[Daox]

A little over a year ago, I showed you guys how to use TEGs to create power with your exhaust heat. To make a long story short, you can totally do it but its really expensive. I calculated over $1100 to generate 210W.

This time around, I'd like to see what we can do with using TEGs and engine coolant heat.

First, lets start at the beginning again with a little recap.





What is a TEG / peltier / Seebeck generator?

Wikipedia says:

A thermoelectric generator (TEG), also called a Seebeck generator, is a solid state device that converts heat flux (temperature differences) directly into electrical energy through a phenomenon called the Seebeck effect (a form of thermoelectric effect). Thermoelectric generators function like heat engines, but are less bulky and have no moving parts. However, TEGs are typically more expensive and less efficient.

This time around, we are looking at using engine coolant as our heat source. This should allow us to use TEGs that don't have to withstand as high of temperatures, and thus reduce cost. However, less temperature differential also means less power output. Will it be worth it? Lets continue on to find out.





Alright, lets find some TEGs!

We could start by finding some TEGs at the normal online shops like ebay and amazon. However, we already know price is a major concern from our last go about with TEGs. So, I'm going to go for the cheapest thing I can find that will work. For that, I checked out amazon. On amazon, I basically found a TEG that I think would work. It is 40mm x 40mm, and it is rated for higher than 100C operating temperatures.

Gimiton SP1848-27145 TEC 40x40mm

Specifications:

Material: Ceramic / Bismuth Telluride
Color: White
Parametric model: SP1848-27145
Temperature(C): 150 degree
20°C difference in temperature : Open-circuit voltage 0.97V ,Generator current :225MA ;
40°C difference in temperature : Open-circuit voltage 1.8V ,Generator current :368MA ;
60°C difference in temperature : Open-circuit voltage 2.4V ,Generator current :469MA ;
80°C difference in temperature : Open-circuit voltage 3.6V ,Generator current :558MA ;
100°C difference in temperature : Open-circuit voltage 4.8V ,Generator current :669MA ;
The above information is for reference only ,it will loses some current when in actual use .
Module weight: 25g / 0.89oz
Module size: 4 * 4 * 0.4cm / 1.6 * 1.6 * 0.2inch (L * W * H)

By looking at this, we can get an idea of how much the one TEG module will generate. We know coolant temps are around 190F when the engine is warmed up. I'm going to use 70F as an ambient temperature. Obviously it will get better or worse depending on the environment. Now, lets convert to units the rest of the world uses.

190F = 88C
70F = 21C

So, we have a temperature difference of 67C. Lets round down to be conservative. That means our TEG will put out 2.4V and 469 milliamps, right? Wrong. Open circuit readings put no load on the TEG. As you put a load on it, the voltage will drop. The same thing happens with solar panels, and batteries. The amperage reading I believe we should be able to take as fact because there must be a load for there to be amperage. So, by my previous experience with TEGs, we can take the open circuit voltage and divide by 2 to get an idea of what we'll actually see while its in use. Thus, we will get 1.2V and 469 mA, or .56W per TEG module.





How many TEGs do you need?

This all depends on how much power you want to generate. A typical small alternator puts out a max of 80A, or around 1100W. So, if you wanted to generate that kind of power you would need 1100 / .56 = 1964 TEGs. Kind of ridiculous, right? How about we look to achieve something more reasonable like reduce the alternator's load by 10A or 135W. That means we will need 135 / .56 = 241 TEGs. Still seems pretty silly. That is over 4 square feet of TEGs to mount and install somewhere!

And, this is really where the TEGs creating power with coolant falls apart. You're talking a ridiculous number of TEGs to create any sort of real power. 10A won't even power a normal car going down the road.



Cost

Let us look at the cost aspect real quickly. The SP1848 TEGs currently cost just under $2 each shipped from China. If we get 240 we pay $480 for ~134W of generating power. We still need to mount them to something, run coolant to that something, and put a heatsink on the other side. So there is plenty of cost there as well. Just the TEGs themselves cost $3.58 per watt. That is actually an improvement over the exhaust powered TEGs which came in at $5.23 per watt.

For kickers, lets also compare this to solar power. Solar panels can be had for under $2 per watt these days. The wonderful thing about solar is you can generate power no matter if you are driving or not. As long as your solar panel is in the sun, you're generating power. This is a huge advantage (unless its overcast of course) as your solar panel can chug along all day long vs just the 30 minutes you're driving to work. Of course this assumes you're running a deep cycle battery, but I digress. Solar is still cheaper, and still almost nobody uses it.



Conclusion

So, can it be done? Certainly. Is it practical? Sadly, no. Not even close. It seems TEG efficiency will need to increase and/or price must decrease a good amount before this would be viable as a DIY project.