Frequently Asked Questions

The term "renewable energies" has become commonplace, because colloquial language creates catchy, short terms and accepts inaccuracies when exact formulations become too complicated. Until someone finds a scientifically accurate and at the same time concise term for these forms of energy (bioenergy, solar energy, hydroelectric power, wind power, geothermal energy and tidal (mass attraction)), we will continue to live with physically "wrong" terms.

The term "alternative energies" was common 15 years ago (it can be found in various course catalogs of technical universities from that time). While the term "alternative energies" brought the aspect of significantly greater environmental compatibility compared to fossil and nuclear energy sources to the fore, the term "renewable" aims at the availability of these energies as a defining criterion:

Measured by human standards, renewable, alternative and regenerative energies seem to be inexhaustible. Inexhaustible means two things: either the existing amount of the individual form of energy is so large that it can hardly be exhausted by human use (e.g. solar energy) or it is renewed promptly and continuously (e.g. biomass) from other "renewable" energies. These are energies that, from the point of view of human history, are available for an infinitely long time (as long as the sun shines, as long as the interior of the earth is hot, as long as masses attract) and are available (= renewed) every day.

The term "renewable energies" is undoubtedly physically incorrect, but it describes an essential, socially relevant property of these energies quite well. Therefore, it is likely to remain in colloquial language for a long time.

With solar thermal energy, collectors convert solar radiation into usable heat. It is usually used via heat exchangers for heating and hot water preparation. Photovoltaic means the direct conversion of solar energy into electricity.

Photovoltaics is the direct conversion of the energy of sunlight into electricity using solar modules made up of individual solar cells. The word comes from "photon" (Greek: light) and "volta" (Italian inventor after whom the unit of electrical voltage "volt" was named).

A solar cell is usually a very thin disc made of silicon and about 15 x 15 cm in size. Contact strips are attached to the front and back, which carry away the current generated by the sunlight in the cell. The silicon is made from quartz sand. Other crystalline and thin-film solar cells are far less common. Their combined market share is less than 10%.

The construction time of a photovoltaic system depends on the capacity and the structural conditions. For systems up to 10 kWp, the installation takes 1 to 3 working days.

PV systems can be installed on flat roofs without any problems. In this case, the modules are set up at an angle with the help of a mounting system so that they are optimally south-facing and have a favorable inclination. At the same time, the inclined installation of the modules ensures the cleaning effect and adequate ventilation. A sufficiently large distance between the modules is important here, as otherwise there will be shading and thus a reduction in yield. To install the same output, the required flat roof area is about twice as large as with a pitched roof variant.

In a grid-connected solar power system, part or all of the solar power generated is fed into the public power grid. In a stand-alone system, the electricity generated is not fed into the public power grid, but is used 100% by the company itself. Island systems are not connected to the power grid.

Wp stands for watt peak. This is a unit that has become established in photovoltaics. It indicates the power that a solar module can achieve in full sunlight (and some other additional conditions) at noon between April and September, e.g. in North America or Central Europe.

Photovoltaic modules use not only the direct sunlight, which only occurs when the sky is clear, but also the diffuse radiation that passes through the clouds. The brighter it is, the more power the modules produce - regardless of whether the sun is directly visible or not. Incidentally, in Germany the diffuse portion makes up about half of the radiation.

Photovoltaics have proven their reliability over many years and in many different applications. Photovoltaics have been used in space travel since the 1960s and have proven themselves there. In north america and europe, many thousands of small and large plants have been built since the 1990s. With a service life of approx. 30 years, an annual decrease in module output of 0.3 to 0.5 percent is currently expected. After that, the cover glass and the metal frame and partly also the solar cells can be recycled, e.g. for the production of new solar modules.

In order to generate the energy put into it again, the solar system has to produce energy for about two years. With a service life of at least 25 years, it will therefore generate more than ten times as much clean electricity as was needed to produce it.

A photovoltaic system consists of the following components, which are individually matched to each other and are therefore adapted to the basic structural conditions of the house:

Solar modules that generate direct current from solar energy.
Inverters that convert direct current into grid-compatible alternating current.
Feed-in meter that measures the electricity fed into the power grid.
Wiring and mounting frame on which the solar modules are attached.
Power storage (optional) that temporarily stores the generated solar power.

Ideally, the inverter is installed in a sheltered location that does not get too warm even in summer. If there is no suitable installation location in the house, there are also inverters that can be installed outside.

Normally not, because thanks to the smooth module surface, rain and snow are usually responsible for cleaning.