  Thermoelectric power generators are used to convert heat into electricity.
Like any other heat engine, the performance of a thermoelectric generator
increases as the temperature difference on the sides increases. It is generally
assumed that as more heat is forced through the thermoelectric legs, their
performance increases. Therefore, insulations are typically used to minimize
the heat losses and to confine the heat transport through the thermoelectric
legs. In this paper we show that to some extend it is beneficial to purposely
open heat loss channels in order to establish a larger temperature gradient and
therefore to increase the overall efficiency and achieve larger electric power
output. We define a modified Biot number (Bi) as an indicator of requirements
for sidewall insulation. We show that if Bi<1, cooling from sidewalls increases
the efficiency, while for Bi>1, it lowers the conversion efficiency.
