How Do Solar Panels Work?
Photovoltaic (PV) solar turns the sun’s light energy into electrical energy that can power our lives.
Solar is booming across the country. Texan homeowners are opting for solar to lower their electric costs and gain access to reliable clean energy. Despite growing popularity, it may not be clear how solar power allows you to turn on the lights. So how do solar panels work, and what makes it such a virtuous power source?
What Is Electricity?
First, the basics.
Electricity comes from the flow of electrons. Electrons are the negatively-charged particles that orbit around the nucleus of an atom. The nucleus is made up of neutrons and positively-charged particles called protons. When excited enough to jump to a higher energy level, electrons can potentially break free from their atoms.
Free electrons can be drawn to another positively-charged particle with which to bond. This attraction creates a flow of electrons from one location to another, creating electrical current.
How Does The Sun Provide Energy?
The sun produces a ton of energy. Enough energy in fact, that ninety minutes of sunlight has the potential to power the entire world for a year. The sun delivers energy in the form of waves — from short ultraviolet waves to longer infrared waves.
Visible light waves (the wavelength that humans can see) emitted by the sun are the optimal length to be absorbed by solar panel cells and used to create electrical current.
When we think of solar today, we envision solar panels atop a roof. This technology is called photovoltaic (PV) solar because it uses sunlight — or visible light waves — to generate electricity. There are other solar technologies — such as solar thermal or concentrated solar power — that work differently from PV solar. Since the overwhelming majority of homeowners getting solar are looking at PV solar, we’ll focus on that technology.
How do Solar Panels Produce Energy?
Solar systems are made up of panels, and each panel contains many solar cells. To understand how solar works, we have to start at the solar cell.
Solar cells have a number of layers. The top glass layer is transparent, which protects the rest of the cell while still allowing light to pass through. The next layer is an anti-reflection coating which helps optimize light absorption and reduce the amount light that’s reflected away.
The next layers are where the real work takes place. These are the semi-conductive silicon layers. A semiconductor is a material that is not generally conductive but can become so under certain conditions. In this case, the silicon layers become conductive when exposed to sunlight.
A solar cell brings together two different layers of semi-conductive silicon in order to form voltage, or an electrical imbalance. Voltage is important so that free electrons have a direction in which to flow. To create this charge imbalance, silicon layers are ‘doped’ with small amounts of other elements.
The top silicon layer is ‘doped’ with an element such as phosphorus. Phosphorus has one more electron than silicon in its highest energy level. This extra electron is not participating in any bond, so this layer is referred to as negative, or N-type, because of the extra electrons.
The bottom silicon layer is ‘doped’ with an element like boron, which has one less electron than silicon in its highest energy level. Therefore, when bonding to neighboring silicon atoms, there is a vacancy where an electron could go. This vacancy can be seen as a positive hole, and for that reason it’s referred to as the positive, or P-type silicon.
By themselves, neither the N-type nor the P-type silicon hold a charge. When the layers are placed together, however, the extra phosphorus electrons flow to occupy the positive holes from the boron. This leaves the top layer with less electrons and a positive charge, and the bottom layer with an excess of electrons and a negative charge. This charge imbalance creates voltage.
When enough light from the sun penetrates the solar cell, silicon can gain sufficient energy to knock loose an electron. Since there is voltage across the two silicon layers, the free electrons are drawn to the N-type silicon whereas the remaining positively-charged silicon is attracted to the P-type layer.
The moving electrons are collected by the metallic grid-structure that rests on top of the N-type silicon. From there, the electrons flow through an external circuit to generate electricity.
Many Solar Cells Make Up A Solar System
PV solar panels use sunlight to generate an electron flow within solar panel cells which is used to create electricity.
A solar cell can only produce several watts of electricity. Considering many appliances require upwards of 1,000 watts to operate, powering a house requires many solar cells working together. Solar cells are housed together in solar panels, with solar panels containing 32 or more individual solar cells. The average residential solar system includes approximately 20 solar panels.
Of course, the exact number of solar panels needed by a home depends on many factors, such as home energy use, home location, and the local utility rate plans.
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