Photovoltaics

Sunlight can be converted into useable electricity. To do this, we need a solar cell. Solar cells are also called photovoltaic cells

‘Photo’ means light, and ‘voltaic’ means relating to electricity, so the purpose of a photovoltaic cell is to turn or transform light from the Sun into a usable form of electrical energy.

Photovoltaic panels around the place

You have probably already seen photovoltaic cells or panels (groups of photovoltaic cells) around, for example, on calculators that don’t have batteries. To operate, they just need to be in the light. You’ve probably seen photovoltaic panels at the bus stop or powering road signs that tell people to slow down if they are going too fast. Large photovoltaic panels are used on lighthouses and on satellites to supply them with electricity.

How photovoltaic cells work

Sunlight is used to make electricity, so the solar cell needs to be made of a material that will allow electricity to work. Electricity is the flow of electrons, so the material needs to allow electrons to flow when required.

Semiconductors

Solar or photovoltaic cells are made of materials that are known as semiconductors of electricity. Semiconductors lie between conductors and insulators in their ability to conduct electricity. Conductors allow electricity (the flow of electrons) to pass through the material easily. Insulators don’t (usually) allow the flow of electrons. Semiconductors are materials that do not usually conduct electricity (like insulators) but can be made to under certain conditions.

The most common semiconductor used in photovoltaics is silicon. By itself, silicon is a non-conductor. This means that the atoms that silicon is made up of do not have electrons that can move around. They are all fixed in place and unable to move. Substances can be added to the silicon through a process called doping, which frees up some of the electrons to move. These electrons are held loosely within semiconductor materials.

Photons

Sunlight is made of parcels or amounts of light energy called photons. Photons have different energies depending on the wavelength and frequency of the light. These wavelengths and frequencies correspond to the electromagnetic spectrum. When photons strike a photovoltaic cell, they may be reflected, pass right through or be absorbed. The absorbed photons provide the energy to generate electricity.

Creating electric current

When photons (with sufficient energy) are absorbed into the semiconducting material, they excite the loosely held electrons, which are dislodged from the material’s atoms.

Special treatment of the material’s surface during manufacturing makes the front surface of the cell more receptive to free electrons so the electrons naturally migrate to the surface. This creates an imbalance of charge between the cell’s front and back surfaces (like the positive and negative terminals on a battery). When the surfaces are connected through an appliance (to create a circuit), electricity flows.

The articles Solar energy, Using solar energy and Renewable energy sources contain useful background information.