How Do Solar Panels Work?

House with steeply sloped terra cotta roof covered in an array of solar panels with trees and shrubs surround it
Residential solar panels are growing in popularity and efficiency.

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Solar panels are devices that collect energy from the sun and convert it into electricity using photovoltaic cells. Through the photovoltaic effect, semiconductors create interactions between photons from the sun and electrons to produce electricity. Learn how the process works and what happens to the electricity generated.

From Solar Energy to Electricity: Step by Step

Each solar panel contains individual photovoltaic (PV) cells made of materials that can conduct electricity. This material is most often crystalline silicon, because of its availability, cost, and long lifespan. The structure of silicon makes it very efficient at conducting electricity.

These are the steps necessary for solar energy to become electricity:

  1. As the sunlight hits each PV cell, the photovoltaic effect is set into motion. The photons, or solar energy particles, that make up the light start to knock electrons loose from the semiconductive material.
  2. These electrons begin to flow toward the metal plates around the outside of the PV cell. Like the flow of water in a river, the electrons create an energy current.
  3. The energy current is in the form of direct current (DC) electricity. Most electricity that is used is in the form of alternating current (AC), so DC electricity has to travel through a wire to an inverter whose job is to change DC to AC electricity.
  4. Once the electrical current is changed into AC, it can be used to power electronics in a house or stored in batteries. In order for the electricity to be used, it must go through the home’s electrical system.

The Photovoltaic Effect

The process of turning sunlight into electricity is known as the photovoltaic (PV) effect. A layer of light-collecting PV cells covers the surface of a solar panel. A PV cell is made of semiconductive materials like silicon. Unlike metals which are great conductors of electricity, silicon semiconductors allow just enough electricity to flow through them.

Electric currents in solar panels are made by knocking an electron loose from an atom of silicon, which takes a lot of energy because silicon really wants to hold on to its electrons. Therefore, silicon cannot generate much of an electric current on its own. Scientists solved this problem by adding a negatively charged element like phosphorus to silicon. Each atom of phosphorus has an extra electron that it has no problem giving away, so more electrons can easily be knocked loose by sunlight. 

A diagram of the cross section of a solar cell showing yellow and red arrows representing sunlight hit the top of the cell. Some is absorbed and some is reflected. The layers also show the movement of electrons represented by circles with a negative sign and arrows pointing up and electron holes represented by circles with a positive sign and arrows pointing down. A circuit is connecting the negative and positive side with an arrow showing the flow of electric current out of the cell.

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This negatively charged, or N-type, silicon is then sandwiched together with a positively charged, or P-type layer of silicon. The P-type layer is made by adding positively charged boron atoms to the silicon. Each boron atom is “missing” an electron, and would love to get one from wherever it can. Putting sheets of these two materials together causes electrons from the N-type material to jump over to the P-type material. This creates an electric field, which then acts like a barrier that keeps electrons from easily moving through it.

When photons hit the N-type layer, they knock an electron loose. That free electron wants to get to the P-type layer, but it doesn’t have enough energy to make it through the electric field. Instead, it takes the path of least resistance. It flows through metal wires that make a connection from the N-type layer, around the outside of the PV cell, and back into the P-type layer. This movement of electrons creates electricity.

Where Does the Electricity Go?

If you’ve ever driven past a home with solar panels or considered getting them for your own house, you might be surprised to learn that most solar homes still need to get electricity from a power company. According to the Federal Trade Commission, a majority of the homes that have solar panels in the United States get about 40% of their electricity from their panels. That amount depends on factors like how many hours of direct sunlight your panels get and how big the system is.

When the sun is shining, solar panels convert sunlight to energy. If they produce more electricity than needed, that electricity is often sent back to the power grid and there is a credit on the electricity bill. This is known as "net metering." In a hybrid system, people install batteries with their solar panels and most excess electricity that’s generated by the panels can be stored there. Whatever is left over will be sent back to the grid.

In gross metering, all electricity that is produced by residential solar panels is immediately sent to the power grid. Residents then pull power back from the grid. However, solar panels don’t always produce electricity. If the sun isn’t shining, homeowners might need to tap into the power grid anyway to draw the electricity. Then they will be charged by the utility company for the energy consumed.  

View Article Sources
  1. "Solar Photovoltaic Cell Basics." United States Department of Energy.

  2. Ramilingam, Kakkan and Indulkar, Chandrasen. "Chapter Three- Solar Energy and Photovoltaic Technology." Distributed Generation Systems, 2017, pp. 69-147., doi:10.1016/B978-0-12-804208-3.00003-0

  3. "Solar Power for Your Home." Federal Trade Commission.

  4. Thakur, Jagruti and Chakraborty, Basab. "A Study of Feasible Smart Tariff Alternatives for Smart Grid Integrated Solar Panels in India." Energy, vol. 93, no. 1, 2015, pp. 963-975., doi:10.1016/j.energy.2015.09.100