166
7 Concluding Remarks
Energy storage materials and devices can reversibly store and release energy in different forms, which not only facilitates the economical conversion of energy, but
also provides a balance between energy demand and supply, especially for renewable
energy sources. In the TES system, thermal energy can be stored in PCMs via latent
heat or in molten salts via sensible heat. Sensible heat is stored or retrieved when the
TES medium increases or decreases its temperature over a temperature span whilst
the latent heat of the TES medium is stored or retrieved in the process of phase
transition undergoing no change in temperature. Besides, an indirect TES method
called thermochemical energy storage in which a second fluid is needed to transfer
heat to enable the reversible chemical storage process can also help store thermal
energy with very high efficiency.
The TES system is applicable to be integrated into different applications categorised by low, medium and high temperature TES applications. Low and medium
temperature TES applications mainly involve heating/cooling facilities at spatially
comfort temperature or a little higher, such as solar water heating and air heating.
High-temperature TES systems are usually incorporated in CSP plants to smooth
the fluctuations of electricity demand between peak and off-peak hours in a day and
minimise the impact of the intermittence as well as improve the energy security and
efficiency. Furthermore, a TES system designed primarily for storage of solar
energy is not necessarily restricted to that source, but can also be used, for example,
to harvest industrial waste heat and geothermal energy.
Molten salts have relatively high specific heat capacities and a large number of
variations, which are available over a wide operating temperature range as TES
media. Typically, inorganic molten salts, such as nitrates, carbonates and chlorides
have been intensively investigated. To enhance the heat capacity of molten salts,
different nanomaterials have been selected as the heat capacity enhancers. It has
been reported that marked enhancement has been obtained with the addition of
nanomaterials in molten salts. In the view of different factors (nanomaterial size,
concentration and structures) that may influence the specific heat capacity,
hypothetical explanations have been proposed to be responsible for the enhancement.
Considering that the study of such a research area is still at the very initial stage
with insufficient experimentation and theoretical references, deep understanding of
interactions between nanomaterials and molten salts based on the systematic
investigation of previous findings is challenging. At the same time, technical
obstacles need to be dealt with for the characterisation of materials at high
temperatures.
Acknowledgement This work received funding from the International Doctoral Innovation
Centre, Ningbo Education Bureau, Ningbo Science and Technology Bureau, and the University of
Nottingham, and also the Ningbo Municipal Government (3315 Plan and 2014A35001-1).
X. Guo et al.
7 Concluding Remarks
Energy storage materials and devices can reversibly store and release energy in different forms, which not only facilitates the economical conversion of energy, but
also provides a balance between energy demand and supply, especially for renewable
energy sources. In the TES system, thermal energy can be stored in PCMs via latent
heat or in molten salts via sensible heat. Sensible heat is stored or retrieved when the
TES medium increases or decreases its temperature over a temperature span whilst
the latent heat of the TES medium is stored or retrieved in the process of phase
transition undergoing no change in temperature. Besides, an indirect TES method
called thermochemical energy storage in which a second fluid is needed to transfer
heat to enable the reversible chemical storage process can also help store thermal
energy with very high efficiency.
The TES system is applicable to be integrated into different applications categorised by low, medium and high temperature TES applications. Low and medium
temperature TES applications mainly involve heating/cooling facilities at spatially
comfort temperature or a little higher, such as solar water heating and air heating.
High-temperature TES systems are usually incorporated in CSP plants to smooth
the fluctuations of electricity demand between peak and off-peak hours in a day and
minimise the impact of the intermittence as well as improve the energy security and
efficiency. Furthermore, a TES system designed primarily for storage of solar
energy is not necessarily restricted to that source, but can also be used, for example,
to harvest industrial waste heat and geothermal energy.
Molten salts have relatively high specific heat capacities and a large number of
variations, which are available over a wide operating temperature range as TES
media. Typically, inorganic molten salts, such as nitrates, carbonates and chlorides
have been intensively investigated. To enhance the heat capacity of molten salts,
different nanomaterials have been selected as the heat capacity enhancers. It has
been reported that marked enhancement has been obtained with the addition of
nanomaterials in molten salts. In the view of different factors (nanomaterial size,
concentration and structures) that may influence the specific heat capacity,
hypothetical explanations have been proposed to be responsible for the enhancement.
Considering that the study of such a research area is still at the very initial stage
with insufficient experimentation and theoretical references, deep understanding of
interactions between nanomaterials and molten salts based on the systematic
investigation of previous findings is challenging. At the same time, technical
obstacles need to be dealt with for the characterisation of materials at high
temperatures.
Acknowledgement This work received funding from the International Doctoral Innovation
Centre, Ningbo Education Bureau, Ningbo Science and Technology Bureau, and the University of
Nottingham, and also the Ningbo Municipal Government (3315 Plan and 2014A35001-1).
X. Guo et al.