AC voltage
Definition: alternating current
Type of voltage present in the alternating current of the power grid. Alternating current is electrical power in which the direction of flow reverses regularly (in 50 Hz the direction changes 100 times per second). Additionally, the voltage itself is not constant, but fluctuates periodically. The advantage of alternating current is the simplicity in transforming the voltage (e.g. to 230 V for the domestic power grid, or to much higher voltages for low-loss transmission over long distances). This is the reason why most power supply grids are alternating current-type grids. (&DC voltage)

A mixture of methane and carbon dioxide, produced by anaerobic digestion of organic waste matter, used as a fuel.

Bioenergy comes from any fuel that is derived from biomass – recently living organisms or their metabolic byproducts. Biomass can include matter such as cow manure. Unlike other natural resources such as petroleum, coal and nuclear fuels, bioenergy is a renewable energy source.

Buildings-integrated photovoltaic generators
Photovoltaic modules are increasingly being used as integrated structural elements in façades and roofs. In the case of roofs, these elements replace the conventional roof covering (in-roof installation), while in the case of façades; they replace glass, natural stone or metal cladding. In visual terms, the integration of photovoltaic into buildings is a particularly attractive solution. It can be used in new build projects as well as for roof and façade renovation.

Carbon dioxide (CO2)
Carbon dioxide (CO2), the colorless and odorless gas, is a natural air component. It is produced during cellular respiration and is used by plants during photosynthesis. It is, however, also created in huge quantities by the burning of fossil energy sources. Due to its excessive accumulation in the atmosphere, it has a greenhouse effect on the atmosphere and it is responsible in part for global warming.

Efficiency refers to the ratio between energy outputs and inputs. By way of illustration: conventional light bulbs convert approximately 3 – 4 % of the energy input into light, while photovoltaic systems / solar cells currently achieve an efficiency of 11 – 17 %.

Energy source
The Earth’s primary and largest energy source, which gave / gives rise to all other energy sources, is the Sun. It drives the water cycle and is therefore the “engine” of hydropower, makes plants grow and was also necessary for the formation of coal, oil and gas.

Global radiation
This is the solar radiation that reaches a horizontal surface on the Earth. It is made up of direct, diffuse and reflected radiation (e.g. from snowfields). The angle between the sun’s rays and the surface is critical for a precise calculation of the energy reaching a surface. This angle varies depending on the time of day and year. For one year, the average global radiation onto a horizontal surface in Germany is around 1,000 kilowatt hours, with some regions being above and others below this value. Southern Bavaria and Freiburg benefit from particularly favorable conditions.

Grid feed meter
Since the introduction of the Renewable Energies Act in Germany, all grid-connected photovoltaic installations have to be fitted with a grid feed meter. It is installed in addition to the existing electricity meter and measures the amount of electricity produced and fed into the public grid by the solar installation in kilowatt hours (kWh).

Grid-connected system
A grid-connected photovoltaic system is one which feeds the electricity it generates into the electricity grid.

High voltage
High voltage is used for regional-to-national low-loss energy transmission. The voltage range is defined from 60,000 volts to 150,000 volts (60 kV to 150 kV), and the usual voltage is 110 kV. For transmission of electrical energy over long distances, a maximum voltage of up to 380 kV is used.

In-roof installation
See “Buildings-integrated photovoltaic generators”.

The direct current generated by the solar cells is converted to grid-compatible alternating current by the inverter. It is therefore the link between the solar modules and the electricity grid.

Definition: kilowatt hour
Abbreviation for kilowatt hour, physical unit of electrical energy and/or amount of energy. 1 kWh = 1,000 watts of power over the period of one hour. Electrical energy is the product of power and time.

Definition: kilowatt peak
The PV generator’s peak power at maximum solar radiation under Standard Test Conditions (STC).

Module inverter
Module inverters are attached directly to photovoltaic modules in order to extract the maximum power from individual modules. They are primarily used when the modules are shaded in the course of the day, since with a combination of several modules; the weakest one always determines the overall power of the system. Disadvantage: the specific costs (Euros per watt) are considerably higher than for more powerful inverters. This is because control, regulation and monitoring are required x times – depending on the size of the installation.

On-roof installation
In on-roof installations, the solar power generator is installed approximately 5 to 15 centimeters above the roof covering using special installation kits made of galvanized steel, aluminum or stainless steel.

Parallel connection
In a parallel connection, the voltage is the same at each resistor. The current is inversely proportional to the resistance values (i.e. the smaller the resistance, the greater the current that flows through it).

Photoelectric effect
The photoelectric effect is when positive and negative charge carriers are emitted from a solid as a result of irradiation.

Photovoltaic module
A photovoltaic or solar module consists of several interconnected solar cells that are embedded between two glass or plastic plates and are therefore protected from the effects of the weather. As a rule, the modules are installed in a frame on a rooftop or a support mount.

A combination of the Greek word “Phos” (light) and the name of the physicist Alessandro Volta. The term describes the generation of electric current from solar energy. The abbreviation for photovoltaic is “PV”.

Photovoltaic generator
Generators convert other forms of energy into electricity. In solar engineering, only all the interconnected photovoltaic modules together are described as a generator or solar plant.

Power expresses the ratio between work output and the time needed for it, or power = work output per unit time. One can also use its equivalent, the energy quantity needed to do said work in the equation, therefore power = energy quantity per time unit. The greater the power of a device is the more energy (or work) is converted/transferred per unit time. Unit: watts (W) or kilowatts (kW).

Rated power
See “kWp”.
Regenerative energy
See “Renewable energies”.

Renewable Energies
All energies which, according to human timescales, there is an endless supply of: solar energy, wind energy, hydropower, biomass and geothermal energy.

Solar Calculator
“Solar System Calculator helps in estimating Solar Power utilization requirement for Commercial, Residential and Industrial Customers. This calculator also has a feature that helps in understanding the economics of installing a Solar PV System”.

Silicon (Si) is the second most abundant element on Earth after oxygen. It is extracted from quartz sand by chemical treatment, cleaned and used in the electronics industry as well as in the manufacture of solar cells.

Solar cell
In solar cells, which in most cases are made of silicon, the influx of light or heat causes positive and negative charge carriers to be emitted (photoelectric effect), thereby producing a direct current. Different material compositions yield different efficiencies:
Monocrystalline silicon: 14 to 17%
Polycrystalline silicon: 13 to 15%
Amorphous silicon: 5 to 7%

Solar energy
The energy from sunlight or other solar radiation such as heat or UV radiation.
Solar module
See “Photovoltaic module”.

Solar radiation
Solar radiation consists of direct and indirect radiation. An example of indirect radiation would be the reflected radiation from the surrounding area, such as that from snow-covered areas or a cloudless sky. The angle between the sun’s rays and the surface is critical for a precise calculation of the energy reaching a surface. This angle varies depending on the time of day and year. In the summer, the irradiation intensity can reach as much as 1,000 watts per square meter.

Stand-alone system
Stand-alone systems facilitate a self-sufficient energy supply and are primarily used in areas that are not connected to the electricity grid. In order to ensure a continuous energy supply, any surplus solar power that is generated is stored in batteries and is taken from these at night (or in case of need).
Abkürzung von:
Standard Test Conditions, see kWp

In order to increase the yields, the modules can be mounted so that they can swivel. Tracking it with electric motors, the module surface follows the path of the sun exactly in the course of the day. Compared with a fixed south-facing installation, this allows the annual yield to be increased by about 30% in our latitudes. The mast support of solar tracking systems allows the choice of an optimal location. This allows a shade-free swivel range of 180°, regardless of the structural conditions.

The conversion from one voltage level to another is usually done by transformers. A transformer reduces or increases the voltage. Transformers are used, for example, to reduce the high voltage in overhead power lines to the low voltage in our sockets.

Utility company
The utility company is your power supplier. Under the Renewable Energies Act (EEG) it is obliged to accept the electricity that you feed into the grid and pay for it in accordance with the feed-in tariffs stipulated in the EEC.

Volt (V)
The unit of electric potential. Named after the Italian physicist Alessandro Volta (1745- 1827). The potential difference is the difference in charge at the poles of a current source. The voltage used in the households of most European countries is 230 volts. The larger voltage unit is 1 kilovolt (kV) = 1,000 volts. Electricity from large power stations is transformed to higher voltages by means of transformers (up to 500 kV in Europe) in order to minimize transport losses through conductor resistance. Closer to the end-users, the current is transformed back to 220/230 V.

Watt (W)
The unit of electrical power. The work or energy expended in 1 second is called power. Thus, for example, the power of a device specifies how much energy it can transfer per second. The quicker the work is done, the greater the power.