Monthly Archives: November 2012

How Solar PV Really Works

Solar PV produces electric current actually in a similar way as batteries albeit much more intelligently as neither any components wear out nor is there any poisonous substance involved (like acid in batteries, which also wears out through use). Solar cells, while also degrading as there is no Perpetuum Mobile in our environment, last a lot longer than those “stone age” or “state-of-the-Arch” energy generation technologies called batteries — PV cells usually last for 25 years with at least 80% of their original capacity — and can produce energy for 35+ years before they become really “sucked-out”.

Over 95% of today’s solar cells consist of the semiconductor material silicon. Semiconductors are materials whose electrical conductivity increases under light or heat.

For the production of solar cells, the silicon is doped, which means that other chemical elements are added to it, either creating an electron surplus (n-conductive layer) or an electron shortage (p-conductive layer). This means that the doped areas become charged, and if two differently doped semiconductor areas convene, a so-called space charge region is created at the boundary layer (p-n junction), meaning there is a difference in electrical potential across the boundary.

This is what makes them somewhat related to batteries which use acid and two different metals to create the same effect for a limited time — until the battery becomes dis-charched or “empty”.

In order to achieve the desired effect in solar cells, the initial silicon material is normally p-doped lightly and a thin surface layer heavily n-doped. This creates the space charge region required for separating the charge carriers, known as electrons (negative charge) and holes (positive charge).
Different than batteries, solar cells do not need any added substances (like acid) in order to work, but the entire process is induced by just exposing them to sunlight (or even just daylight, i e it also works on an overcast day).

When the energy from the sunlight hits the semiconductor material, the photons transfer their energy to the material, and the electrons and holes achieve a higher energy state, allowing them to move. The negatively charged electrons will move to the positively charged region, and the positively charged holes move to the negatively charged region. This process repeats itself, and the net flow of charge across the boundary is the electricity that is generated by that cell! To generate usable amounts of electricity, cells are arranged into modules, which are in turn arranged into your PV array.

The front contact is a metallic grid, enabling the sunlight to penetrate into silicon between the contacts. Moreover, solar cells are also coated with an anti-reflection coating, serving to protect the cell and to reduce energy losses resulting from reflection. This layer gives the solar cells their typical bluish black appearance.

The basic output is then converted to voltages and currents in accordance with specifications needed using rectifiers, inverters or micro inverters, and similar electrical equipment.