Decarbonisation Technology - February 2025 Issue

recombine in an exothermic reaction, the stored energy is released as needed. The amount of heat stored is equal to the reaction’s enthalpy. For example, zeolite has a heat density of about 200 kWh/m³, and silica gel has about 230 kWh/m³. Table 1 presents the advantages and limitations of sensible, latent, and thermochemical heat storage systems. Sand batteries can store large amounts of heat at high temperatures, making them ideal for applications needing stable and efficient heat retention. They help solve renewable energy challenges like intermittency and variability by storing excess energy and releasing it when needed, improving the energy grid’s efficiency and reliability. Developing sand battery technology can lead to better thermal energy storage systems, providing a scalable and practical solution for both industrial and residential needs. This article explores the potential of sand batteries to contribute to a more sustainable and resilient energy future. Sand battery benefits Sand, used as sensible heat storage and commonly referred to as a ‘sand battery’, represents an innovative approach to energy storage. This method utilises the unique thermal properties of sand to absorb, store, and release heat efficiently. It offers a cost-effective and scalable solution for thermal energy storage, making it a promising technology for various applications, including renewable energy integration and industrial heat management. Sand is widely distributed across diverse geological settings such as rivers, beaches,

shallow seas, lakes, and desert dunes. Its primary constituents comprise silica (in the form of quartz), feldspar and additional minerals such as carbonates, micas, amphiboles, and pyroxenes. Sand’s thermal conductivity depends on its type, moisture content, and temperature. Dried coarse sand has an average thermal conductivity of 2.05 W/m·°C, while dry fine sand is about 1.76 W/m·°C. With a heat transfer coefficient of 0.06 W/m²·°C, sand can retain heat for extended periods. Additionally, it can store significant amounts of heat in a compact volume at temperatures of 800-1,000°C, making it an effective medium for thermal energy storage (Odoi-Yorke, et al., 2024) . Furthermore, sand is a cheap and abundant material. The sand battery offers several significant advantages over other thermal energy storage solutions. It can store large amounts of energy, requires low maintenance, and is highly scalable. In addition, CO₂ emissions are negligible during the operation of systems powered by clean electricity or heat sources. However, there are some carbon emissions associated with the construction materials and the construction phase itself. Sand battery process Typically, electricity is supplied to resistive heating coils to heat a sand bed, with air serving as the heat-carrying medium. The sand bed, composed of either pure sand or a mixture with metal scraps, can absorb heat up to temperatures of 800-1,000°C. The charging process involves transferring heat to the sand to store thermal energy, during which the sand’s temperature

Sand-lled storage vessel

Outlet water

Inlet water

Electricity to resistive heating coil

Air-water heat exchanger

Circulating air duct

Figure 1 Schematic diagram of sand battery operation