  Accurate measurement of efficiency for thermoelectric generator (TEG) is of
great importance for materials research and development. Approximately all the
parameters of a material are temperature dependent, so we can't directly apply
the $\eta_\text{max}$ formula for efficiency calculation in the large
temperature range. To overcome that problem, we tried to calculate the
efficiency of TEG by dividing large working temperature range into a number of
small temperature difference. The aim is to make temperature dependent
parameter to be constant for that small temperature range. Using maximum
individual efficiency of each segment obtained by $\eta_\text{max}$ in the
equation of $\eta_\text{overall}$, which gives overall efficiency. The
$\eta_\text{overall}$ of TEG using $Bi_2Te_3$ and $TAGS$ as thermoelectric
materials come out to be $7.1\%$ and $8.94\%$, respectively, which is close to
experimental results. For the high-temperature region, we have used $SiGe$
material in TEG and found out $\eta_\text{overall}=3.5\%$. The cumulative
efficiency obtained by keeping one end temperature fixed with another end
varying can be applied in real life application, i.e. automobile sector. The
present work provides a simple way for the design engineers to calculate the
efficiency of TEG by using the temperature dependent materials parameters like
thermal conductivity, electrical conductivity, and Seebeck coefficient on which
$z\bar{T}$ depends.
