How photovoltaic works

For 4 billion years, the sun’s radiation has been supplying the Earth with heat and light – without which life would not be possible. This radiation (= photons) is generated by nuclear fusion in the sun’s core. When a photon hits a silicon atom, its electrons are knocked out of place, which creates an electrical charge. As a result of this process, radiation is converted directly into electrical energy. This is known as the photovoltaic effect. In Germany, an average of 1,000 kWh of solar energy per metre squared can be produced each year. This is equivalent to the energy content of 100 litres of fuel oil.

How photovoltaics works

System technology

Photovoltaic systems can be connected, via a network operator, to the public electricity grid to feed in power (on-grid systems) or they can be used for self-sufficiency purposes (off-grid systems). A photovoltaic system incorporates the following components:

  • Solar module (interconnected assembly of solar cells)
  • Inverter
  • Mounting system
  • Storage system optionally

In principle, photovoltaic systems can be installed on flat or pitched roofs, can be integrated into the facade of a building or can be set up on open land.

Module technology

A solar module consists of electrically connected solar cells. In a solar module, the individual cells are soldered into a row to form electrically connected cell strings. The cell strings are connected to cell plates by diodes and laminated into a vacuum between support glass, EVA film and Tedlar film. An aluminium frame binds the completed laminate unit. There are three types of solar cell:

  • Monocrystalline solar cells: Are cut into thin slices (wafers) from a pulled silicon rod with an even crystal structure (monocrystal). They are dark blue or black in colour.
  • Polycrystalline solar cells: Are cut from a cast silicon block. The poly cells look bright blue.
  • Thin-film solar cells

 

As a basic rule, monocrystalline solar cells work more efficiently, but are a little more expensive to produce.

Inverter

The inverter converts the direct current (DC) produced by the solar modules into alternating current (AC). This is then fed into the public electricity grid. Depending on the model being used, one or more module strings can be connected to a string inverter. System control devices (data communication) are used to monitor the power produced, how much electricity is consumed and how much is fed into the grid.