In its purest form, crystalline silicon is a poor conductor of electricity. This is because unlike in the case of good electrical conductors like copper, its atoms are too tightly grouped in a crystalline structure to be released freely. It thus needs to be mixed with atoms from other materials – for instance, phosphorous.
Phosphorous when mixed with silicon allows for more electricity to be carried and its electrons require a lot less energy to be released. This process is called `doping’. The resultant silicon `doped’ with phosphorous is called N-type (where `N’ stands for Negative). We all know that it takes two kinds of charges to create an electrical charge – negative and positive. As a result, the other part of the silicon is doped with boron to become the P type (where `P’ stands for Positive). When and N-type and P-type come in contact, an electrical filed is created.
There are two types of silicon: mono-crystalline and multi-crystalline. Mono-crystalline silicon is produced by slicing wafers of diameter 100 mm to 200 mm from high-purity single crystal ingots. Multi-crystalline silicon is made by sawing a cast block of silicon first into bars and then sliced into wafers.
• Each Crystalline Silicon cell is about 220 micron thick and can generate 0.5V.
• Cells are generally grouped in sets of 36 or 72 in number and usually soldered together in series to produce a module with an output to charge a 12V battery.
• These cells are hermetically sealed under toughened, high transmission glass to produce highly reliable, weather-resistant modules that may be warranted from 10 to 25 years depending upon the applications or customer requirements.