Called also battery or solar battery. Rechargeable storage unit for electrical energy. Used for storing solar energy produced during the sunlight and consume it later when needed. The direct current generated by the solar system is stored in the battery (12-volt systems) using a charge controller and can supply the DC consumers as required. If AC consumers need to be operated, an additional inverter must be connected to the battery.

Current which changes its flow direction regularly. Alternating current is an electrical current that continually changes its direction from positive to negative and from negative to positive. The sinusoidal frequency curve passes through the zero point once during a period. The number of periods per second is the frequency (Hz = Hertz). Alternating current is standard domestic current. It changes its direction 100 times per second (50 Hz) and has a nominal voltage of 230 volts. It is also called AC. A solar or photovoltaic module generates direct current (DC) which is converted into alternating current by an inverter.

A bidirectional meter measures the energy fed into the public grid and the internal consumption of self produced solar energy.

Carbon dioxide, a gas which is produced during combustion, and which is the main cause of climate change. For a comprehensive view of CO2 emissions per kWh for various energy sources, it is necessary to take into consideration not only the actual process of power generation, but also the CO2 costs expended during the manufacture and procurement of the raw materials, installation of the system, transportation, and deconstruction.

Electrical current which always flows in the same direction is called direct current or DC. The current flows from the positive to the negative pole. Photovoltaic systems also produce direct current, which is converted into grid-compliant alternating current so that it can be fed into the grid. DC cables have a larger cross section than AC cables. They are therefore harder to lay and also more expensive when installed in photovoltaic systems. This means that DC cables are kept as short as possible and the inverter is installed close to the modules. Direct current is mainly used for devices with low power, e.g., flashlights or car batteries.

The output of destructive substances into the environment, e.g., carbon dioxide.

A generator generates electrical energy. 

Effect whereby certain gases or dust in the earth’s atmosphere prevent long-wave heat radiation which is reflected from the earth’s surface from escaping into space, leading to an increase in the temperature in the earth’s atmosphere.

Gas which absorbs or reflects radiation reflected from the earth’s surface and contributes to the process of increasing the temperature of the atmosphere.

Network of all power lines that serve the public power supply. Public power grid, integrated network: all power stations and consumers are connected to each other (networked) in the power grid. There is the low-voltage grid, with 230 or 400 volts, to which private households are usually connected. There is also the medium-voltage grid (10 to 30 kV), the high-voltage grid (50 to 150 kV), and the extra high-voltage grid (220 or 380 kV). Photovoltaic systems feed current into the low-voltage grid. The inverters convert the direct current produced by the solar system into alternating current. They have a cut-off device in case the voltage exceeds the acceptable values; however, this only happens very occasionally (in accordance with IEC standard 60038, the upper limit for voltage is 230 volts plus 6%). 

Solar power system which is connected to the power grid and is not used exclusively for private power supply. A photovoltaic system which feeds the electrical current generated into the public power grid is grid connected. In contrast to stand-alone systems, this system does not require storage batteries (accumulators). An inverter is used to convert the direct current generated by a photovoltaic system with a grid connection into grid-compliant alternating current, which is then fed into the public grid, and is compensated according to local feed-in legislation. The current required for the household continues to be obtained from a utility grid operator. The utility grid operator is not necessarily the same as the operator of the public power grid who pays the feed-in compensation for the solar power. This means that electrical current from renewable energy sources (green electricity) may be purchased by an alternative supplier.

Device for converting direct current into alternating current. Photovoltaic modules generate direct current from sunlight. This direct current must be converted into alternating current in the inverter so that the electrical energy can be used in the household or fed into the public grid. There are various types of inverters which are defined by their power range and internal connection method. There are three classic types of inverters: microinverters, which are designed for outputs from one or two photovoltaic modules. String inverters, which usually have one to three maximum power point trackers (MPPT) for connecting multiple strings to supply power of up to several kilowatts. Central inverters providing power up to the megawatt range. Generally, a distinction is drawn between inverters with transformers and inverters without transformers.

The power of the solar radiation on a certain area. The irradiation intensity specifies the power which the sun radiates on an area of 1m2. On the ground, it is about 1000 W/m2.

Unit of power, 1 kW = 1000 W. 

Unit of measurement of work 1 kWh = 1000 Wh Unit for energy (in contrast to power: unit of energy/time = kW).

Peak power of a solar power system. The size of a photovoltaic system is specified in kW peak (kWp, peak power) according to the power of the solar generator. This value refers to the optimum power of the solar modules under standardized test conditions (1000 W/m2 radiation, 25 C module temperature, 1.5 air mass). The power of the solar generator decreases accordingly if it is cloudy, the module has heated up or the air mass factor is higher (the system is working under partial load). At our latitudes, a 1 kWp photovoltaic system (corresponds to an area of 8-10 m2) can generate around 700 to 900 kWh of electrical current a year. The average annual current consumption of a four-person household in Germany is around 4000 kWh.

Frequency of the mains voltage in the electrical AC voltage transmission network. The mains frequency is a specific characteristic of AV voltage networks. It is country-specific and is typically 50 Hz (e.g., the European integrated network) or 60 Hz (e.g., USA). The mains frequency varies due to different load situations within the distribution network. It is used as a control parameter for grid stabilization.

Electrical voltage in the low-voltage power grid, i.e., at the lowest level of the distribution network. The voltage in the low-voltage power grid is country specific. In Germany, for example, it is 230 volts or 400 volts in single phase or three-phase operation; in the USA it is 120 volts or 208 volts. In addition to the mains voltage, the mains frequency is also an important characteristic for the transmission network.

Technical device for acquiring a cumulative technical variable such as heat quantity or electrical energy.

Special type of inverter with low nominal power and low input voltage so that it can be connected to individual modules. Microinverters are inverters which work in the power range of several hundred watts and with a very low input voltage way below 100 V. They are assigned to individual modules, i.e., one or two modules are linked to an inverter. This means that the individual modules of a photovoltaic generator can be operated independently of each other at their respective optimal operating points without affecting each other. This is not possible with photovoltaic generators using a classic string-type connection. A typical application for microinverters is a photovoltaic generator which is partially shaded over the course of the day. In this case, the use of microinverters means that only the shaded modules experience a reduction in power, while the rest of the modules can supply their maximum yield at all times.

A solar module converts solar energy directly into electrical current using the photovoltaic effect.

Monitoring the operating data of a photovoltaic system. The operating and performance data of a photovoltaic system are an important indicator of effectiveness and cost effectiveness. AC and DC power, currents, and voltages are usually measured. Variables such as radiation and temperature can also be recorded. The data is then available for calculating the performance ratio, for example. In smaller systems with microinverters and string inverters, production data acquisition is usually integrated into the inverter. Large photovoltaic power stations are also monitored on the DC side by separate measuring units because the central inverters are unable to measure to a enough level of detail due to the way the system is connected. Monitoring on the DC side is required for effective operational management and targeted maintenance of the system.

Device which enables the solar power system to always run at its maximum power point. The MPP tracker is a device in the inverter which sets the current and voltage of the photovoltaic generator so that it is operated at its maximum power point. This means that the solar system achieves its maximum power.

The maximum power of a solar power system reported by the manufacturer. 

A photovoltaic or PV system, also known as a solar power system, is a power station which converts part of the solar radiation into electrical energy using solar cells. The solar cells in the solar generator generate electrical energy directly from the light that falls on them. They generate direct current. This is converted into grid-compliant alternating current so that the energy can be used in the house itself or fed into the public grid. This task is performed by the grid feed-in device or inverter. In principle, it is possible to use the direct current as it is. However, apart from devices for camping, there are hardly any consumer devices on the market which have a DC connection. In grid-connected systems, the solar power is not stored, but is instead used immediately in the same household, by neighbours or by another consumer in the power grid. In standalone systems, the electrical current is stored in accumulators.

The sunlight or solar radiation consists of both direct and indirect radiation. The proportion of solar radiation which passes directly through the earth’s atmosphere without scattering is known as direct radiation. This is the case when the sky is clear. In contrast to diffuse radiation, direct light casts shadows. Direct radiation makes up around 50% of global radiation on average over the course of a year. It can be used to generate heat as well as to generate solar power. Indirect radiation is diffuse radiation and reflected radiation. Diffuse radiation reaches the earth’s surface through a hazy atmosphere. The sunlight is scattered by clouds, mist or fog and does not hit the earth in a straight line, as direct radiation does. Diffuse light is characterized by the fact that there is no clear boundary to the shadows cast depending on lighting conditions. Indirect radiation makes up around 50% of global radiation on average over the course of a year. The direct and diffuse solar radiation which falls onto a reception surface from the environment is called reflected solar radiation. Only the reflected and diffuse radiation falls on the areas under shadow.

Refers to energy from sources which either renew themselves over the short term or which are not depleted through use. Energy sources which do not use up any finite resources, but instead tap into natural, self-renewing cycles are described as renewable (solar, wind, hydraulic power, bioenergy). The tides, ocean current, and geothermal energy are usually included too.

The alignment of a roof to the cardinal directions is a key factor with respect to the yield of a solar system. A south-facing roof is best for generating solar power or solar heat. However, a deviation in alignment to the west or east is not as disadvantageous as you might assume. If the roof is rotated 45° to the east or west, it may still be possible to exploit up to 95% of the potential, depending on the roof tilt. And even if the roof is aligned exactly to the west or east, it is still possible to exploit up to 85%.

Indicates how a solar system is integrated into the roof. Solar systems can be attached to the roof in a variety of ways. On flat roofs, they are elevated, on sloping roofs, the collectors and modules can also be mounted elevated above the roof cladding or integrated into the roof cladding, which is the more elegant option in terms of appearance. Some companies now offer modules which are fitted into frames, which can be mechanically and visually integrated into the surrounding roof area. The latest technology is solar roof tiles and solar roof systems, which involve covering the entire surface of the roof with large collectors (“energy roofs”).

The installation of a solar system on the roof. When solar systems are roof-mounted, the solar collector or solar module is installed around 5 to 15 centimetres above the roofing using special assembly kits made of galvanized steel, aluminium or stainless steel. The DIN rails are attached to the rafters using roof hooks. Systems in which the collectors or modules are connected to a rail system are particularly easy to mount as there is no need for further work to screw them onto the roof. When retrofitting a solar system into existing buildings with sloping roofs, on-roof mounting is cheaper than roof integration as the existing tile covering is only penetrated at a few points and the water-tightness of the roof is not compromised. However, in-roof mounting is often the most attractive option from an aesthetic point of view.

The angle at which a roof tilts, a key factor with respect to the yield of a solar system. The setting angle of the roof toward the sun directly influences the yield of the solar system and affects the power and heat energy recovered accordingly. The seasonal movement of the sun means that the system benefits from a steeper setting angle in winter than in summer because the sun is lower in the sky. On average across the whole year, the optimum angle of installation is 45° for thermal systems and 30° for photovoltaic systems. However, in the case of solar thermal systems, it is important to take into consideration whether they are used exclusively for heating domestic water or are also used for supporting a heating system. If they are used for supporting a heating system, more energy will be required in winter. This means that, under some circumstances, a steeper angle of installation may be a better option for these systems. Flat roofs are always suitable for solar systems as both the alignment and the installation angle can be selected freely.

The solar cell is an electrical component which converts sunlight directly into electrical energy.

Silicon which does not have a crystal structure. The amorphous solar cells, which vary in colour from red-brown to black, are manufactured from gaseous silane. This means that they do not have a crystalline structure like monocrystalline or multicrystalline cells, but instead have a disordered structure. Their efficiency is lower than that of crystalline cells, but they can use diffuse light more effectively. Amorphous solar cells are often used in the leisure sector.

Silicon which consists of a single crystal. Solar power systems made of monocrystalline silicon can be identified by their black colour. In monocrystalline solar cells, the material (silicon) is arranged in a completely regular crystal at the atomic level. Monocrystalline solar cells are often used for grid-connected solar systems; their efficiency is higher than that of polycrystalline solar cells, but so is their price.

Use of solar energy for cooling. Solar thermal technology is usually used in the form of collectors for generating useful heat (industrial water, heating water, and process heat). Because more energy is required globally for cooling (e.g., rooms) than for heating and producing water, cooling is a logical use for solar collectors. In warm climates, the requirement for indoor cooling coincides with high levels of solar radiation, so using the sun for cooling is an obvious solution. Previously, cooling systems were generally powered electrically. Solar cooling systems are environmentally friendly and can complement or completely replace conventional air conditioning systems. Up to now, the only disadvantage has been that the system technology for solar air conditioning is more expensive than for conventional systems. Solar cooling systems are cheaper to run because solar energy is available for free.

Component of a solar power system. Because individual solar cells only provide low power (approx. 1.5 W), they are connected to a solar module. This consists of a glass cover and, in most cases, an aluminium frame, which provides stability and is used for fastening. The cover on the top lets light through, while simultaneously protecting the solar cells from the wind and weather. It is fastened to the roof or the facade in this form. An individual solar cell is approx. 12.5 x 12.5 cm large; modules are available in various sizes. A module can have a power of between 50 and 300 watts, depending on the number of cells. Solar modules can be silicon-based, polycrystalline with a glittering crystal structure or monocrystalline with a uniform cell surface. Thin-film modules are not constructed from cells, but are instead made by coating a carrier layer (e.g., glass or copper rails) with a photoactive semiconductor material. The low consumption of materials and energy during manufacture and the possibility of a high degree of automation offer significant potential for savings when compared to crystalline silicon technology. The carrier material for thin-film cells can, in theory, be cut to meet any requirements. This means that even freer customizations with respect to size can be offered. However, thin-film modules have a lower efficiency overall and require more space to achieve the same amount of power. The maximum cell efficiency of monocrystalline cells is 18%, for polycrystalline cells it is 15%. Thin-film cells have cell efficiency ratings of up to 14%. The solar modules are fastened to the roof or the facade with a variety of systems.

The word is made up of “solar” = sun and “thermic” = heat. Solar thermal systems in a residential building heat domestic water for the shower, sink, etc. The washing machine and dishwasher can also be supplied directly with hot water from the solar system using an adapter. This means that electrical current, which would otherwise be required for heating the water, can be saved. Solar systems for supporting heating systems produce a larger quantity of hot water than systems for heating domestic water by increasing the collector surface on the roof. These systems can then also support the heating system during the transitional months (spring and autumn), saving energy on heating. Other options for solar energy use: passive solar energy use increases energy yield, for example if thermal insulation is used or the house is constructed in a south-facing direction. Drying washing in the sun is also a passive use of solar energy. In photovoltaics, sunlight is used to generate electrical current using solar modules.

Vehicle which is fuelled by solar power e.g., a solar car, solar scooter or solar boa.

Pump which is operated with solar power. Direct current pump which obtains its electrical current from a solar module, e.g., pond pumps or circulating pumps in a solar system.

Star at the center of our solar system. Astrophysicists estimate the age of the sun to be 5 billion years. Energy is released as hydrogen nuclei fuse together to form helium nuclei inside the sun. This energy released by the fusion process radiates into space in the form of electromagnetic radiation, and a small fraction of this reaches the earth. The sun provides the earth with more energy in a quarter of an hour than humanity uses in an entire year.

The change in voltage, current, and power in solar modules as a function of the ambient temperature. The temperature coefficients TK(Pmpp), TK(UOC), and TK(ISC) are usually specified in %/K for photovoltaic modules. The current from photovoltaic modules generally decreases as the temperature increases, while the voltage increases. The power of photovoltaic modules is proportional to the product of current and voltage. The temperature coefficient of the current is generally weighted more heavily than that of the voltage, which means that the power of solar modules usually decreases as the temperature increases.

The tilt of solar systems on racks or roofs. The angle at which the roof components of a solar system are installed is an important factor with respect to the yield. Due to the seasonal differences in the movement of the sun through the sky, the tilt angle is flatter in summer and steeper in winter. It is preferable for the sunlight to hit the modules from a position which is as close to perpendicular as possible. On average across the whole year, the optimum tilt angle is 45° for solar thermal systems and 30° for photovoltaic systems. In the case of solar thermal systems, it is important to take into consideration whether they are used exclusively for heating domestic water or are also used for supporting a heating system. If the system is used for supporting a heating system, more energy will be required in winter. A steeper installation angle of 50° or 60° should therefore be selected.

The primary application for transformers is to increase or decrease AC voltages. The circuits are electrically isolated at the same time. Transformers are essential for the cost-effective transmission of electrical energy over long distances by means of high-voltage lines.

Physical variable which specifies how much work or energy is required to move an object with a specific electrical load within an electrical field.

A slice of silicon cut from a block which is turned into a solar cell as a result of special further processing. Wafers are thin slices of semiconductor material, which, in photovoltaics, is usually silicon. Wafers are used in the chip industry and in photovoltaics. The solar industry used to work with waste from the chip industry, but now wafers are manufactured specifically for photovoltaics. The silicon is supplied in single-crystal, multicrystalline or polycrystalline blocks (ingots) and is cut into thin slices. The wafers undergo multiple processing steps to be turned into solar cells, which are then combined to form modules.