Peltier Question: size and rating

[charmrus]

Im looking to purchase some Peltier juntions for power generation experiments and am a bit confused by what I should get.  They are listed by thier wattage and size.  The wattage thats listed is for what it consumes for use as a cooling device.  Im seeing wattage differences for same sized package also.
Basically what Im in need of is how would I figure which or what  attribute I should be using for comparision for getting the most bang for the buck.  Would 2 30mm pcs be better then 1 60mm pc.  Is there a "potential" density to the different sizes/wattage?

I realize that the temp. difference from one side to the other makes a difference but how would I compute that into wattage/size?

Thank you for any help given.

[sushimoto]

Hi,

here is a list of types available.

This one is sorted by Qmax (W)
http://www.dr.neumann-peltier.de/peltier-chips-sortierung-q-max.pdf

hope it helps.

[crazyoldfart]

I have several different values, 80 watt , 120 watt and 250 watt , all with voltages around 18 volts for maximum and 4, 6 and 8 amp respectively. they all need a temperature differential of 100 degrees to reach 2/3 rds their rated value. 100 degrees differential is pretty hard to achieve in everyday life. but you can drive a couple of high intensity LED's with a difference of only 40 degrees or so. with  a single 80 watt device and a temperature differential of 40 degrees , I was able to get around 5 volts @ almost 2 amps without voltage drop. On a much larger scale this could work very well, in my opinion.