Renewable Energy: Solar Photovoltaic (PV)

PV basics:

1. Solar electric systems are simple to operate and have no moving parts. 

2. PV cells operate on the physical principle that electric current will flow between two semiconductors with different electrical properties when they are put in contact with each other and exposed to light. 

3. A collection of these PV cells constitutes a PV panel, or module. PV modules, because of their electrical properties, produce direct rather than alternating current (AC). Direct current (DC) is electric current that flows in a single direction. 

4. In the simplest systems, DC produced by PV modules is used directly. In applications where AC is necessary, an inverter can be added to the system to convert the DC to AC

PV construction:

1. PV cells are “sandwiches” of silicon, the second most abundant material in the world. Ninety-nine percent of today’s solar cells are made of silicon.

2. One layer of silicon is treated with a substance to create an excess of electrons. This becomes the negative or “N” layer. 

3. The other layer is treated to create a deficiency of electrons, and becomes the positive or “P” layer. 

4. Assembled together with conductors, the arrangement becomes a light-sensitive NP junction semiconductor. It’s called a semiconductor, because, unlike a wire, the unit conducts in only one direction; from negative to positive. 

5. When exposed to sunlight (or other intense light source), the voltage is about 0,5 Volts DC, and the potential current flow (amps) is proportional to the light energy (photons). In any PV, the voltage is nearly constant, and the current is proportional to the size of the PV and the intensity of the light.

6. Photovoltaic cells are made from hyper pure silicon that is precisely doped with other materials. The hyper pure silicon substrates used to make PV cells are very expensive.