> An Experts in Team Project <
1
Energy Storage in the European Power Grid:
A Review on Thermal and Electrochemical
Energy Storage
Magnus Dahle, Karoline Egholm, Ole-Kristian H. Ellingsen, Thomas Franang and Nora T. Raknes
Abstract—The European Union has set the
objective of providing 80% of its total energy
consumption utilizing renewable energy sources
within 2050. To realise this goal, a well-developed
storage system is a prerequisite. Large scale energy
storage will most likely become an important feature
of the electricity grid already in 2020. Emerging
thermal and battery storage technologies can supply
an increased storage capacity in regions where
conventional storage is difficult or impossible.
However, this paper concludes that there exists no
single energy storage technology, as of 2014, which
satisfies the needs of the future power grid.
Moreover, the future power grid should be
composed of multiple energy storage technologies
presented in this paper, distributed according to
their advantages between EU’s member states
depending on their natural energy resources.
Index Terms—Battery, Concentrated
Power, Energy Storage, Power Grid
Solar
I. INTRODUCTION
The European society has an increasing need for
energy while the problems concerning emission of
carbon dioxide and global warming are increasing.
A persistent challenge for renewable energy
sources, e.g. running water, wind and solar power,
is the unpredictability due to changing weather
conditions and the societies’ fluctuating energy
consumption during the day. This report will focus
on energy production from wind and solar and
how much of this energy will be rejected due to
lack of correlation in production and demand.
Solar and wind energy differ in their production
characteristics. Solar energy will fluctuate
following a clear pattern, meaning it will produce
during the day, and not during the night. Wind will
fluctuate, and not following such a clear pattern. It
might produce several days in a row due to strong
wind, and nearly nothing at all in cases with low or
too strong wind.
To compensate for the variation in production, the
energy surplus can either be exported to
neighbouring countries, stored to be used during
shortages or it can be rejected by not producing in
these situations. The alternative to stop production
will lead to revenue losses and should therefore be
avoided. It will not always be possible to export
the surplus due to correlation in weather conditions
and therefore energy production in neighbouring
countries, and in cases when they do not correlate,
the surplus might not be able to be exported due to
restriction in transfer capacity in the power system.
Energy storage does not have these disadvantages
and is the focus in this review. The report will also
investigate the economic and political potential of
storing renewable energy and how different
technology can be used to achieve this. The
technology’s availability, energy storage capacity,
loss due to storage leakage, price efficiency,
possible area or geographical restrictions, and its
influence on local environment will be taken into
consideration.
II. RENEWABLE ENERGY AND ENERGY
STORAGE IN THE EU
In the Lisbon Treaty, ratified on December 1st
2009, article 194 states that the European Union
shall aim to ensure security of supply, promote
interconnectivity of the energy networks and an
increased development of renewable energy [1].
EU has committed itself to increase its share of
renewable energy to 20 % overall, with some
countries obligated to increase further by 2020 [2].
If this goal is reached purely by using intermittent
renewables, the grid operators will struggle to
compensate for the variable production [3]. Today
the EU only has an installed energy storage
capacity equivalent to 5 % of total production
capacity. This means that by 2020, several
European countries will need to increase their
energy storage capacity. There are also several
countries that have a goal of reaching 80%-100%
renewable energy production by 2050. Germany
and Spain are both aiming at a share of 80% [4].
Despite this, there is no clear, common strategy to
> An Experts in Team Project <
increase the storage capacity [3]. Several
countries, including Spain, have no regulation at
all.
Both Spain and Germany are countries with a
significant share of renewable energy in terms of
wind and solar energy. It is therefore interesting to
use these countries as examples for energy storage
solutions. With such a large share of energy that
fluctuates it is important to even out the production
curve and relate it to the demand curve. Energy
storage will help doing this by storing energy
when there is a surplus and delivering the stored
energy in a shortage situation. These fluctuations
depend on the source used for production. Solar
energy mainly alters between a surplus in the day
and a shortage in the night which creates a need
for a storage system which can store from 12 to 24
hours. Wind alters more irregularly with
intermittent periods which may be from minutes to
weeks. This creates a need for an energy storage
system which is more flexible and can store for
longer periods of time.
There is also a difference in restrictions for wind
and solar energy production. Since solar energy
production has a lower load production than wind
energy production, the installed power is high [4].
This is not a problem on most days, but when there
is a lot of sun the production will be very high and
the energy system receiving this power must be
equally large to be able to receive all the energy. It
is not realistic to have a storage system that can
handle such an amount of power, therefore some
of the production will be rejected. For wind energy
it is not the power that restricts the energy storage
system but the energy capacity. The installed
power does not have to be very high, but if it is
windy for a longer period, the energy storage
system needs to have a larger energy capacity to
receive all the energy which the wind produces
since it will not have the opportunity to drain the
storage during this time. Since these technologies
often are part of the same system it is difficult to
choose an energy storage system that satisfies both
needs. It can therefore be wise to use different
energy storage for each energy production
technology.
In the cases where Germany and Spain achieve a
renewable energy share of electricity production of
80% they will have to reject some of the energy if
they do not have an energy storage system. T.
Weiss and D. Schulz have analysed the amount of
energy rejected depending on the share of wind
2
and solar energy in the system. In the case where
the production favours solar power, the amount of
energy rejected in Germany and Spain would be
29.04 TWh and 20.75 TWh respectively. If it
favours wind energy the amount would be 15.85
TWh and 11.80 TWh respectively [4]. This is the
total loss, but it will not be economically feasible
to store all this energy. The share that can be
stored will depend on which technology that will
be used and the economical requirements.
III. POTENTIAL ENERGY STORAGE
TECHNOLOGIES
This report investigate technologies with potential
for storing large amounts of energy over a time
period of 24 hours, weeks or longer. Assuming the
storage devices to be stationary, weight and
volume is of less importance. However, the cost of
operation and maintenance will be crucial for the
technology combined with renewable energy
production, as it has to be industrial competitive
with power production using fossil fuels. It has
been conducted a brief survey considering multiple
possible technologies for large scale energy
storage, in which follows. Among these
technologies, the electrochemical storage using
large scale batteries and thermal storage using
molten salt technology will be given a more
thorough exposition.
A. Hydrogen storage
Applying hydrogen for energy storage (HES)
implies using surplus of electricity production to
produce hydrogen gas, which is kept in large
storage tanks. Conversion back to electricity may
be achieved by utilizing fuel cells, or by
combustion to heat water in which powers a steam
turbine [5]. There are several ways to produce
hydrogen, the most common are either to
electrolysis or to derive it from natural gas, the
second being the cheapest [5]. To store the energy,
either tanks or geological formations can be used,
depending on the local geography. Hydrogen
storage has the benefit of an infinite time horizon
of storage as storage tanks may be designed for
negligible leakage. The greatest challenge of
storing hydrogen gas is due to its low particle
density, meaning it requires huge storage volume
compared to other energy storage technology for
the same amount of energy stored. Research
concerning hydrogen storage widely considers new
alternative methods of storing hydrogen in solid
state [6].
> An Experts in Team Project <
B. Batteries
Batteries store the energy electrochemically using
redox-reactions in different materials. By
transferring electrons between materials with
different electrostatic potential it is possible to
store and utilize the electrons for energy storage
and -production [6]. To extract the energy, the
electrons are forced through an outer circuit. The
driving force of the battery is the inertness of the
chemical compounds [7]. In terms of large scale
energy storage, batteries may be constructed in
large stacks of modules, ultimately meaning the
limiting factor of storage capacity is due to
installation volume available [App A]. Also,
batteries in general depend on stable operation
temperatures and some technologies rely on
environmentally poisonous components. These are
challenges which ongoing research deal with and
the concept of large scale storage utilizing batteries
(BES) are already commercial [8], [App. A].
C. Supercapacitor
A supercapacitor is a capacitor where the
conductor is replaced with dual-layer nodes and
cathodes, and the dielectric is replaced with a nonconducting liquid. This causes the charge surface
of the conductors, the anode and cathode, to be
approximately ten thousand times larger. The
super capacitors greatest disadvantage is that
applying high voltages may electrolyze the liquid,
resulting in dielectric breakdown and immediate
discharge. This heavily limits the potential of
storing large amounts of energy [9]. However,
supercapacitor energy storage (SCES) is highly
commercial for small scale storage [10].
D. Superconductors
Superconductivity is a phase transition phenomena
that occurs for solids in the transition to the critical
temperature of the substance, generally somewhere
between 0 and 100 Kelvin. During the phase
transition, Cooper-pairs form on the surface of the
material. The Cooper-pairs eliminates the
electrical resistance in the wire, enabling currents
to be flow without any ohmic resistance. This
allows current to flow in a coil with virtually no
losses. Superconductivity is a quantum mechanical
phenomenon and as of 2014, no physical theory
has completely describes this phase [11].
Superconducting magnetic energy storage (SMES)
exploits the zero-loss attribute to contain currents
over time. However, the superconducting material
relies on stable low temperatures and also has an
upper limit of how strong current it may carry
3
before the Cooper-pairs break down and electrical
resistance rapidly increases [12].
E. Flywheels
The Encyclopedia of Energy [13] defines a
flywheel as a “rotating object, such as a wheel,
often used for opposing and moderating by its
inertia any fluctuation in speed in the machinery
with which it revolves; also capable of storing
mechanical energy”. This means that the flywheel
can serve two purposes in the electricity grid. The
first is to suppress changes in demand in the grid
by supplying and absorbing power, the other is to
store excess energy in the power system. The
flywheel consists of a rotor, ball bearings, and a
machine that works as both motor and generator.
Due to the high losses, 2-3% per hour [5] it is not
suitable for long time energy storage. Furthermore,
the total possible amount of energy stored using
flywheels is limited by which material it is
constructed by, as this will dictate what mass the
unit will have and what rotational velocities it may
spin with.
F. Pumped Hydro Storage
Pumped hydro storage (PHS) stores energy by
using a pump to move water from a low reservoir
to a higher one, thus increasing the potential
energy of the water. To extract the energy, water is
released from the higher reservoir, transforming
the potential into kinetic energy, and sent through
a turbine at a lower altitude. Pumped hydro storage
has a total round trip efficiency of 75-85% [3]. The
technology is well established and proven, and
research only considers improving efficiency of
turbines and pumps. However, PHS is highly
dependent on the local geography. Creating a
reservoir by e.g. building a dam, results in great
encroachment on the local environment in which
will be covered by water. Dam construction also
has high initial investment costs, causing it to be a
high risk investment for companies.
G. Compressed Air
The principle behind compressed air energy
storage (CAES) is to increase the pressure of the
air, using a compressor, and storing it in large
containers. A turbine is then driven by the
expanding gas to power a generator. The main
component is the storage space. In order to contain
large amounts of energy, it is necessary to have
huge storage facilities. While it is possible to use
tanks, geological formations or abandoned mines
may provide a larger storage volume [5]. The
process produces heat during compression and
> An Experts in Team Project <
4
consumes heat during expansion. If this energy can
be stored for later use, the round-trip efficiency is
around 65-75% [5], but this would require an
enormous heat exchanger [3]. CAES obviously
offers low energy density, and requires vast
volumes. The technology seems applicable for
offshore oil and gas production in which may
compress air for storage in drained fossil fuel
reservoirs.
implies that the technology may be well suited for
long time storage. A difficulty using this
technology is the generally low efficiency of
thermal electricity production, but the heat can
also be applied in a district heat system.
H. Thermal Storage
By using concentrated solar power it is possible to
both generate and store energy in a single plant.
The method uses mirrors to reflect concentrated
sunlight on a small area, a so called Hot Spot. A
liquid is sent through the hot spot to be heated, and
this heat is transferred, using a heat exchanger,
either to steam for a steam turbine, or to melt salt
stored in thermal isolated tanks. The storage losses
are relatively low compared with other energy
storage technologies, only 1% annually [14]. This
Energy Storage Technology
Limiting
factor
Time horizon of
Storage
Efficiency
[%]
Build Costs
[$/kW]
Energy Density
[kWeh/m3]
Hydrogen Storage
Volume
Infinite
80-90
N/A
900
Battery
Volume
Days
80-95
5.55×102
30
Supercapacitor
DBV(1)
Minutes
80-95
8.00×10-2
N/A
Superconducting Magnetic
Energy Storag
Material
Minutes
~100
3.50×102
0.04(2)
Flywheel
Material
Hours
80-90
8.00×102
4000
Pumped Hydro Storage
Volume
Infinite
75-85
1.32×103
N/A
Compressed Air
Volume
Infinite
70-80
7.74×102
8
Thermal Storage (Salt)
Volume
Years
30-45
1.38×101
200
Table 1 – “Summary of Energy Storage Technologies”
The data is gathered from multiple sources; [11], [12], [13], [14], [15], [5], [16], [17], [18], [6], [19], [20], [21], [22],
[23], [24], [25]. Also, the sources refer to different commercial projects meaning utilizing other designs or techniques for
the same technological concepts yields great uncertainty in numerical values. Other values depend on local parameters and
conditions. Hence, the table should only be used as a guideline for comparison. (1)Dielectric breakdown voltage. (2)Energy
density of SMES is calculated per cross section of coil (m2), instead of volume.
> An Experts in Team Project <
IV. LARGE SCALE BATTERIES
There exists multiple different types of batteries,
all based on unique technology with different
advantages. For the purpose of stationary large
scale energy storage, SINTEF Researcher Ole Kjos
promotes the molten salt batteries (MSB) as a
feasible and qualified solution. These batteries
have
the
advantage
of
consisting
of
environmentally friendly components which at the
same time are commonly available giving them
lower cost relative to other technologies [App. A].
Furthermore, the Sodium-Sulphur (NaS) Battery is
an example of an MSB which is constructed and
used in the American, Japanese and other power
grids to balance non-uniform power consumption
throughout the day. However, some components
are expensive and these batteries are mainly used
as an alternative solution to extensive changes in
power grids [App. A], [8]. Another difficulty is the
chemical sulphur being self-igniting in contact
with oxygen and in 2011; a NaS battery caught fire
after internal leakage of hot molten material [8].
Ongoing research concerns changing battery
design and finding low-cost components to replace
the more expensive parts [App. A].
Donald R. Sadoway currently leads a research
team at Massachusetts Institute of Technology
(MIT) who are investigating the possibility of
liquid metal batteries. The idea is using antimony
and magnesium as positive and negative electrodes
respectively, separated by the molten salt
electrolyte MgCl2-KCl-NaCl [15]. A prototype for
large scale storage is under development and is
assumed to be ready during 2015. Hopes are
reaching a cost close to $500/kWh [16], storing
ultimately 2MWh contained within a volume of a
12 meters long container [17].
A concern considering battery technology in
general is how their performance depends on
temperature and cycle life. However, with today’s
technology of thermal isolation combined with the
battery’s own production of heat during discharge
and recharge, temperature management is a minor
issue. The real challenge consists of keeping the
discharge and recharge cycle continuous without
longer periods of time to avoid the battery from
cooling. If the battery is chilled, leakage increase
rapidly during both standby and discharging, and
external power will have to be supplied to the
battery system [App. A].
5
The cost of installing large scale battery modules
are highly variable and accurate numbers
considering the pricing of such storage devices are
difficult to estimate. In 2013, Electric
Transmission Texas (ETT) began utilizing a new
4MW NaS installation with a final total cost of
approximately $70 million, giving a $17.5 per W
[18]. Due to continuously changes in the industrial
production methods, one should expect the cost
per unit of energy stored to drop the next years.
Also, when considering large scale storage for the
energy grids, battery installations are relatively
large, meaning they are ordered and constructed on
commercial contracting resulting in varying
pricing and specifications [App. A]
V. THERMAL ENERGY STORAGE
Thermal storage is applied by saving energy in
terms of heat to be utilized later directly or
transformed into electricity. The energy is
conserved either by sensible or by latent heat
storage. Sensible heat storage is related to the
increase of temperature in some media described
by the material’s heat capacity when exposed
temperature differences. Latent heat storage makes
use of phase change materials (PCMs), which
absorbs or release heat under constant temperature
while undergoing a phase transition [19]. Latent
heat storage applying PCMs is one of the most
efficient methods considering thermal energy
storage, as the stored energy density is much
higher than for sensible heat storage. Furthermore,
the required difference of the PCM’s temperature
between storing and releasing energy is lower than
for the sensible storage [20].
There exist multiple sources of thermal energy to
harvest and store, including but not limited to solar
energy and geothermal heat. This paper will
consider using solar power for latent heat storage
as this application is already commercial and well
utilized. Harvesting heat from solar energy may be
achieved using parabolic trough solar or heat tower
technology which is most proven and has lowest
cost considering large scale power plants [21].
This technology applies the principle of
concentrating solar power (CSP). Automated
mirrors guide and focus solar radiation to some
stationary point and raise the temperature to about
200-600 degrees C. Latent heat is then stored by
forcing a phase transition of a PCM, which is then
transported for storage to thermal isolated
containers. The molten salt may then be extracted
to undergo a new phase transition turning the salt
> An Experts in Team Project <
back to its solid state releasing the stored latent
heat. This thermal energy is then used to vaporize
water which in turn powers a steam turbine
producing electricity [21].
The commercial profitability of the system’s
thermal energy storage (TES) heavily relies on the
PCM’s energy density in terms of the phase
transition, and the cost and maintenance of the
thermal isolated storage containers. The
corporation Bright Source Limitless (BSL) built
and now operates vast CSP plants at different
locations in the US, using water as their PCM and
producing about 500 MW of power in average.
The choice of water enables BSL to run the steam
directly from the heating tower after boiling to the
steam turbine producing electricity [22]. However,
steam occupies a huge amount of space making it
less suitable for large scale storage.
Introducing an intermediate step of some other
PCM, the material should be chosen exclusively
for its thermal properties. Dunn [14] and Farid [20]
present different feasible PCMs with distinct
advantages. Common PCMs are different mass
percentage combinations of salts, typically sodium
and potassium nitrates. The mixture of 60:40 mass
percentage of Na- and K-nitrite respectively is
often denoted as Solar Salt with favourably
melting point of 220ºC and thermal stability limit
at 600ºC [14]. The solar salt is superior to steam in
terms of energy storage, having a volumetric heat
capacity of approximately 0.559 Wh/(Km3), which
is 3500 times that of the steam’s at about 500ºC.
The complete, empirical Rankine cycle for which
the salt transfers heat and boils water to run the
turbine producing electricity, has an efficiency of
about 38% when converting heat to electricity
[14].
Torresol Energy is a Spanish company specializing
on building CSP plants applying molten salt
technology. In 2014, they operate three plants, one
utilizing heating tower technology, while the other
twos apply parabolic troughs, both supported by
thermal energy storage modules. The tower
produces almost 20 MW during the day, and is
able to deliver 15 hours of this power only using
stored energy, yielding a total storage capacity of
about 300 MWh. Consistently, the trough plants
each produces 50 MW in daytime and may store
up to 350 MWh of energy [23]. The total project’s
build and maintenance cost is publically unknown.
6
VI. DISCUSION
Energy storage may provide a solution to the nonsynchronized
renewable
production
and
consumption rates. Storing 70% of the estimated
rejected energy will require energy storage
modules with a least total capacity of 11 and 8
TWh for Germany and Spain respectively.
Considering large scale batteries, these are well
suited for photovoltaic solar power production
[App. A]. This is due to the definite periodicity of
day and night, which makes facilitating battery
design concerning charge and discharge cycles
easier. Batteries supporting wind energy provide a
greater challenge as there is little or no periodicity
in wind resources suited for synchronization with a
battery’s charging cycle. Wind energy requires a
storage medium that can work inconsistently,
changing between storing and delivering quickly
as well as being able to save the energy long
enough to balance high and low wind periods. In
that respect, pumped hydro storage or compressed
air are more suited than batteries or thermal.
Thermal energy storage is in cohesion with
thermal solar plants, and highly commercial as
already illustrated concerning CSP plants.
Combining thermal energy storage with electricity
producing like photovoltaic solar or wind power is
not explicitly utilized, most likely due to the
energy loss from converting electrical power to
thermal and reversing this process. However,
within the storage container, it is possible to
reduce the annual energy leak to one percent [14],
making thermal storage applicable for longer, nonconstant periods of storage. Thermal energy
storage may therefore be applied for supporting
wind farms. It should be taken into account that
such a system would require a steam turbine
beside the windmills’ own generators, increasing
the cost of building and maintaining the system.
Alternatively, windmills could accompany CSP
plants, but this would require massive
geographical area and huge thermal storage
modules.
If the combined CSP-windmill plant demands such
huge areas, a lower running cost alternative may
be building artificial dams, applying hydro pump
storage. This may provide a better solution as the
relative efficiency of using surplus power to pump
water into dam for storage is over 70%, compared
to the thermal of about 38%. Also, one should
include comparison of maintenance cost of dams
against thermal isolated containers. Ultimately, the
> An Experts in Team Project <
problem may be reduced to geographical
difficulties as thermal storage modules may in
principle be placed anywhere assuming sufficient
area, e.g. vast desert regions with sufficient sun
and wind potential. Dams on the other hand, also
heavily depend on differences in altitude.
VII. CONCLUSION
As the situation is per 2014, large scale energy
storage is not a necessity. However, as EU’s main
share of energy production becomes renewable,
climate and weather conditions’ influence on
production will no longer be negligible. Large
scale energy storage will most likely become an
important feature of the electricity grid already in
2020. If the 2050 goal are realised, and 80% of
EU’s total energy consumption is to come from
renewables, a well-developed storage system is a
prerequisite. The EU, and several of the individual
members, lacks a coherent strategy for the
implementation of energy storage. If there are no
political incentives to expand and promote the use
of energy storage, then the profitability of the
technology will be crucial to the implementation.
An additional study into the economic challenges
regarding energy storage is recommended to
further explore this subject. The EU’s strategy
towards 2050 should be to promote different types
of technology and collaboration between the
different member states to better exploit the
countries contrasting resources of wind, sun, water
and geographical challenges.
VIII. BIBLIOGRAPHY
[1] European Union, "Article 194," European
External Policy Advisors, 2007. [Online].
Available: http://www.lisbontreaty.org/wcm/the-lisbon-treaty/treaty-onthe-functioning-of-the-european-union-andcomments/part-3-union-policies-and-internalactions/title-xxi-energy/485-article-194.html.
[Accessed 29 04 2014].
[2] European Commision, "Europe 2020 - EUwide headline targets for economic growth,"
04 2011. [Online]. Available:
http://ec.europa.eu/europe2020/pdf/targets_en
.pdf. [Accessed 29 04 2014].
[3] European Commision, "Energy: What do we
want to acheive?," [Online]. Available:
http://ec.europa.eu/energy/infrastructure/doc/
energy-storage/2013/energy_storage.pdf.
7
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[Accessed 14 01 2014].
D. S. T. Weiss, "Development of Fluctuating
renewable Energy Sources and its Influence
on the Future Energy Storage Needs of
Selected European Countries," stoRE,
Germany, 2013.
P. W. Parfomak, "Energy Storage for Power
Grids and Electric Transportation: A
Technology Assessment," Congressional
Research Service, USA, 2012.
SFFE, "SFFE - Senter for fornybar energi
(Energilagring)," 2011. [Online]. Available:
http://www.sffe.no/?page_id=67. [Accessed
25 02 2014].
Fornybar.no, "Fornybar.no," ?. [Online].
Available:
http://www.fornybar.no/energibarere-oglagring#top. [Accessed 25 02 2014].
N. I. LTD, "NAS Batteries," NKG Insulators
LTD, 2014. [Online]. Available:
http://www.ngk.co.jp/english/products/power
/nas/index.html. [Accessed 27 March 2014].
H. Ibrahima, A. Ilincaa and J. Perronb,
"Energy storage systems—Characteristics
and comparisons," Renewable and
Sustainable Energy Reviews, pp. 1221-1250,
6 2008.
Maxwell Technology, "Maxwell Technology:
Ultracapacitors," Undated. [Online].
Available:
http://www.maxwell.com/ultracapacitors/.
[Accessed 1 4 2014].
C. Kittel, Introduction to Solid State Physics,
Cambridge: Wiley, 2004.
P. Tixador, N. T. Nguyen, J. M. Rey, T.
Lecrevisse, V. Reinbold, C. Trophime, X.
Chaud and F. Debray, "SMES Optimization
for High Energy Densities," French National
Research Agency, France, 2012.
J. Hull, "Flywheels," in Encyclopedia of
Energy vol II, Cleveland, Elsevier Academic
Press, 2004, pp. 695-704.
R. I. Dunn, P. J. Hearps and M. N. Wright,
"Molten-Salt Power Towers: Newly
Commercial Concentrating Solar Storage,"
Proceedings of the IEEE, pp. 504-515, 2 2
2012.
D. Bradway, H. Kim, A. Sirk og D. Sadoway,
«Magnesium–Antimony Liquid Metal
Battery for Stationary Energy Storage,»
American Chemical Society, pp. 1895-1897,
12 January 2012.
> An Experts in Team Project <
[16] C. Martin, "MIT’s Liquid Metal Stores Solar
Power Until After Sundown," Bloomberg, 7
March 2014. [Online]. Available:
http://www.bloomberg.com/news/2014-0306/mit-s-liquid-metal-stores-solar-poweruntil-after-sundown.html. [Accessed 3 April
2014].
[17] D. Sadoway, "Donald Sadoway: The missing
link to rewnewable energy," Technology
Entertainment Design (TED), March 2012.
[Online]. Available:
https://www.youtube.com/watch?v=Sddb0Kh
x0yA. [Accessed 24 March 2014].
[18] E. T. Texas, "Electric Transmission Texas
Brings Largest Utility-scale Battery in the
United States to One of Oldest Cities in
Texas," Electric Transmission Texas, 2014.
[Online]. Available:
http://www.ettexas.com/projects/presnas.asp.
[Accessed 18 March 2014].
[19] S. M. Hasnain, "Review on sustainable
thermal energy storage technologies, part I:
Heat storage materials and techniques,"
Energy Conversion and Management, vol.
39, no. 11, pp. 1127-1138, 1997.
[20] A. M. K. S. A. K. R. S. A.-H. Muhammed M.
Farid, "A review on phase change energy
storage: materials," Energy Conservation and
Management, no. 45, pp. 1597-1615, 2003.
[21] E. L. D. K. E. Z. G. C. R. G. R. M. Hank
Price, "Advances in Parabolic Trough Solar
Power Technology," Journal of Solar Energy
Engineering, vol. 124, pp. 109-105, 2002.
[22] B. Energy, "Projects - Development
overview," BrightSource Energy, 2014.
[Online]. Available:
http://www.brightsourceenergy.com/projects#
.U1jr9VfjHHi. [Accessed 5 April 2014].
[23] T. E. Investments, "Torresol Energy Plants,"
Torresol Energy Investments, 2010. [Online].
Available:
http://www.torresolenergy.com/TORRESOL/
plants/en. [Accessed 16 March 2014].
[24] A. M. Svensson, S. Sunde and V. Preben,
"Energilagring," Senter for fornybar energi,
2011. [Online]. Available:
http://www.sffe.no/?page_id=67. [Accessed
26 February 2014].
[25] Z. Yang, J. Zhang, M. Kintner-Meyer, X. Lu,
D. Choi, J. Lemmon and J. Liu,
"Electrochemical Energy Storage for Greed
Grid," Chemical Reviews, pp. 3577-3613, 4
8
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
March 2011.
R. Ramsdal, "Teknisk Ukeblad," 2013.
[Online]. Available:
http://www.tu.no/kraft/2013/05/02/skalbygge-verdens-storste-batteri. [Accessed 25
02 2014].
J. Gates, "Energy.gov," 2012. [Online].
Available:
http://energy.gov/sites/prod/files/ESS%20201
2%20Peer%20Review%20%20Notrees%20Wind%20Storage%20%20Jeff%20Gates,%20Duke%20Energy.pdf.
[Accessed 25 02 2014].
O. E. Kongstein, O. S. Kjos, A. M. Martinez
and E. Sheridan, "Gemini: Forskningsnytt fra
fra NTNU og SINTEF," 02 12 13. [Online].
Available: http://gemini.no/2013/12/kanlagre-vind-og-sollys/. [Accessed 01 04 2014].
Allaboutbatteries.com, "All About Batteries,"
12 1 2011. [Online]. Available:
http://www.allaboutbatteries.com/BatteryEnergy.html. [Accessed 25 02 2014].
Miljødirektoratet, "Miljøstatus: Batterier," 31
10 2013. [Online]. Available:
http://www.miljostatus.no/Tema/Kjemikalier/
Produkter/Batterier/. [Accessed 1 4 2014].
A. Akhil, S. Swaminathan and R. K. Sen,
"Cost Analysis of Energy Storage Systems
for Electric Utility Applications," Sandia
National Laboratories, New Mexico, USA,
1997.
D. Linzen, S. Buller, E. Karden and R. W. De
Doncker, "Analysis and Evaluation of
Charge-Balancing Circuits on Performance,
Reliability, and Lifetime of Supercapacitor
Systems," IEEE TRANSACTIONS ON
INDUSTRY APPLICATIONS, USA, 2005.
C. Liu, Z. Yu, D. Neff, A. Zhamu and B. Z.
Jang, "Graphene-Based Supercapacitor with
an Ultrahigh Energy Density," Nano Letters,
pp. 4863-4868, 10 2010.
C. Abbey and G. Joos, "Supercapacitor
Energy Storage for Wind Energy
Applications," IEEE Transaction on Industry
Applications, Canada, 2007.
A. K. Shukla, S. Sampath and K.
Vijayamohanan, "Electrochemical
supercapacitors: Energy storage beyond
batteries," GENERAL ARTICLES , pp. 16561661, 5 12 2000.
R. Hebner, J. Beno and A. Walls, "Flywheel
Batteries Come Around Again," IEEE
> An Experts in Team Project <
9
SPECTRUM, pp. 46-51, 4 2002.
[37] Acquire Media, "Acquire Media," 21 7 2011.
[Online]. Available:
http://files.shareholder.com/downloads/BCO
N/1351874287x0x484774/8f3d8164-64094b96-a1d6979c2c17c0bb/BCON_News_2011_7_21_Ge
neral.pdf. [Accessed 1 4 2014].
[38] C. Abbey and G. Joos, "Supercapacitor
Energy Storage for Wind Energy
Applications," IEEE Transactions on
Industry Applications, pp. 769-776, 3 6 2007.
[39] Multiconsult, "Fornybar: Energibærere og
lagring," 2014. [Online]. Available:
http://fornybar.no/energibarere-oglagring#el2. [Accessed 22 2 2014].
Det vi jobber med er saltsmeltebatterier, disse har
den fordelen at de kan konstrueres av billige, lett
tilgjengelige og miljøvennlige materialer. Vanlige
salter å bruke er NaCl, CaCl2, KCl, alle disse er
vanlige og lett tilgjengelige. NaCl er jo for
eksempel det vi til daglig kaller "salt", og som vi
bruker i maten.
Det finnes allerede to 1.
generasjons
saltsmeltebatterier,
NAS
(http://www.ngk.co.jp/english/products/power/nas/
index.html) batterier og ZEBRA batterier. NAS
brukes i dag i strømnettet noen steder for å kunne
lagre og avgi strøm for å balansere for ujevn bruk,
disse batteriene er akkurat litt for dyre til å bli
brukt overalt til å f.eks. lagre fornybar energi, men
de er mye billigere enn f.eks. Lithium batterier, og
i en del situasjoner er de billige nok til at det er
mer lønnsomt å installere dem enn å gjøre andre
ombygginger av strømnettet. Om dere ikke har
gjort det enda så er det en del gode lenker fra
wikipedia artikklene til disse teknologiene
IX. APPENDIX A – EMAIL FROM SINTEF
RESEARCHER OLE KJOS (NORWEGIAN)
Vårt prosjekt fokuserer på å studere andre typer
saltsmelte batterier som kan åpne for høyere
ytelser til samme, eller lavere pris. En av målene
våre er blant annet å kunne designe oss rundt et par
av de dyreste komponentene slik at vi kan få ned
produksjonsprisen. Vi har ikke kommet i gang
med selve arbeidet enda, så jeg kan ikke gi noen
konkrete tall på ytelsene, men målet vårt er i
utgangspunktet å utvikle et batteri med samme
lagringskapasitet, større lade og utladingsstrøm og
lavere pris enn NAS batteriene har i dag.
Hei! Det er en interessant problemstilling dere ser
på, og den er ganske lik den som ligger til grunn
for vårt prosjekt som vi akkurat har startet.
Prosjektet er finansiert av forskningsrådet
(EnergiX-programmet) og går ut på å utvikle
billige batterier med stor kapasitet for å kunne
brukes til mellomlagring av strøm fra fornybare
energikilder. Dette er et langsiktig prosjekt, så det
vi utvikler er selve teknologien som i fremtiden
kan ligge til grunn for produksjon av batterier.
I dag er ikke problemet veldig stort, siden det i de
fleste land er ganske liten andel fornybar energi,
men i fremtiden er dette en problemstilling som
kan være med å begrense utbredelsen av fornybar
energi. Det største problemet i dag er Tyskland,
hvor de har hatt dager med over 60% av
energiforsyningen sin fra fornybar energi (Sol og
vind). På sånne dager må de rett og slett ha fossile
kraftverk som står på "tomgang" slik at de fort kan
produsere strøm om været endrer seg, ellers vil
hele landet kunne få et massivt strømbrudd. Det å
ha kraftverk stående i reserve slik fører til at de
slipper ut en del CO2 uten å produsere noe som
helst strøm, de slipper ut mindre enn de ville gjort
om de laget strøm, men uansett er det egentlig
"unødvendige" utslipp og kostnader som kunne
vært unngått hvis det f.eks. var en tilstrekkelig stor
batteribackup i strømnettet.
Det er også en stor gruppe på MIT som forsker på
neste generasjons saltsmeltebatterier, de ser på en
litt annen tilnærming enn det vi gjør, men ideen er
den samme, vi tar utgangspunkt i det som fungerer
i dag (NAS og ZEBRA), ser på hva som er de
dyreste / mest begrensende komponentene og
prøver å gjøre noe med dem. Proffessoren som
leder den gruppen heter Donald Sadoway, og er en
enormt driftig fyr. Han hadde et foredrag på TEDkonferansen om akkurat energilagring, det ligger
på youtube, og anbefales sterkt. Det er godt
forklart på en enkel måte, kanskje litt for enkelt for
deres bruk, men uansett et veldig godt eksempel på
hvordan et faglig tema kan formidles til "vanlige
folk"
https://www.youtube.com/watch?v=Sddb0Khx0y
A
Litt mer konkret om de tallene dere spør om, tall er
vanskelige å fastslå nøyaktig, for det første så
utvikler produksjonen seg hele tiden, så man må
forvente at prisen stadig går nedover. Dessuten er
> An Experts in Team Project <
dette snakk om ganske store installasjoner, og de
bestilles på kontraktsbasis, ikke som hyllevare.
Det finnes derfor ganske mange, og avvikende tall.
Denne rapporten er fra 2011, så den er litt gammel,
men
er
veldig
grundig
https://www.youtube.com/watch?v=Sddb0Khx0y
A
Denne rapporten er om en NAS batteriinstallasjon
som er gjort i Texas, USA, så tallene her er veldig
konkrete og kommer fra et virkelig case. Så vidt
jeg husker er dette batteriet satt opp med
hovedtanke på å jevne ut forskjeller i bruk
gjennom døgnet (det er mye kullkraft i texas, og
kullkraft er vanskelig å justere opp og ned i
produksjon). Prinsippet blir uansett det samme
som for fornybar energi, man jevner ut forskjeller
mellom
produksjon
og
forbruk.
http://www.ettexas.com/projects/presnas.asp
Har også lagt med en meget godt review artikkel
som omhandler lagringsteknologi for fornybar
energi. Denne artikkelen er veldig omfattende, og
gir dere mange referanser dere kan følge videre
innenfor de temaene dere synes er mest
interessante.
Energilagringskapasiteten er egentlig ikke noe
problem i det hele tatt på noen saltsmeltebatterier,
du betaler en gitt mengde $ per kWh, og batteriet
bygges så stort du har råd til. Disse batteriene er
ofte plassert i forbindelse med knutepunkter i
strømnettet, dette er gjerne usentrale plasseringer
hvor tomteareal er billig.
Temperaturavhengigheten er et viktig spørsmål,
som mange tror har stor betydning, men når
batterier bygges såpass store som disse, og med det
som finnes av avanserte isolasjonsmaterialer i dag,
så er det ingen problem med tanke på å holde på
varmen i flere døgn. Når batterier lades og tappes
utvikles det varme, på mobiltelefoner og PC'er kan
man kjenne dette, og det er i slike situasjoner et
problem. For saltsmeltebatterier derimot er det
dette som er hovedvarmekilden.
Så lenge
batteriene enten lades eller tømmes så blir de også
varmet. Problemet kommer hvis et batteri blir
stående ubrukt i lang tid. Da må det tilføres varme
i form av strøm (tappes ofte fra batteriet). For
solceller er disse batteriene perfekte, solen skinner
om dagen så batteriene lades, om natten tømmes
batteriene og neste morgen lades de igjen. Ved så
korte sykluser er det ingen utfordring. For
vindkraft kan det være vanskeligere om det båser
10
lenge i strekk, eller er vindstille lenge i strekk.
Når batteriet er fullt må ladingen stoppe, og om det
da ikke blir vindstille i løpet av 1-2 døgn så må
man begynne å tilføre varme til batteriet. Denne
tiden kan forlenges ved å bruke mer isolasjon, men
da stiger også prisen, så det blir en avveiing om
hva som er billigst av å bruke strøm til å holde det
varmt, eller å bruke penger på mer isolasjon.
Det finnes også forslag om at man kan fryse
saltsmeltebatterier for å lagre energi over lang tid.
Når batteriet er frosset vil det ikke være noe særlig
selvutladning siden alt er "låst fast", men det
krever energi å tine batteriet igjen, og det sliter på
materialer å fryse / tine.
Nå har dere i alle fall en del å lese på, så kan dere
jo bare komme med mer konkrete og
oppfølgingsspørsmål om dere ønsker det.
Vennlig hilsen:
Ole S. Kjos
-----Original Message----From: Magnus [mailto:[email protected]]
Sent: 12. mars 2014 12:00
To: Ole Kjos
Subject: Spørsmål ang. bruk av batterier som
energilagringsenhet
Hei,
Viser til hyggelig telefonsamtale idag, 12. mars.
Vi er en gruppe bestående av fem NTNU-studenter
som arbeider med et "Eksperter i Team"-prosjekt
som omhandler ny energi med spesifiseringen
energilagring. Vi er interessert i å undersøke hvor
mye av den fornybare energien (hovedsaklig i
EU/Europa) som går tapt som følge av
nødvendige, men uforutsigbare værforhold med
tanke på f.eks. vindkraft. I den forbindelse ønsker
vi videre å undersøke hvor mye energi som kan
lagres ved høy produksjon under lite forbruk, som
da kan brukes i ettertid.
Vi utreder (blant andre metoder) om batterier og
håper da du kan svare på noen spørsmål eller
henvise til litteratur. Her følger noen spesifiserte
spørsmål:
Vi ønsker et batteri med,
- lang levetid (helst i størrelsesorden flere år), lite
vedlikehold
- lav kostnad per lagret energi
> An Experts in Team Project <
Vi ser for oss et et stort, stasjonært batteri som kan
drive et x antall husstander over en foreløpig
ubestemt tidsramme. Volum og vekt er mindre
viktig. Hva slags batteriteknologi overholder disse
kravene best?
11
Og vi ønsker å vite om batteriets egenskaper i form
av,
- energilagringskapasitet
- temperaturavhengighet
- tidsramme, hvor lenge energien kan lagres (10-24
timer, 1-2 uker ..osv), i forhold til lekasje