Environmental Engineering Reference
In-Depth Information
Figure 4.31
Solar Module with Resistive Load at Different
Operating Conditions
If the current
I
through the resistance is set equal to the current of the solar
cell [see Equation (4.34)], the common voltage and the operation point can be
found by solving the equation for the voltage
V
. However, numerical methods
are needed to obtain the solution.
For a
graphical estimation of the operating point
, I-V characteristics of the
resistance and solar cell characteristics are drawn into the same diagram. The
intersection of both characteristics then provides the operating point.
Figure 4.31 illustrates that the operating point of a solar module varies
strongly with the operating conditions. Here, the module is operated close to
the MPP at an irradiance of 400 W/m
2
and a temperature of 25°C. At other
irradiances and temperatures, the module is operated sub-optimally and the
output power is much less than the possible maximum power. Voltage and
power at the resistive load vary significantly.
DC-DC converter
The power output of the solar module can be increased if a DC (direct
current)-DC converter is connected between solar generator and load as
shown in Figure 4.32.
The
converter
generates a voltage at the load that is different from that of
the solar generator. Taking up the previous resistance example, Figure 4.33
shows that the power output of the module increases at higher irradiances if
the solar generator is operated at a constant voltage. The power output can be
increased even more if the solar generator voltage varies with temperature, i.e.
if the voltage increases with falling temperatures.
Good DC-DC converters have efficiencies of more than 90 per cent. Only
a small part of the generated power is dissipated as heat. Input power
P
1
and
