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)

Accumulators or solar batteries are used for storing solar power in stand-alone systems for decoupling power generation and power consumption times. This way, solar power can be available at night, for example.

The unit for the electric current.

The angle of inclination at which the solar modules are installed is important in terms of yield. The seasonal path of the sun means that the angle of inclination is flatter in the summer and steeper in the winter. Based on the annual average, the optimum angle of inclination for our parts of the world is approx. 30° – it increases accordingly as one approaches the equator. (>Orientation)

The Azimuth angle describes the deviation from the southern direction (southern hemisphere: northern direction). A solar power system produces the highest power yield at an Azimuth angle of 0 degrees, but even in a 45 degree Azimuth angle the energy yield of modules with a 30-degree inclination still reaches about 95 percent of the maximum value. (>Orientation)

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 photovoltaics 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), 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.

Central inverters are particularly suitable for building up photovoltaic systems with a homogeneous structure (modules of the same type with an identical alignment and inclination). They are used for installations from 100 kW upwards and, in most cases, are designed for outdoor installation.

The amount of carbon dioxide (CO2) saved as a result of using a solar installation depends on the fuel that it replaces (gas, heating oil, coal) and the conventional energy that is used (electricity, district heating), and is proportional to the amount of fuel and energy saved. The amount of CO2 emissions avoided is obtained by multiplying the saving by the so-called emission factor (unit: kg of CO2 per kWh of fuel saved or tons of CO2 per MWh). The CO2 reduction is a measure of a solar installation’s contribution to climate protection.

There are various data communication systems for monitoring photovoltaic installations. In most cases, these are installed additionally, and record the amount of electricity generated, thus providing information about the proper operation of the installation. Today, monitoring is possible via Internet, e-mail, cell phone or large-format displays.

Data storage device that logs the operating data of the inverters and enables operational monitoring of the solar installation over a longer period.

Direct current voltage produced by solar cells and/or modules, which can be stored in batteries. In direct current, the electrical charge always flows in the same direction. (>AC voltage)

For solar power plants, the revenue from the sale of electricity (according to the German Renewable Energy Sources Act, EEG) is compared with the investment costs.

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 %.

see "Energy payback time".

The period of time that a solar power system requires to generate as much energy as was required for its manufacturing.The energy return times of photovoltaic systems are between three and maximum seven years. According to a study performed by the Technical University of Berlin, PV plants that are based on amorphous silicon have an energy payback time period of only 17 to 41 months. Thus, PV plants have a positive energy balance. Power stations that are operated with fossil fuels cannot achieve energy payback, since they constantly consume additional fuels.

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.

The direct current generated in the solar cells is converted to alternating current by an inverter and fed into the public electricity grid.

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.

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).

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

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.

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.

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.

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

The electrical power of a solar cell under a given amount of solar radiation depends on the voltage and cell temperature. MPP (Maximum Power Point) stands for the operating point at which this power reaches a maximum. The MPP changes constantly (depending on the solar radiation and the temperature) and has to be detected a new continuously (> MPP Tracking).

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.

A device which adjusts the current and voltage of the photovoltaic generator to ensure that it operates at "Maximum Power Point".

An inverter which, to a large extent, combines the advantages of several string inverters (separate MPP control of individual strings) and a central inverter (low output-related costs).

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.

A patented housing concept by SMA, in which the interior of the housing is divided into two compartments. The compartment containing the sensitive electronic equipment is dustproof and waterproof, while the second compartment, which contains transformers and throttle valves as well as other non-sensitive components, can be actively cooled if required.

In order to make the most effective use of solar radiation, modules and collectors are oriented toward the sun in such a way that the solar power yield is as high as possible. In this context the sun's angle of incidence and the "Azimuth angle" come into play, as well as the modules' and/or collectors' angle of inclination. The Azimuth angle indicates, in degrees, the amount by which the module surfaces deviate from an exact southern orientation. The angle of inclination relates to the horizontal deviation. Solar cells / modules can be continuously adjusted with the use of the trackers to make sure that they face the sun all of the time.  (>Azimuth angle)

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).

Peak oil production. As a fossil fuel, mineral oil is not in unlimited supply, unlike, for example, solar or wind energy. Consequently, our worldwide oil reserves are becoming scarcer all the time. However, the real problems will not just appear when the oil “runs out”, but when we reach peak production. The most recognized model on this subject was developed by the geophysicist Dr. M. King Hubbert. This model is known as the "Hubbert Curve". The Hubbert Curve is a bell-shaped curve, with crude oil production rising at first, then reaching its peak before steadily declining. The top of the curve represents peak oil production, also called "Peak Oil". This more or less coincides with the point at which 50% of reserves have been used up.
From this point on, the amount of oil that is extracted will fall year after year – while demand from China and India is constantly growing. Experts believe that this point will be reached by 2010 at the latest, perhaps even sooner. This will lead to further oil price rises and more frequent conflicts over resources – with unforeseeable consequences for the industrialized countries in particular. Although oil extraction will continue for a few more decades, the critical question is how soon the cheap oil will run out and supply bottlenecks start. Several scenarios assume that the consequences of global climate change will hit us at the same time – as a result of the greenhouse effect caused by the burning of fossil fuels. More info at: http://www.peakoil.com/

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

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 photovoltaics is "PV".

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.

No planning permission is required for rooftop solar installations. Planning permission is only required in the case of listed buildings. Installations in open spaces should be regarded separately, however, as they are classed as independent structures.

See "Data communication"

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).

See "kWp".

See “Renewable energies”.

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

In a series connection, the current is the same at every point. The voltage is divided in proportion to the resistance values (i.e. the greater a resistance, the greater the voltage at this point).

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.

A grid monitoring concept from SMA Technologie AG. For example, SMA grid guard® monitors the voltage and frequency of the connected AC network according to set parameters in order to prevent islanding when connecting to the grid. The SMA grid guard® concept permits the hassle-free and reliable connection of SMA inverters to almost any conceivable network situation at home and abroad.

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%

The energy from sunlight or other solar radiation such as heat or UV radiation.

See "Photovoltaic module".

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 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).

Standard Test Conditions, see kWp

The combination of several solar modules connected in series.

In string technology, the photovoltaic generator is subdivided into individual module surfaces and each of these individual "strings" has its own string inverter allocated to it. This technology allows the system costs to be reduced while at the same time making installation a lot easier and increasing the energy yield and system availability.

The purpose of support programs is to make renewable energies and energy saving measures more economical. They are intended to reduce CO2 emissions and improve the market situation for companies operating in the renewable energies sector. In Germany, financial support to promote the use of renewable energies is provided by the federal government, the federal states, city councils and local authorities, as well as tax offices and some utility companies.

Photoactive semiconductors are applied on a substrate (glass, stainless steel foil) to form a thin film. The advantages of thin-film cells are their low manufacturing costs, lower susceptibility to shading and greater shape flexibility. One drawback is the lower efficiency compared with pure crystalline silicon cells.

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.

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.

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.

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.