Granular materials such as sand and rocks are studied to present an additional HTF to represent an efficient and costeffective alternative. Low cost solid particulates can store and transport heat at temperatures over 1000°C. **_Examples:_** - Dead Sea salt, concrete bed and Basalt rocks are more economically attractive relative to molten salt plant because they eliminate the extra cost associated with freeze protection, no pressurizing problem, no corrosion. Finally, natural stones can operate at higher temperature and do not suffer from cracking due to cyclic charging and discharging. - For the purpose of heat recovery, a moving bed heat exchanger (MBHX) is applied and tested. In this study, the dense granular mass is gravitydriven through a heat exchanger. The performance of the MBHX with the utilization of Sand, Basalt, and a Mixture of Sand and Basalt as a granular material was experimentally investigated. It is found that the effectiveness of the MBHX using a mixture of 50% sand and 50% basalt improved by 30% compared to using sand alone.

TES system using underground rock carven is considered as an attractive alternative for largescale storage, because of low thermal conductivity and chemical safety of surrounding rock mass. Based on some successful applications of cavern storage and hightemperature storage reported in the literature, the applicabilities and practicabilities of storage media and technologies for largescale cavern thermal energy storage (CTES) were reviewed Ex: Basalt rocks

Seasonal sandbed solar thermal storage systems are an excellent option for storing heat for climates in regions with long periods of freezing temperatures. The present study shows a proof of concept of a sandbed seasonal solar thermal storage that needs additional controls for residential heating application. The system could also be used to provide heat for unoccupied spaces such as garages and greenhouses. Can also be used for solar powerplants were the intent of the receiver is to be used as a part of a sensible thermal energy storage system for concentrated solar power plants based upon the concept of storing solar heat in sand particles for a later discharge through a specific sandsteam heat exchanger. The results of the analysis indicate low efficiency figures that can be caused by imperfections on the experimental setup and on the original design. Several paths of improvement are discussed in conclusion.

Within all the properties that define the suitability of a material to store sensible heat, waste materials stand out especially for their low costs and availability. This heat recovery could be used for cogeneration, energy efficiency measures, passive heat recovery, solar cooling, etc. In this case, a solid by-product from the potash industry is tested in two different shapes to be used for industrial sensible heat recovery in high temperature, in a range of 100–200 °C. This heat recovery could be used for cogeneration, energy efficiency measures, passive heat recovery, solar cooling, etc. In this case, it is mostly made of NaCl

The solar heat energy is stored in a thermally insulated water tank and used in the heating period. The heat is also stored in the ground if necessary, using the ground loop of the heat pump if the water tank’s temperature rises above a certain threshold. If the temperature is too low for direct heating, then the heat pump can be used to extract the stored energy. This can also be performed under the form of a large subterranean buffer tank filled with water. Heat and cold can be added to or extracted from the tank through conductivity via its wall.

Thermal oils have the advantage that they act both as the heat transfer and the heat storage medium for medium to high temperature domestic applications. These applications include steam generation and cooking of food. Although thermal oils are more expensive than water which is in abundance, the use of water in medium to high temperatures is limited by its boiling point. For small scale domestic applications which require non-sophisticated heat exchangers, thermal oils can be utilized.

A new concept for longterm solar storage is based on the absorption properties of aqueous calcium chloride. Water, diluted and concentrated calcium chloride solutions are stored in a single tank. An immersed heat exchanger and stratification manifold are used to preserve longterm sorption storage, and to achieve thermal stratification. The feasibility of the concept is demonstrated via measurements of velocity, CaCl2 mass fraction, and temperature in a 1500 liter prototype tank during sensible charging.

Using compressed water system to store heat. A startup and a research project have been found on this topic. No direct suppliers - GLIDES: A novel Ground Level Integrated Diverse Energy Storage (GLIDES) system which can store energy via input of electricity or heat and deliver dispatchable electricity. The proposed system is lowcost and hybridizes compressed air and pumpedstorage approaches that will allow for the offpeak storage of intermittent renewable energy for use during peak times. GLIDES, stores electricity mechanically in the form of compressed gas that displaces water in high-pressure vessels. - Insentropic: PHES Thermal Stores are split into layers to achieve high efficiency of thermal transfer, low pressure drop and higher energy density than other 'packed bed' stores. The PHES Thermal Stores work by direct heat exchange between high pressure gas and particles of crushed rock or gravel. It will be a stand-alone energy storage system called Pumped Heat Energy Storage (PHES). The cycle uses a proprietary reciprocating heat pump/engine (developed in-house). It will take electricity from the grid to charge the system.

The electricity is first transformed into the chemical potential of the working fluid by means of varying the refrigerant or absorbent mass fraction in the working fluid storage tank. When cooling, heating or dehumidifying is needed, the potential stored in the tank can then be transformed into cold/heat energy by means of absorption refrigeration/heat pump or into dehumidification/desiccation energy by means of absorption dehumidification.