U.S. patent application number 13/031853 was filed with the patent office on 2011-09-15 for energy transfer system comprising a phase change material.
Invention is credited to Henrik STIESDAL.
Application Number | 20110219771 13/031853 |
Document ID | / |
Family ID | 42711779 |
Filed Date | 2011-09-15 |
United States Patent
Application |
20110219771 |
Kind Code |
A1 |
STIESDAL; Henrik |
September 15, 2011 |
ENERGY TRANSFER SYSTEM COMPRISING A PHASE CHANGE MATERIAL
Abstract
An energy transfer system for absorbing, temporarily storing and
releasing energy is disclosed. The described energy transfer system
comprises (a) a first container containing a Phase Change Material,
(b) a heat generation element, which is connectable to an external
energy source and which is capable of charging the Phase Change
Material with thermal energy, wherein energy provided by the
external energy source is used, and a heat extraction element,
which is connectable to an external heat engine and which is
capable of extracting thermal energy from the Phase Change
Material, wherein the external heat engine is capable of converting
the extracted thermal energy into electric energy. It is further
described an energy transfer arrangement comprising two of such
energy transfer systems, and a method for absorbing, temporarily
storing and releasing energy.
Inventors: |
STIESDAL; Henrik; (Odense C,
DK) |
Family ID: |
42711779 |
Appl. No.: |
13/031853 |
Filed: |
February 22, 2011 |
Current U.S.
Class: |
60/670 ;
165/104.17 |
Current CPC
Class: |
F28D 2020/0047 20130101;
F28D 20/021 20130101; Y02E 60/14 20130101; F28F 2270/00 20130101;
Y02E 60/145 20130101 |
Class at
Publication: |
60/670 ;
165/104.17 |
International
Class: |
F01K 21/00 20060101
F01K021/00; F28D 20/02 20060101 F28D020/02; F28D 17/00 20060101
F28D017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 11, 2010 |
EP |
10156250.2 |
Claims
1.-14. (canceled)
15. An energy transfer system for absorbing, temporarily storing
and releasing energy, the energy transfer system comprising a first
container containing a Phase Change Material; a heat generation
element, which is connectable to an external energy source; and
which is adapted to charge the Phase Change Material with thermal
energy, wherein energy provided by the external energy source is
used; and a heat extraction element, which is connectable to an
external heat engine and which is adapted to extract thermal energy
from the Phase Change Material, wherein the external heat engine is
adapted to convert the extracted thermal energy into electric
energy.
16. The energy transfer system as set forth in claim 15, wherein
the Phase Change Material comprises a metal.
17. The energy transfer system as set forth in claim 16, wherein
the metal is aluminium.
18. The energy transfer system as set forth in claim 15, wherein
the first container is made at least partly from an iron alloy.
19. The energy transfer system as set forth in claim 15, wherein
the heat generation element comprises an inductor.
20. The energy transfer system as set forth in claim 15, further
comprising a second container, which encloses at least partly the
first container; and a thermal insulation material, which is
arranged between the first container and the second container.
21. The energy transfer system as set forth in claim 20, wherein
the thermal insulation material comprises a composite ceramic
material.
22. The energy transfer system as set forth in claim 15, wherein at
least a heating portion of the heat generation element is in
physical contact with the Phase Change Material.
23. The energy transfer system as set forth in claim 15, wherein at
least an extracting portion of the heat extraction element is in
physical contact with the Phase Change Material.
24. The energy transfer system as set forth in claim 15, wherein
the heat extraction element is a steam-liquid loop of the external
heat engine, and wherein the external heat engine is a part of a
power production system.
25. The energy transfer system as set forth in claim 24, wherein
the power production system comprises a controller adapted for
controlling a fluid flow within the steam-liquid loop.
26. The energy transfer system as set forth in claim 15, wherein
the energy provided by the external energy source is electric
energy and the energy transfer system further comprises a frequency
controller, which is adapted for controlling a frequency of a
voltage and current being associated with the electrical energy
provided by the external energy source.
27. The energy transfer system as set forth in claim 15, wherein
the energy provided by the external energy source is electric
energy and the energy transfer system further comprises: a
frequency controller, which is adapted for controlling a frequency
of a voltage or current being associated with the electrical energy
provided by the external energy source.
28. An energy transfer arrangement for absorbing, temporarily
storing and releasing energy, the energy transfer arrangement
comprising: a first energy transfer system as set forth in any one
of the preceding claims and a second energy transfer system as set
forth in any one of the preceding claims, wherein the first energy
transfer system and the second energy transfer system are arranged
parallel with respect to each other.
29. The energy transfer arrangement as set forth in claim 28,
wherein the heat generation element of the first energy transfer
system and the heat generation element of the second energy
transfer system are connected with each other and are connectable
to the external energy source and heat extraction element of the
first energy transfer system and the heat extraction element of the
second energy transfer system are connected with each other and are
connectable to the external heat engine.
30. The energy transfer arrangement as set forth in claim 28,
wherein the heat generation element of the first energy transfer
system and the heat generation element of the second energy
transfer system are connected with each other and are connectable
to the external energy source or heat extraction element of the
first energy transfer system and the heat extraction element of the
second energy transfer system are connected with each other and are
connectable to the external heat engine.
31. A method for absorbing, temporarily storing and releasing
energy, the method comprising: providing a first container
including a Phase Change Material; charging the Phase Change
Material with thermal energy, wherein the thermal energy is
introduced to the Phase Change Material by a heat generation
element, which is connected to an external energy source and which
receives energy from the external energy source; temporarily
storing the thermal energy within the Phase Change Material;
extracting thermal energy from the Phase Change Material by a heat
extraction element, which is connected to an external heat engine;
transferring the extracted thermal energy to the external heat
engine; and converting the transferred thermal energy into electric
energy by the external heat engine.
Description
FIELD OF INVENTION
[0001] The present invention relates to the field temporarily
storing thermal energy. In particular the present invention relates
to an energy transfer system for absorbing, temporarily storing and
releasing energy. Further, the present invention relates to an
energy transfer arrangement comprising two of such energy transfer
systems. Furthermore, the present invention relates to a method for
absorbing, temporarily storing and releasing energy.
ART BACKGROUND
[0002] The production of electric power from various types of
alternative energy sources such as wind turbines, solar power
plants and wave energy plants is not continuous. The production may
be dependent on environmental parameters such as wind speed (for
wind turbines), insulation (for solar power plant) and wave height
and direction (for wave energy plants). There is very often little
or no correlation between energy production and energy demand.
[0003] One known approach to solve the problem of uncorrelated
electric power production and electric power demand is to
temporally store energy, which has been produced but which has not
been demanded, and to release the stored energy at times at which
there is a high demand. In the past there have been suggested many
different methods to temporarily store energy. Suggested methods
are for instance (a) mechanical energy storage methods e.g. pumped
hydro storage, compressed air storage and flywheels, (b) chemical
energy storage methods e.g. electrochemical batteries and organic
molecular storage, (c) magnetic energy storage, and (d) thermal
energy storage. With respect to thermal energy storage it is noted
that water has a high heat capacity which in principle could allow
for efficient thermal storage using water as the heat storage
material or heat storage medium. However, unless sophisticated
pressure vessels are used the maximum temperature of heat capacity
storage in water is limited to 100.degree. C. (100 degrees
Celsius). Since for large capacity storage the cost of pressure
vessels would be prohibitive, the use of water as a heat storage
material is limited to a maximum temperature of 100.degree. C.
However, a maximum temperature of 100.degree. C. is much too low in
order to provide any useful thermodynamic efficiency of a heat
engine, e.g. a steam turbo generator, which is to be operated on
demand for release of the stored thermal energy. Consequently, the
benefits of the high heat capacity of water cannot be exploited in
practice for high-volume energy storage.
[0004] Alternative heat storage media include solids and molten
salts. Solids may be heated to high temperatures that could lead to
good thermodynamic efficiencies of related heat engines. However,
solids generally have low heat capacity, and this leads to high
volume requirements and to a low energy density. Molten salts
generally have higher heat capacity than solids and they have the
additional benefit that, when being in the liquid phase, they can
be pumped, thereby facilitating arrangements of low-loss storage
tanks with high-power heat exchangers. However, molten salts have
the drawback that they are generally not stable at temperatures
much above 400.degree. C., thereby limiting the thermodynamic
efficiencies of related heat engines. They also have the drawback
that initial melting and re-melting on unintended solidification is
very difficult due to the low conductivity of crystalline
salts.
[0005] One solution to the problem of low energy density of solids
is to use a material that incurs a phase change at the relevant
operating temperature. The amount of heat respectively heat energy
Q stored in a material which does not undergo a phase change within
the temperature range of a heat storage cycle, i.e. during an
energy storage process comprising the increase of the storage
material temperature from Ti (corresponding to the minimum starting
or initial temperature) to Tf (corresponding to the maximum end or
final temperature) can be calculated by the following equation
(1):
Q = .intg. Ti Tf m Cp ( T ) T ( 1 ) ##EQU00001##
[0006] Thereby, m is the mass of the heat storage material and
Cp(T) is the specific heat capacity of the heat storage material,
which according to the basics of thermodynamic is a function of the
temperature T.
[0007] Provided that the specific heat capacity of the heat storage
material does not have a pronounced dependency on temperature, this
leads to a linear relation between the increase in temperature and
the amount of stored heat. For a material or medium which does
undergo a phase change during the heat storage cycle an additional
energy is absorbed or released when the material melts or
solidifies respectively. The melting and solidification process
happens at a substantially constant temperature as indicated in
FIG. 6. Such a material is denominated a Phase Change Material
(PCM). FIG. 6 illustrates how heat is absorbed or released by a PCM
when the PCM undergoes a phase change from solid to liquid and back
or from liquid to solid. Specifically, when starting at the solid
phase at a temperature Ti, the temperature of the PCM first
approximately linearly increases with the amount of heat input h.
When the temperature has reached the melting temperature Tm, the
temperature stays constant for a while until the fusion heat or
melting heat .DELTA.hm has been absorbed and all the PCM has become
liquid. After this, the temperature of the liquid PCM again
linearly increases with the further amount of heat input h. It is
mentioned that the gradient dT/dh is different for liquid phase as
compared to the solid phase. Thereby, the gradient dT/dh
corresponds to the specific heat capacity of the solid respectively
the liquid PCM.
[0008] For heat storage purposes preferably a PCM material is
employed, which comprises a high melting heat. Thereby, additional
energy storage capacity is provided by the phase change, i.e. when
the PCM changes from solid to liquid and back. For a temperature
increase of a PCM from Ti to Tf, wherein the melting temperature Tm
of the PCM in between Ti and Tf, the amount of heat Q which is
stored in the PCM can be calculated by the following equation
(1):
Q = .intg. Ti Tm m Cps ( T ) T + m .DELTA. hm + .intg. Tm Tf m Cpl
( T ) T ( 2 ) ##EQU00002##
[0009] Thereby, m is again the mass of the PCM, Cps(T) and Cpl(T)
are the specific heat capacity of the solid PCM respectively the
liquid PCM and .DELTA.h is the latent heat respectively the melting
heat of the PCM.
[0010] One problem related to the known heat storage systems is
that for large scale energy storage, such as for storing energy
produced from wind farms for longer time periods (hours), the
capacity of known heat storage systems is not sufficient. If one
would scale up a known heat storage system to a system having
sufficient capacity for such purposes, the prize of such a scaled
up system would be relatively high, which makes a scaled up system
unattractive because of economical reasons. Even further, for a
scaled-up heat storage system it is difficult and not
cost-effective to recover the stored energy.
[0011] There may be a need for providing a system and a method
which allow for an improved heat storage capability.
SUMMARY OF THE INVENTION
[0012] This need may be met by the subject matter according to the
independent claims. Advantageous embodiments of the present
invention are described by the dependent claims.
[0013] According to a first aspect of the invention there is
provided an energy transfer system for absorbing, temporarily
storing and releasing energy. The provided energy transfer system
comprises (a) a first container containing a Phase Change Material,
(b) a heat generation element, which is connectable to an external
energy source and which is capable of charging the Phase Change
Material with thermal energy, wherein energy provided by the
external energy source is used, and (c) a heat extraction element,
which is connectable to an external heat engine and which is
capable of extracting thermal energy from the Phase Change
Material, wherein the external heat engine is capable of converting
the extracted thermal energy into electric energy.
[0014] The described energy transfer system is based on the idea
that energy provided from an external source can be temporarily
stored in the form of thermal energy within a Phase Change Material
(PCM). If at a later time there is a demand for electric energy, at
least some of the stored thermal energy can be released to an
external heat engine.
[0015] The described energy transfer system may ensure that a
surplus of energy, in particular electric energy, which may have
been produced for instance by one or more wind turbines and/or by
one or more solar plants at times with low demands for electricity,
can be used to charge the PCM with thermal energy and thereby the
surplus electricity can be stored as thermal energy respectively
heat. Even further it is ensured by the described energy transfer
system that the stored energy can be released and transferred to an
external heat engine for use for electricity production. A suitable
external heat engine may be for instance a steam turbine. The step
of providing thermal energy from the PCM to an external heat engine
may be regarded as providing or releasing thermal energy from the
PCM.
[0016] The thermal energy can be stored in a single-phase energy
storage process by temperature changes only. This means that the
range of the temperature changes does not include the melting point
temperature of the PCM. Alternatively, the thermal energy can be
stored in a two-phase energy storage process, wherein in addition
to one or two of the above described single-phase energy storage
processes the energy is further stored in a latent energy storage
process. This means that the range of a corresponding temperature
change includes the melting point temperature of the PCM. Which
energy storage process is preferably to be used depends on the
specific application and in particular on the amount of energy put
into the described energy transfer system for storage.
[0017] It is mentioned that in principle also a three-phase energy
storage process is possible. This means that the range of the
temperature changes includes both the melting point temperature of
the PCM and the boiling point temperature of the PCM.
[0018] Preferably, the external energy source provides electric
energy, which is converted into thermal energy by means of the heat
generation element.
[0019] It is further mentioned that it is also possible that
charging the PCM with thermal energy does not result in a
temperature increase of the PCM. This is the case if at the
beginning of the energy absorption the PCM has a temperature, at
which already a phase change occurs. In this case the charged
thermal energy is used only for a phase change of at least a
portion of the PCM.
[0020] It is mentioned that in order to have a mechanically stable
energy transfer system of course the first container has to be made
from a material which has a higher melting temperature than the PCM
at a maximum temperature of any possible heat storage circle.
[0021] It is further mentioned that in order to realize an
effective insertion of thermal energy into the PCM two or even more
heat generation elements may be used. The same applies for an
effective heat extraction, which may be realized by employing two
or even more heat extraction elements.
[0022] According to an embodiment of the invention the Phase Change
Material comprises a metal, in particular aluminium. This may
provide the advantage that the PCM has a comparatively high melting
point temperature. Specifically, aluminum has a melting point
temperature around 660.degree. C. and a latent heat coefficient
which is relatively high. Therefore, aluminum is a suitable
material for the described energy transfer system. Further, the
level of the melting point temperature makes it feasible to provide
appropriate containers and isolation material as well as heat
generating and heat extraction elements which can operate optimal
within a temperature range around the melting point of and exploit
the excessive potential for latent energy storage.
[0023] It is mentioned that there are of course also other
materials, which are suitable for being used as the PCM of the
described energy transfer system. Specifically, PCMs which have a
melting point between 200.degree. C. and 800.degree. C. are good
candidates for the PCM of the described energy transfer system.
[0024] According to a further embodiment of the invention the first
container is made at least partly from an iron alloy. The use of an
iron alloy may provide the advantage that the first container
comprises mechanical properties, which make the first container
suitable for securely containing a PCM with a comparatively low
melting point temperature. The PCM may be for instance aluminum
which has a lower melting point temperature than iron.
[0025] According to a further embodiment of the invention the heat
generation element comprises an inductor. This may mean that the
heat generation element is or comprises an inductive element such
as for instance a coil or at least a part of a coil.
[0026] Induction heating is a process of heating an electrically
conducting material by electromagnetic induction. Thereby, eddy
currents are generated within a conductive or metallic material and
the ohmic resistance of the material leads to a heating of the
material. Induction heating being used for putting or introducing
thermal energy into the PCM may provide the advantage that this is
a highly efficient process with a high degree of utility.
Typically, the inductor of the heat generation element is powered
by electric energy.
[0027] According to a further embodiment of the invention the
energy transfer system further comprises (a) a second container,
which encloses at least partly the first container, and (b) a
thermal insulation material, which in arranged in between the first
container and the second container.
[0028] This may provide the advantage that a good thermal isolation
between the first container respectively the PCM and the
surroundings of the described energy transfer system can be
realized. Hereby it may be ensured that once having supplied energy
to the PCM material for storage, the thermal insulation material
ensures that energy is only lost only at an incremental rate to the
surroundings during the storage of the thermal energy within the
PCM.
[0029] According to a further embodiment of the invention the
thermal insulation material comprises a composite ceramic material.
This may provide the advantage that it can be ensured that thermal
energy stored in the PCM is not released to the surroundings and it
is also ensured that the insulation material has material
properties suitable for the material to be used in the temperature
range of suitable PCMs of the described energy transfer system.
[0030] The composite ceramic material may be for instance an
air-bubbled ceramic material, which may be arranged between two
layers of a ceramic material. Thereby, the ceramic material of the
air-bubbled portion may be the same or may be different from the
ceramic material of the layers.
[0031] According to a further embodiment of the invention at least
a heating portion of the heat generation element is in physical
contact with the Phase Change Material. This may provide the
advantage that no extra intermediate heat distribution media has to
be warmed up before the thermal energy is introduced into the PCM.
Thereby, energy losses into an extra intermediate heat distribution
media can be effectively avoided and all of the heat generated by
the heating portion will be transferred to the PCM. Preferably, the
whole heat generation element is in physical contact with the
PCM.
[0032] The physical contact between the heating portion and the PCM
allows that known and reliable techniques can be used for the
introduction of thermal energy into the PCM. The thermal energy
introduction can be realized for instance by means of a heating
resistor respectively an electrical resistive heater.
[0033] According to a further embodiment of the invention at least
an extracting portion of the heat extraction element is in physical
contact with the Phase Change Material. A direct physical contact
between the PCM and the heat extraction element may provide the
advantage that substantially no losses occur in the process of
transferring released thermal energy from the PCM to some means
which can further distribute the released energy to the external
heat engine for use and utilization.
[0034] According to a further embodiment of the invention the heat
extraction element is a steam-liquid loop of the external heat
engine. Thereby, the external heat engine is a part of a power
production system.
[0035] The power production system may be a steam turbine. The
steam turbine can be used for generating electric power.
[0036] By realizing the heat extraction element as a steam-liquid
loop it may be ensured that the described energy transfer system is
closely connected to a power production system whereby the
utilization of released thermal energy is optimized with a high
utilization ratio. Furthermore it is ensured that the released
thermal energy can be utilized by known techniques.
[0037] Preferably the operating medium of the steam turbine is
water. In this case the steam-liquid loop may be called a
steam-water loop.
[0038] According to a further embodiment of the invention the power
production system comprises a control mechanism, which is adapted
for controlling a fluid flow within the steam-liquid loop.
[0039] The control mechanism may ensure that the amount of thermal
energy can be controlled, which amount is released from the PCM and
which amount is transferred to the external heat engine via the
fluid travelling within in the loop. At the external heat engine
the fluid can be used for driving the power production system
and/or for cooling components of the power production system, which
components are at an extreme high temperature.
[0040] The fluid may be in particular a steam and/or a liquid, in
particular water, which is flowing through the liquid/water
loop.
[0041] According to a further embodiment of the invention the
energy provided by the external energy source is electric energy
and the energy transfer system further comprises a frequency
controller, which is adapted for controlling a frequency of a
voltage and/or current being associated with the electrical energy
provided by the external energy source.
[0042] This means that the described energy transfer system is
capable of receiving electric energy from the external energy
source. This makes it very easy to use a surplus of electricity,
which has been produced for instance by wind turbine(s) or solar
plant(s) at times with low demands, to charge the PCM with thermal
energy such that the surplus of electricity can be stored as
thermal energy. Even further, by controlling the frequency of the
electrical energy applied to the heat generation element it is
ensured that an optimal heating respectively thermal energy
charging of the PCM can be obtained.
[0043] If the heat generation element comprises the above described
inductor, i.e. the heat generation element is an induction heat
generation element, the depth and the effect of the heat depends on
the frequency of the applied electric power and can be adapted
accordingly in order to realize an optimized introduction of
thermal energy.
[0044] According to a further aspect of the invention there is
provided an energy transfer arrangement for absorbing, temporarily
storing and releasing energy. The provided energy trans-fer
arrangement comprises (a) a first energy transfer system as
described above and (b) a second energy transfer system as
described above. The first energy transfer system and the second
energy transfer system are arranged parallel with respect to each
other.
[0045] The described energy transfer arrangement is based on the
idea that a concatenated energy storage and transfer system can be
provided, which comprises two or even more interconnected energy
transfer systems as described above. By concatenating two or more
of the above described energy transfer systems it can be ensured
that a major energy storage and transfer system can be tailored to
specific tasks and requirements. For instance if a specific major
energy storage and transfer system with a capacity exceeding one of
the above described energy transfer systems is required, then two
or more of these systems can be concatenated in order to increase
the total capacity of the concatenated major system.
[0046] It is mentioned that the parallel arrangement of the two
energy transfer systems refers to a functional and not to a
structural or geometric arrangement. This means that both energy
transfer systems are directly connectable to the external energy
source and both energy transfer systems are directly connectable to
the external heat engine.
[0047] According to an embodiment of the invention (a) the heat
generation element of the first energy transfer system and the heat
generation element of the second energy transfer system are
connected with each other and are connectable to the external
energy source and/or (b) the heat extraction element of the first
energy transfer system and the heat extraction element of the
second energy transfer system are connected with each other and are
connectable to the external heat engine.
[0048] Relating to the heat generation elements it can be ensured
that the individual heat generation elements can be coupled to the
external source e.g. in a parallel connection which in turn ensures
that energy provided from the external energy source can be equally
distributed to the various heat generation elements. Relating to
the heat extraction elements it is ensured that the individual heat
extraction elements can be coupled to the external source e.g. in a
parallel connection.
[0049] According to a further aspect of the invention there is
provided a method for absorbing, temporarily storing and releasing
energy. The provided method comprises (a) charging a Phase Change
Material with thermal energy, wherein the Phase Change Material is
contained within a first container and wherein the thermal energy
is introduced to the Phase Change Material by a heat generation
element, which is connected to an external energy source and which
receives energy from the external energy source, (b) temporarily
storing the thermal energy within the Phase Change Material, (c)
extracting thermal energy from the Phase Change Material by a heat
extraction element, which is connected to an external heat engine,
(d) transferring the extracted thermal energy to the external heat
engine, and (e) converting the transferred thermal energy into
electric energy by the external heat engine.
[0050] Also the described method is based on the idea that a
surplus of energy can be stored for an amount of time and this
surplus can be extracted, transferred and converted at a time at
which the request for energy is higher. In other words, the step of
(a) heating up the PCM or charging the PCM with thermal energy and
the step of (b) extracting thermal energy from the PCM are carried
out at different points in time.
[0051] Furthermore, the described method may also be carried out
under conditions where only a partial phase change of the PCM
occurs. Such a partial phase change means that the PCM is not
completely melted when being charged with thermal energy and/or
when being heated up. Accordingly, when energy is extracted from
the PCM not the complete PCM is solidified.
[0052] It is mentioned that the extracted thermal energy from the
PCM may in addition be provided for the simple use of direct
heating processes such as for residential and/or for industrial
heating and cooling.
[0053] It has to be noted that embodiments of the invention have
been described with reference to different subject matters. In
particular, some embodiments have been described with reference to
apparatus type claims whereas other embodiments have been described
with reference to method type claims. However, a person skilled in
the art will gather from the above and the following description
that, unless other notified, in addition to any combination of
features belonging to one type of subject matter also any
combination between features relating to different subject matters,
in particular between features of the apparatus type claims and
features of the method type claims is considered as to be disclosed
with this document.
[0054] The aspects defined above and further aspects of the present
invention are apparent from the examples of embodiment to be
described hereinafter and are explained with reference to the
examples of embodiment. The invention will be described in more
detail hereinafter with reference to examples of embodiment but to
which the invention is not limited.
BRIEF DESCRIPTION OF THE DRAWING
[0055] FIG. 1 shows the main components of an energy storage and
energy transfer system in accordance with a first embodiment of the
invention.
[0056] FIG. 2 shows the main components of an energy storage and
energy transfer system in accordance with a second embodiment of
the invention.
[0057] FIG. 3 shows the main components of an energy storage and
energy transfer system in accordance with a third embodiment of the
invention.
[0058] FIG. 4 shows an induction coil integrated in the thermal
isolation material of the energy storage and energy transfer system
shown in FIG. 3.
[0059] FIG. 5 shows a steam electric power plant which is connected
to an energy storage and energy transfer system in accordance with
a fourth embodiment of the invention.
[0060] FIG. 6 illustrates how thermal energy is absorbed or
released by a PCM when the PCM undergoes a phase change from solid
to liquid or from liquid to solid.
DETAILED DESCRIPTION
[0061] The illustration in the drawing is schematically. It is
noted that in different figures, similar or identical elements are
provided with the same reference signs. For the sake of conciseness
identical elements which have already been explained with reference
to a previous Figure will not be explained again when being
comprised in a later Figure.
[0062] FIG. 1 shows the main components of an energy storage and
energy transfer system 100 in accordance with a first embodiment of
the invention. A first container 110 comprising a PCM 115 is
enclosed by a second container 120. The two containers 110, 120 are
at least partly being thermally isolated from each other by a
thermal isolation material 125.
[0063] At least one heat generation element 130 is receiving energy
from an external energy source 170. The energy being received by
the heat generation element 130 is used for heating the PCM 115.
According to the embodiment described here the provided energy is
electric energy, which is converted into thermal energy by the heat
generation element 130. Further, at least one heat extraction
element 140 is providing thermal energy to an external heat engine
180. This provided thermal energy is used for electricity
production.
[0064] From the illustrated embodiment shown in FIG. 1 it can be
seen that the heat generation element 130 is in direct physical
connection with the PCM 115. This allows for an effective heat
transfer from the heat generation element 130 to the PCM 115 for
instance if the heat generation element 130 is a conductive heater
e.g. in the form of resistive heating elements and if the PCM 115
comprises or is a material with suitable thermal conductive
properties.
[0065] It is mentioned that for the resistive heating elements,
energy may be supplied to the elements as an AC- or a DC-voltage
(and of course a corresponding AC- or DC-current).
[0066] FIG. 2 shows the main components of an energy storage and
energy transfer system 200 in accordance with a second embodiment
of the invention. From FIG. 2 it can be seen, that the heat
generation element 130 is not in physical connection with the PCM
115. This will be an effective method of trans-ferring heat to the
PCM 115 if the element 130 comprises at least one inductive heating
element. In this case energy is preferably supplied to the heat
generation element 130 as an AC-voltage. Thereby, the frequency of
the AC may be the frequency of a utility grid. In order to adapt
the applied frequency a frequency controller 235 is provided. With
this frequency controller 235 the frequency of the AC voltage can
be scaled to another frequency than the frequency of the utility
grid. The frequency may also for various embodiments be alternated
during operation.
[0067] For an even further embodiment of the invention, the heat
generation element 130 may be directly connected to the utility
grid. Thereby, a surplus of energy on the utility grid can be
provided to the system 200.
[0068] It is mentioned that the heat generation element 130 may be
separated in a plurality of sub-elements. Further, the heat
generation element 130 and/or the corresponding sub-elements may be
one or more induction coils made of for instance copper.
[0069] Furthermore, the heat generation element 130 may be actively
cooled e.g. by ventilating air or a applying a cooled fluid such as
cooled water.
[0070] FIG. 3 shows the main components of an energy storage and
energy transfer system 300 in accordance with a third embodiment of
the invention. As can be seen from FIG. 3, the at least one heat
extraction element 140, which is used for extracting thermal energy
from the PCM 115, can be located such that it is not in direct
physically contact with the PCM 115.
[0071] FIG. 4 shows an induction coil 432, which may be integrated
for instance in the thermal isolation material 125 of the energy
storage and energy transfer system 300 shown in FIG. 3. The
windings of the induction coil 432 are not in direct physical
contact with the PCM 115 to be heated, but are separated by some
refractory material 412.
[0072] FIG. 5 shows a steam electric power plant which is connected
to an energy storage and energy transfer system 500 in accordance
with a fourth embodiment of the invention. As can be seen from FIG.
5, at least one heat extraction element 140 is connected to the PCM
115 and is providing energy to an external heat engine, which
according to the described embodiment is a steam turbine 580.
[0073] The steam turbine 580 is used for electricity production.
Water is fed into the heat extraction element 140 and is heated by
the PCM 115. As the temperature of the PCM 115 may be higher than
the boiling point of water, steam is generated and fed to the steam
turbine 580. The steam enters the steam turbine 580 where it
expands and pushes against blades to turn a generator shaft of an
electric generator 582 to create electric current. After the steam
has passed through the steam turbine 580, a condenser 585 convert
it to water, which in turn is returned by non depicted pumps to the
heat trans-fer element 140 as cold water in order to repeat the
described thermodynamic cycle.
[0074] The generated electric current respectively the generated
electric power is fed to a utility grid 590.
[0075] In order to recapitulate the above described embodiments of
the present invention one can state: The system and the methods
disclosed within this document relate to the storage of energy from
an external source in a Phase Change Material (PCM) and to the
release of at least a fraction of the stored energy to an external
heat engine. The energy can be stored in a sensible energy storage
process by temperature changes only i.e. where the ranges of the
temperature changes in the PCM do not comprise the melting point
temperature of the PCM. Alternatively and/or additionally, the
energy can be stored in a latent energy storage process i.e. where
the range of the temperature changes of the PCM comprises the
melting point temperature of the PCM. Which particular energy
storage process is used depends on the amount of energy which is
supposed to be put into the system for storage. Once having
supplied energy to the PCM for storage, a thermal isolation
material, which at least partly encloses the PCM, ensures that only
a limited energy is released to the surroundings during storage. A
PCM is a substance with a high heat of fusion and is therefore
capable of storing and releasing amounts of energy by exploiting
that heat which is absorbed or released when a PCM experiences a
phase change. In general, the energy storage can be achieved
through either of solid-solid, solid-liquid, solid-gas, and
liquid-gas phase changes. However, in practice changes from solid
to liquid and back are currently preferred. Through an energy
storage process, the PCM initially behaves as a sensible heat
storage material i.e. the temperature of the PCM rises as it
absorbs heat. When the temperature reaches the melting temperature
of the PCM, the material absorbs large amounts of heat at a
substantially constant temperature until the material entirely has
become liquid. The release of energy is achieved by a reverse
process where the material solidifies. Which material is preferred
to be used for the PCM is dependent on the specific task and the
properties of the material e.g. (a) melting temperature in the
desired operating range, (b) high latent heat of fusion, (c) high
conductivity, (d) rate of volume change on phase transformation,
(e) chemical stability and/or (f) price. The PCMs can be organic or
inorganic. For various embodiments of the invention, the PCM is
Silicon (Si) or preferably Aluminum (Al).
[0076] It should be noted that the term "comprising" does not
exclude other elements or steps and "a" or "an" does not exclude a
plurality. Also elements described in association with different
embodiments may be combined. It should also be noted that reference
signs in the claims should not be construed as limiting the scope
of the claims.
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