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There are a variety of different devices that use sunlight to generate power, but the basic way that a solar cell works is the same. In a photovoltaic (PV) cell, there are two layers of silicon, both of which are doped, or lightly mixed, with a certain element. Typically, one side is doped with boron and the other with arsenic.
Because of the way each element bonds to the silicon, the layer containing boron, called the n-type layer, has a surplus of free electrons. The other side, the p-type layer, has a deficit of electrons, called holes. The p-type layer and n-type layer are pressed closely against each other and linked by a wire connected to an external load. This creates a circuit in the solar cell.
When sunlight of the right energy level hits the n-type layer, which is on top, it excites some of the free electrons, which break loose from their natural state — pairs — and flow across the boundary between the layers to create a current. This only works if the two layers of the cell are pressed directly into each other. This is usually accomplished by fabricating both sides as part of the same process.
The current flows through the p-layer into the wire, which goes to the load, generally used to store electricity. Direct current (DC) is produced. If alternating current (AC) for household appliances is desired, the DC current is put through an alternator.
After flowing through the load, the current continues back into the n-layer, which is lacking in electrons in some areas due to the current. The process continues. A current is generated without any mechanical input. Unfortunately, the materials used to make solar cells can be quite expensive.
For protection, the top layer of the solar cell is covered with a glass plate affixed with transparent resin. The entire setup is called a p-n junction diode. More sophisticated cells use a series of p-n junction diodes.
The first solar cells were only 1% efficient. Today, commercial solar panels are between 5% and 15% efficient. There are currently millions of dollars going into research on improving these percentages.
Frequently Asked Questions
What is a solar cell and how does it generate electricity?
A solar cell, also known as a photovoltaic (PV) cell, converts sunlight directly into electricity through the photovoltaic effect. When photons from sunlight hit the solar cell, they knock electrons loose from atoms within the semiconductor material, typically silicon. This flow of electrons creates an electric current, which can be harnessed for power.
What materials are solar cells made of?
Solar cells are primarily made of silicon, a semiconductor that is abundant and has ideal electronic properties for PV applications. Silicon cells can be either monocrystalline, made from a single crystal, or polycrystalline, made from multiple crystals. Some thin-film solar cells use materials like cadmium telluride or copper indium gallium selenide.
How efficient are solar cells at converting sunlight into electricity?
The efficiency of solar cells varies depending on the material and technology used. As of 2023, typical commercial solar cells have efficiencies between 15% and 20%, according to the National Renewable Energy Laboratory (NREL). High-efficiency models can exceed 22%, while emerging technologies in the lab have demonstrated efficiencies over 40% under specific conditions.
Can solar cells produce electricity on cloudy days or at night?
Solar cells require sunlight to generate electricity, so their output decreases significantly on cloudy days and stops at night. However, they can still produce a small amount of power under diffuse light conditions. Energy storage systems can store excess energy generated during sunny periods for use when solar cells are not producing power.
What is the lifespan of a solar cell, and do they degrade over time?
Solar cells are designed to be long-lasting, with many manufacturers offering warranties of 25 years or more. Over time, solar cells do degrade, with an average annual degradation rate of about 0.5% for silicon PV cells, according to the International Energy Agency (IEA). This means after 25 years, many solar panels still operate at about 87.5% of their original efficiency.
How does the cost of solar cells compare to other forms of energy generation?
The cost of solar cells has plummeted over the past decades, making solar energy increasingly competitive with traditional energy sources. According to the International Renewable Energy Agency (IRENA), the cost of solar photovoltaics has dropped by 82% since 2010. This trend, combined with low operating costs and government incentives, makes solar a cost-effective option in many regions.