Almost everyone has experienced relief from the scorching summer heat by putting around a wet towel over the head. This is due to the phenomenon of phase-change material: A matter that discharges or absorbs energy when it transitions from one of the fundamental state of matter to another such as solid, liquid, or gas.
The damp towel cools down because water is a phase-change material that absorbs heat when it is evaporated, i.e. when it transitions from liquid state to gas state.
In recent times, a phase-change material’s (PCM’s) ability to absorb and discharge energy has attracted more attention because of shift of the society from fossil fuel to renewable energy sources that are only available intermittently. This is because of unavailability of sunlight at night and variation in wind speed, it is not possible to capture energy when it is required. This requires energy to be stored for future use.
Meanwhile, PCM offers promise as a storage solution, but their use has been limited till date by seemingly uncontrollable technical challenges.
A detailed paper published in Nature Energy describes the one challenge that has been addressed through a remarkably simple idea. This involves expanding the use of PCMs for heating and cooling that is energy efficient.
Any thermal energy storage system has two important standards: One is energy density that refers to the amount of energy that can be stored per unit volume, and second is power density, which is the rate at which the energy can be extracted from that system per unit mass.
It is desirable to have high levels of both, both most systems display either low energy density but high power density, or its exact opposite.