Solar panels convert sunlight into electricity through the photovoltaic effect. Photons in sunlight transfer energy to electrons inside a semiconductor, usually silicon. The electrons move through an external circuit, producing direct-current electricity. An inverter then changes that direct current into alternating current for household appliances.
The process has 5 main stages:
How Solar Panels Work at a Glance
| Stage | What happens | Result |
|---|---|---|
| 1. Sunlight reaches the panel | Photons strike photovoltaic cells | Light energy enters the cell |
| 2. Silicon absorbs photons | Photons transfer energy to electrons | Electrons become mobile |
| 3. Charges separate | An electric field separates electrons and holes | A voltage develops |
| 4. Electrons flow | Electrons move through metal contacts and an external circuit | Direct-current electricity is produced |
| 5. The inverter changes the current | The inverter converts DC electricity into AC electricity | Electricity can power a home or enter the grid |
1. Sunlight Reaches Photovoltaic Cells
A solar panel contains many photovoltaic cells. Each cell uses a semiconductor, most commonly crystalline silicon.
Sunlight consists of particles called photons. Each photon carries an amount of energy based on its wavelength. When photons reach a photovoltaic cell, some reflect off the surface, some pass through the material, and others are absorbed.
2. Silicon Absorbs the Sunlight's Energy
When silicon absorbs a photon with enough energy, the photon transfers that energy to an electron.
The added energy frees the electron from its usual position in the material. This creates two charge carriers:
- A mobile electron with a negative charge
- A positively charged hole, which represents the electron's former position
The movement of these charge carriers allows the solar cell to produce electricity.
3. The Solar Cell Separates the Charges
A solar cell contains two differently treated layers of semiconductor material. These layers are commonly called the p-type and n-type layers. The boundary between them forms a p-n junction.
The p-n junction creates an internal electric field. The field pushes electrons in one direction and holes in the other, which reduces the chance that they will immediately recombine. This separation creates a voltage across the cell.
Without the electric field, many electrons and holes would recombine before they could produce useful electricity.
4. Electrons Flow Through an External Circuit
Metal contacts on the front and back of the cell collect the separated charges.
When the contacts connect to an external circuit, electrons move through that circuit from one side of the cell to the other. This movement creates an electric current.
A solar cell produces:
- Voltage, created by separated electrical charges
- Current, created by moving electrons
- Power, produced when voltage and current work together
One photovoltaic cell produces a small amount of power, so solar panels connect many cells to create a useful electrical output.
5. Solar Panels Produce Direct Current
Photovoltaic cells produce direct current, or DC electricity. With direct current, electrical charge moves in one direction.
Most household appliances and the utility grid use alternating current, or AC electricity. An inverter converts the panel's DC electricity into AC electricity.
A typical home solar system may include:
- Solar panels that generate DC electricity
- An inverter that converts DC electricity into AC electricity
- Electrical wiring and safety equipment
- A utility meter or grid connection
- Optional batteries for storing electricity
The U.S. Department of Energy identifies the inverter as the component that converts the DC electricity from solar modules into the AC electricity used by household appliances.
What Happens to the Electricity After the Inverter?
The converted AC electricity can be:
- Used immediately: The home uses the electricity as the panels generate it.
- Stored: A battery stores surplus electricity for later use.
- Sent to the grid: Excess electricity flows through the utility connection, subject to local rules and system design.
When the panels do not produce enough electricity, such as at night, the home can draw power from a battery or the utility grid.
Why Do Solar Panels Not Convert All Sunlight Into Electricity?
Solar cells cannot use every photon equally well. Some sunlight reflects away, some passes through the cell, and some of the absorbed energy becomes heat instead of electricity.
Common sources of energy loss include:
- Wavelength limitations: Photons with too little energy may pass through the cell, while excess photon energy can become heat.
- Reflection: Some sunlight never enters the semiconductor.
- Recombination: Electrons and holes can recombine before reaching the electrical contacts.
- Electrical resistance: Wires and other materials resist the movement of charge.
- Temperature: Higher operating temperatures generally reduce photovoltaic performance.
- Shading and dirt: Obstructions reduce the light reaching the cells.
Solar-cell efficiency measures the percentage of incoming solar energy converted into usable electrical power.
Do Solar Panels Need Direct, Bright Sunshine?
No. Solar panels can produce electricity from diffuse sunlight, so they can still generate power in overcast conditions. Weaker sunlight provides less energy, though, so panels generally produce less electricity than they would under clear, strong sunlight.
Photovoltaic panels do not generate electricity at night because there is no sunlight. A battery or grid connection is needed to provide power after sunset.
Solar Photovoltaic Panels Versus Solar Thermal Systems
Solar photovoltaic panels convert sunlight directly into electricity through semiconductor cells.
Solar thermal systems use mirrors or collectors to capture sunlight as heat. That heat can produce steam or drive another process that generates electricity. Solar thermal systems are different from the photovoltaic panels commonly installed on rooftops.
The Simple Explanation
Sunlight enters the silicon cell, photons transfer energy to electrons, the p-n junction separates the charges, electrons move through a circuit, the cell produces DC electricity, and an inverter changes it into AC electricity.
That is how solar panels turn sunlight into usable electrical power.