Silicon the raw material used to produce solar photovoltaic. This is the second most abundant element on Earth.

There are three main types: monocrystalline, polycrystaline, amorphous...

Monocrystalline or "single crystal" Modules
The first generation of solar cells
great conversion rate (12-16%) (23% in laboratory conditions), but
expensive process of production
Another disadvantage - it takes a lot of energy to obtain pure crystals
Polycrystalline Modules
lower production costs, requiring less energy to produce
11-13% conversion efficiency (18% in the lab)
Amorphous
newer technology, lower production costs,
but unfortunately the lower efficiency (80-10%) (13% in the lab)                                         
This process can use very thin layers of amorphous Silica (From 0.3 to 1.0 microns compared to 500 microns for other types). Using vacuum spraying process, very thin layers can be applied to glass, metal or even flexible plastic surfaces. Amorphous Silicon commonly used in consumer goods such as calculators and watches.

Amorphous panels It takes about twice the surface to produce the same amount of electricity as monocrystalline or polycrystal and its output deteriorates quickly over time, given the shortcomings of amorfni modules better respond to diffuse the fluorescent light and work better at higher temperatures.

One solar cell always produces a voltage of about 0.5 volts, regardless of its size.
At higher voltages, you need to connect individual cells in series
More solar, more power, which is measured in ampere
We can also connect modules in parallel to increase current
                                     
The most common are solar panels for 12 volt systems. To achieve this voltage, 24 cells would be sufficient, but for charging the batteries and how to compensate for voltage photovoltaic panel usually contains between 28 and 40 cells for higher voltage. You do not really need to think about individual cells. All you need to know is that the cells within the modules are protected from moisture and connected to work as a whole.
Panels should produce more than 12 volts in order to recharge 12 volt batteries. Voltage can be compared with the pressure of water in the intestine. If the "pressure" of electrons is not large enough, electricity can not "break" until the rechargeable batteries.
Voltage can drop for several reasons:
At high temperatures. (As opposed to solar thermal energy for heating, photovoltaic for less when it's very hot! In tropical climates should be installed panels with a higher voltage.)
Long distribution wires to connect. It is important that the wiring between the panels and other parts of the installation to be as short as possible.
As the voltage can sporediti with the pressure of water in the intestine, the flow of energy or water or an electron in passing. Through a thin tube long will it take to meet water from the pool than to use thicker hose with the same pressure.