SOLAR PANEL ITS PHYSICS

THE PHYSICS OF SOLAR PANEL

The founding father of modern-day electronics is Professor Max Planck (Max Karl Ernst Ludwig Planck). He was only 42 years old and was professor of theoretical physics at the university of Berlin. On December 13 of 1900 he presented his theoretical explanation of quanta of light at a meeting of the PHYSIKALISCHE GESELLSCHAFT in Berlin. The day before presenting his epoch-making paper Planck was telling his son Erwin while taking a walk in his garden “son, tomorrow I am going to shake the very foundation of physics”. Plank had his fear of telling the world that light can also travel in the form of energy packets which he called quanta and came out with world famous equation

E = h.f

E = energy

h = Planck’s universal constant

f = frequency of light or electromagnetic spectrum

This audacious departure from the classical physics’ contention that light travels in the form of waves won him the Nobel Prize in 1918.

Albert Einstein taking the cue from Planck’s quantum theory went a step further and argued that a photon (light quantum) with sufficient energy can dislodge electron from metal surface. When this prediction was mathematically proved by Einstein and called it as PHOTO ELECTRIC EFFECT fetched him a Nobel Prize in 1921. Photo electric effect is the heart of the working of solar panel. Photoelectric effect obviously tells you that photon from the sun light can produce electricity. But how? Here comes the ingenious unfolding of the human mind and brain. It all started with the serendipitous observation

In 1940 RUSSEL OHL discovered P-N junction and photovoltaics effects in silicone that led to the development of junction transistors and solar cells in the mid-1930s Russel Ohl an electrochemist at the Bell Telephone laboratories in New Jersey USA was investigation the use of silicon rectifiers as radar detectors. (A rectifier is an electronic system which makes alternating current inti direct current). He found that increasing the purity of silicon helped to improve their detection ability. On 23rd February 1940 he tested a small silicon slab which yielded surprising results. He observed that different parts of the crystal yielded different electrical results. Ohl observed that different parts of crystal contained different types of impurities. One impurity the element phosphorus, yielded a slight excess of electrons in the sample while the other boron led to a slight deficiency later to be recognizes as “holes”. Ohl called the Yielded the regions with excess electrons n-type (negative) the regions with electron deficient with “holes” as p-type (positive). The surface where these two regions met became known as P-N JUNCTION. Light striking this junction stimulated electrons to flow from the N side to the P side resulting in an electric current. Ohl DICOVERED ULTIMATELY THE PHOTOVOLTAIC EFFECT THAT POWERS SOLAR CELLS. The P-N junction became the most common form rectifier used in the electronic industry and has since become a fundamental building block in the design of semiconductor devices.

This serendipitous discovery of 1940 by Russel Ohl. was utilized in 1948 by William Shockley, Walter H. Brattain and John Bardeen to invent transistors which led the three to win the Nobel Prize in 1956.

In the meanwhile, attempts by Jack Kilby of Texas Instruments and Robert Noyce of Fairchild Semiconductors to miniaturize transistors led to the invention of integrated circuits which are popularly known today as MICROCHIPS. Kilby and Noyce were awarded the Nobel Prize for this feat in the year 2000.

Robert Noyce left Fairchild Semiconductors to establish INTEL the famous chip manufacturing company. Noyce passed away in the year 1990 and Nobel Prize is not awarded posthumously

Russell Shoemaker Ohl is recognized for patenting the modern solar cell. Ohl was a notable semiconductor research worker whose serendipitous observation on silicone crystals led to the inventions of transistors and microchips.

Now let us look into the physics and working of solar cells. Solar cell panels have become a very essential instrument to beat electricity crunch. This is amply demonstrated by the roof top solar panels coming up in USA, especially in Texas. The photograph I present here is a roof top panel of my neigbour in Denver Colorado.

Solar panels are made up of a series of silicone crystalline cells sandwiched between a front glass plate and a rear polymer plastic back sheet supported within an aluminum frame

The principles and working of solar panel rests on three powerful pillars, Max Planck’s quantum theory, Albert Einstein’s photo electric theory and P-N junction concept emanated out of Bell Telephone Laboratories by Russell Ohl. To make working solar cell the thin crystalline silicon wafers are treated with elements boron (B) and phosphorus (P). This treatment in electronic language is called DOPING. Doping literally means poisoning. Yes, it is true we are poisoning pure silicone with phosphorus and boron, making silicone a semiconductor. For the passage of electricity materials are divided into three categories. The conductors like metals the semiconductors like our doped silicone and insulators like rubber wood and plastics. To understand doping we have to invoke Bhors model of atomic structure. The atomic structure of silicone is like this. It has 14 electrons at three energy levels.

The three energy levels of silicon atom

When it is doped with phosphorus it looks like this. See the red arrow showing loosely held extra electron

Boron doped silicon atom. No extra electron so it called HOLE FROM BORON ATOM. It is positive (+) in nature.

FORMATION OF P-N JUNCTION

The credit for the concept and creation of P-N junction goes to Russell Ohl of the Bell telephone Labs USA. P-N junction is the heart of solar cell. When we put the N type and P type silicone in contact with each other, something interesting and useful happens. The point where the two types meet THE JUNCTION electrons from the N type layer diffuse over into the P type layer leaving behind an area with a slight positive charge in the N type layer. The reverse happens in the P type layer, the Holes diffuse into the N type layer leaving behind a slight negative charge in a region of the P type layer. This creates an electric field. This is called a DEPLETION LAYER. Depletion layer in this context is a misnomer. It suggests the charges are depleted because using coulomb’s law the charges are used up forming a strong electric field

Free electron and hole

pair formed by photon

Light travels in packets of energy (Max Planck’s quanta), The generation of electric current happens inside the depletion zone of the PN junction. The depletion zone is the area around the P-N junction where the electron from the N type silicon, have diffused into the holes of P type silicon. When a photon of light is absorbed by the N type silicon it will DISLODGE the loosely held electron, creating a FREE ELECTRON AND A HOLE PAIR (Einstein’s photoelectric effect). The free electron and hole pair have sufficient energy to jump out of the depletion zone. If a wire is connected from the cathode (N type silicon) to the anode (P type silicon) electrons which reached the N layer will flow through the wire. The electron is attracted to the positive charge of the P Type silicon and travels through the external load creating a flow of electric current in the form of DC current This current can be used to charge the battery in your solar powered calculator or solar powered wrist watch, if the solar cells are inside the calculator or wrist watch. If the solar panels are on roof top the DC current thus produced can be conducted to an inverter installed inside the house. The inverter converts the DC current produced to AC current to run the domestic equipment.

Professor K.A.Balasubramanian

Ph.D. (IARI-New Delhi), Ph.D. (Imperial College-London), D.I.C. (Imperial College -London)

Denver, Colorado