Thermal energy (heat) storage is crucial for many advanced applications. For instance, one of the practical issues with solar power plants is the requirement for an efficient way to store, conserve, and then discharge the extra heat gathered between periods of strong sunlight for use at nighttime or other times.

When the excess heat supply and utilization times differ, lots of issues might occur with waste process heating. When there are significant heating requirements and power costs make heat storage comparable with other methods of heating, heat storage can also be utilized in many applications.

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Many new technological advances are occurring, and there are several different kinds of widely viable systems. The basic types of thermal storage methods include: Latent heat storage, which uses heat saved when materials transform from one phase to the other by melting, & sensible heat storage, where the storage medium’s temperature fluctuates with the quantity of heat contained.

Sensible Heat Storage

Increasing the storage medium temperature produces sensible heat (energy) storage. Therefore, long-term stability, large specific heat capacity, compliance with its enclosure, and most crucially, cheap are desirable characteristics for the storage material. Based on the kind of heat storage medium, it may be divided into two distinct categories.

1. Liquid storage medium
2. Solid storage medium

1. Liquid Storage Medium

Liquids used for heat storage are widely available and affordable. Here are a few liquid storage options:

• Water Storage

At low temperatures, one of the best storage options is water. It is inexpensive & readily accessible, and it has a greater specific heat than other substances. Water can be used in a diverse range of temperatures, such as 20 to 95 °C.

• Salty Water Storage

By using solar ponds, it is possible to quickly and affordably collect and store large amounts of solar thermal heat (45–97°C) from the sun. They have the ability to be used for producing electricity, industries heat transfer, and applications including space cooling and heating.

• Other Fluid Storage

Oils and salts (molten) are now the most widely proposed alternatives for water. On a mass basis, the thermal capabilities are 15-35% that of water. These alternatives, meanwhile, have a smaller vapor pressure than water and can operate at temperatures reaching 350°C. Because of stability & safety issues, oils are restricted to temperatures below 400 degrees Celsius and can be pretty pricey.

2. Solid Storage Medium

Solid materials such as sands, stone, metal, brick, concrete, and so on can be utilized for both high and low temperature storage of thermal energy. Because these substances do not freeze or melt, energy can be kept at high or low temperatures. Here are a few solid storage options:

• Storage in Rocks

Thermal transfer fluid will flow through the loosely packed solid rock bed known as the pebble bed. Thermal energy is conserved and reused by recycling airflow into the hot bed while pumping hot gases into the fixed bed. The amount of energy stored in a fixed bed storage system is influenced by a number of factors, such as the density, size and shape, in addition to the medium’s thermos physical characteristics.

• Storage in Building Fabric

Both new and old buildings can use energy storage, and it can be connected with their air and water transport channels. Ceramic brick, which can be made of olivine, magnesite is the most common type of storage material. Passive or active storage solutions can also utilize building mass and structure concrete.

• Storage in Metals

Inorganic salts or metals make up the majority of materials considered for large temperature power storage. Aluminum, zinc and magnesium have been mentioned as good examples of metals. When high heat conductivity is needed and the price is not as important, using metal media may be beneficial.

Latent Storage Medium

It is a promising technique which is associated with phase shifts between liquids, gases, and solids. The phase change substance is frequently placed in a container with lengthy, narrow pipes. The collector’s solar thermal energy is passed through the pipes during a thermal storage cycle, melting the Phase change material by storing the energy as both sensible heat and latent heat of fusion.

The stored energy in the phase change material would be taken up and delivered to the heat load by the flow of low temperature air. As a result, latent thermal storage devices employ both sensible heat in the solid & liquid phases, as well as latent heat originating from a phase change during the storage device’s melting or freezing.

Phase Change Material (PCMs)

When substances change phase, they absorb and release heat energy. The Three main groups of PCMs are

1. Inorganic PCMs
2. Organic PCMs
3. Eutectics PCMs

Conclusion Remarks

The 2 main stored thermal energy methods being investigated nowadays for various uses. The research of sensible heat storage, which stores energy in pebbles or liquid, is currently at a higher level. But at the other side, latent heat storage is an emerging technology which has recently been considered extremely potential because of the many practical benefits it provides. Work is being conducted to improve latent heat storage systems in 2 directions: phase transition materials and heat exchangers.