Peltier on car manifold to generate electric?

[Other-Power]

I had a thought and I am sure that others have had it to.

Why not use a Peltier device on the exhaust manifold to nab some power.
I have seen a 400 watt unit on eBay. 

I have no practical experience of these devices but i believe the devices are only 10% efficient when driven in revers

Am i missing something here, all seems to good to be true?

Thanks

Jon

[Philip R]

The car would be more efficient if driven forward, using the gears. Driving in reverse stops you clocking miles on the odometer. .

The US Department of Energy are researching this at one of their national Labs, Argonne, I believe.

More seriously, a large peltier device needs a good heat sink and a high differential temperature to drive it.(More suited to petrol than diesel).  If you drive a turbo diesel, the exhaust turbine has extracted some thermal energy from it. Also a mass penalty, lugging it around. However, for motorway cruising at constant speed, could be very useful. Maybe more beneficial to traction applications.

On the topic of excess mass. The topic of engine and exhaust heat recovery storage has come up again in one of the plumbing trade mags, for the purpose of unloading it and keeping the house warm. surely would be very range limited, due to its mass, size and heat output of the engine.
PhilipR

[Other-Power]

More seriously, a large peltier device needs a good heat sink and a high differential temperature to drive it.(More suited to petrol than diesel).  If you drive a turbo diesel, the exhaust turbine has extracted some thermal energy from it. Also a mass penalty, lugging it around. However, for motorway cruising at constant speed, could be very useful. Maybe more beneficial to traction applications.

On the topic of excess mass. The topic of engine and exhaust heat recovery storage has come up again in one of the plumbing trade mags, for the purpose of unloading it and keeping the house warm. surely would be very range limited, due to its mass, size and heat output of the engine.
PhilipR

I was thinkng to mount any unit up stream of the turbo, my car has a fix vane turbo so not the most efficent device, plenty of spare thermal heat.  Also, I belive the deisels have higher burn temps then petrols, this being why they are more efficent in the first place, so more chance of waste heat.

It would be very easy to make a large heat sink on a metal car for the peltier device using the cars body work.

I was thinking that 40 watts would power my radio and the ECU not much power but over time.

Cheers

Jon

[Baz]

Car alternators are terribly inefficient so a few more pence spent there would do far more.

[Ivan]

Yes, it's a very good idea. If you put enough of them on the exhaust, you'd be able to produce as much as the alternator. Cooling is actually quite easy when you're whizzing through the air at high speed - so easier than it might first seem. If you can generate enough to get rid of the alternator, you are reducing engine load by a significant percentage, so the car will become slightly more efficient as a result. An american company has done this with truck engines, generating 1kW from the exhaust. They saw a significant reduction in their fuel bills as a result.

The efficiency is rather less than you would think. Typical TEGs (thermoElectric Generators) work at around 1% efficiency, although 2% is possible with perfect design. There are 5% efficient products proposed, but not on the market, to my knowledge.

[spaces]

If you really want to minimize the alternator wasting precious fuel, first make sure you have a good battery which holds its charge well (lots of energy is required topping up a slightly 'sad' one for the first 15 minutes of driving), then fit a switch into the exciter circuit. Being able to switch off the alternator when you don't need it makes a surprising difference - although you don't want one of those cars with lights which are always on, obviously. This is what many racing cars do, often the circuit is opened when your right foot goes down hard - the thinking being that there is less drag when it would most count, ie on a part throttle.

An old fashioned diesel which requires no electricity other than for lights and fan motor would be an ideal candidate, not the sort of car which requires 1000x more computing power than Apollo 11 required to get to the moon. Additionally, a dog-clutch assembly could be used to actually stop the thing turning, which also uses more power than you'd think, even when there is no load. Removing the belt altogether would be even better, but this is unlikely to be easy on moderns.

Something I mentioned on a CFL thread was that while everybody was getting keen on throwing away filament bulbs in the house (where the waste energy heats the house so central heating works less hard) on a car the only purpose waste heat ever serves with a car's lighting is to melt away falling snow. Given the inefficiency of the alternator which in turn is driven by an engine which is 30-something% efficient and the resistance in wiring, connectors and switches then to produce almost 160W continously (two headlamps, four sidelamps) must take the best part of 1kW - supplied by petrol or diesel which is taxed at nearly 70% on your taxed income. For a car which does many shorter journeys (<10 miles?) in winter it would be more sensible to buy another battery which is either installed in parallel in the car (then both recharged from the grid regularly) or swapped every other day when fully charged and uncouple the alternator until a long journey looms. A 20W PV panel on the car roof might even suffice. Mpg typically drops by 4 or 5 in winter, which isn't all electrical load but even so...

[Other-Power]

I think there is some mileage in trying to reduce alternator loading.


one thing that I have thought is that fans speeds are controlled by a resistor so even on low, the fan is pulling near full power.

I think I want to study how much power my car will use getting to and from work.

I have a Wattson meter that I will put on my car and see how much power I use.

It would be interesting to see if anyone has modded there alternator arrangement or done a study on their car load?

Cheers

Jonathan

[spaces]

Just read the mention of engine and exhaust heat recovery storage. Could you provide a link to this please, PhilipR? To tap into the cooling system is easy, storage of 150 litres of hot water slightly less so but hardly impossible and making use of downpipe heat would be possible too, if a little more involved. I also like the idea of storing coolant in a vacuum flask to keep it hot overnight, as Saab did many years before the Toyota Prius/Pious demonstrated it was possible.

On a large turbo diesel vehicle with a 100kW engine (134hp) you could say that on an average longer journey 50kW is the average output from the engine. So if the engine is 30% efficient (theoretically more but not in practice) over that journey (kinetic energy output)  - then 35kW will be wasted as heat. Say that 40% (off the top of my head, does anyone know measurements?) of the waste heat is recovered by the coolant (the rest exhaust and radiation and convection) then that leaves 14kW which can be used from the cooling system. Call it 10kW after losses from the pipework and insulated tank.

I reckon about 7kWh are required to raise 150 litres of water by 40C, ignoring losses. So in just under an hour water a 150 litre tank would be raised from 10C to 50C. I think bothering with extracting heat from the exhaust would be unecessary complication at first. Anyone fancy putting this into practice? Something liek a Tam105 pump (as many veg oilers and biodiesel makers use) would transfer the 150 litres sufficiently quickly from the car tank to a house tank. A 15kW coil from an old copper cylinder inside the car tank could act as heat exchanger for the vehicle's coolant.
Instead of sending the engine coolant through the radiator as the thermostat opens it would be easy to divert it to the storage tank coil, with a thermometer in the tank a manual (or automatic) bypass to the radiator could be easily plumbed. The tank would have to be outside the vehicle and well insulated as well as baffled, something like a 4x4 would have plenty of room underneath without chopping into the body. But I can imagine the pause on the end of the phone if you bother to try to explain to the insurance company you are heating your house from your car, while driving...  

Smaller tanks for smaller cars, but I like the idea of a hot bath for 'free' after a long journey. Since veg oil powers the fleet, it's as green a bathe as anyone this side of a hot spring would experience!

[Other-Power]

Use a phase change material like petroleum based wax to reduce size and wight for same number of units.

[spaces]

How much more efficient would that be though, by the time water had then been reheated from it? How much more efficient is it theoretically?

I prefer to have a tank of 50-60C water under the car than a tank of hot wax. Less hazardous and not introducing another potential contaminant in the case of failure/accident.

[spaces]

I started a new topic about heat recovery from motor vehicles: http://www.navitron.org.uk/forum/index.php/topic,15103.0.html - it seemed rather off-topic here.

[Ivan]

Use a phase change material like petroleum based wax to reduce size and wight for same number of units.

Run through the figures. Sadly, you'll find there's almost no difference between any phase change material and the heat capacity of water. The only positive difference in favour of the phase-change material, is that the same amount of heat energy can be stored at a lower temperature (but ultimately, the maximum amount of heatenergy storage available per kg of material is very similar).