It can be seen
from Fig. 3(a) that the optimal current of the hybrid system at the
local maximum power output point (MPP) is almost the same as that of the PV module at the MPP in the hybrid system, but is different
from that of the single PV module at the MPP. The reason is that
the efficiency of the TEG is smaller than 3% for a given RL2=R, so that
the MPP of the hybrid system is mainly given by the PV module in the
system. If the load resistance RL2 is optimized, the optimal current of
the hybrid system at the MPP will be different from that of the PV
module at the MPP. Fig. 3(b) shows clearly that there exists an optimal
current Iopt at which the efficiency of the hybrid system attains
its local maximum value gmax. Obviously, gmax is an important
parameter, because it determines an upper bound for the efficiency
of the photovoltaic–thermoelectric hybrid system. It is worthwhile
to note that the current at the maximum efficiency, Iopt, is another
important parameter of the solar-driven hybrid system.
It can be found from Eq. (27) that when the efficiency of a solardriven
photovoltaic–thermoelectric hybrid system attains its maximum
for a given value of GAPV , the power output also attains the
maximum and can be written as