Custom Thermoelectric - Peltier

# TEG FAQ

Q. How efficient is a TEG?
A. Current BiTe based TEGs have a maximum efficiency of about 7%. This efficiency is defined as the amount of electrical energy produced divided by the amount of heat moving through the TEG. This efficiency is very dependant on the temperatures provided to the TEG. For 6% efficiency, the TEG needs about 270°C of temperature difference between the hot and cold faces. Temperature differences less than 270C will equate to lower efficiencies.

Q. What is the maximum delta T that can be used with a TEG?
A. The maximum temperature for our TEGs is 320C. The minimum temperature is -60C. Therfore, the maximum delta T is 380C. Using cold side Temperatures below 0C will yield lower and lower additional power gains as temperature decreases.

Q. What is the low temperature limit of a TEG?
A. The low level temperature limit is -85C. Be careful down at these temperatures as the TEG materials will become very brittle and easily damaged if not handled carefully.

Q. If I have a cold side of -40C and a Hot side of 30C, will it generate the same amount of power as between 30C and 100C?
A. Although the delta T is the same (70C), the power produced by the colder temperatures will be less. This is because the semiconductor material we use in the TEGs has a peak efficiency around 150C. As temperatures get further away from this peak, the efficiency drops therefore producing less power. This efficiency drops significantly below 0C.

Q. My heat source is too hot for the TEG. What can I do?
A. There are several things you can do;

1. If applicable, adjust the fuel rate or fuel to air ratio that is generating the heat in the first place. Many times, the same tasks can be accomplished with lower temperatures.

2. Place the TEGs further “downstream” of the actual heat source where temperatures should be lower.

3. Attenuate the heat by passing it either through a heat shedding design or by passing it through materials that conduct less or a combination of both.

1. A heat shedding sink would be a heat path that allows a portion of the heat to be transferred to the ambient air or another sink before the rest of the heat arrives at the TEG. See attached pictures.

2. Materials that conduct less (have a lower thermal conductivity). Countless options available. Typically aluminum and copper are used as excellent conductors of heat with thermal conductivities of around 200 W/mK and 390 W/mK respectively. Instead, use steel to “slow” the heat transfer down so that the final temperature at the hot side of the TEG is acceptable. Steel has a thermal conductivity of around 15 W/mK. Many other materials mostly consisting of metals and ceramics can be used in varying thicknesses to accomplish the same task. You can also use more than one attenuating material. Remember to make sure the materials can withstand the temperatures you will be subjecting them to.

4. Keep in mind that heat sources are usually finite. As you start to cover surfaces with TEGs the temperature of the hot side will drop because you are dissipating a portion of the heat with each TEG. For example; a fuel source may produce 1000 watts of heat in a small stove. If you measured the outside of the stove, its temperature may indicate 700C. Placing 1 TEG on the surface with its included cold side heat sink could absorb as much as 200-250 watts of that heat. Two TEGs would absorb 400 to 500 watts of the heat. If you measured the outside of the stove with two TEGs mounted, you will find the temperature to be considerably less.