular and distributed solutions, such as PCM thermal batteries.

In this article, we will analyze the operation of sand thermal storage, its strengths and challenges, explaining why a configuration with multiple smaller storage units can be a more effective design choice than a single large system in meeting user demand.

How Does Sand Thermal Storage Work?

Sand thermal storage utilizes the thermal capacity of sand to store and release heat. This process occurs in three main phases:

1. Heat Charging
   • Thermal energy is transferred to the sand through electric resistances or heat exchangers. Existing systems heat sand quantities ranging from 100 tons to 2000 tons.
   • The sand is heated up to 600-1000°C.
2. Energy Storage
   • The material retains heat for a maximum of two weeks with relatively low losses. Larger systems can store heat for 3-4 months.
   • The duration of thermal energy storage depends on the system’s insulation.
3. Heat Release
   • The stored heat is recovered and used to power district heating systems or other high-power applications.
   • The transfer occurs via heat exchangers that provide thermal energy to fluids that transport it where needed, such as steam or pressurized water.

Most Common Applications

• Integration with solar thermal plants (CSP - Concentrated Solar Power)
• Storage of energy from intermittent renewable sources
• Heat recovery from industrial processes
• District heating
• Cogeneration applications

Limitations of Sand Thermal Storage

Despite its advantages, sand thermal storage has some drawbacks that make it less suitable for certain applications compared to other thermal energy storage solutions.

2.1 High Thermal Inertia
Heat release is not immediate, making it difficult to use energy flexibly. As a result, it is not suitable for applications that require fast and dynamic thermal supply.

2.2 Space Requirements and Infrastructure Complexity

• Sand thermal storage systems require large storage volumes, making them difficult to implement in space-constrained environments.
• Integration with existing systems may require significant modifications.

Why Is It Better to Have Multiple Small Storage Units Instead of One Large One?

One of the main alternatives to sand storage is the use of modular and distributed thermal storage systems at user sites, which allow heat to be stored in multiple smaller units instead of concentrating it in a single facility.
The advantages of a modular configuration include:

1. Greater Flexibility
   • Each unit can operate independently, optimizing heat delivery.
2. Scalability and Customization
   • Companies can gradually increase storage capacity without having to build a large infrastructure from the outset.
   • Ideal for growing facilities or businesses looking to optimize costs gradually.

I-TES Thermal Batteries

I-TES thermal batteries are storage systems that achieve high discharge power, unlike inertial ones, allowing for a faster response to variations in energy demand.
I-TES thermal batteries can, in certain types of systems, be a more versatile and high-performance alternative to sand thermal storage.

• Easy management: allow for controlled heat storage and release.
• Simple integration: depending on size, they can be installed in industrial plants, district heating systems, and residential setups.
• Scalable solution: instead of a single large system, heat can be distributed across multiple modular units.
• Waste heat recovery: improves industrial process efficiency, reducing energy waste.

Sand thermal storage is an interesting technology for district heating and industry, but it has limitations in terms of flexibility and scalability.
I-TES thermal batteries can, in certain cases, be a more effective choice, thanks to their modularity and ability to better manage heat. For many applications, a distributed system is more advantageous than a large centralized storage unit.
Flexibility is also essential for photovoltaic systems, where efficient storage allows energy utilization even without sunlight. To learn more, read: Do photovoltaic panels work without sunlight? With thermal battery storage, yes.