VGB POWERTECH 10 (2019)

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Heat storage systems
Heat storage systems in
heat and power generation
Matthias Meierer
Kurzfassung
Wärmespeichersysteme in der
Wärme- und Stromerzeugung
Im Zusammenhang mit den aktuellen Veränderungen
der Struktur der Energieversorgungsanlagen
in Deutschland und Europa stellt
sich die Frage nach Möglichkeiten der Energiespeicherung.
In dem vorliegenden Beitrag werden Möglichkeiten
der Wärmespeicherung in Anlagen zur
Wärme- und Stromerzeugung dargelegt. Neben
der Beschreibung der eingesetzten physikalischen
bzw. chemischen Prinzipien und der zugehörigen
Anlagenkonzepte wird auf den Stand
der Entwicklung und technische Anwendungen
eingegangen. Dabei bilden realisierte Speichersysteme
in Kraftwerken und KWK-Anlagen
einen Schwerpunkt. Aktuelle Entwicklungen
und Möglichkeiten für zukünftige Speichersysteme
werden aufgezeigt.
l
Authors
Dr. Matthias Meierer
Grosskraftwerk Mannheim AG
Mannheim/Germany
Introduction
The operation of power plants and systems
must be safe, environmentally compatible,
and cost-effective [1, 2]. Especially in view
of an optimised level of energy efficiency, it
is advisable to operate combined heat and
power units. However, since the demand
for electrical power and/or heat often does
not coincide with the actual output (i.e.
of heat and power generation plants), it is
important to look into the technical possibilities
of storing energy. The demand for
energy storage systems has risen distinctly
due to the current structural changes in
the power supply industry in Germany and
Europe, i.e. as a result of the increased use
of renewable energy sources (e.g. wind,
photovoltaic applications, and biomass) in
power generation. The primary objective is
therefore to achieve an adequate and balanced
power supply situation despite of
frequent fluctuating power production.
The paper at hand will focus primarily
on heat storage systems that are suitable
for combined heat and power generation
plants. The applied physical and chemical
principles and the associated plant
concepts, as well as the current state of
the art and the technical applications will
be described. The main examples will be
energy storage systems which have been
implemented in regular power plants and
CHP plants. Fundamental criteria that are
of relevance in such heat and energy storage
systems are:
– storage capacity (in MWh),
– charging and discharging capacity
(in MW),
– time response (gradients during load
variations, periods for energy intake and
output, variations over time, etc.),
– storage temperature or temperature differential,
– system efficiency (especially in view of
energy losses),
– environmental compatibility, and
– cost-efficiency.
Energy storage systems/overview
Basically, energy can be stored in electrical,
mechanical, chemical or thermal systems
(Figure 1).
Within the context of the shaping of a
general expert opinion (e.g. in connection
with investment decisions), especially issues
concerning the selection of the best
suitable system in a given case and its
proper dimensioning arise. Besides technical
parameters (capacity, output, efficiency,
etc.), the system’s integration into the
processes of the existing energy supply and
distribution system are of particular importance.
In addition, the aspects of plant
management (availability, flexibility, complexity,
control capability, etc.) and plant
maintenance (repairs, wear and tear, maintenance
requirements, recurrent tests, and
inspections, etc.) need to be taken into account
[3, 4]. In the case of large-scale projects
(e.g. pumped-storage or underground
hydroelectric power plants), the primary
objectives are often related to the official
approval procedures where environmental
aspects (nature conservation, environmental
compatibility, public involvement in the
decision-taking process, etc.) are of special
interest. The procedures in this context often
require a large amount of time and, as
experience has shown, are difficult to predict
in terms of implementation and final
results. And, of course, the basic economic
conditions must be taken into consideration,
i.e. in addition to costs (e.g. of capital
investment, operation, maintenance,
taxes, fees, and other charges), the actual
proceeds need to be looked at as well. Especially
in cases where major capital investments
are involved and where the plants
are expected to have very long service lives
(large-scale plants of life cycles of 40 or 50
years or more), long-range concepts and
adequate fundamental conditions need
to be worked out. The paper in hand will
focus on large-scale stationary energy storage
systems in power plants that are capable
of generating both electrical power and
heat. The following examples have been
chosen to represent various storage technologies
that are in use today.
Electrical energy storage [5, 6]
Accumulators and batteries are used for
storing electrical energy. Different types
of accumulators/batteries are available for
this purpose (lead-acid battery, lead-gel
battery, nickel-metal-hydride battery, lithium-ion
battery, sodium-sulphur battery,
redox-flow battery, etc.). On a global scale,
only very few large-scale electrical energy
storage systems have been implemented
that have capacities of more than 10 MW
(< 100 MW). Many ongoing R&D projects
are currently focusing on the development
and testing of different types of accumulators
and systems. In addition to their nu-
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