How does a solar module work?

Introduction


Solar modules work based on Photoelectric effect and in the simplest words, light energy conversion to electricity is photoelectric effect. There are different applications for photoelectric effect, but all are same basis.
We want to take you back to school to teach you about the photoelectric effect in a practical way. It’s not rocket science! Basically, we will find atomic model of matter and we will see there are some tiny particles that their actions and reactions provide energy.

Matter atomic model


Basically, scientists try to explain nature phenomenon by pattern that could be repeated in many cases explanation. Science explain quality of phenomenon and answer first curious minds question as (how?) and then quantity of phenomenon by answering second question as (how much?). Therefore, scientific models through theories could be helpful because they can explain nature phenomenon repeatedly like urban rules and they are valuable how long they are working.

There are three major scales in science that scientists are dealing with. Huge as stars, ordinary as common life and tiny as atoms. Unfortunately, there is not a unique theory for all of the scales explanation (however they are related together in many ways), then there are different theories in different scales. Now, tiny or atomic scale time.

Democritus in ancient times describe the smallest portion of matter as Atom and he thought it is unit of matter like a brick as unit of building but more investigations in recent centuries showed something should be inside of the unit and then scientists tried to understand Atom system. In words, they understood Atom is a system that some particles inside are working together!

Finally, they named major particles as Electron, Proton and Neutron. On the other hand, they found out Electron has negative and Proton has positive charge.


Electrons turning around the nucleus on a certain distances that are called levels and Protons and Neutrons located in center of the Atom. Now, number of levels in an Atom of a specific element beside number of Electrons on its last level could be element ID. This is basic rule of major elements arrangement in periodic table (columns 1-2 and 13-18).

Therefore, rows show levels and column in major elements show number of last level Electrons. As an example, Si has 3 levels (2,8,4) and 4 Electrons at last level.


Then, at column number 18 maximum number of Electrons at last level could be 8. Elements less than 4 Electrons on last level are conductors like metals and more than 4 are insulator. Then, elements by 4 Electrons at last level should be Semiconductor.

Now, there is a question. If Electrons in an Atom located specifically, is manipulation possible?

The answer is positive but there should be external Energy source like heat, light or others. Then, last level Electrons can get energy and make more distance from nucleolus.

Second question. Can we achieve Energy by manipulation like a power plant?

The answer is positive what expected in solar cells. When Electrons are stimulated by an external source of energy as light, heat or misc. Electrons go further but when source remove, refer to Energy Conservation Law (Energy is fixed in the world. In words, it is not created or it is not destroyed. Only it can convert to the types of Energy as Electricity, Magnetism, Heat …) Electrons pay back all Energy they achieved and go back to initial level.

In short, Electrons agitation by light source, change its position and when it comes back pay back all Energy achieved. Remember steam power plant that fuel (Chemical Energy) burns and make super heat vapor then vapor runs Turbine and Turbine turns Generator what produce Electricity.


Photovoltaic Cell

If there is a closed loop system, Electricity generating by Photovoltaic cell according to the above principles is possible. Light Photons agitate Electrons and they will turn in the circuit.


Now, deeper investigation shows how it works. First N type and P type of semiconductor is important. Basically, there in nature there should be different potential and then Energy transferring possibility. This is same as water on a Ball on a sloped surface.

Of course, there are different types of potential and then there could be different physical systems. In semiconductors charges play potential role. Base of common semiconductors are Silicon but there must be potential and closed loop to generate Electricity. Then, Silicon is dopped to Phosphorus and achieve 1 more Electron as N type semiconductor and negatively charged. On the other hand, Silicon is dopped to Boron with 1 Electron less as P type and positively charged and then loop components are ready.


When N and P type semiconductors connect make Depletion region and it is expected whole negative and positive charges neutralize each other. If it was correct, it would be no chance to make a closed loop and then Energy generator because they would be in short circuit.

Fortunately, nature is perfect. Negative and positive charges attract each other on depletion zone but not whole of the charges have the possibility. Then, some negative and positive charges neutralize each other on depletion zone and make a barrier that does not permit rest of charges neutralize each other.


Photovoltaic under sun irradiance agitates negative and positive Charges that coupled and neutralized in depletion region and push each of them back to their initial region and if sun irradiance (external Energy source) remove, they will come back to each other in depletion zone. But there a lots of sun irradiance Energy and we can use.


Agitated charges wait to find a way back to neutral condition and then there is a potential. Now closed loop time. If semiconductors connect from the other sides, there will be a chance to neutralize each them and provide us Electricity.


When a couple of charge is agitated by sun irradiance and push back to their initial region and then flow through the circuit (closed loop) the other charges in N and P semiconductors find each other on depletion zone and scenario will be repeated.

AFSHIN BAKHTIARI

AE Solar Senior Engineer



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