HOW THERMOELECTRIC TEG GENERATORS WORK

The basic concept of Thermoelectric Generators TEG's (Seebeck Effect) is outlined below. We have been manufacturing TEG Power Generators for the last 10 years. A full 70-80% of the interest in these products comes from people who have only minimal knowledge of the technology. Based on the requests for pricing and products availability, interest in this field has exploded in the last three years. Thermoelectric modules work on two different principals:

1. Peltier Effect: This effect introduces power to the module with a resultant cooling of one side and heating of the other. These types of modules are low amp (typically in the 6 amp range) and are designed for low temperature exposure of no more than 70°C to 90°C hot side. Higher temperature exposures will cause the module to either break apart, couples joints to melt and are not good power generators!

2. Seebeck Effect: This effect creates a temperature differential across the module by heating one side of the module and cooling the opposite.

Correct terminology is essential to any technology. A Seebeck Module is a power generator and a Peltier Module is a cooling module. You can use a peltier modules as a generator but will not be able to produce much power because of materials used to bond the device together are low temperature under 220°F. To produce meaningful power you will need to expose the hot side to temperatures in the 350 to 700°F range! Also have the cold side remove heat and maintain temperatures of 100°F or lower if possible!

Thermoelectric Generators using the Seebeck Effect work on temperature differentials. The greater the differential (DT) or Delta Temperature, of the hot side compared to the cold side, the greater the amount of power (Watts) will be produced.

Two critical factors dictate power output :

1. The amount of heat flux that can successfully moved through the module (HEAT FLOW). The higher the hot side as compared to the cold side the greater the heat flux movement!

2. (DT) Delta Temperature - the temperature of the hot side less temperature of the cold side.

Great effort must be placed on both the heat input design and especially the heat removal design (Cold Side). The better the TEG Generator construction is at moving heat from the hot side to the cold side and dissipating that heat once it arrives to the cold side, the more power will be generated. Unlike solar PV, which use large surfaces to generate power, Thermoelectric Seebeck Effect modules are designed for very high power densities. On the order of 50 times greater than Solar PV !

Thermoelectric Seebeck Generators using liquid on the cold side perform significantly better than any other method of cooling and produce significantly more net additional power than a pump consumes (based on system size).

For any thermoelectric power generator (TEG), the voltage(V) generated by the TEG is directly proportional to the number of couples (N) and the temperature difference (Delta T) between the top and bottom sides of the TE generator and the Seebeck coefficients of the n and p- type materials.

The standard material we work with is BiTe. The best efficiency that can be achieved with this material is approximately 6%. But once the material is placed into a constructed module the efficiency drops to 3 to 4% depending on DT because of thermal and electrical impedance!

No other semiconductor material can perform as well as BiTe as far as efficiency is concerned at temperatures below 300°C.

Other material like PbTe are used but are far less efficient at lower temperatures, and must be used at significantly higher temperatures (in the 500 to 600°C hot side range) and may not be commercially available and are 5 times more expensive than BiTe to purchase!

New materials such as CMO Calcium Manganese Oxides and Cascades of Oxide on the hot side and Bi2Te3 on the cold side are designed to optimize temperatures where the material is the most efficient are now available exclusively through our Tecteg Mfr. division. These material and mosules are the first of their kind to be offered commercially in 40 years!

In fact Cascades have never been offered commercially and until now were only samples ina a lab!

Power output based on (DT) is very predictable and well documented for BiTe, but access to this information is difficult to find. With power generation, the thinner the length or thickness of the module, the greater the amp output or rating. This is because the heat flow quicker threw thinner elements. But because of this DT are much more difficult to obtain so special designed cold side removal designs must be used in order to exploit high amperage devices.

You can have a 25 amp module the same size (typically 40 mm x 40 mm) as a 3 amp module, but length x width and height of the pellet or elements determines how much heat can pass through the module. The ratio of the height compared to the actual width x length determines the overall amperage of the module. As the height of the pellet is shortened, the ability of heat flux to pass more quickly through the module increases allowing greater power generation as long as (DT) can be maintained. That same 25 amp modules will produce over 8 times the amount of power as the 3 amp module. But 8 times the heat would need to pass thru that 25 amp module in order to produce that increase power. It is imperative that the (DT) be maintained. The module simply acts as a bridge. The larger the bridge area to length, the greater the flow of heat and resulting power output.

Our Low Temperature Modules (TEG2) are high amp modules with contacts that are soldered using SnSb solder on both sides. Although, the temperature of the solder has a 240°C melting point the solder begins to degrade at about 200°C . Therefore, we recommend the hot side stay below 190°C to allow for small temperature variations.

Our High Temperature Modules (TEG1) use flame spraying high temperature metal aluminum on the hot side and can withstand much higher temperatures in the range of 300° to 320°C hot side and have considerably larger tolerances when it comes to incidental higher temperature over shots. So much so, that you can expose the hot side to 340°C intermittently with very little module degradation. This technique is much more expensive to implement and therefore the cost is reflected in the price of the modules.

The third TEG Module series offered are the CMO described above and for more detailed specifications click CMO Spec's

Temperature of the hot side is probably the most critical component when considering Thermoelectric Generators. (DT) needs to be in the 100 C range to get a viable power output from each module.

In cases where all you need is a milliwatt of power, than temperature becomes less critical.

An Example:

If you want to produce a 100 watt TEG thermoelectric generator and the TEG's power output is based on a

DT of 100 C ( Hot side - Cold side)

Therefore:

1. You need at least 2000 watts of heat on the hot side given a 5% efficiency conversion to produce 100 watts of power.

2. To produce 100 watts of electrical power you are required to dissipate 1900 watts of heat on the cold side continuously as only 100 watts is being converted to power. The quicker and better you can remove the heat being transferred from the hot side via the modules the more power will be produced!

How critical is (DT)? The same 100 watt TEG above will produce:

~ 175 watts: If DT is increased to 150°C.

~ 225 watts: If DT is increased again to 200°C.

******As long as the modules are designed for high temperature (TEG1).******

Therefore,

1. (DT) is the most critical criteria of power generation

2. Heat flux, or flow of heat through the TEG Modules (Seebeck Effect) is second

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Revised 10/2012

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