How Thermoelectric Power Generation Works
The basic concept of thermoelectric Generators TEG’s (Seebeck effect) is outlined below to explain to the Layman and also Engineers who are not familiar with the technology. We have been manufacturing TEG Power Generators for the last 10 years. A full 70-80% of the interest comes from persons whom have only minimal knowledge of the technology. Based on the requests for pricing and products available, interest in this field has exploded in the last three years. Thermoelectric modules work on two different principal :
- Peltier Effect: This effect introduce power to the module with a resultant cooling of one side and heating of the other these type of modules are low amp typically in the 6 amp range and are designed for low temperature exposure of NO MORE THAN 100°C to 110°C hot side. Higher temperature exposure will cause the module to either break apart or the soldered couples to melt from high heat making them poor choices for power generation!
- Seebeck Effect: This effect is created by temperature differential across the module from heating one side and cooling the other side by moving the heat flux away as fast as it moves through the module . You cannot describe a peltier module and say it produced power as many laymen do in the BLOGS. Please describe a Seebeck effect module as a power generator and a Peltier module as a cooling module.
Thermoelectric Generators using the Seebeck Effect work on a temperature differentials. The greater the differential (DT) of the hot side less the cold side, the greater the amount of power (Watts) will be produced. Two critical factors dictate power output :
- The amount of heat flux that can successfully move through the module.
- The temperature of the hot side less the temperature of the cold side Delta Temperature (DT).
Great effort must be placed on 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 as it moves thru the module array 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 then any other method of cooling and produce significantly more net additional power than the pump consumes.
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 600°C hot side range and are commercially available but very expensive!
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 constructed into a module, efficiency drops to 3 to 4% because of thermal and electrical impedance. No other semiconductor material can perform as well as BiTe as far as efficiency is concerned. Other material such as PbTe are used but are far less efficient, and must be used at significantly higher temperatures (450°C- 600°C) hot side and are not commercially available!
Power output based on (DT) is very predictable and well documented, 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.
You can have a 25 amp * module the same size typically 40 mm x 40 mm as a 3 amp module * in module size, but length or height of the pellet or element determines how much heat can pass thru the module. The ratio of the length compared the actual width x depth determines the overall amperage of the module. As the height of the pellet is shortened ability of heat flux to pass more quickly thru the module allows for 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 watts will need to pass thru that 25 amp module in order to produce that power. It is imperative that a 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 AgTn solder on both sides. Although, the temperature of the solder has a 240°C melting point the solder begins to degrade at about 190-200°C . Therefore we recommend the hot side stay below 190C 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°C hot side and have considerably larger tolerances when it comes to incidental higher temperature over shouts. So much so that you can expose the hot side to 320°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.
Temperature of the hot side is probably the most critical component when considering Thermoelectric Generators. (DT) Delta T needs to be in the 100°C range to get a viable power output from each modules.
In cases where all is needed is a milliwatt temperature becomes less critical.
To finalize we will include an example:
If you want to produce a 100 watt TEG thermoelectric generator. The TEG’s size is based on a DT of 100 C (Hot side - Cold side)
- Need at least 2000 watts of heat on the hot side given a 5% efficiency conversion.
- Require to dissipate 1900 watts of heat on the cold side continuously as only 100 watts is being converted to power.
- How critical is DT. The same 100 watt TEG.
- If DT temperature is increase to 150°C your output would increase to roughly 170 watts.
- If DT increased again to 200°C your power output would increase again to roughly 260 watts.
Therefore, DT is the most critical criteria of power generation along with the movement of heat thru the TEG Modules (Seebeck Effect).
* Amp modules are for cooling and heating not representative of power output.