Technologies and Applications

Photovoltaics

Thanks to the global availability of solar energy, PV offers an attractive solution for generating both grid-connected and off-grid electricity.

Advantages of photovoltaic electricity generation

• Quiet, emission-free electricity generation.
• A wide array of applications, ranging from very small devices, such as solar-powered pocket calculators, to electricity generation for domestic usage and large-scale installations with an output of several hundred megawatts.
• No moving parts – the installations have a long service life, with a low level of maintenance required.
• Very environmentally friendly – using and disposing of silicon entails no danger to the environment.
• Currently, silicon is the primary material used in the manufacture of PV cells and since it is the second most common element on earth, sourcing is inexpensive.

How a PV cell works
PV cells consist of one or more semiconductor materials and enable solar energy to be directly converted into electrical energy. In order to elicit the so-called photoelectric effect, the semiconductor material must be “doped”. Chemical elements are added to produce two layers, a p-conductive layer with a positive charge carrier surplus and an n-conductive layer with a negative charge carrier surplus. Due to this imbalance, an inner electrical field forms on the barrier layer, which produces a charge separation on incidence of light. The charge carriers released in this process can be conducted through contact with metal and used as direct current (DC) by an electrical device or fed into the network as alternating current (AC) via an interconnected inverter. For higher capacities, PV cells are usually interconnected in modules.

Types of technologies
German companies are world leaders in the research and development of new PV technologies. A prerequisite for positive future market development is further reductions in costs, for example, by maximising the degree of efficiency and reducing the amount of material used, as well as increasingly utilising the technologies in other areas of application. The following PV technologies are therefore set to gain importance in the future:

(1) Concentrator photovoltaic systems (CPV)
Mirror and lens systems are used to concentrate a high level of light intensity on the PV cell. As a result, degrees of efficiency of up to 43.6 % can currently be achieved. This technology has high potential for reducing production costs and therefore represents a cheap source of electricity supply for the future.
Concentrator photovoltaic thermal systems (CPVT) additionally use the thermal power of the sunlight and can reach efficiency levels of 70 %. This technology can be applied in municipalities and industries.

(2) Organic photovoltaics (OPV) 
Organic PV cells consist of hydrocarbon compounds which are, as with amorphous silicon, applied to a substrate material. The advantage of organic PV cells over inorganic ones is that their performance does not drop in the presence of less sunlight and higher temperatures. This allows for a higher solar electricity yield. The colourfulness and flexibility of the material opens up opportunities for aesthetic applications. Current research focuses on higher levels of efficiency and lifetime.