Energy Storage - Review and Discussion

This report provides a review and discussion on energy storage systems, including mechanical, thermal, electrical, and chemical energy storage. It discusses the technologies in use, their advantages and limitations, and the future prospects of energy storage. The report also highlights Australia's role in promoting energy storage technologies.

Running Head: Energy Storage – Review and Discussion
Title: Energy Storage – Review and Discussion
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Date of submission: 27/05/2019
Authors Note
The current report is presented as part of the requirements to complete the course work.

Energy storage - Review and Discussion 2
Introduction:
Contemporary developments in the technology applications have created need for
complex and more effective energy storage requirements. As of now energy applications are
utilizing diverse energy sources viz., mechanical, electrical, chemical, thermal etc. The
selection of particular type of energy source and storage means depends on the specific
energy application and will depend on the environment in which the energy storage device is
working in. The key objectives of the energy storage systems consists in general developing a
more resilient energy storage technology as well developing technologies those are cost
effective too. New energy storage requirements like renewable energy applications called for
development of different energy storage systems(Guney and Tepe 2017,P,1190).
Technological advancements coupled with the invention of more advanced materials is
enabling these objectives getting fulfilled. The following part of the discussion is focussed
on the evaluation of diverse energy storage applications and will critically discuss the
technologies in usage, the status quo of each of these technologies. Further the future
prospects and the possible developments in the energy storage technologies are discussed in
detail.
Overview of Energy storage devices and Technologies in use:
Mechanical Energy storage systems: Mechanical energy storage systems will utilize the
principles of mechanical energy generation and storage to save energy in this form. Typically
in the scenarios, like when off-peak electrical energy is available, the energy generated will
be stored in mechanical energy format and it will be re-tapped back in the peak times when
electrical energy is not sufficient to meet the demands. Some of the strategies being
employed at present for mechanical energy storage means is flywheel energy storage (FES)
where in the flywheel will receive the energy and will store it in the form of rotational energy
in that(Arani et al 2017,P.16). Typically Flywheel will function as a reservoir of energy in
this condition. Pumped hydropower storage (PHS) contained in employing the excess energy
to pump the hydro fluid to higher potentials, from where at the times of energy needs, the
fluid at higher potential will be utilized back into kinetic energy forms. Compressed-air
energy storage is contained in compressing air when cheaper off peak power is available, the
compressed air will then get transported into the chambers specially created for the storage of
the compressed air and subsequently this will be employed back to generate power, when

Energy storage - Review and Discussion 3
electrical energy is not available as per the energy demands. The efficiency of operation of
PHS systems is about 75 to 80%. CAES system advantage lies in the fact that the energy that
can be employed for power generation can be reduced by about 40% when CAES based
compressed air storage systems is employed. However the availability of underground
storage means like abandoned mines etc needed for such storage means. It is feasible to
employ this technology when supporting geographical systems are available for energy
storage. Carbon reinforced fibre materials and nano carbon tube based materials are some of
the materials that are being employed for Flywheels at present to enable more strength and
subsequent higher energy storage. Hydro-energy systems can be employed for convenient
energy retrieval for convenient time gradient. Flywheel energy storage is cheaper and can be
employed for energy flows without interruption. However the limitations include frictional
losses in the FES, material limitations for high intense energy storage. For hydro pumped
energy storage applications, need for large space and investments for large reservoirs makes
up the limitations. Further for compressed air energy storage requirements the key limitations
include topological requirements that the air storage requires. In any case the mechanical
energy storage is one of the pioneer energy storage technology and is much simpler.
Thermal energy storage systems: Thermal energy storage (TES) systems comprise usage
of thermal energy conversion and phase change principles(Alva et al 2017,P.699) The excess
energy available at different process operations can be tapped, like in the case of waste heat
recovery applications, solar energy utilization applications and energy saving in the buildings
etc. Energy available at each of these channels will be utilized later for the sake of either
heating up the temperature of the storage material or the energy available can be employed
for the sake of melting the phase change material employed for the thermal energy storage
system(Amrouche et al 2016,P.369). In the first case, the thermal energy storage systems is
termed as sensible heat storage system and in the second case it is called as latent energy
storage system(Sarbu and Dorca 2019, P,60). In any case in the later times when there is need
for energy tapping the heat contained in the storage material will be retrieved back either by
cooling it down to room temperature or alternatively it can be solidified by letting it to
liberate the energy contained in it. The key detriment in the adoption of the particular
sensible heat storage system is the cost of the material employed for thermal storage as well
as the physical properties of the same. At low temperature range of applications like in the
case of 100 degree Celsius and below, water can be used as cheapest energy storage
application. It has low cost and has capacity to take up sufficient thermal capacity to store

Energy storage - Review and Discussion 4
higher energy contents. For higher temperature range variety of materials are available at
present, combination of oils and hydraulic substances are being employed for higher
temperature heat storage applications. Even materials like clay, sand etc are feasible to get
employed as thermal energy storage means. Phase change materials (PCM) like molten
metals(Fernandez et al 2017,p.276). Eutectic Aluminium- Silicon Alloy Al-Si12 can storage
energies beyond 560 degree Celsius and more. Other important group of TES is Thermo-
chemical energy storage systems. In these systems the thermal energy received by the
material will be employed to store energy in the form of chemical bonds. Energy will enable
dissociation and again rebonding facilitates energy release in these materials. Hydration of
salts is a good example for energy storage and retrieval in this category of thermo-chemical
energy storage systems. Solar pond is a special group of thermal energy storage system which
can be employed for low range temperature energy storage. The solar pond is cheaper in cost
and will also work on to tap the energy and will provide the same for energy utility
applications(Aneka and wang 2016,P.367). Any quantity of thermal energy storage can be
done employing the solar pond technologies. However the application is limited to solar
energy storage. The recent developments in the technology include using different
combination of salts to improve the overall performance of the pond performance. Both
sensible thermal energy storage as well as latent heat thermal energy storage
principles(Geissbuhler et al 2016,P.660) are being employed in this technology(Aydin, casey
and Riffat 2015,P.359).
Figure 1 Principle of PCM based energy storage
Electrical energy storage systems: Electrical energy storage systems gained prominence
with wide spread usage of renewable energy generation systems like photovoltaic devices as
well as wind energy generation systems. Electrical energy storage systems employed in this
connection will have capacity to store energy and supply them back at times of instable

Energy storage - Review and Discussion 5
energy availability. Depending on the amount of the energy storage capacities as well as the
time required for energy storage variety of electrical energy storage means are available at
present. Most commonly employed energy storage devices include lead-acid battery energy
storage systems, Li-Ion batteries as well as Li-Ion capacitors etc. Electrical energy storage
applications will work both for the sake of stable energy storage as well for the sake of low
carbon impact over the community. Electrical energy can be stored by converting the same
into mechanical energy like in the case of flywheels, can be employed directly to store energy
in the form of compressed air systems, hydroelectric storage systems etc. However the basic
underlying principle in all these technologies is to convert the available electrical energy to
mechanical energy and subsequently employing the same for variety of applications. In any
case, the electrical energy when required to be stored for mobile applications, it need to be
stored in batteries. Recent development of the electrical cars, employ high capacity batteries
which can storage energy for large traction requirements, also the process of charging such
batteries is also very easier, in less time more amount of electrical energy can be stored in
these systems. Ni-MH batteries(Zhang et al 2018, P,3100) are providing range upto 200 km
per charge and New Lithium ion batteries are developing range upto 480km per charge(Ren,
Ma and Cong 2015,P,230). Alternatives to the existing battery materials include vanadium
Redox flow batteries; they can be employed extensively as alternatives to the conventional
lead-acid batteries for better performance requirements(Luo et al 2015,P.539). The new
evolving technologies are directed to meet large energy storage requirements and eco-
friendliness (Larcher and Tarascon 2015, P.19) Capacitors and super capacitors for electrical
energy storage fall in this category of energy storage systems.
Figure 2 Time dependence of capacitor charging

Energy storage - Review and Discussion 6
Super capacitors are employable in the applications where in there will be large current
discharges for small cycles of time duration. As there are no any chemical constraints like in
the battery systems, superconductors can be employed for large range of capacities. The
limitations for this device are the dielectric constants of the capacitor material. By employing
right material, the capacity of these substances can be improved a lot. Super conducting
energy storage devices practically offer long range of application cycles, Also the technology
is useful for applications like overcharging safety, low temperature operating performance
etc. Also the overall charging time for this technology is quite less.
Chemical Energy storage systems: Principles of chemical energy based energy storage
used in the energy usage in the batteries. From portable consumer energy appliances to large
scale online and off-grid connected applications, batteries can be successfully employed as
chemical energy storage systems. Both the stationary and mobile applications can employ
such chemical energy storage systems. Chemical energy storage systems are closely related
with the electrical energy storage (battery) systems. However still they are other class of
energy storage means apart from batteries (Olabi 2017). Redox Flow batteries (RFBs) are
being employed as recent chemical energy storage systems. Redox flow batteries are
economic and will meet the requirements of the medium to large scale energy storage
requirements. True redox flow batteries will contain all the chemical species in active
condition in the fully dissolved solution in all the times. Whereas hybrid redox flows batteries
will contain one chemical specie as plated as solid in the electro chemical cell during the
charge process. Examples of true RFBs include Vanadium-Vanadium and iron-chromium
systems. Hybrid RFBs will include Zinc-Bromine and Zinc-Chlorine systems. Recent trends
in the chemical energy technology include employing proton exchange membrane technology
for the sake of water electrolysis using excess energy available. The products of the
electrolysis viz., hydrogen and oxygen will be stored as energy requirements in future.
Hydrogen can be employed directly for energy generation(Singh, Singh and Kumar
2016,P,35). Also synthetic natural gas generation(Giglio et al 2015,P.30) can be
accomplished by methanization principles, hydrogen generated through this technique can be
mixed with carbon dioxide and synthetic natural gas can be generated for the sake of energy
storage requirements.

Energy storage - Review and Discussion 7
Figure 3 Synnatural gas generation and storage systems
Other similar techniques include generation of methane, liquid hydro carbons like methanol,
ethanol and higher alcohols. Ammonia generation is another popular form of energy storage.
The recent developments are being focussed on to develop more energy intense storage
systems along with more safety and with eco-friendliness.
Australia role in promoting energy storage technologies:
Federal government of Australia in line with its drive to improve the dependency on
renewable energy is floating support to energy storage devices. Several energy storage
technologies are being promoted both by federal government directly and in support from
private partnerships. Battery based energy storage technologies are promoted heavily by the
Australia government. Hydro Tasmania has already working in this direction with huge
investment spanning millions of dollars in this direction. The vision of Australia at present to
develop competency of about 2000MW on demand electricity generation and integration with
the main grid is materializing at present. Energy storage applications make up the key role in
realizing these ambitious projects (council, n.d.).
Discussion and Conclusion
Each of the above energy storage systems does find their versatility in specific type of
application. Each of these technologies are useful in a specific range of energy storage and
also their applicability is justified by the total cost and the complexities involved in the
process of energy storage and the retrieval of the same. Also the eco-friendliness of the
technology employed and the compatibility of the same with the energy usage systems will
decide the applicability of the energy storage device in the particular application. The most
important advancement in the technology includes using new materials for improving the
performance and making them safer as well. For example in the battery frontiers, new

Energy storage - Review and Discussion 8
materials are being explored to improve the capacity of the energy storage and also they are
being explored to make them much safer and environmentally friendly.

Energy storage - Review and Discussion 9
Appendix (Calculations)
Flywheels
Energy stored in flywheel can be computed as follows,
Energy will be stored in flywheel in the form of rotational kinetic energy.
The total KE stored in the flywheel will be given by,
KE =1/2* I* ω2------------------------ (1)
Where I is the moment of inertia of the flywheel and ω is the rotational velocity of the
flywheel.
I the moment of inertia of the flywheel is given by the equation,
I =k*M*R2---------------------------- (2)
Where k is the inertial constant of the flywheel
R is the radius of the flywheel
I is the moment of inertia
From equation 1 and 2 it is very evident that for higher energy storage requirements more
massive flywheels are needed. Or otherwise the size of the flywheel is to be very large.
Thermal energy storage:
Typical energy storage capacity in sensible thermal energy storage systems will be as follows,
Suppose m is the mass of the substance
Cp is the specific heat of the substance employed for energy storage
δT is the temperature difference before taking heat and after taking heat
The thermal energy stored is given by Q = m* Cp * δT -------------- (3)
Equation 3 indicates that for higher energy storage more massive or more specific heat substances
are needed for energy storage.

Energy storage - Review and Discussion 10
References
Journals
Alva, G., Liu, L., Huang, X. and Fang, G., 2017. Thermal energy storage materials and
systems for solar energy applications. Renewable and Sustainable Energy Reviews, 68,
pp.693-706.
Amrouche, S.O., Rekioua, D., Rekioua, T. and Bacha, S., 2016. Overview of energy storage
in renewable energy systems. International Journal of Hydrogen Energy, 41(45), pp.20914-
20927.
Aneke, M. and Wang, M., 2016. Energy storage technologies and real life applications–A
state of the art review. Applied Energy, 179, pp.350-377.
Aydin, D., Casey, S.P. and Riffat, S., 2015. The latest advancements on thermochemical heat
storage systems. Renewable and Sustainable Energy Reviews, 41, pp.356-367.
Arani, A.K., Karami, H., Gharehpetian, G.B. and Hejazi, M.S.A., 2017. Review of flywheel
energy storage systems structures and applications in power systems and
microgrids. Renewable and Sustainable Energy Reviews, 69, pp.9-18.
Fernández, A.I., Barreneche, C., Belusko, M., Segarra, M., Bruno, F. and Cabeza, L.F., 2017.
Considerations for the use of metal alloys as phase change materials for high temperature
applications. Solar Energy Materials and Solar Cells, 171, pp.275-281.
Geissbühler, L., Kolman, M., Zanganeh, G., Haselbacher, A. and Steinfeld, A., 2016.
Analysis of industrial-scale high-temperature combined sensible/latent thermal energy
storage. Applied Thermal Engineering, 101, pp.657-668.
Giglio, E., Lanzini, A., Santarelli, M. and Leone, P., 2015. Synthetic natural gas via
integrated high-temperature electrolysis and methanation: Part I—Energy
performance. Journal of Energy Storage, 1, pp.22-37.
Guney, M.S. and Tepe, Y., 2017. Classification and assessment of energy storage
systems. Renewable and Sustainable Energy Reviews, 75, pp.1187-1197.

Energy storage - Review and Discussion 11
Larcher, D. and Tarascon, J.M., 2015. Towards greener and more sustainable batteries for
electrical energy storage. Nature chemistry, 7(1), p.19.
Luo, X., Wang, J., Dooner, M. and Clarke, J., 2015. Overview of current development in
electrical energy storage technologies and the application potential in power system
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Olabi, A.G., 2017. Renewable energy and energy storage systems.
Sarbu, I. and Dorca, A., 2019. Review on heat transfer analysis in thermal energy storage
using latent heat storage systems and phase change materials. International Journal of
Energy Research, 43(1), pp.29-64.
Ren, G., Ma, G. and Cong, N., 2015. Review of electrical energy storage system for vehicular
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Singh, A.K., Singh, S. and Kumar, A., 2016. Hydrogen energy future with formic acid: a
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Websites
council, C. e., n.d. [Online]
Available at: https://www.cleanenergycouncil.org.au/resources/technologies/energy-storage
[Accessed 27 May 2019].