Civil Engineering Reference
In-Depth Information
Table 3 Potential materials for chemical reaction storage identified during IEA SHC Task 32
(Pinel et al.
2011
)
Material
name
Dissociation reaction
Energy storage
density of
AB GJ/m
3
Turnover
temperature
(C)
Realization
potential
(%)
AB
,
B+
A
Magnesium sulphate
MgSO
4
7H
2
O
MgSO
4
H
2
O
2.8
122
9.5
Silicon oxide
SiO
2
Si
O
2
37.9
4,065
+HF: 150
9.0
Iron carbonate
FeCO
3
FeO
CO
2
2.6
180
6.3
Iron hydroxide
Fe(OH)
2
FeO
H
2
O
2.2
150
4.8
Calcium sulphate
CaSO
4
2H
2
O
CaSO
4
H
2
O
1.4
89
4.3
endothermic in nature. Similarly, when the individual components are combined
together, the stored heat energy in them can be retrieved again, which is an
exothermic reaction.
In the desorption process, the individual components obtained as the outcome
can be stored separately, and when the energy demand arises, the working pairs
can be combined together to form the parent chemical component. The thermo-
dynamic properties and realization potential of some major thermochemical heat
storage materials (or minerals) utilized in practice are summarized in Table
3
.
For brevity, the operating characteristics of some closed and open adsorption/
absorption types of the thermochemical energy storage systems are explained in
the following section.
4.9.1 Closed Adsorption Energy Storage System
The modular high energy density heat storage (Modestore) prototype system was
first developed by the AEE INTEC in Austria, which was integrated with the solar
collectors of 20.4 m
2
intended for catering the heating and domestic water pro-
duction purposes (N'Tsoukpoe et al.
2009
). This system was classified under the
closed adsorption energy storage, wherein the working pair or functional materials
utilized for the chemical processing was silicagel/water. Silicagel, the well-known
compound for adsorbing the moisture from vapour, was preferred as the adsorbent,
and the water acts as the sorbate in this system. The operating principle of this
system is depicted schematically in Fig.
9
.
Factually, during the charging cycle, the heat energy trapped from the solar
radiation is supplied to the silicagel through the dedicated heat exchanger
arrangement. The temperature of the heat source is about 90 C, which when added
to the silicagel makes it to release the water vapour (through desorption principle).
The released water vapour then gets condensed in the condenser as shown, and
the components (dry silicagel and water vapour) are stored separately for further
usage. The time of storage of the reactive constituents may vary depending on the
seasonal TES requirements on a long-term basis.
