Electric Bikes - TE-bike (Thermoelectrical bike)
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05-08-09, 09:02 AM
People all know that the most efficient way to store energy in the form of a liquid fuel but the best traction engines are electric, so why not build a vehicle with a fuel tank and a small burner that will heat to a battery of Peltier cells, generating electricity and feeding an electric motor system? What do you think?
05-08-09, 09:34 AM
Sounds hot and heavy.
I think it's hard to tell whether it will work, or work well, without trying it.
Give it a try if you have the time!
It's not clear to me what the efficiency of peltier cells is, but I think it might be far worse than the efficiency of a combustion engine. I've read that commercially available peltier cells are less efficient for refrigeration than standard (compressor based) refrigerators, at least.
05-08-09, 07:57 PM
This is the concept behind fuel cells. Only instead of "burning" the fuel, they use catalytic oxidization to react the fuel with air to directly generate electric current. Some of them are also extremely hot in operation; I believe 600 degrees F is common. Fuel cells are a more efficient method of harnessing the chemical to electrical energy conversion.
To actually "burn" the fuel to generate heat to excite the peltier cell may be far less efficient than heating water to drive a steam turbine generator.
Here's a link to a number of discussions and articles on applications of peltier cells for energy recovery from heat generating sources. I haven't read them all so I am not sure what there findings are on energy conversion efficiency:
05-08-09, 08:11 PM
I think a quick search of the internet, and you could find your own answer.
But since you didn't, the answer is that peltier cells are very, very inefficient at producing electric energy.
05-12-09, 02:28 PM
If you can invent a device that converts low grade heat (e.g. relatively small temperature differences) to electricity efficiently, you will be very, very rich. It would be the ultimate co-generation device.
05-12-09, 03:54 PM
Maybe go the other way.
Build a box or tube with the cells mounted "hot" side to outside ambient, and the "cold" side inside, where you introduce a measured amount of liquid helium into the chamber at a set rate from your insulated helium container, for the proper temperature gradient to work the cells.
Direct the cold air "waste" coming off the chamber towards your body = air conditioning as you ride.:)
05-13-09, 10:48 AM
Peltier junctions (besides not being very efficient) also have the problem of thermal fatigue, and this occurs if they are used as heating/cooling elements, or the other way--as thermo-electric cells.
The temperature difference between the two sides causes stress in the semiconductor junctions that join the two sides. (the side plates are ceramic to minimize the expansion problems, but this still occurs) To maximize the lifetime of the cells, the best method is to "start" and "stop" them v-e-e-e-r-r-r-y slowly. You're not supposed to hook them straight to a power source with a regular switch; the ideal controller circuit setup takes at least an hour (or more) to switch them from zero% to 100%, and it should also go just as slow when powering them down.
Peltier junctions are a nifty concept, but they have a couple drawbacks if you are going to go building anything around them.
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