Specifications

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sunlight, it still only puts out 4.4A, which makes or 12V x 4.4A = 53W. This results in
22W of un-generated power. If the PV panel were allowed to operate at 17V and
generate its maximum of 75W, 75W/12V = 6.25 would be delivered to the battery. This
is much better than the 4.4A before, and obviously will result in a quicker recharge of
the battery. Again, this is all assuming full sunlight. The I-V curve of PV panels changes
for each amount of sunlight it receives. The figure below shows multiple I-V curves for a
certain PV panel at different sunlight levels.
Figure 5 - I-V Curve of a PV Panel at Various Sunlight Levels
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So how is it that an MPPT charge controller works, you ask? As you can imagine, there
isn‟t a simple answer. There are multiple methods for tracking and adjusting for the
maximum power point. To simplify this complex answer, only the most popular methods
will be discussed here. In order to “track” the maximum power point (MPP), an algorithm
is used to sample dP/dV (the dotted line in figure showing the I-V and P-V cure of the
75W PV panel). If the slope is positive, the algorithm knows it must adjust the voltage
further in the same direction. This process is repeated until the slope is found to be
negative, at which point the algorithm adjusts the voltage in the opposite direction. This
can result in oscillations around the MPP, but will keep the voltage much closer to that
of the MPP than a traditional charge controller can. To adjust the voltage that the solar
panel is operating at, a high frequency DC to DC converter is employed. Most of today‟s
MPPT charge controllers are 93 97% efficient and yield a 10 - 40% power gain in the
winter and 10 - 15% power gain in the summer.
Another issue to consider is that when using multiple generators, they are likely not all
in the same state, and therefore don‟t all have the same maximum power point. This
applies to arrays of solar panels, wind generators, and combinations of the two. When
using multiple different types of solar panels, they will have different properties and
therefore different MPP‟s, even when they are under the same conditions. Even multiple
PV panels that are exactly the same can have different MPP‟s, due to manufacturing