Specifications
12
battery packs generally cost between $60 and $150 each, weigh about 1 pound each,
have a storage capacity up to 12800mAh, and come in 7.4V and 11.1V variants. They
are designed to be deep cycled many times and are readily available at hobby shops
and on the internet. One major downfall of lithium based batteries is that extreme care
must be taken when charging lithium based batteries, as there is a risk of explosion if
charging procedures listed by the manufacturer are not strictly followed. Due to the fact
that these battery packs do not come in the voltage or storage capacity we need, we
would again have to use multiple battery packs.
4.1.2 Maximum Power Point Tracking
There are many factors that can and will decrease the power generation efficiency of
the systems wind turbine and solar panels. Each of these factors are constantly
changing, making it impossible to make a one-time adjustment or correction for these
power generation losses. This is where maximum power point tracking (MPPT) comes
in handy. The goal of MPPT is to electronically maximize the power generation
efficiency at any given conditions.
There are many operational conditions that can contribute to the power generation
losses. Perhaps the largest and most important is the voltage at the battery. When
using a conventional charger to re-charge a depleted battery, the generator is in effect
connected directly to the battery. This forces the generator to run at the current voltage
of the battery, which is undesirable because this voltage is unlikely to coincide with the
voltage at which the generator produces its maximum power. The figure below shows
an I-V curve for a typical 75W PV panel.
Figure 4 - I-V and P-V Curve of a Typical 75W PV Panel
Permission Pending
As you can see, at 12V, the panel only produces about 53W. If the panel were allowed
to operate at its optimal voltage of about 17V, it would generate 75W of power. This is
exactly the purpose of an MPPT charge controller. It will allow the generator to operate
at the voltage which maximized power generation, and then turns that extra power
generated into more current at the same 12V. For example, say this 75W solar panel
outputs 75W at 4.4A and 17V under full sunlight. If it is forced to run at 12V under full