Christine Krüger
Electric energy storage as an element
of low-carbon energy supply
Originally published in:
Energia Ambiente e Innovazione. Speciale 1-2015: Transition and global challenges
towards low carbon societies. ENEA, Roma 2015, pp. 17-20
http://www.enea.it
speciale
ENERGY & CLIMATE CHANGE
Electric energy storage as an
element of low-carbon energy supply
Energy storage is one option to provide the electricity grid with flexibility. Short-term storage can
provide system services for power quality, whereas medium-term storage allows to shift significant
amounts of energy over some hours up to days. Seasonal or long-term storage can, for example, be
provided by the power-to-gas technology. Significant amounts of storage will be necessary, especially
when a fully renewable supply is approached. New mechanisms are needed to ensure anticipatorily that
sufficient flexibility is in the system at any time.
DOI: 10.12910/EAI2015-004
n C. Krüger
Introduction
Energy demand and supply have to be in balance at
all times. That is crucial especially for the electricity
system: A mismatch endangers the stability of the
supply grid. In a conventional energy system, the
balance is ensured by the in-time production of energy
from fossil fuels. When moving towards a low-carbon
energy supply, the energy from those fossil power
plants needs to be replaced by feed-in from renewable
energy sources. However, renewable feed-in is less
flexible than fossil generation, since electricity is
generated when the wind blows or when the sun shines,
not when it is needed. This means a loss of flexibility
in electricity generation. To compensate for that loss,
new forms of flexibility are needed. There are several
options to achieve that: apart from energy storage,
n Contact person: Christine Krüger
[email protected]
grid extension, demand side management or overinstallation of renewables can also contribute. None
of this options is going to be the only solution, but a
concerted use of all of these will most probably turn
out to be the best answer to the challenge of balancing
renewable energy supply. It is therefore important
to keep in mind that storage is one among several
balancing options.
Storage technologies
There are several electric storage technologies that
differ in size, response time, capacity, power and in the
kind of energy used to store electricity. Figure 1 gives
an overview over those technologies.
Short-term storage does not allow to shift larger
amounts of energy, but can respond within milliseconds
and has a high output power. That qualifies it to provide
system services, such as inertia control or reactive
power, which are important for voltage quality in
transmission grids.
The term medium-term storage identifies storage
EAI Speciale I-2015 Transition and global challenges towards low carbon societies
17
Sp
technologies that are able to store and provide energy
for minutes up to some days, such as pumped hydrostorage or large batteries.
Long-term storage is also referred to as “seasonal
storage”. It is a kind of storage that provides energy over
long periods, ranging from several days up to months.
It is an alternative to having fossil backup capacities
and becomes important in systems with high shares
of renewables. Technologies suited to those tasks are
either pumped hydro-storage with very large reservoirs
or the use of the so called power-to-gas technology, i.e.
the conversion of electricity to hydrogen via electrolysis
and the optional further processing with carbon-dioxide,
which results in methane. Both forms of gas can be used
in different gas-appliances.
Cross-sectoral storage is another kind of storage that
uses links between the electricity and other sectors. For
example, heat pumps and combined heat and power
plants (CHP) are links between electricity and heating.
When these are equipped with thermal storage,
they give extra flexibility on the electrical side: their
electricity consumption or production can be shifted
to proper times, thereby providing a “virtual electricity
storage”. In the transport sector, electric vehicles
are likely to be a widely spread technology in the
future. Their batteries can be charged in suited times,
providing a virtual storage compared to uncontrolled
charging.
Also, there is a huge potential in electrifying appliances
that have so far been fuelled by other forms of energy.
In a renewable energy system, this has a double use:
on the one hand, decarbonising electricity is easier
than other forms of energy. On the other hand, if the
consumption of those appliances can be timed, this
gives additional flexibility to the electricity system.
When will storage be needed?
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This is not a question aiming at a certain point in time, but
at the share of renewables. Figure 2 gives an overview
over different phases of storage demand. In a system
with low to medium renewable shares, storage rather
promotes fossil base-load power plants: By providing
Electric Storages
an additional load in times of high
Overview
renewable feed-in (going along
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conventional power plants.
FIGURE 1 Overview over electric storage technologies
01 October 2014
LCS R NET 2014 –Source:
C. KRÜGER
STORAGE
Slide 8
Wuppertal Institute
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EAI Speciale I-2015 Transition and global challenges towards low carbon societies
Systemic Research Questions
When will we need storages?
that sufficient flexibility already
exists when it is needed.
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capacity markets or regulatory
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instruments. These mechanisms
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of the energy system towards
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different stages of transformation
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framework for storage when it
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To
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demand for storage technologies,
01 October
2014
LCS R NET
– C. KRÜGER
- ENERGY STORAGE
19
Wuppertal Institute
FIGURE
2 Development
of2014
flexibility
demand
over share ofSlide
renewables
additional research is necessary.
Source: own figure based on [2, 3, 4]
Studies have been conducted
and have given first ideas, but
deeper insights are necessary since the energy supply is
renewables, the larger the storage needed. Storage
a highly complex system.
demand rises particularly fast when approaching
Even though the amount of future storage demand
100%, as large amounts of energy need to be stored to
is uncertain, conceivably rather large storage
ensure sufficient energy supply at all times.
capacities will be needed. Therefore it is important
Locally, short-term storage can already be necessary
to prepare storage for the future: research is needed
at an earlier stage. Conventional power plants do not
to decrease storage costs across technologies. New
only provide energy, but also system services such
business models for storage have to be developed and
as reactive power control. Short-term storage is one
demonstrational projects need to be funded in order to
option to compensate the loss of conventional plants’
gain experience, especially regarding new promising
system services.
technologies.
Apart from the task of balancing energy, storage also
Since the installation of large storage units has a high
comes into the grid for other purposes. For example,
impact on nature and landscape, public acceptance is
the batteries for electric vehicles’ or for solar home
likely to become crucial to storage. Therefore concepts
systems have different primary functions, but can also
are needed to involve stakeholders in participatory
be used for grid balancing.
processes from early planning stages.
Recommendations regarding energy storage
Along with the rising share of renewables, new forms
of flexibility are needed in the electricity grid. In
the short to medium term, measures such as flexible
power generation, demand side management and grid
extension might be sufficient but, in the long-term,
storage will be necessary to balance the electricity
supply.
Therefore, new mechanisms are required, which ensure
ENERGY & CLIMATE CHANGE
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Conclusions
With rising share of renewables, new flexibilities are
needed to match energy demand and supply. Energy
storage is one among other balancing options which
are able to provide this flexibility. In a near system near
100% renewable share, storage will be indispensable.
By now, there is only a low demand for electricity
storage from the electricity grid perspective, but there
EAI Speciale I-2015 Transition and global challenges towards low carbon societies
19
Speciale
re fe renc es & not es
are other reasons for implementing storage systems,
such as PV self supply or electric vehicles. A significant
demand for storage will presumably not occur before
the next two to three decades. But to enable a purposeful
and system compliant integration of storage, in-depth,
20
multidisciplinary research needs to be conducted to
provide a profound base for creating suited regulatory
frameworks.
Christine Krüger
Wuppertal Institute for Climate, Environment and Energy, Wuppertal, Germany
[1] M. Sterner, I. Stadler, Energiespeicher - Bedarf, Technologien, Integration, Springer-Verlag, Berlin, Heidelberg, 2014.
[2] VDE Studie: Energiespeicher für die Energiewende, Energietechnische Gesellschaft im VDE (ETG), Frankfurt a.M., June 2012.
[3] Stromspeicher in der Energiewende, Agora Energiewende, Berlin, September 2014.
[4] EFZN Studie: Eignung von Speichertechnologien zum Erhalt der Systemsicherheit, Energieforschungszentrum Niedersachsen, March 2013.
EAI Speciale I-2015 Transition and global challenges towards low carbon societies