WO2013014147A1

WO2013014147A1 - Thermoelectric generator having a thermal energy store

Info

Publication number: WO2013014147A1
Application number: PCT/EP2012/064473
Authority: WO
Inventors: Martin Kautz; Stefan Lampenscherf; Jochen SCHÄFER
Original assignee: Siemens Aktiengesellschaft
Priority date: 2011-07-28
Filing date: 2012-07-24
Publication date: 2013-01-31
Also published as: DE102011080011A1

Abstract

The invention relates to an arrangement (1) and a method for energy conversion using a thermoelectric generator (2) which comprises thermoelectrically active layers. The arrangement (1) has at least one top layer (3) having high thermal conductivity, which is arranged above the thermoelectrically active layers of the thermoelectric generator (2). A phase change material (4) is arranged between the layers of the thermoelectric generator (2) and the at least one top layer (3) in thermal contact with the layers of the thermoelectric generator (2) and the at least one top layer (3).

Description

description

Thermoelectric generator with thermal energy storage

The invention relates to an arrangement and a method for energy conversion with a thermoelectric generator comprising thermoelectrically active layers. The arrangement comprises at least a top layer with high Wärmeleitfä ^¬ ability, which is disposed on the thermo-electrically active layers of the thermoelectric generator.

Thermoelectric generators (TEG), as they are known for example from DE 100 04 390 AI, can generate electricity by utilizing a temperature difference using semiconductor material. The life and the efficiency of a thermo ^¬ electric generator depend heavily on the temperatures and their range of variation. Disadvantages are, above all, strongly fluctuating temperatures with high peak values. At these temperatures, a thermoelectric generator can not operate continuously under optimum operating conditions. Strong temperature fluctuations lead to thermal stresses, which over time can lead to irreversible destruction of the thermoelectric generator. Temperature peaks, for example, can cause liquefaction of solder, which leads to thermal destruction of the thermoelectric generator.

In the prior art attempts to prevent damage to the thermoelectric generator constructive measures ^¬ men such as insulation. However, these lead to the fact that the efficiency of the thermoelectric generator ver ^{¬ is} reduced.

The object of the present invention is therefore to provide an arrangement with a thermoelectric generator and a method for its use, which overcomes the problems described above. In particular, it is an object to provide an arrangement with a thermoelectric generator, which operates stable over time, is relatively insensitive to temperature fluctuations and prevents destruction of the thermoelectric generator by thermal stresses and very high temperatures.

The stated object is achieved with regard to the arrangement for energy conversion with a thermoelectric generator having the features of claim 1 and with regard to the method for operating a thermoelectric generator having the features of claim 7.

Advantageous embodiments of the inventive arrangement for energy conversion having a thermoelectric generator, and the method for operating a thermoelectric genes ^¬ rators are evident from the associated dependent claims in each case. The features of th claims nebengeordne ^¬ can paint a plurality of associated dependent claims can be combined with each other and with features of a respective associated sub-claim or preferably also with memory ^¬.

The arrangement according to the invention for energy conversion comprises a thermoelectric generator having thermoelectrically active layers, and at least one cover layer with high thermal conductivity, which is arranged over the thermoelek ^¬ trically active layers of the thermoelectric generator. Furthermore, the arrangement comprises at least one layer which comprises a phase change material and between the layers of the thermoelectric generator and which is arranged at least one cover layer, in thermi ^¬ schem contact with the layers of the thermoelectric generator and the at least one cover layer.

The at least one layer of phase change material spei ^¬ chert heat at a high capacity. As a result, it can absorb heat quantity at high temperatures and lead to a reduction in the maximum or peak temperature at the thermoelectric generator. At low temperatures at the thermoelectric generator, the phase change material can amount, thereby leading to a stabilization of the temperature at the thermoelectric generator without large temperature extremes. As a result of the path buffering of the temperature extremes, the arrangement according to the invention can work relatively stable in terms of time and is relatively insensitive to temperature fluctuations. Destruction of the thermoelectric generator by thermal stresses and temperature peaks can be prevented.

The thermoelectric generator may be constructed from at least one thermoelectrically active layer comprising one or more stacks of juxtaposed layers, the layers having a layer sequence of p-type semi-conductive and n-type semiconductive layers with an insulating layer therebetween. These may be electrically connected to one another such that always two successive semiconductive layers are electrically connected across the insulating layer. As a result, a current flow along a temperature gradient within a semiconducting layer can take place and be used via the electrical connection. Thus, from a temperature gradient originated e.g. By using waste heat or by using the heat generated by solar radiation, electrical power generated or electrical power can be obtained.

The phase change material may be composed of a mixture of different union under ^¬ chemical substances. The chemical composition of the phase change material from unterschiedli ^¬ chen chemical substances can be selected depending on an optimum operating temperature and / or a high heat capacity. If the temperature of phase change is near the loading ^¬ operating temperature or is identical, then the thermoelectric generator can be operated substantially at its operating temperature by the arrangement. This leads to a high efficiency in the conversion of heat into electrical energy. Destruction of the thermoelectric generator by temperature peaks is avoided. The phase change material stores especially during the phase change a large amount of heat and can thus buffers at a temperature close to or equal to the temperature of the phase change particularly good Tempe ^¬ raturspitzen and lead to a steady operation of the thermoelectric generator with high efficiency ^¬ degree.

The phase change material layer may comprise a structure for mechanical stabilization. As a result, a mechanical deformation and a possible destruction of the arrangement during operation can be counteracted.

The layer with phase change material may comprise a heat conduction ^¬ structure. This may be identical to the structure for mechanical stabilization. For example, a metal grid, which is fluidically permeable to serve as thermal conductivity ^¬ structure and / or as a structure for mechanical stabilization. It is also possible to use structures such as meandering or comb-shaped cooling coils. As a result, local temperature differences on the surface of the thermoelectrically active layer or layers are avoided. Local peak values of the temperature are reduced, and the functi ^¬ on the inventive arrangement ver ^¬ repaired by a homogeneous temperature distribution in the layer of the phase change material.

The phase change material of the layer comprising the phase Wech ^¬ selmaterial may be stored. This can be done for example in a thermally insulated device, such as a thermo vessel or container, which is fluidly connected to the layer comprising the phase change material layer. Thus, in addition amount of heat from the thermoelectric generator off or be supplied to it. The advantages described above are thereby achieved more.

An inventive method for operating a thermo ^¬ electric generator, in particular a previously described nen thermoelectric generator may include that a phase change material is used, the Temperaturstabiii tion of the thermal gradient across the thermoelectric generator.

The phase change material can stabilize the temperature to values of an optimum operating temperature T _{B of} the thermoelectric generator.

A substantially homogeneous temperature in the phase change material can be generated over a surface of the thermoelectric generator via a heat conduction structure.

It can take place via a storage of phase change material, a temporal stabilization of the temperature gradient of the thermoelectric generator.

By means of phase change material can be done a capping of temporally occurring temperature peaks on and / or in the thermoelectric generator.

For the inventive method for operating a thermo ^¬ electric generator, the above-mentioned, associated with the inventive arrangement for energy conversion advantages.

Preferred embodiments of the invention with advantageous developments according to the features of the dependent claims are explained in more detail with reference to the following figures, but without being limited thereto.

Show it:

Fig. 1 is a schematic sectional view of an arrangement

1 with a thermoelectric generator 2 for the use of solar energy according to the prior art, and

Fig. 2 is a schematic representation of a temperature-time diagram of an arrangement 1 shown in Fig. 1, and 3 shows a schematic sectional view of an arrangement 1 according to the invention for the use of solar energy with a thermoelectric generator 2 and a layer of phase change material 4, and

4 shows a schematic representation of a temperature-time diagram of an arrangement 1 according to the invention shown in FIG. 3.

1 shows a schematic sectional view of an arrangement 1 with a thermoelectric generator 2 for the use of solar energy according to the prior art. The Anord ^¬ voltage 1 for energy conversion comprises a plate-shaped or sheet-shaped thermoelectric generator 2, which comprises thermoelectrically active layers. Such thermal moelektrischer generator 2 is generally known, for example from DE 100 04 390 Al, and will therefore not be described ge ^¬ more precisely in the following. At least one cover layer 3 is arranged on the thermoelectric generator 2. It may be a glass plate or an absorber, such as a blackened metal plate. This is arranged in thermal contact area on the thermoelectric generator 2.

2, a temperature-time diagram of the arrangement shown in Fig. 1 is shown schematically. In operation, the cover layer 3 is heated intermittently via a heat source 5, for example by solar radiation. Alternatively, serve as a heat source 5, a fluid which stores waste heat and the cover layer 3 flows over. The heat source 5 heats the cover layer 3 to a temperature T _D whose change in the course of time follows the temperature of the heat source 5 or the heat radiation.

The cover layer 3 is in thermal contact with the ther ^¬ moelektrischen generator 2. On the side of the thermoelectric generator 2, which the side in contact with the deck Layer 3 is opposite, there is a lower tempera ^ture T ₂ , as the temperature ΤΊ on the side in contact with the cover layer 3. The temperature ΤΊ on the side of the cover ^¬ layer 3 is substantially by the temperature T _{D of} the cover layer third given or both temperatures ΤΊ and T _D are the same. The temperature T2 on the opposite side is essentially determined by the ambient temperature of the arrangement, eg the air temperature in the shade. Their time course is usually similar to the temperature Ti, but with much lower amplitude or temperature maxima and minima than in ΤΊ. This leads to a greatly vary the temperature ^¬ ΤΊ and an almost constant or slightly changing with time temperature T2 during operation of the thermoelectric generator. 2

The thermoelectric generator 2 produces from the tempera ^¬ turdifferenz Ti T2 minus a current or electrical Leis ^¬ processing. At an optimum operating temperature T _B , the thermoelectric generator 2 operates at a maximum efficiency. In this context, the operating temperature T _B is to be understood as the mean value of the temperature T 1 and the temperature T 2. Varies this operating temperature T _B by strong variations in temperature Ti and / or the temperature T _2, or the operating temperature T _B removed of the optimal operating temperature T _B, operates the thermoelectric Ge ^¬ erator 2 most of the time decreased with a response ^¬ degrees. This means that the thermoelectric generator 2 according to the prior art works most of the time with a ge ^¬ lower efficiency than would be possible optimally.

Strong fluctuations of the temperature Ti compared to the temperature T2 lead to mechanical stresses in the thermoelectric generator 2 and possibly to its destruction. For example, layers may "chip off" or be mechanically deformed.These deformations or spalling can lead to irreparable damage to state-of-the-art arrangement 1. Very high peak values of the temperature Ti can occur. NEN lead to the destruction of the thermoelectric generator 2, for example by softening solder joints.

FIG. 3 shows a schematic sectional illustration of an arrangement 1 according to the invention. This comprises, in addition to the cover layer 3 and the underlying arranged thermoelekt ^¬ cal generator 2 a layer of phase change material 4. The phase change material 4 is in thermal contact with the thermoelectric generator 2 and is disposed between the thermoelectric generator 2 and the cover layer 3.

The phase change material 4 changes state at a certain temperature T _P its aggregate state, for example from fixed to liquid ^¬ sig. For example, when it reaches its melting temperature T _s , it becomes liquid. In the phase change the phase Wech ^¬ selmaterial 4 stores energy E _PW. These are from the phase change mate ^¬ rial 4 when, for example, to fixed returns from liquid if the ambient temperatures fall below the temperature T _s. Due to the high heat capacity, which consists in ausge ^¬ sought materials during the phase change, the phase change material 4 leads to a stabilization of the temperature in the region of the temperature of the phase change. Temperature fluctuations are "buffered away" in this area Only when the phase change energy of the phase change material 4 is reached or when the phase change has completely occurred does the temperature of the phase change material 4 begin to change again.

In FIG. 4 is a schematic representation of a Tempe ^¬ temperature-time diagram of a erfindungsge ^¬ MAESSEN arrangement 1 shown in Fig. 3 is illustrated. In variations of temperature T _D of the coating layer, for example, by variations in the sunlight or heat temperature, which takes place via the temperature of the phase change of time, the phase change material ^¬ 4 stores heat. As a result, the temperature Ti at the thermoelectric generator 2 changes little. Part of the temperature change is via the phase change material whose temperature T _PCM is in the phase change range no or only very slight changes have been "weggepuffert" until the completion of Pha ^¬ senwechsels.

On the thermoelectric generator 2, a relatively constant temperature i prevails on the side facing the cover layer. On the opposite side, the temperature T ₂ prevails, which by nature varies less and corresponds substantially to the ambient temperature, eg of the air. About the difference between Ti and T2 is produced by the thermoelectric generator 2 electric current or electrical power. Due to the lower fluctuation of the tempera ^ture Ti compared to the temperature T2 less mechanical stresses in the thermoelectric generator 2, and destruction of the assembly 1 by strong Temperaturschwankun- conditions or temperature peaks can be avoided. As a result, the life of the assembly 1 can be increased.

At a certain, ie the optimum operating temperature T _B , the thermoelectric generator operates particularly effectively, ie with high efficiency. When selecting a phase change material 4 with a temperature of the phase change near or equal to the optimum operating temperature T _{B of} the thermoelectric generator 2, a particularly high efficiency of the arrangement 1 can be achieved. Despite the temperature fluctuations of the temperature T _{D of} the cover layer 3, the phase change material keeps the temperature Ti at the thermoelectric generator 2 close to the optimum operating temperature T _{B of} the thermoelectric generator 2. As a result, the temperature Ti and, with a slight change in the temperature T2, the average value of the thermoelectric generator 2 Temperature Ti and the temperature T2 are maintained at a value T _B at which the thermoelectric generator 2 operates optimally. This means that the thermo ^¬ electric generator operates most of the time with a maximum ^¬ possible efficiency.

The phase change material 4 leads to a more uniform temperature compared to an arrangement 1 without phase change material 4, over the entire surface of the thermoelectric In order to support this effect and / or for an increase in the mechanical stability, structures may be incorporated in the layer with phase change material 4, which contribute to the mechanical stabilization and / or better heat conduction. This is not shown in the figures for the sake of simplicity. Thus, for example, a metal grid, which is fluid-permeable, serve as a heat-conducting structure and / or as a structure for mechanical stabilization. It is also possible to use structures such as meandering or comb-shaped cooling coils. These are arranged between cover layer 3 and thermoelectric generator 2 in thermal contact with the latter and penetrated by phase change material 4. As a result, local temperature differences on the surface of the thermoelectrically active layer or

Layers avoided. Local peak values of the temperature are reduced and the function of the inventive arrangement 1 is improved by a homogeneous temperature distribution in the layer of the phase change material 4.

The embodiments described above may be used alone or in combination as well as in connection with the prior art.

For example, the phase change material 4 of the layer comprising the phase change material 4 can be stored. This example can be used in a thermally insulated device such as a thermal done vessel or container which is fluidically connected to the phase-change material layer 4 comprising ver ^¬ prevented. This is not shown in the figures for the sake of simplicity. By storing Phasenwechselma ^¬ material 4, for example, in liquid form in an external device, additional amount of heat from the thermoelectric generator 2 off or can be supplied to him. The advantages described above are thereby achieved more.

Claims

claims

1. arrangement (1) for energy conversion with a thermoelectric generator (2), which thermoelectrically active

Comprises layers, and with at least one cover layer (3) with high thermal conductivity, which is disposed over the thermoelectrically ^¬ active layers of the thermoelectric generator (2), characterized in that at least one layer which comprises a phase change material (4), between see the layers of the thermoelectric generator (2) and the at least one cover layer (3) in thermal contact with the layers of the thermoelectric generator (2) and the at least one cover layer (3) is arranged.

2. Arrangement (1) according to claim 1, characterized in that the thermoelectric generator (2) is constructed from at least one thermoelectrically active layer, which comprises one or more stacks of layers arranged side by side, wherein the layers have a layer sequence of p-type conductive and n-type semiconductive layer having an insulating layer therebetween, which are electrically connected to each other such that always two consecutive semiconducting layers are electrically connected across the insulating layer, so that current flow along a temperature gradient within a semiconducting layer

Layer takes place.

3. Arrangement (1) according to one of the preceding claims, characterized in that the phase change material is made up of a mixture of different chemical substances, in particular depend on an optimal operating Tempe ^¬ temperature and / or a high heat capacity.

4. Arrangement (1) according to any one of the preceding claims, character- ized in that the layer with Phasenwechselmate ^¬ rial (4) comprises a structure for mechanical stabilization.

5. Arrangement (1) according to one of the preceding claims, characterized in that the layer with Phasenwechselmate- rial (4) comprises a heat conduction structure.

6. Arrangement (1) according to one of the preceding claims, characterized in that the phase change material (4) of the layer with phase change material (4) can be stored, in particular in a thermally insulated device.

7. A method for operating a thermoelectric generator (2), in particular a thermoelectric generator (2) according to any one of the preceding claims, characterized in that a phase change material (4) is used for temperature stabilization of the thermal gradient across the thermoelectric generator (2).

8. The method according to claim 7, characterized in that the phase change material (4) stabilizes the temperature to values of an optimum operating temperature T _{B of} the thermoelectric generator (2).

9. The method according to any one of claims 7 or 8, characterized in that via a heat conduction structure in a substantially homogeneous ^¬ temperature in the phase change material (4) over a surface of the thermoelectric generator (2) is generated.

10. The method according to any one of claims 7 to 9, characterized in that a temporal stabilization of the Tempera ^¬ turgradienten the thermoelectric generator (2) via a storage of phase change material (4).

11. The method according to any one of claims 7 to 10, characterized in that a capping of temporally occurring temperature peaks on and / or in the thermoelectric generator (2) by means of phase change material (4).