Solar panel system

Depending on their raw material and technology, solar panels can produce electricity at different levels of efficiency.

Efficiency ( η {displaystyle eta } eta , “eta”) is a percentage of the solar energy that a solar panel converts into electricity.

Types of solar panels

Several types of solar panels are distinguished according to the raw material:

Crystalline solar cells: solar cells made with mono- and polycrystalline technology are the most common solar cell technology today. Batteries based on silicon semiconductors were introduced in 1954.

Monocrystalline silicon solar cells: silicon is expensive but efficient. The efficiency of state-of-the-art panels is 18%, under laboratory conditions 25% (the theoretical limit is 33.7% for solar cells with a single p-n junction). They are at their maximum output in perpendicular sunlight, and are often used as part of so-called solar tracking devices.

Polycrystalline silicon solar cells: slightly cheaper but less efficient. Their efficiency is around 15%. They are relatively less expensive and less expensive.

Gallium arsenide compound solar cells: although so far mainly used on satellites and not economical when used in a single layer, they can be stacked up to 8 layers (p-n junctions). This allows efficiencies of up to 46% in concentrated sunlight: one was already in use at the end of November 2014.
Amorphous silicon solar cells: cheaper but only 5-8% efficient. They require less silicon to manufacture than monocrystalline because the active layer is only 1 µm thick.

Other compound semiconductor solar cells: efficiency less than 15%. Examples: cadmium telluride, copper indium diselenide (CIS) and copper indium gallium selenide solar cells. They require little semiconductor material because the active layer is only 1-2 µm thick.

Organic dye-based solar cells: They operate on the electrochemical principle, the light-absorbing material being an organic dye. They are based on organic solar cells. Their efficiency is only 2-4%, but their production could become extremely cheap in the future.

Solar cells made from organic materials (polymers): cheap, but only 2-5% efficient

Solar cells based on organic-inorganic perovskites have reached an experimental efficiency of 20%, with very rapid progress, promising low manufacturing costs. Some developers expect them to be on the market as early as 2017.24 See also the figure in the Efficiency chapter, where the red lines with empty circles represent progress. (Graph from English Wikipedia)

In the EU-funded CPVMatch project (research by nine research institutes (German, Italian, Spanish and French) and industrial companies – coordinated by Fraunhofer ISE in Freiburg), light is focused on small solar cells using optical lenses. The experimental system is aimed at the Sun with a two-axis solar tracking mechanism. Its efficiency is 41.4%.

It is possible to increase the efficiency, which may require more complex technology; logically, this would be more expensive, neglecting the potential for leaps and bounds in technology. Thus, the theoretical efficiency limit (33.7%) could be exceeded by, for example, stacking several thin layers of solar cells (p-n junctions), each sensitive to a shorter wavelength of light in steps. The efficiency can be further increased by operating at higher light concentrations (500X) using optical lenses or mirrors.

Nowadays, research and development is not limited to achieving higher efficiency, but is rather in the direction of efficiency x lifetime/production cost, with the aim of achieving the shortest possible payback time. This objective can be achieved by using thin-film based batteries: their individual efficiency is lower, but several layers can be assembled and their production costs are many times lower than those of conventional silicon-based batteries.