Solar Electric (Photovoltaic) Systems
Solar electric systems are reliable, efficient, and economical. They increase the value of your home or business, and provide clean solar energy for decades. Tax credits and incentives pay half or more of the cost of installing the system in many areas. Mr. Sun designs and sells systems across the globe, and installs systems in Oregon and Washington. For questions or a consultation, please contact us.
How the Sun Produces Energy
Harnessing solar energy to produce electricity is a relatively simple process. Solar panels absorb sunlight and produce direct current (DC) electricity. An inverter turns the DC electricity into AC (alternating current) electricity. The AC electricity passes through your breaker panel to provide electricity to your home.
When more solar electricity is produced than you can use, the excess power flows back through your meter to the power lines (or grid). When this happens, you receive a credit from your utility company. Sometimes this is described as “spinning your meter backwards.”
The Science of Photovoltaics
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) semi-conductive 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 across 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 silicon 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 resultingelectrical 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 electricity must be converted to AC. This job is performed by an inverter.
Residential roof-mounted PV system
Beaverton Library commercial PV System