How solar power works ?

 

This is how solar power works

INTRODUCTION

Let's start in the heart of a single solar cell particle of light which we call photons. Photons enter the solar cell and are absorbed by available electrons. Exciting the electrons to a higher energy level. Excited electrons travel out of the cell and through an external circuit where they exchange this newly gained energy to do work.

The spent electrons return to the cell ready to absorb more photons. The supply of extra electrons and the force that turns a solar cell into a sort of electron pump or motor comes from joining two special types of silicon material together to generate a reaction. Where they meet is called a p n junction.

P-N JUNCTION

In making a P-N junction a silicon atom has 14 total electrons at various energy levels or shells with four in its outermost shell. Electrons in the outer shell are used for bonding with other atoms. Stable atoms generally favor eight electrons in the outer shell so, silicon atoms share electrons when bonding to meet that number we need extra electrons to do work. It's possible to add small amounts of impurities to silicon that changes its molecular structure this is called doping.

N-type silicon n meaning negative Is doped with phosphorus.  Phosphorus has five electrons in its outer shell where four are used to bond with neighboring silicon atoms leaving an extra free electron.

P-type silicon p for positive is doped with boron which has three electrons in its outer shell leaving an extra open space or hole when bonding with silicon. When an electron leaves an open spot other electrons naturally fill it in sequence. For our purposes, it's convenient to track the open space or hole as it moves. In the standard atom model electrons are represented as having a negative charge for convenience in our model we can think of holes as having a positive charge and track that space as it moves through the cell. 

THE SPACE CHARGE REGION

The space charge region forms at the junction where P and N-type silicon meet. When these doped silicon types are layered unequal electrons and available spaces or holes naturally seek to recombine across the junction attempting to equalize. However just because doped silicon creates this intentional electron imbalance doesn't mean the full atoms can simply merge across the gap. Natural forces keep the rest of the atom's structure rigidly in place and intact.

Atoms generally have the same number of orbiting electrons as protons in the nucleus as well as neutrons and doped silicon does as well. P-type silicon has an extra electron but also an extra proton.

Electrons just naturally move around a lot easier than protons. When these electrons wiggle free and try to equalize. The imbalance creates special electrically charged atoms with unequal electrons to protons called ions. Again even though these atoms are now in the state. They're fixed in the silicon structure and won't move. These opposing positively and negatively charged ions eventually prevent further electron and hole diffusion giving the space charge region a precisely designed width strength and so on.

An electrical field exists in the space charge region. Excited electrons are attracted and swept in the positive direction and holds in the negative direction. As such electrons can't go backward and must travel an external circuit to recombine with open space instead of simply doing. So, inside of the cell and wasting their newly gained photon energy as heat.

SUPPORTING STRUCTURES

let's look at other parts of the solar cell that support the core process.

Anti-reflective material

 Polished silicon alone wastes a lot of light by reflection so, an anti-reflective coating is added or improved efficiency. There are many types of anti-reflective material in this example. A grid of microscopic inverted pyramids directs and captures light at many different angles giving it maximum opportunity to enter the cell and remain longer inside photons can be absorbed in any point throughout the cell.

For example;-  short wavelength high energy blue light is absorbed readily near the surface while long wavelength lower energy red light can require more depth or time inside the cell to be absorbed.

 FRONT CONTACT

 metallic fingers are screen printed and bonded to the top of the cell they're designed for optimal charge collection but minimal shading.

 PASSIVATION LAYER

A special coating over the rear surface helps prevent early recombination of electrons and holes and gives light another chance to bounce through the cell and be absorbed.

ALUMINUM REAR CONTACT

A rear aluminum layer completes the electrical circuit electrical contacts protrude through the passivation layer.

MODULE

ENCAPSULANT

 The encapsulant is an adhesive that seals around the solar cells protecting them from harmful outside elements and keeping them firmly in place. A common encapsulate material called EVA ethyl vinyl acetate is stable under high temperatures and UV exposure and is also a transparent glass. Top layer a thick layer of low iron glass protects the cell from outside conditions and provides structural strength while also allowing maximum light passage. Low iron reduces the reflective impurities that give the normal glass a faintly greenish blue tint back sheet. Polyvinyl fluoride film or Tedlar forms a thin near impenetrable protective back layer to prevent damage to sensitive internal parts during installation and day-to-day function.