Thermal energy storage system (TESS)provides a great means to correct the mismatch between the energy supply and demand. During on sun hours, the excess thermal energy available is stored in TESS and the stored energy is retrieved for producing electricity during off-sun hours. The application of such systems range from low temperature cooling systems to high temperature CSP technology.Thermal energy can be stored in three different ways, viz., Sensible Heat Storage (SHS), Latent Heat Storage (LHS) and Thermochemical Energy Storage (TCES).
In SHS system, thermal energy is stored in the storage material by raising thetemperature. SHS utilizes the heat capacity of the storage material to store the thermal energy. Materials such as Molten salt, oil, rock, concrete, cast steel, etc. are used in SHS system.In LHS, thermal energy is stored in the materials during the phase changeof the material at a constant or near constant temperature.Salt hydrates, Metals, Eutectics, Paraffin’s, etc. are employed as PCMs.
Our research team at IIT Guwahati possess a long-term experience (past 10 years) in thermal modelling and testing of sensible and latent heat thermal energy storage systems.
An experimental setup was developed for testing lab scale storage models. A synthetic thermic oil (Hi–Tech Therm 60) is used as heat transfer fluid in this experimental setup. Both SHS and LHS models were tested using this experimental setup. SHS materials such as Concrete and Cast steel were tested on 10 MJ scale. Also, a 12 MJ LHS model was developed using a ternary mixture comprising of potassium nitrate, sodium nitrate and sodium nitrite in theweight proportion of 53:7:40, which has the melting point of approximately 142 °C.
Due to an increased interest in the field of renewable energy particularly in solar energy, numerous thermal energy storage materials have been identified and developed during the past few years.Even though the improvements in terms of storage techniques are remarkable, there is a need to develop a TESS that operates over 300 °C to make concentrating solar power technology cost competitive. The current research at IIT Guwahati is aimed at developing and testing of high temperature sensible, latent and thermochemical energy storage models that operate over 300 °C. Anexperimental setup is developed (shown in Fig. 2.) at IIT Guwahati for testing SHS and LHS models at higher temperatures.
Thermochemical heat storage (THS) systems rely on the energy absorbed
and released in
breaking and reforming molecular bonds of certain materials in a
completely reversible
chemical reaction. The utilisation of TCES materials offers a compact,
efficient and economic TESS. These systems provide higher energy
density, higher exergy efficiency and long term storage. At present,
our research team is focused on identifying potential TCES materials
and development of thermal model for predicting energy storage and
discharge characteristics. In future, characterization of the
potential TCES materials and preliminary experimental studies on lab
scale prototypes will be conducted.Hydroxides, carbonates and metal
hydrides are in major consideration.
Solar dryers are devices that use solar energy or radiation to dry substances, especially agricultural products in order to preserve it. The solar dryer haveabsorbing surface which absorb solar radiation and gain heat from it.The heat energy is used to remove the moisture content from the products, hence it dries up the product. There are three general types of solar dryers: Direct, Indirect and Mixed mode.
Direct solar dryers expose the substance to be dehydrated in direct sunlight. Here the product directly gain the heat from sunlight and get dried. In this case there can be chances for contamination of product by dust from wind, by birds, insects, or animals.
In case of indirect type of solar dryer, air is heated separately by using solar air heater and the hot dry (low % of Relative Humidity) air is pass to the dryer chamber, where the product is placed for drying. Here direct sunlight is not allowed to fall on the product as,direct sun can chemically alter the contents of the products and making them less appetizing.
In mixed mode dryer the solar radiation is allow to enter the drying chamber to heat up the product inside the dryer and hot air is also supplied to the drying chamber from separately connected solar air heater. In this case the dryer receives heat from both solar radiation and hot air, due to which the drying rate is faster in mixed mode dryer.
The solar thermal lab at IIT Guwahati mainly focusses on the following –
