Thermoelectric generator array

Abstract

A method and system for employing thermoelectric generators for capturing otherwise lost thermal energy associated with operation of an electric vehicle.

Claims

1. A system for thermoelectric generation in a vehicle, comprising, at least one thermoelectric generating element associated with a vehicle body with one side thermally conductively exposed to the ambient air having an ambient temperature, a flow structure to supply the other side of said thermoelectric generating element with an air flow of differing temperature, so as to dynamically maintain a thermal gradient across said element.

2. A system according to claim 1, comprising at least two thermoelectric elements each having one side conductively exposed to the ambient air and its other side exposed to differing temperature air flow in the flow structure, and a control means to switch between said generating elements when the ambient temperature differential relative to the vehicle changes.

3. A system according to claim 1 in which the thermoelectric elements are arranged in a multiple array.

4. A system according to claim 2 in which the thermoelectric elements are arranged in a multiple array.

5. A system according to claim 2 in which one side of said thermoelectric elements is thermally conductively connected to a vehicle roof panel.

6. A system according to claim 5, in which the other side of the thermoelectric elements is exposed to air in the vehicle interior ducted below the roof panel.

7. A system according to claim 6 in which said vehicle in which at least one source of waste heat is exhausted into said vehicle interior so as to assist in maintaining said thermal gradient.

8. A system according to claim 7, in which said vehicle, while stationary and while the relatively colder side of said thermoelectric array is exposed the ambient cold temperature, uses vehicle interior air heated by the greenhouse effect to flow past the other side of said array to maintain said thermal gradient.

9. A system according to claim 8, in which said vehicle, while moving, exposes the exterior of said vehicle convectively to cold ambient air flow to cool one side of said thermoelectric elements and uses waste heat from the vehicle interior flowing past the other side of said thermoelectric elements to maintain said thermal gradient.

10. A system according to claim 9, in which said exterior vehicle panel is a roof panel.

11. A system for thermoelectric generation in a vehicle, comprising, at least one thermoelectric generating element associated with a vehicle body with one side thermally conductively exposed to a relatively warmer exterior ambient air having an ambient temperature, a flow structure to supply the other side of said thermoelectric generating element with a relatively cooler air flow, so as to dynamically maintain a thermal gradient across said element.

12. A system according to claim 11, in which said relatively cooler air flow is supplied by interior waste air from a cooling cooling system of said vehicle.

13. A system according to claim 12, in which said one side of said array is associated conductively with a vehicle roof panel.

14. A system according to claim 13 in which, while said vehicle is stationary, exposes said roof panel to solar radiant heating.

15. A system according to claim 14 in which said relatively cooler air flow is supplied from the exterior of said vehicle from a source cooler than said heated roof panel.

16. A system for thermoelectric generation in a vehicle, comprising, at least one thermoelectric generating element array associated with a vehicle body with a hot side associated with a vehicle body panel and thermally conductively exposed to the ambient air having an ambient temperature, at least one thermoelectric generating element array associated with said body panel with a cold side associated with said vehicle body panel, a flow structure associated separately with each to supply the other side of said thermoelectric generating element array with an air flow of differing temperature, so as to dynamically maintain a thermal gradient across said element, and a control means to switch between said arrays depending on the changing ambient temperatures to which said vehicle body panel is exposed.

17. A system according to claim 16 is which said vehicle body panel is a roof panel.

18. A system as claimed in claim 16 wherein said thermoelectric generating element array associated with said body panel with a hot side associated with said vehicle body panel has a first size, and wherein said at least one thermoelectric generating element array associated with said body panel with a cold side associated with said vehicle body panel has a second size different from said first size.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 illustrates a TEG electric generator schematic and device.

[0017] FIG. 2 illustrates hot and cold TEG arrays.

[0018] FIG. 3 illustrates a TEG array on a vehicle roof.

[0019] FIG. 4 illustrates a power supply and heat exchangers suitable for use in implementing another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] It is helpful at this point to describe some more background about thermoelectric generation and existing devices, which are incorporated into the designs described below.

[0021] The basic operation of a thermoelectric module (TEG) is illustrated in FIG. 1. Two different material elements, shown on the left of FIG. 1, an n-doped element, and a p-doped element, are arranged electrically in series, but thermally in parallel, between a dynamic heat source and a dynamic heat drain, or cooler source. All of the n and p elements are connected at their upper ends (or, at one end, to avoid any implication of orientation limitation) by a thermally and electrically conductive means to the heat source, and thermally conductively connected (only) at their lower (other) ends to the cooler source. It is important the n and p elements per se maximize electrical conductivity, while limiting thermal conductivity. This is important so as to maximize charge flow, while minimizing the end to end thermal flow that would tend to reduce the driving thermal differential or gradient (flux). The doping serves to increase electrical conductivity, while not increasing thermal conductivity per se. These elements are incorporated in commercially available TEG units, shown on the right in FIG. 1, which may be wired in large numbers in series, as described further below.

[0022] The conventional wisdom for TEGs is that only a very large thermal differential or flux is useful. It is true that efficiency and capacity increase proportionately to the size of that thermal differential. There is also a perception that, in an engineering sense, that large differential, especially the high temperature at the hotter side, will subject the units to a high degree of thermal and mechanical stress. That hotter side is also, certainly in the case of IC engine vehicles, a very hot and very caustic environment, subject to a great deal of flux, making the thermal connection at the hot side subject to durability issues. The subject invention works against that received wisdom, as will be detailed below.

[0023] Conventional materials for the n and p elements are chosen based on the temperatures that are likely to be experienced. One common material is Bismuth Telluride (Bi.sub.2Te.sub.3), which is effective around room temperature. As noted, while large temperature differentials cannot be expected to either side of room temperature, the subject invention works in spite of, and even with, what would otherwise be considered a drawback.

[0024] Preferred embodiments according to the invention are described by reference to the figures.

[0025] The invention is designed to work in conjunction with a vehicle structure that can serve either as a source of heat energy from the ambient, or as a “sink” or drain of heat to the ambient. This interchangeability can occur seasonally, of course, but can even occur within a day during a given season. This either/or use of an ambient source/sink is not one that is recognized in those few sources that suggest the use of TEGs in a vehicle context, which, so far as is known, disclose only the use of a structure that is a source of high temperature heat energy only, and which does not change seasonally. Likewise, only the use of high heat flux or differential is contemplated, and only in problematical areas (engine block, exhaust system) that would be difficult to exploit as a practical matter. By stark contrast, the subject invention seeks to harvest energy at the margins and use a lower heat flux, in conjunction with a novel method of taking advantage of a variability in that flux, and in a structural context that is far more durable and practical.

[0026] As illustrated in FIG. 3, a suitable vehicle body structure is chosen that provides the necessary ambient exposure to hot or cold, and also a practical means of dynamically maintaining an opposite side of the necessary heat flux. For example, the metal roof structure of a typical vehicle, including EVs, is continually exposed to the ambient, and has a relatively large surface area. That ambient exposure is static when the car is parked, and dynamic when it is operating, but continual in either case. An array of TEGs of the type shown in FIG. 1 may be mounted in the space beneath the underside of the roof panel, in a thermally conductive fashion, as shown in FIG. 3. For example, only an array of “hot” TEGs, that is, ones in which the hot side shown in FIG. 1 could be thermally connected to the underside of the roof panel heat source. This could make sense in an area where only relatively hot ambient temperatures are expected, that is, relatively hotter than the interior cabin of the vehicle. A large array of such TEGs could be ganged together in series, and most of the available under roof mounting area could be used. Each unit would be suitably electrically insulated from the other. The relatively hotter upper and outer surface of the roof panel, in an environment like the American southwest, would be hot even when the vehicle was moving, and even hotter when sitting parked in the beating sun. The surface can be considered to be exposed to the ambient air, even when the primary mechanism of exposure thereto is radiant, (from solar rays) and not convectively, as when the vehicle was moving.

[0027] As best shown in FIG. 2, in the available volume below the roof underside mounted TEG array, a channel could be provided for a cooling air flow to the opposite, cool side of the TEG array. This flow channel need not be deep, and there would be sufficient volume available inside the vehicle head liner, or the headliner itself could provide the flow channel. That flow channel would be fed with relatively cooler air, as from the vehicle interior. Such vehicle interior air is typically dynamically cooled regardless, and continually expelled as it becomes stale and fresh air is drawn in. The expelled air could be fed past the cold side of the hot array, and thus the heat flux dynamically maintained, essentially for free. In addition, relatively cooler outside air could be ducted into the cooling space beneath the colder side of the hot TEG array, for the express purpose of providing and maintaining that heat flux (dynamic temperature gradient or differential). Such outside air could effectively be kept out of the cabin interior so as to not interfere with its air conditioning. Both sources of cooling air could be blended as needed and, again, both would be essentially free.

[0028] When the car is parked, the cooler side air flow would not be readily available from the vehicle's cooling system. The other side of that coin, however, is that the roof could become very hot indeed, primarily from radiant solar heating and it is the temperature differential that's significant. The car interior is typically cooler, just by virtue of being shaded (by that same roof) and or by tinted windows. Extra interior shading is often provided by vehicle owners, as by front window screens, and such screening could be automatically provided as an adjunct to the subject invention. Furthermore, some systems could be designed to periodically cool the interior air as the car was parked, either actively and passively, and that relatively cooler air could be used, in conjunction with a very hot roof, to create the necessary heat flux and exploit it. In addition, ambient air could be pulled in from the shaded area beneath the car as the car was parked and ducted beneath the hot TEG array.

[0029] Regardless of the various potential means for providing the cooling air necessary to maintain the flux, the total current and voltage so provided could be used in several possible ways. It could directly power its own fans or valves or control systems, and use the excess power to directly power other vehicle accessories, or to charge lower power batteries for such accessories. Furthermore, with the addition of a converter, such as that shown in FIG. 4 below, the total voltage could be stepped up and boosted to a level sufficient to charge the traction batteries. For example, if each TEG produced a maximum of 5 volts and a TEG array consisted of 8 TEG's then the array would provide an output of 40 volts. This could then be regulated and calibrated to provide an output of 48 to 50 volts, as desired. This additional operation would also use energy, of course, but there would be conditions under which the temperature flux could be sufficient to make such boosting feasible.

[0030] It is the unique advantage of the subject invention to recognize and exploit the ever changing “short dams” of potential thermal energy that develop between the ambient air and the vehicle interior air. The prior art suggests the use of a free or waste heat source in a vehicle, but not the use of an ambient heat source as disclosed above. The prior art on the use of TEGs in vehicle is even less suggestive of the use of an ambient cold source in relation to a relatively warmer heat source within the vehicle cabin. In cold climates, or during the cold season in moderate climates, the same roof panel would become very cold, especially when parked in the shade, and especially when exposed to a cold air stream as the vehicle was driven. An additional (or potentially only) array of “cold’ TEGs could be incorporated. These would be installed as shown in FIGS. 3 and 4 above, but with the cooled side thermally conductively joined to the underside of the roof panel. Then, in cold weather, there would be a temperature differential created relative to the now warmer interior cabin air of the vehicle, which would be ducted to the warmer side of the TEG array. The deliberately heated air in the cabin vehicle also has to be continually evacuated as it becomes stale, and that still warm exhausted air could be so ducted. A suitable temperature sensing control system would be provided to switch between arrays depending on ambient and interior temperatures, and use whatever temperature gradient was available. The system could potentially be designed to switch even as conditions changed on a daily basis. For example, in winter, the greenhouse effect can warm the vehicle interior significantly relative to the outside of the roof panel. Though the differential so created might not be large, both the heat and cold source are free, and could last for a long time as the vehicle was parked.

[0031] The control system could be designed to detect the size of and direction of such thermal differentials or gradients (flux) and automatically switch between arrays as needed. The system as disclosed could work in any vehicle, including an IC engine vehicle, though it would be most economically feasible in an all-electric vehicle.

[0032] The invention and system as disclosed are subject to variations and improvements. In addition to using only one array, hot or cold depending on geographic environment, two arrays of varying size could be used, a smaller hot side array where the hot weather heat flux is higher (and fewer TEG elements needed), and vice versa. A cold side array could be mounted in an area likely never to see any solar heating, such as a side panel. New nano materials may be developed in the future that are more efficient than the off the shelf units disclosed above, and those could easily be substituted.