A New Way to Store Thermal Energy

Thermal Storage – Phase Change Material – PCM

Researchers at MIT have developed a new concept in the form of new chemical composite providing a substitute of storing heat from the sun or any other source during the day in a type of thermal battery.  This could release the heat whenever required for instance in the case of cooking or heating after dark.  A common method to thermal storage is to utilise it as a phase change material – PCM where input heat tends to melt the material and its phase change from solid to liquid stores energy.

When the PCM is cooled back down lower than its melting point, it is inclined to turn back to solid wherein the point of stored energy is released as heat.  There are several instances of these materials comprising of waxes or fatty acids utilised for low temperature applications as well as molten salts utilised at high temperatures.

However presently PCMs tend to need a great amount of insulation and are inclined to pass through that phase change temperature wildly thereby dropping their stored heat comparatively quickly.  On the contrary the new system tends to utilise molecular switches which alters the shape with reaction to light.  When integrated into the PCM, the phase-change temperature of the hybrid material could be accustomed with light enabling the thermal energy of the phase change to be maintained well lower than the melting point of the original material.

Fatty Acids/Organic Compound  for Thermal Energy Storage

The new discovery by MIT postdocs Grace Hans and Huashan Li together with Professor Jeffrey Grossman have been reported in the journal Nature Communications.  Grossman has explained that the trouble with thermal energy is that it is hard to hold on to it.  His team then created what is essentially add-ons for the purpose of traditional phase change material or `little molecules which tend to undergo structural change when the light is said to shine on them.

He further added that the trick had been to locate a method of integrating these molecules with conventional PCM materials in order to release the stored energy as heat, when needed. He also mentioned that there were several applications which would be useful in storing thermal energy in a way that enables you to activate it whenever essential.

This was achieved by the researchers by merging the fatty acids with organic compound which are inclined to response to a pulse of light.  With the help of this method, the light-sensitive component is said to change the thermal properties of the other component that stores as well as discharges its energy. Hybrid material tends to melt when it is heated and thereafter when exposed to ultraviolet light; it tends to remain melted after it has been cooled back.

Solidification & Super-Cooling , Method for Thermal Storage

Thereafter when activated by anther pulse of light, the material re-solidifies and returns back the thermal phase-change energy.  Grossman, who is the Morton and Claire Goulder and Family Professor in Environmental Systems and also a professor of materials science and engineering, had stated that by integrating a light-activated molecule in the traditional image of latent heat a new type of control knob for properties like melting, solidification and super-cooling is added. According to Hans, the system could make use of any source of heat and not just solar.

Readiness of waste heat is extensive from industrial processes to solar heat as well as heat coming from vehicles which is generally wasted.  Connecting some of that waste could offer a means of recycling the heat for beneficial applications. Hans has explained that technically they are installing a new energy barrier so that the stored heat does not get released instantly.

He further mentioned that the energy tends to remain for a longer period till the optical trigger is activated, in its chemically stored system.  The stored heat, in its initial small scale lab version, had shown that it tends to stay steady for around 10 hours while a device of identical size storing heat directly would dispel it within a few minutes.

Thermal Energy Density – Significant

There is no fundamental reason as to why the same cannot be tuned to move higher. Grossman stated that in its preliminary proof-of-concept method, the temperature change or super-cooling which was accomplished for thermal storage material could go up to 10 degrees C (18 F) and they anticipate to still go higher.  Hans states that in this version the energy density is quite significant even though a conventional phase-change material is used.

The material tends to store around 200 joules per gram which according to her is very good for any organic phase-change material.  According to her, people have already shown interest in utilising this for cooking in rural India.  Such methods could be used in drying agricultural crops or for space heating.  Grossman had commented that their interest in this work was to portray a proof of concept though they were of the belief that there is plenty of potential for utilising light-activated materials to hijack the thermal storage properties of phase change materials.

Storing Thermal Energy – Scope of Prospective Applications

Junqia Wu, professor of materials science and engineering at the University of California at Berkeley who was not involved in the study, stated that this is a highly creative research, where the key is that the scientists mingle a thermally driven phase-change material with a photo-switching molecule, in order to build energy barrier to stabilize the thermal energy storage.  He further stated that he was of the opinion that the work is significant since it provides a practical way of storing thermal energy that had been challenging in the past.

The design of MIT team for storing thermal energy had scope of prospective applications and ultimately the technology can offer a solution for people in developing countries which do not have a traditional power grid.  Besides absorbing heat from the Sun the system has the capability of harnessing water energy from industrial procedures which means that it could absorb the energy released as heat from heavy machinery and thereby release that energy later to heat a living space. The work had been aided by the Tata Centre for Technology and Design within the Energy Initiative of MIT.

Tags : TechnologyThermal Energy

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