Well, the spec sheet for this unit **broken link removed** says...
Properties of the 13 Watt Module, HZ-14
Physical Properties Value Tolerance
Width & Length 2.95" (7.5 cm) ±0.01 (0.25)
Thickness
(Special Order) 0.2" (0.508) ±0.01 (0.25)
±0.002 (0.05)
Weight 115 grams ±3 grams
Compressive Yield Stress 10 ksi (70 MPa) minimum
Number of active couples 71 couples ----
Thermal Properties
Design Hot Side Temperature 230°C (450°F) ±10 (20)
Design Cold Side Temperature 30°C (85°F) ±5 (10)
Maximum Continuous Temperature 250°C (480°F) ----
Minimum Continuous Temperature none ----
Maximum Intermittent Temperature 400°C (750°F) ----
Thermal Conductivity* 0.024 W/cm*K +0.001
Heat Flux* 9.54 W/sqcm ±0.5
Electrical Properties (as a generator)*
Power** 19 Watts minimum
Load Voltage 2.38 Volts ±0.1
Internal Resistance 0.3 Ohm ±0.05
Current 8 Amps ±1
Open Circuit Voltage 5.0 Volts ±0.3
Efficiency 4.5 % minimum
* At Design Temperatures
** At Matched Load, refer to the graphs for properties at various operating temperatures and conditions.
Again, if they weren't so expensive at $209 each, I'd get some to play with
Lousy efficiency though