How Solar Electric Works
Electrical current is produced when electrons move through an electrical field. In the case of solar electric photovoltaic systems this process occurs in the photovoltaic cell, diagrammed below. A simplified way to think about a PV cell is that it works like an LED in reverse. With an LED, you put electricity in and light comes out, with a PV cell, you put light in and electricity comes out. This is simplified, but not too far from reality- the physical construction of the two devices is quite similar.


The main components of a photovoltaic cell are two layers of doped (impure) semiconductive silicon. The N-Layer is blended with phosphorous, making it rich in electrons and negatively charged. The P-Layer is blended with boron, making it electron-poor and leaving positively-charged holes in the P-Layer's crystalline silicone structure where electrons can fit. At the junction of the N and P-Layers a mixing occurs creating an electrically neutral barrier in between them. This barrier makes it difficult for the N-Layer's extra electrons to jump over to fill the holes in the P-Layer and creates a balanced electrical field. If electrons from the N-Layer were to travel to the P-Layer it would imbalance the electrical neutrality and the electrons would seek a path to flow back accross the electrical field in order to restore the balance.

A conductive metal layer is attached to the top of the N-Layer and bottom of the P-Layer, and these conductive layers are wired to an electrical load, creating a closed circuit and a current path from the P-Layer to the N-Layer. The metal layer on top is a mesh lattice in order to allow sunlight through.

Whenever energy is added to silicone it can cause some electrons to break from their crystalline structure and leave their atoms, creating a hole. These electrons then wander around randomly until they find another hole to fall back into. In the case of a photovoltaic cell, energy from the sun hits the electron-rich N-Layer in the form of light photons and causes electrons to break free. If they are close enough to the P-Layer these electrons can jump across the electrical field and fill the P-Layer's holes. The resulting electrical imbalance encourages these electrons to flow back to the N-Layer along our current path, generating electricity.
In order to be used in your home, the PV-generated DC eletricity must be converted to AC. This job is performed by an inverter, like the one pictured right.

For more information on how solar electric systems work, please look at our class schedule, or contact us with your questions. 		PV Inverter
Electrical inverter and meters

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