= Solution
A <thermoelectric generator> uses the <Seebeck effect>: a maintained <temperature> difference across suitable conductors produces an open-circuit electromotive <force>. For a pair of legs,
$$
V_{\rm oc}=\int_{T_c}^{T_h}(S_p-S_n)\,dT
\simeq S_{\rm eff}(T_h-T_c)
$$
when the effective <Seebeck coefficient> is approximately constant. Repeated p- and n-type legs are usually connected electrically in series and thermally in parallel.
\b[Connecting a load lets part of the heat flowing from the hot side to the cold side become electrical <power>.] Both a heat source and a cold-side heat-removal path are necessary: a uniformly warm device with no maintained <temperature> difference supplies no sustained output. Internal electrical resistance, heat leakage, contact losses and the finite <temperature> difference reduce the harvested <power>; the converter is a heat engine rather than a source of energy from <temperature> alone.
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