Specifications

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