Solar Cell Electricity – How It Works
We have all seen solar cell electricity generators by now, blue or black panels dotted around, silently generating pollution free electricity. But how do they do it?
The key to understanding how they do it lies in the chemistry of the elements used. Each panel is an array of individual cells. Each cell generates a small voltage and together they produce a useable current.
Each cell uses what is called a p-n junction to convert sunlight to electricity. This does not mean much to most of us so a clear explanation is required.
Silicon is the main component of each cell. Silicon is special because it is what is called a semiconductor. This means that under certain conditions it will conduct electricity whereas at other times it will not. For our purposes, we will assume it is conducting, ie allowing electrons to move through it.
The silicon in solar cells is doped which means has specific impurities added. Silicon is either doped with another element that has a shortage of electrons (called p-doped for positive or has an excess electrons (called n-doped for negative).
A solar cell consists of a wedge of p-silicon and a wedge of n-silicon. In between these wedges is a one-way gateway, a barrier that allows electrons to go from the n- to the p- wedge, but not back the other way.
That creates what is called a p-n junction.
Now we have a flow of electrons that move naturally from the n- silicon to the p-silicon. This is natural; it’s just the charges balanging out. But…
HOW DOES THIS GENERATE ELECTRICITY?
The p-silicon layer of the solar cell does not have a strong grip on the electrons that move into it from the n-silicon layer. When sunlight falls on the p-layer, the electrons break free of the layer and begin to move. As the electrons cannot go back through the one way barrier, the only way they can move is through the circuit the cell is connected to. That is why the solar cell will generate a current if it is attached to a circuit.
If a solar cell is NOT attached to a circuit, there is no opportunity for electron flow and all it will do in the sunlight is heat up.
Roger.
For more details on the operation of solar cells, the chemistry involved, types of cells and much more, visit http://www.green-planet-solar-energy.com. This site gives clear explanations of the major concepts behind the operation of solar cells.
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