VODASUN Glossary - The solar lexicon

All terms explained from A-Z!




























The purchase guarantee is a central element of the Renewable Energy Sources Act (EEG), which was introduced in Germany in 2000. It guarantees operators of photovoltaic, wind power or biomass systems a fixed payment for the electricity they feed into the public grid.

The EEG obliges grid operators to prioritise the use of electricity from renewable energy sources and to pay the system operators a feed-in tariff for 20 years.

Purpose of the purchase guarantee
The purchase guarantee is therefore an important mechanism for promoting the energy transition and achieving climate targets. The remuneration is intended to incentivise investment in renewable energies. This gives investors and operators of renewable energy plants security and minimises the risk of investing in a constantly developing technology.

The correct alignment of solar modules is the key to success for any photovoltaic system.

The aim is to position the panels in such a way that they capture the maximum amount of sunlight, which in turn maximises electricity production. To get the most out of solar panels, it is crucial to position them so that they utilise direct sunlight as effectively as possible.

Although south-facing is often considered the golden standard, panels facing east or west can also deliver impressive results, especially as they produce electricity during peak consumption times in the morning and evening.

Not forgetting the angle of inclination of the panels. The rule is simple: the more directly the sun's rays hit the panels, the more energy they can generate. For areas in Central Europe, an angle of 30 to 35 degrees is usually considered ideal.

The amortisation period, also known as the payback period, is the time frame in which a photovoltaic system (PV system) recoups the initial investment costs through the income generated. So you could say it's about the time until the investment "pays off".

In essence, amortisation is a process that shows how the expenses for a project are covered by the resulting income.

So if you buy a photovoltaic system for 15,000 euros and it generates 3,000 euros a year in profit, you will have recouped your investment after five years. The time it takes to amortise the investment plays a major role in deciding whether or not to make such a purchase.

In the world of solar energy, the anti-reflective coating on solar modules plays a key role. This fine coating on the top of the modules works wonders by minimising the reflection of sunlight and thus increasing the efficiency of the modules.

Why is such a layer necessary?
It's due to the simple fact that some of the sunlight that hits a solar panel is normally reflected back into space instead of being converted into useful electricity. The anti-reflective coating comes into play here by cleverly adapting the way in which light is reflected from the surface of the module. The result: more light is captured and converted into electricity, which increases the overall yield of the solar system.

In the context of energy supply, self-sufficiency refers to the ability to operate independently of the public power grid. Obtaining electricity from your own sources, such as solar panels, increases this degree of independence.

When considering the benefits of a solar energy system, the degree of self-sufficiency plays an important role. It shows what proportion of annual electricity consumption can be fully covered by your own solar system and how much electricity still needs to be purchased from the grid.

The self-sufficiency rate indicates the degree of independence achieved as a percentage. A solar system without additional storage usually achieves self-sufficiency of around 30 to 35 per cent. Conscious consumption, such as using the washing machine during the day instead of in the evening, can increase this value and thus save costs. The integration of an energy storage system can significantly increase the self-sufficiency rate to 70 to 80 per cent or more.


The base load in the context of photovoltaics refers to the constant electricity consumption that is always present regardless of the time of day and weather conditions. As a rule, this consumption is lowest at night and thus defines the base load.

Photovoltaic systems can cover this base load by generating electricity during the day and feeding it into the public grid. In this way, dependence on fossil fuels can be reduced and the energy transition driven forward.

Solar batteries, also known as solar batteries or solar energy storage systems, are devices that have the ability to store the electrical energy generated by solar systems for later use.
They convert this energy into a chemical form and release it again as electrical energy when required.

Originally, they were mainly used in self-sufficient systems, so-called stand-alone systems, to store electricity that was not used immediately instead of letting it expire. More recently, however, solar batteries are also increasingly being used in grid systems to maximise self-consumption of self-generated electricity.

Boron plays a crucial role in the production of solar cells, as it contributes significantly to improving their performance. It is primarily used to enrich the silicon, the core component of almost all solar cells, in the p-layer, which usually forms the back of the solar module and is positively charged.

This enrichment serves to increase the electrical conductivity of the module, whereby boron is particularly suitable due to its three valence electrons.

In addition to boron, gallium, indium and aluminium are also used as alternatives for this process, but boron remains a preferred element in solar cell technology due to its specific properties.

The term Back Surface Field (BSF) comes from solar cell technology and refers to the surface on the back of a module. This is the side facing the roof.

The back surface field has a special function: this side facing away from the sun is positively charged and thus improves the conductivity of the entire module. This prevents the loss of electrons and the solar current can flow from module to module at full voltage.

In other words, the so-called doping of the back surface field provides the positive charge and protection against electron loss.

A bypass diode is an electrical component that is installed in photovoltaic solar modules as a safety measure. These semiconductor diodes reduce the effect of partial shading on energy production and protect against overheating. This is because if a PV module or cell is partially shaded, a high resistance state or electron jam can occur. The module heats up - possibly to such an extent that there is a risk of fire.

This has an effect on the current flow and the power of the entire module, as the module is only as powerful as its weakest cell. The bypass diode manages to divert the current around the shaded area and therefore does not disturb the unshaded part of the module in its energy production.

Bypass diodes are normally installed in each photovoltaic cell and are connected in parallel.


A charge controller, also known as a solar charge controller or solar regulator, is an electronic device used in photovoltaic systems to control and monitor the charging process of batteries. The main purpose of a charge controller is to protect the batteries from overcharging or deep discharging in order to extend their service life and ensure an efficient energy supply.

A commissioning report in photovoltaics is a document that documents the official completion and successful commissioning of a photovoltaic system. It contains important information about the installation, connection and function of the system.

Typically, details such as the installed output of the photovoltaic system, technical specifications, test results, date of commissioning, manufacturer information, electrical parameters and other relevant data are recorded in the commissioning log. It serves as formal confirmation that the system has been properly installed and complies with the applicable standards.

The commissioning report is not only an important document for the system operator, but can also be requested by grid operators and insurance companies to ensure that the system is operating safely and efficiently. It also provides support for any warranty claims and contributes to transparency and quality assurance in the field of photovoltaics.

Components or parts are all smaller functional units of a system. With a PV system theclassicn components are the modules (panels), cables and roof hooks as well as the mounting frame, inverter, electricity storage and electricity meter.

CO2, also known as carbon dioxide, is a colourless, odourless and non-flammable gas that occurs naturally in the atmosphere. It is one of the most important greenhouse gases and plays a central role in global climate change.

How is CO2 produced?

CO2 is sometimes produced during cellular respiration in many living organisms, for example when we breathe. The animal industry is also responsible for large quantities of greenhouse gases. However, CO2 is released particularly when fossil fuels, i.e. carbon-containing materials such as oil, gas and coal, are burnt. This use in industry, transport and buildings is one of the main reasons for the increase in CO2 levels in the atmosphere.


Degression describes the principle according to which the amount of the feed-in tariff is calculated. This is an annual reduction in the remuneration that plant operators receive for every kWh of electricity fed into the grid. Self-produced electricity also includes electricity from photovoltaic systems. An alternative to feeding electricity into the grid is to use an electricity storage system.

The degression is based on several factors, such as the production costs of modules and the feed-in volume of the previous year. Generally speaking, the more PV systems are installed in Germany, the lower the feed-in tariff is, meaning that the tariff has been falling continuously for years. This alone makes the purchase of a solar system worthwhile.

People often think of development plans primarily in terms of building houses, but they also play a role that should not be underestimated in the world of solar energy, especially in the construction of large photovoltaic systems. These systems, usually designed as ground-mounted systems, must fulfil certain criteria in order to be eligible for remuneration for electricity fed into the grid.

A crucial point here is that the plant must be located within the area covered by a development plan. This is determined by Section 32 of the Renewable Energy Sources Act (EEG), whereby the exact definition of the scope of application can be found in Section 30 of the Building Code.

Compliance with these conditions is essential for the operator of the system to be entitled to have the electricity generated purchased by the energy supplier and remunerated accordingly.

Due diligence comes from the English and means "due care". So that thisrefers to the precise examination and analysis prior to leasing, buying or selling a PV system, particularly with regard to commercial and economic, legal and technical conditions.


The EEG levy (Renewable Energy Sources Act) is a fixed component of the electricity price and contributes to the promotion of green electricity. It ensures that the price difference between traditionally generated electricity from fossil fuels and green electricity from renewable sources is equalised.

Electrical voltage, symbolised with (U), is the measure of the difference in electric field strength between two positions, an essential factor for the movement of electricity. Volt (V) is the unit in which this voltage is measured.

Within the photovoltaic sector, different voltage levels are crucial, including the open-circuit and short-circuit voltage. The open-circuit voltage reaches its maximum value at a current of zero. In contrast, the short-circuit current is present at minimum voltage and maximum current.

The unit of measurement for electrical energy transfer is the watt (W), where one watt is equal to one joule per second. One kilowatt (kW) corresponds to 1,000 watts. In the case of solar systems in particular, however, the term nominal output is often used, expressed in kilowatts peak (kWp). The "Peak" in the name refers to the maximum performance of the system under optimum test conditions.

The emergency shutdown for photovoltaic systems is a safety device that is used to interrupt the power supply to the system in an emergency. This may be necessary, for example, in the event of maintenance work, faults or hazardous situations.

It usually consists of a switch or a device to ensure that there is no electrical hazard when working on the system and to be able to react quickly in an emergency.

The German Renewable Energy Sources Act (EEG) stipulates that your energy supplier, often referred to as the grid operator, is obliged to take the electricity that you produce with your photovoltaic system and feed into the public grid and remunerate you accordingly.

Before accepting your solar power, the grid operator checks its grid compatibility. The feed-in point, i.e. the point at which your electricity flows into the grid, is determined within this framework. This regulation applies to photovoltaic systems with an output of up to 30 kWp. For systems that exceed this capacity, prior authorisation from the grid operator is required for the feed-in.

An energy supply company (EVU) is a company that specialises in the generation, transmission, distribution and sale of energy. These companies play a central role in the provision of solar energy for various applications, from private households to industrial facilities.

The main tasks include the installation and operation of solar systems, the transport of the solar power generated through the network and the sale and distribution of solar energy to end consumers.

An expert opinion is a document prepared by an expert that assesses the condition and functionality of a photovoltaic system.

The following points are analysed in the report:

  • General information:System description, location, year of construction, system manufacturer.
  • Technical inspection:Solar panels, inverters, cabling, installation.
  • Electrical testing:power measurement, yield analysis, residual current protection.
  • Maintenance and servicing:Documentation of the maintenance history, recommendations for future maintenance intervals.
  • Summarised assessment:Assessment of the condition and functionality of the system, with recommendations for repairs or improvements if necessary.


In 2000, the Renewable Energy Sources Act (EEG) introduced feed-in tariffs - a kind of financial incentive for feeding solar power into the public grid.

The aim of this measure was to encourage homeowners to install solar systems and thus actively contribute to the energy transition. As of January 2024, the tariff is 8.20 cents per kilowatt hour.

With so-called full feed-in, all the electricity produced ends up directly in the public grid without the system owner deriving any direct benefit from it. The company's own requirements are covered entirely externally, as no self-generated electricity is used.

This contrasts with partial feed-in, also known as surplus feed-in, where part of the electricity produced is used for own consumption and only the excess is fed into the grid. This method ensures a basic level of self-consumption, which can be supplemented by purchasing from the grid if necessary.

Another option is the use of a solar energy storage system, which temporarily stores the electricity produced and thus enables it to be used even when there is no direct sunlight - an attractive alternative to drawing electricity directly from the grid.

A feed-in meter documents how much electricity you feed from your own energy source, such as a solar system, into the general electricity grid instead of keeping or storing it for your own use. This device enables you to receive remuneration for the electricity supplied to the grid, with the level of remuneration being determined by the Federal Network Agency.

The feed-in meter is the centrepiece of billing when it comes to calculating the financial credit you receive for every kilowatt hour of electricity fed into the grid.

In contrast, a consumption meter records how much electricity you draw from the grid.
Owners of photovoltaic systems may also be interested in a bidirectional meter that combines the functions of feed-in and consumption in a single device. Regularly checking your feed-in meter is important to ensure that you receive the full remuneration to which you are entitled and that no money is lost due to any malfunctions.

Fire protection encompasses all measures taken to prevent a fire. Ideally, this takes into account local fire protection regulations, technical guidelines and standards as well as building-specific features.

Flat roofs are all roofs with an angle of inclination of less than ten degrees.

In order to install a PV system on a flat roof, elevation is essential. An elevation is the installation of a bracket or racks for solar modules. This is intended to compensate for the insufficient angle of inclination and ensure that the angle of irradiation is approximately perpendicular to the module surface.

A foil roof refers to a roof construction in which a flexible, often waterproof foil is used as the main covering material. These films are usually made of plastics such as PVC (polyvinyl chloride) or TPO (thermoplastic polyolefin). The use of foils instead of traditional roofing materials such as tiles or slates offers various advantages:

  • Lighter than traditional roofing materials
  • Flexibility for uneven and complex roof shapes
  • The installation is very simple
  • Waterproof
  • serve as integrated roof waterproofing


In photovoltaics, the term "generator" refers to the part of a solar power system that is responsible for converting sunlight into electrical energy.

The photovoltaic generator is therefore the overall system that converts sunlight into usable electrical energy. It is important to note that the term "generator" is not used here in the traditional sense of a mechanical generator, but refers to the entire set of components that work together to generate electricity from solar energy.

Gigawatt (GW) is a unit of measurement for power and represents one billion watts. In the photovoltaic industry, this unit is used to express the capacity of solar systems.

Gigawatt peak (GWp) refers to the maximum output under ideal conditions (optimum solar radiation, temperature, orientation). The amount of energy actually produced is measured in gigawatt hours (GWh). 1 GWh corresponds to the energy that a plant with a capacity of 1 gigawatt would produce in one hour.

A grid operator in photovoltaics is responsible for the operation and maintenance of the electricity grid. It plans, builds, maintains and operates transmission and distribution grids that transport electricity from generators to consumers.

It must ensure that the electricity generated by the systems is fed into the grid efficiently and reliably. To this end, it monitors grid stability, provides feed-in and withdrawal capacities and handles feed-in contracts and invoicing with the system operators. In addition, the grid operator is responsible for the safety and reliability of the electricity grid by recognising and eliminating bottlenecks and faults in the grid.


The harvest factor in photovoltaics describes how much energy a photovoltaic system generates over its lifetime compared to the energy required for its production, transport, installation and disposal.

A higher harvest factor signals a more efficient and environmentally friendly production of energy. This key figure is crucial for assessing the ecological footprint and the overall environmental impact of photovoltaic systems. A positive harvest factor indicates that the system produces more energy than is consumed over its entire lifetime, which indicates a favourable energy balance.

In the fascinating field of solar energy, the term "high voltage" refers to an electrical voltage that is generated in solar energy systems and is often higher than the standard grid voltage.

This special type of voltage is generated at the moment when the direct current coming from the solar cells is converted into alternating current suitable for the electricity grid. A key element in this process is the inverter. The benefits of this high voltage are particularly evident in its ability to transport the electricity produced efficiently over long distances, a property that is particularly invaluable for large photovoltaic systems.

A hot spot in photovoltaics refers to localised overheating or heating in a solar module. These hot spots can occur if a certain area in the module generates more current than the rest. This can be caused by partial shading, defects in the cells or poor connections.

Excessive heating at a hot spot can lead to degradation of the cells and impair the performance of the entire module in the long term. It is therefore important to avoid hot spots and ensure that photovoltaic systems are free of shadows and malfunctions. Monitoring systems in solar modules can help to detect hot spots at an early stage and take appropriate measures to maximise the efficiency and service life of the system.


The term inverter is synonymous with the inverter, which plays a crucial role in PV systems. An inverter converts the direct current (DC current) generated by the solar modules into usable alternating current (AC current).

Solar modules generate direct current, whereas most electrical appliances and the public power grid use alternating current. The inverter therefore plays a decisive role in converting the solar energy generated into a form suitable for consumption or feeding into the grid.



Kilowatt (kW) is a unit of power in photovoltaics. It is used to measure the amount of electrical energy generated or consumed per unit of time.
1 kW corresponds to 1,000 watts.

With regard to photovoltaic systems, the nominal output of the system is often specified in kilowatts (kW). This indicates how much electrical power the system can produce under standardised conditions.


A lease is an agreement between two parties whereby one party grants the use of its property to the other party for a fee. The lessee pays the lessor a utilisation fee and in return receives the rights to the income generated from the leased property.

In the case of roof leases, there are various agreements in which the lessor usually participates in the income from the PV system. Typical models include:

  • A percentage share of the investment income.
  • A flat-rate fee per kilowatt output.
  • A flat fee per square metre of roof area.
  • A one-off payment of a predetermined amount.
  • An advance payment that is made monthly, semi-annually or for the entire period of use.


A maintenance contract is a binding agreement between a PV system manufacturer and a system operator. Although PV systems are generally considered to be low-maintenance, regular maintenance offers clear advantages as it guarantees long-term yields and warranty claims.

Maintenance contracts can be designed in a variety of ways. Some, for example, include annual maintenance, while others also provide for a visual inspection, often on a quarterly basis. Remote monitoring is also becoming increasingly important.

The megawatt hour is an extended unit of measurement for energy, abbreviated to MWh, which is often used in industry or other areas in which large quantities of electrical power are quantified. 1 MWh corresponds to 1,000 kWh.

1 micrometre corresponds to one thousandth of a millimetre or one millionth of a metre and is abbreviated to µmA solar cell has a layer thicknessof crystalline siliconandis currentlyaround200 to 240 micrometres (0.2 – 0.24 mm).

Mismatch is the power loss that can occur due to inconsistencies between the individual solar cells in a photovoltaic module. Each solar cell in a module has slightly different electrical properties due to manufacturing variations or environmental influences.

A mismatch can affect the overall performance of a photovoltaic system, as the weakest modules can limit the performance of the entire system. To minimise mismatch, optimisers or microinverters are used to ensure that each module achieves its maximum output, regardless of the conditions of the other modules.

The module efficiency in photovoltaics describes the efficiency with which a solar module converts solar energy into electrical energy. Expressed as a percentage, it is the ratio of the electrical power generated by the module to the irradiated solar power.

A higher efficiency means that more sunlight is converted into electricity, which means that the module works more efficiently. Most modules have efficiencies of between 15 % and 22 %, although innovative technologies can achieve higher values.

High efficiency is particularly important where roof space is limited or space is restricted, as modules with high efficiency generate more power in a smaller space. Efficient modules therefore help to maximise the overall output of photovoltaic systems.

A module string in photovoltaics refers to a series of solar modules that are electrically connected together to operate as a single unit in a photovoltaic system. These modules are connected in series, which means that the electrical current flows through each module before being passed on to the next.

The purpose of a module string is to increase the voltage in order to fulfil the requirements of the inverters. Inverters are used in photovoltaic systems to convert the direct current (DC) generated into alternating current (AC) that is suitable for use in the power grid or in buildings.


The nominal voltage in photovoltaics refers to the voltage at which a solar module or photovoltaic system reaches its maximum output under standard test conditions.

Nominal voltage is specified in volts (V) and is a factor for the compatibility of solar modules, inverters and other system components. The nominal voltage of a solar module is typically between 20 V and 40 V, while the nominal voltage of an inverter must be adapted to the voltage of the domestic grid (e.g. 230 V in Europe).

Similar to the rated power, the rated voltage is a guide value and the actual voltage may vary under real conditions due to factors such as temperature, irradiation and ageing of the modules.


The open-circuit voltage is the voltage measured at the connections of a solar cell or solar module. It represents the highest electrical potential difference that the solar cell can achieve under current conditions and is therefore a key indicator of the maximum output.

Measured in volts (V), the open-circuit voltage varies depending on the intensity of the sunlight, the module temperature and the characteristic features of the material. This parameter is crucial for assessing the efficiency of solar modules and plays a key role in the planning and monitoring of photovoltaic systems.

Operating costs or running costs are all those costs that are incurred on a recurring basis. Typical time intervals for the calculation are one month or one year. The operating costs of a photovoltaic system amount to around 2 - 3 % of the investment costs per year. The question of operating costs is strongly related to the type of system and can also depend on local meteorological conditions.

The main cost factors are maintenance and monitoring, repair, cleaning, insurance and the financing of the PV system. The costs for PV insurance should be estimated at around 0.3-0.8 % of the system purchase price.

Self-consumption includes the electricity that operators of systems generate themselves and consume in their buildings either directly or at a later date using an electricity storage system. Electricity that is fed into or drawn from the grid does not fall under self-consumption.

With a photovoltaic system, the primary goal is to maximise the proportion of self-generated electricity. This increases independence from the public electricity grid and helps to reduce the financial outlay for electricity costs.


In photovoltaics, parallel connection refers to a connection of solar cells or modules in which the electrical connections are connected in parallel. In a parallel circuit, the voltage remains constant while the current is added. This makes it possible to increase the total current without affecting the total voltage.

In the context of solar cells or modules, parallel connection makes it possible to adjust the electrical parameters in order to optimise the overall efficiency and performance of the photovoltaic system. Parallel connection can increase the total current, especially if several modules are connected in parallel to an inverter. This is a common practice in solar power systems in order to maximise the overall output.

The peak power is measured in the unit watt peak (Wp) and serves as a reference value for comparing the performance of solar cells or modules. It indicates how much energy can be generated per unit of time under optimum conditions.

The actual output of a photovoltaic system may deviate from the peak output due to environmental conditions, module inclination, shading and other factors.

Photovoltaics is the conversion of sunlight into electrical energy using solar cells. This technology enables electricity to be generated directly from sunlight by photons (particles of light) hitting the solar cells and setting electrons in motion. These electrons set in motion generate an electric current.

Photovoltaic systems consist of several interconnected solar cells arranged in modules. The energy collected can either be used for self-consumption, stored in batteries or fed into the power grid.

According to §3 para. 2 of the German Renewable Energy Sources Act (EEG), the operator of a plant is anyone who uses it to generate electricity from renewable sources or mine gas, regardless of who owns the plant.

In addition to the legal definition, system operators are often responsible for more, including the operation, maintenance and repair of their photovoltaic systems. They are often also responsible for monitoring electricity generation and handling transactions with the electricity supplier. The financing of the photovoltaic system, whether through equity, bank loans, subsidies or a rental solution, depends on the system purchase model chosen.

The power tolerance indicates the extent to which the actual power of a photovoltaic module can deviate from the nominal power. This tolerance is expressed as a percentage and takes into account possible fluctuations during the manufacturing process and measurements.

Photovoltaic modules usually have a power tolerance of ±3 per cent, which means that the actual power can be between 194 and 206 watts if the nominal power of the module is 200 watts.

Profitability is another term for economic efficiency. The calculation of the economic efficiency of a solar energy system depends on numerous factors. This often includes the amount of the investment costs and the financing interest rate. In the case of solar thermal systems (with or without condensing boilers) and heat pumps, the profitability calculation is usually based on the annual savings of fossil fuels (such as gas, oil or coal).

In contrast, a photovoltaic system is financed primarily through the annual feed-in tariff. The operator of this system can call himself an electricity producer and the system can be depreciated for tax purposes, as the operator is considered an entrepreneur for VAT purposes.



The rated power in photovoltaics is the maximum electrical power that a solar module or photovoltaic system can generate under standardised test conditions.

The nominal power is specified in watts (W) or kilowatts (kW) and serves as a reference value for comparing the performance of solar modules.

It is important to note that the actual performance of photovoltaic systems under real conditions depends on various factors, such as

  • actual solar radiation
  • Ambient temperature
  • Inclination angle of the modules
  • Shading

If light hits a surface, it can be partially reflected. This process is known as reflection, and the reflected radiation is called reflected radiation.

With regard to photovoltaics, reflected radiation can play a role, as solar modules absorb the incident sunlight, while reflected light can be partially lost. Efficient photovoltaic systems therefore maximise light absorption and minimise reflection losses.

Reflection losses refer to the energy loss caused by the reflection of sunlight on the surface of a solar module. When sunlight hits the surface of a photovoltaic module, some of it can be reflected instead of being absorbed by the module. These reflected light rays are lost as energy and cannot be used to generate electricity.

In order to maximise the efficiency of photovoltaic systems, manufacturers try to minimise reflection losses. This is often achieved by applying anti-reflective coatings to the surfaces of the solar cells or modules. Anti-reflective coatings reduce reflection and increase light absorption, resulting in improved energy yield.

Regenerative energy, also known as renewable energy, refers to the inexhaustible forces of nature that are constantly renewing themselves.

Within the photovoltaic sector, solar energy is used to generate electricity. Photovoltaic systems, which convert sunlight directly into electricity, play a key role in promoting a sustainable energy supply. This technology allows us to utilise the endless supply of sunlight effectively and at the same time significantly reduce the environmental impact compared to traditional energy sources.

The roof orientation refers to the direction to which the roof faces. Together with the roof pitch and shading, it plays an important role in the yield of a PV system.

Although a south-facing orientation is normally regarded as ideal, photovoltaic modules can also deliver a significant proportion of their output with deviating roof pitches and orientations. It is therefore possible to orientate solar modules to the east or west and achieve similarly high yields. Above all, these modules can then produce electricity during the main usage times in the morning and evening. This means that less electricity needs to be stored temporarily as it is consumed directly.

In technical jargon, roof alignment is often referred to as the azimuth angle. In solar technology, the azimuth refers to the angle between the vertical plane and the meridian plane of a celestial body. This term may seem complex at first, but it is quite simple to understand.

The azimuth angle is used to provide precise information about the roof alignment. This is because with solar systems, every single degree has a major impact on the subsequent yield of the modules. A perfect south orientation has a south azimuth of 0°, a west orientation of 90° and an east orientation of -90°. The north-facing orientation of a roof occupies a special position. The azimuth here is 180°. If the roof of the house faces south-east, then there is a south azimuth angle of -45°. With a south-west orientation, the angle is then 45°.

Roof hooks are the link between a photovoltaic system and the roof. They fix the substructure of the PV system to the rafters so that it cannot move and is securely fastened even during storms. Without roof hooks, the metal rails of the PV substructure on which the solar modules are mounted cannot be fixed to the roof.

The assembly
The mounting rails for the photovoltaic modules are attached to the front of the U-shaped bracket, opposite the perforated plate. The roof hook is guided outwards through a recess in the roof tile. Today, there are specially adapted roof hooks for many standard tiles, which are available for various roof types such as slate roofs, Frankfurt tiles, plain tiles or shingle roofs.

The term roof pitch refers to the indication of how steep a roof is and is regularly given in degrees. It is responsible for a wide range of decisions relating to the roof, such as the type of roof covering or the installation of a photovoltaic system.

For PV systems, the roof pitch is particularly interesting because it has a strong influence on the yield of the system. Vertical sunlight on the modules is ideal for the photovoltaic system. In Germany, this is achieved on average with a roof pitch of 35 degrees.

However, deviations are certainly tolerable; for example, roof pitches of 30 degrees are also ideal for the installation of a PV system.


Semiconductors play a central role in the photovoltaic industry. They are the basis of solar cells, the smallest components of photovoltaic systems. Semiconductors are materials that are neither good conductors nor good insulators. Their electrical conductivity lies between that of metals and non-metals. Solar cells utilise the photoelectric effect to convert light energy into electrical energy. This effect means that electrons in a semiconductor can be triggered when they are irradiated with sunlight.

There are two layers of semiconductor material in a solar cell: an n-layer and a p-layer. The n-layer has a surplus of electrons, while the p-layer has a shortage of electrons. When light hits the solar cell, electrons are triggered in the n-layer. These electrons can then flow into the p-layer and generate a current there.

A series connection in photovoltaics describes the connection of solar modules one behind the other, i.e. in series.

In a series connection, the total voltage increases while the total current remains constant. This makes it possible to generate higher voltages, which is particularly necessary in applications where a higher voltage is required, for example when charging batteries or operating inverters to convert direct current into alternating current.

Shading, also known as shadowing, plays an important role in the field of photovoltaics, as it can impair the performance of individual solar cells within a system.

If a solar cell is exposed to shade, this can disrupt the electrical flow and increase the resistance in the affected cells. The result? These cells either no longer produce any electricity at all or only a fraction of what they could produce under optimum conditions. This effect can have a negative impact on the overall yield of the system, as even slight shadows lead to a noticeable drop in output.

Shading can be divided into two types: that which depends on the season and that which does not. Seasonal shading is caused by the changing position of the sun, which explains why solar systems often generate more energy in summer than in winter. Non-seasonal shading changes throughout the day and is caused by objects such as trees, chimneys or buildings, which cast different shadows depending on the time of day.

How can shading be reduced?
For homeowners, this means analysing the geographical location and optimum alignment of the solar panels in advance. An effective method of minimising the effects of shading is the use of bypass diodes. These clever little components conduct the current around the shaded areas and thus help to maintain the flow of energy through the remaining cells.

The short-circuit current is an important parameter in photovoltaics that indicates the maximum current that can flow through a photovoltaic module when it is short-circuited. In a short-circuited state, the connections of the module are directly connected to each other so that the current can flow unhindered.

The short-circuit current is often considered together with other parameters such as the open-circuit voltage and the maximum power point of a PV module in order to assess its performance and suitability for certain applications.

The snow load refers to the weight and load that snow exerts on solar modules and the associated mounting systems. The amount and type of snow as well as the pitch of the roof influence the snow load.

The effects of snow load on a roof depend on various factors, including the roof pitch, geographical location and type of snow. Fresh snow is lighter than compacted old snow, while wet snow has the highest weight. However, when wet snow compacts into ice at the edge of the roof, an additional load is created that is parallel to the roof surface.

It is important that photovoltaic systems and their mountings are designed to withstand regional snow loads in order to minimise damage and safety risks. Regional building regulations and standards often specify the minimum requirements for the design of photovoltaic systems with regard to snow load.

A solar collectoris a Part of the photovoltaic system that is used to convert sunlight into electrical energy. In photovoltaics, solar collectors usually consist of solar cells or photovoltaic modules made of semiconductor materials. These materials generate electrical currents when they are hit by sunlight, resulting in a direct conversion of light energy into electrical energy.

Solar energy refers to the energy obtained from the conversion of sunlight into electrical or thermal energy.

This is achieved by utilising solar cells in photovoltaic systems. Solar energy is a sustainable and renewable resource that helps to promote environmentally friendly energy sources. It offers a clean alternative to conventional energy sources and helps to reduce greenhouse gas emissions.

Solar thermal energy is a technology that utilises the thermal energy of the sun to heat water or heat rooms. In contrast to photovoltaics, which converts sunlight directly into electrical energy, solar thermal energy focuses on converting solar energy into thermal energy.

In solar thermal systems, solar collectors are used to capture sunlight and absorb the heat it contains. This heat is then used to heat water, which in turn is used in heating systems or to heat water. Solar thermal energy is used in private households as well as in commercial and industrial environments to reduce the need for conventional heating and hot water systems and to utilise a more sustainable energy source.

The solar yield of a PV system refers to the average annual amount of solar power generated by the system. The financial return, especially in the area of photovoltaics, is centred on income from feed-in tariffs and electricity cost savings. These can be determined using a photovoltaic calculator or by making enquiries.

The yield depends on various factors such as the orientation of the PV system, the efficiency of the modules, the quality and efficiency of the components and the regional solar conditions. The intensity of solar radiation is primarily determined by the geographical location of a place, its altitude above sea level and the distance to the equator.

Yields from years with high and low solar radiation balance each other out over the service life of a photovoltaic system.

The surface load describes the load per unit area that a solar system exerts on the roof. It depends on various factors, such as the module and roof type, inclination and additional loads due to snow, wind and the mounting frame. The surface load is particularly important for flat roofs, as stronger wind forces occur here, which require heavier anchoring.

Before installing a solar system, the stability and statics of the roof should be checked, especially in older houses.


The efficiency of solar cells generally decreases with increasing temperatures, which is why a low temperature coefficient is crucial in order to minimise the reduction in performance. The temperature coefficient indicates the extent to which the output of a solar module decreases when the ambient temperature increases by one degree Celsius.

In order to further minimise power losses, it is necessary to cool the solar modules sufficiently. This is primarily ensured by efficient ventilation of the modules. The temperature coefficient is therefore an important parameter for assessing the quality of a solar module.

The installation of solar systems on trapezoidal sheets is particularly easy thanks to the special shape of these corrugated sheets. The front of the sheets is trapezoidal in shape, which gives them the ability to withstand greater loads, such as large amounts of snow.

Trapezoidal sheets are often used to cover large roofs, for example in stables, sheds or commercial halls. Thanks to the uncomplicated installation of solar systems using special brackets, even previously unused roofs can be utilised to generate renewable energy. Installation can be carried out retrospectively by attaching rails and screws that are adapted to the sheet metal, or by using prefabricated brackets directly on the trapezoidal sheet.

For a safe installation, it is crucial that the trapezoidal sheet has a sufficient thickness of at least 0.88 mm to withstand the loads of a PV system.


Uninterruptible power supply (UPS) in relation to photovoltaics refers to a technology that aims to ensure a continuous power supply for electrical consumers even if the main power grid fails. This system is often used in conjunction with solar systems to ensure that the solar power generated is also available in the event of grid disruptions.

A UPS for photovoltaic systems usually consists of battery storage and an inverter. As soon as the main power supply fails, the UPS automatically switches to the stored energy and continues to supply the connected devices with power, ensuring an uninterrupted power supply. This is particularly useful for protecting critical loads such as emergency lighting, security systems or sensitive electronic devices from failure and maximising self-consumption of solar power.


The electrical voltage in photovoltaics refers to the potential that is generated in a solar cell or solar module by converting sunlight into electrical energy. When photons hit the solar cell, they trigger an electric current, which leads to a voltage.


A wallbox is a practical charging station for electric cars that allows you to charge your vehicle safely, quickly and easily. Basically, it functions as a kind of socket specifically for electric cars. Interestingly, the word "wallbox" translates as wall charging station. The terms wallbox, charging station and wall charging station are therefore often used interchangeably. These charging stations offer a convenient way to charge your electric vehicle and help to make electromobility more efficient.

The watt hour (Wh) is a unit of measurement for electrical energy. It corresponds to the consumption of an electrical appliance with an output of 1 watt for one hour.

A simple example: A 60-watt light bulb that lights up for one hour therefore converts 60 Wh.




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