VW Golf with exhaust thermoelectric power: +5% MPG
 

http://ecomodder.com/imgs/2009-Rowe-VW-TE.jpg

Search the forums here and you'll find more than a couple of threads about using waste heat from the exhaust to generate electricity.

Here's a working example:

Source: [ZTnews] VW & BMW Putting TEGs Automobiles | International Thermoelectric Society via Green Car Congress: Volkswagen Shows Thermoelectric Generator for Waste Heat Recovery

Sounds like they need a larger deep cycle battery so they can capture and use more of the energy. 600W is 50A @ 12V. Thats not too far from the max output of a normal alternator. I sure as heck know that a car doesn't use 50A just running down the highway, yet they only get 30% of electricity production from it?

I wonder what's the cost of installing a gizmo like that? Maybe they could show up in the aftermarket, or just DIY.

The real problem is that thermoelectric devices just aren't real efficient, so only a small part of the exhaust heat gets converted.

A closed loop water to steam system would be much more efficient in my opinion.

How much heavier it would be? Well, thats the problem...

Heavier and more complicated. The plus side of the thermoelectric approach is it's (probably) solid state & dead reliable.

Tim: you're right, their figures don't add up. 600w production in highway use, yet they're claiming that offsets 30% of power needs. Which means the car needs 2000 watts to drive down the highway? Don't think so. Their figures need explaining.

Maybe the clue is "600 W(e)". What's (e)? I haven't seen that before.

only thing that i can see is that 600 watts is fully warmed up and that it might take a while for it to warm up, even tho it really shouldn't, either that or it might be an estimation of power out put in all weather conditions as it's output might be more in sub freezing weather and lower in hot weather.

I don't buy it. It may get 600 Watts running flat out in first gear on the highway but typical driving I doubt it. I also have serious doubts about the 5% better mileage. If the thermal electric generator supplies 1/3 the electrical power that would mean that the alternator saps 15% off your mileage. Its bunk and bogus claims.

This is just sensationalistic marketing hype.

Actually if I recall, from MetroMPG's and other's posts, the alternator disconnect has been showing about a ten percent gain in overall FE. Please correct me if I'm wrong. The TE generators do work but as has been stated are highly inefficient-- unless a newer technology has been released, they are generally between 3-5% efficient.
Doesn't matter what gear the vehicle is in, just the temperature differential between the "cold" side and the "hot " side of the junction.

Here is a link to one manufacturer of these junctions.
Hi-Z Technology, Inc.

Here is a link to a study performed using their devices a few years ago.
http://www.hi-z.com/papers/ICT%20200...ing(China).pdf

The main problem(just like solar panels) is the hi cost. Apparently the prices are decreasing if the devices are actually going to be placed in cars.

JJ

"Doesn't matter what gear the vehicle is in, just the temperature differential between the "cold" side and the "hot " side of the junction."

Does this mean thermoelectric exhaust generators as these, work better in cold climates?

There has been a lot of talk here recently re retaining, reusing wasted heat...all these proposed/suggested systems do in fact work, but cost is high in retrofit mode...

Probably by the time we get it right everyone will be going electric?

Just another scheme to separate the rubes from their money.

You'd be able to give your vehicle the "basjoos treatment" for less money and you know the "basjoos treatment" works.

MetroMPG's car is so optimized he could go on a diet and loose 5 pounds and get a 10% improvement. His results in magnitude of improvement are not typical gains for an average car.
Driving in first at high rpm is the best way to heat up the exhaust. The car is burning the most fuel it can in a given time and the engine is under the least load, hence the pistons are extracting the least power from the combustion gases and the hotter the exhaust gases.

Actually winding a car up in neutral at full throttle would be better for heating the exhaust but you would probably throw a rod. :rolleyes:

Probably not a whole lot unless that cold air is directed to the TE junction. We're talking about temperature differentials of a few hundred degrees C in general(once the car is warmed up).

Alright, I'll give you that one, but I sure wouldn't want to be driving around in first gear all day :)
JJ

The thing is that the output in city driving is probably a lot less due to lower average power output and a small difference in temperature. The 600W is probably max output on the highway with the average output around 100-200W.
The thing is alternator energy efficiency, like ICE energy efficiency, isn't linear AFAIK, which is why we're seeing things like dual-speed alternators, and the like. If this thermoelectric system can replace lightly loaded and inefficient alternator operation, then it could very well increase fuel efficiency by ~5% since the other 5% is when the alt is more heavily loaded and more efficient. It also depends on the manufacturer's alt operating parameters, which may be more efficient for a compact car that's focusing on efficiency light a Metro or Civic CX/VX as opposed to a car that focuses more on other stuff.

What happened to this guys idea.
Johnson Electro Mechanical Systems

Anyway, There are already Chinese 250 watt per sq. foot thermjunctions for sale although they need a temp difference of about 400C & 25C to operate near that (never bought one, maybe they lie)

I agree with roflwaffle...
I would not doubt a 5% mileage gain, many alternators are not real efficient across their range; couple the belt and frictional losses that should be childs play to get a 5% increase with smarter alternator management.

Okay here is the smell test on the 5% mileage improvement.

600W = 0.805HP

If it takes less than 17HP to operate a car the claims might be valid.

Note: This system only supplements the alternator and doesn't remove it.

Keep in mind the alternator is only roughly 50% efficient. So, in order to generate 600W, you need to generate 1.6hp.

Nice work VW.
It always amazes me how these brilliant engineers pull a rabbit out of the hat every few years. Vehicles have come such a long way.

Good catch. So that would raise the bar to 34 HP. However it forces the alternator to operate in its lower efficiency range which would reduce the net savings.

I have often wondered why the alternator isn't just cycled on when it would be at its most efficient range then cycled off when it won't be. Sure your battery would experience some small discharge/recharge cycles but I would think the efficiency gain would be enough to justify slightly lower battery life.

Perhaps its time for battery management on cars?

For a car that size at an average speed of ~50mph, assuming city and highway travel, it would only need about half that in terms of power, probably less with more city driving and more with more highway driving. The bonus is that the output of this device scales with engine output.

I wouldn't compare watts to HP directly considering HP on an ICE is peak and doesnt translate directly to fuel consumption. Its a very rough comparison at best.

TEC CPU cooler
 

Here's a product that uses TEC. It' is the reverse of what we are trying to demonstrate here, but it does run on 12V, which is handy for vehicles. Can this be reversed to generate electricity rather than consume it?

Freezone Elite CPU Chiller

actually 3-5% is quite efficient considering that the ICE itself is only 20%. i calculated the possible energy efficiency for a steam engine generator from waste heat and it was in the same ball park.

The answer is yes.
JJ

TECs are terribly inefficient, but in quantity I don't see why they wouldn't work, any area where your temperature delta exceeds roughly 90 degrees will supply enough voltage under load to make a TEC worth it's salt in a car. But from testing your talking the best efficiencies of MAYBE 3-5 percent...most of it is lost to internal resistance...they however work better at colder temperatures, this is something that might be beneficial in the liquid cooling system...just food for thought.