Specifications

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