Alternating current is defined as electric current which changes its direction (polarity) in regular repetition. Negative and positive instantaneous values complement each other in such a way that the current is zero on a time average. The opposite of alternating current is direct current (DC), which does not change in time (apart from switching operations or influence effects), or, in extended meaning, which is a periodic current whose direct component has priority. It is mixed current (in the extended meaning).
The most common electrical power supply in the world is the sinusoidal alternating current. The simple generation and simple transformation of the alternating voltage are the reasons for this preference.
Designation for the path of solar radiation through the atmosphere to the earth. The angle of the sun in the sky affects how much sunlight reaches our atmosphere. When the sun is vertical, it takes the shortest path, but when it is lower on our horizon, the light travels a longer distance before reaching us. This means that more of the sun’s rays are scattered and fewer of them reach the Earth’s surface.
Alignment refers to both the way in which the solar modules are mounted in a particular direction (in the northern hemisphere, usually towards the south) and the angle at which they are set up. In Germany, solar modules are usually tilted between 10° and 30° in order to optimize the irradiation yield over the entire year and align it with the average azimuth of the sun.
In the energy industry – i.e., on the electricity market – electricity/gas customers and suppliers are grouped together in a so-called balancing group. These are virtual energy quantity accounts managed by transmission networks and generally accessible by end customers or balance responsible parties. These accounts include everything that is fed into the grid in a given area.
“BoS” stands for Balance of Systems. These are all other components of a functioning photovoltaic system, except solar modules and inverters. The BoS consists of all the substructures, power cables and other small parts needed to install a rooftop or ground-mounted solar system on site.
Defective, dirty or shaded cells/modules are bridged. The current flows past them, the power of the system is only reduced by the power of the bridged cells/modules.
Characteristic curve measurements are an excellent way to determine important characteristic values of modules in a PV system and to localize possible performance problems. This is usually done with specialized measuring equipment. The most important characteristic values, such as the maximum power point, indicate whether a module is functioning properly or is producing deficient yields due to degradation, hot spots or other damage.
Crystalline solar cells consist of high-purity silicon on a crystal basis and are differentiated into monocrystalline or multicrystalline. During the manufacturing process it is cut into thin slices (wafers). Taking into account the production costs, crystalline solar cells are more expensive than thin film. However, they make up for the higher price with their much better efficiencies.
The data logger is a stationary data storage device that archives inverter data and enables continuous operational monitoring of the photovoltaic system. This also works over long periods of time.
As solar modules age, their efficiency decreases. A common assumption is that the performance is degraded at a rate of 0.5% per year.
The accident prevention regulation “Electrical installations and equipment” DGUV V3 stipulates that electrical work equipment must be regularly checked for proper condition. This inspection is part of preventive maintenance and must also be performed regularly in PV systems.
Diffuse solar radiation refers to the sun’s rays that are reflected or scattered by various surfaces before they hit your PV modules. It too can be used to generate solar energy, especially when it is dark in winter. It contributes a lot to the electricity production of PV systems at this time.
Direct current is a type of current that always flows in the same direction, while alternating current changes direction at regular intervals. The electricity generated by a solar panel is direct current, while the power grid uses alternating current. Inverters convert direct current into alternating current before passing it on.
Direct radiation is the part of solar radiation that reaches the earth’s surface directly. Direct radiation is solar radiation that is reduced mainly by reflection, scattering or absorption. A common reason for this is when the sky is cloudy.
“Due diligence” refers to a carefully conducted type of risk assessment, the analysis of which aims to evaluate the strengths and weaknesses of an asset, such as a PV system.
The “Renewable Energies Priority Act” is part of the comprehensive package of directives aimed at achieving climate protection goals. These include goals such as moving Germany away from fossil fuels, transforming the energy supply and increasing the share of renewable energies in the power supply to at least 80 percent by 2050. The EEG offers investors and plant operators security through fixed compensation rates. The EEG has been copied by more than 50 countries and regions worldwide.
This factor is intended to represent the ratio between the electrical power generated by a PV module and the power of the solar radiation incident on that PV module.
Photovoltaic modules have an efficiency between 10 and 25%, depending on the technology. They can be degraded for a variety of reasons (e.g., contamination, module damage). There are many different types of management and improvements that can be made to ensure stability.
The electric potential of a point is the ratio of the potential energy of that point and the charge of the body. Voltage is the potential difference between any two points in an electric field.
Electroluminescence is a unique process that captures images of the PV modules with a special camera. To do this, the PV modules are reverse energized in the dark, causing them to begin generating light in the infrared range. This makes it easier to identify damaged cells that may have broken into smaller pieces, for example. Other problems, such as shorted solar cells or minute hairline cracks, can also be identified.
The feed-in tariff, a stipulation in the corresponding “Renewable Energy Sources Act”, has proven its worth. For PV power plants, there are different prices for different sizes. For example, smaller rooftop solar plants receive a higher feed-in tariff than large ground-mounted plants.
Feed-in tariffs are a long-term incentive that creates considerable investment security. The amount you are paid must be recorded by your feed-in meter. The invoice can then be sent automatically to the responsible grid operator or billed directly by the grid operator via credit.
Feed-in meters have been mandatory in Germany for grid-connected solar systems since the introduction of the EEG. With this feed-in meter, which is installed in addition to the normal gas and electricity meter, you can measure the energy fed into the grid.
1,000,000 x kilowatt hour (kWh)
1000 x megawatt hour (MWh)
The measurement of global radiation is a common measure of the total radiation incident at a point on the earth’s surface. It is measured in W/m² and includes both direct and diffuse radiation.
Photovoltaic systems in Germany are generally connected to the public grid and feed the electricity generated into the distribution grid. The direct current generated in photovoltaic modules is converted into alternating current with the help of inverters in order to feed it into the grid.
A solar hotspot (German: “heißer Fleck”) is simply a localized overheating of a module. Harmful heat damages the cells, in the worst case the entire module can be destroyed. Localized overheating can be caused by shading, for example.
The direct current generated by the solar cells is converted into grid-compliant alternating current. This allows you to power your household appliances while relying on a clean power source. The conversion between DC and AC provides an interface between the solar panels and your home’s power grid.
This unit is used in the power industry to measure electrical energy production. If a power plant produces 1000 watts for one hour, it has produced one kilowatt-hour. Two other energy units commonly used to measure energy output are the megawatt-hour and the gigawatt-hour.
The usual unit of measurement for solar power plants is kilowatts. One megawatt is equal to 1 million watts, and one kilowatt peak is equal to one thousand watt peaks. The “p” in these abbreviations comes from the English word “peak,” which refers to the maximum power output of a solar cell or panel over a period of time. For photovoltaic modules and systems, the value refers to the rated power. It is measured under standardized test conditions (irradiation 1000W/m², 25°C module temperature and AM 1.5). At higher irradiation or lower temperatures, the performance can also be correspondingly better, whereas at lower irradiation or higher temperatures, it can be worse.
The performance of a PV system cannot be maintained without regular maintenance. For example, the following checks and measurements can be performed as part of routine maintenance: We perform a visual inspection not only of the various modules, but also of the frames and inverters. For example, we measure current and voltage curves. In addition, we check all plug-in and terminal points for proper condition.
The Maximum Power Point (MPP) marks the point at which a solar cell produces its maximum power. This is calculated from the applied voltage multiplied by the current and changes as environmental parameters such as solar irradiance change.
1,000 x kilowatt hour (kWh)
1,000 x kilowatt peak (kWp)
One of the most important aspects of technical management is system monitoring. This involves checking for faults and malfunctions in electrical power generation plants and then eliminating them.
It is used to detect and eliminate short-term yield losses and to counteract insidious effects such as the reduced performance of a system due to progressive soiling or degradation. This ensures good performance of the solar plant in the long term.
Network security management is the process of reducing the power consumption of a solar system during times of high grid load, e.g. when electricity cannot be transported to where it is needed due to transmission restrictions. Larger PV systems of 100 kWp have been participating in NSM since July 1, 2012, and can be curtailed to 60%, 30%, or 0% of their rated capacity, depending on the situation. This NSM process allows maximum network capacity and also prevents power outages. The systems are generally used by the distribution network operator with telecontrol devices or ripple control receivers.
(Photovoltaic) ground-mounted systems, or PVFs, include all solar systems that are not building- or object-mounted. It is a permanently installed system where the photovoltaic modules can be oriented at an appropriate angle (called the azimuth angle) to the sun. One way to increase the yield of ground-mounted systems is to use tracker systems that follow the path of the sun.
Power, measured in watts (W), is the rate at which electricity is produced by a generator. It is determined by multiplying voltage and current.
The Performance Ratio is a number calculated to represent the potential electrical productivity of a particular photovoltaic system. The Performance Ratio is the ratio between the actual energy fed into the system and the potential energy that can be generated by radiation when these factors are taken into account. The Performance Ratio describes how much of the collected energy is used for heating or electricity generation; This can be calculated using in-loco measurements, such as looking at data provided by radiation sensors and pyranometers.
The term photovoltaic refers to the process of converting solar radiation into electrical energy. All PV systems are based on the principle of the photoelectric effect, in which direct current is generated by illumination with light. The power of a solar panel is determined by the intensity of solar radiation and orientation, as well as a number of other factors.
The photovoltaic effect is the generation of electricity from light. When light falls on a semiconductor, electrons (with opposite charge) are separated and driven out of the material by an electric field. In a solar cell, these electrodes are made of silicon mixed with boron or phosphorus. Light photons in the form of sunlight break the bonds between atoms, creating an electrical voltage.
A photovoltaic module consists of several solar cells connected in series (series connection), often encased in plastic or glass to protect them from the environment. As a generator, they form the heart of a PV system, as they produce electricity. (see also photovoltaics)
Crystalline solar modules can be damaged by HVS (High-Voltage-Stress) and thus reduce their performance. HVS is a type of degradation. It mainly occurs only in crystalline modules, but some thin-film modules are also affected. PID can be detected by both electroluminescent and thermographic tests. PID is caused by the high system voltages and resulting leakage currents between the solar cells, the embedding material, the glass and the grounded aluminum frame of a PV module. The charge carriers on the anti-reflective layer accumulate and become electrically inactive, which means they no longer generate electricity. In principle, PID is reversible.
Pyranometers are the most commonly used sensors for measuring global and diffuse radiation. A blackened thermopile, thermocouples in series, can be used as a sensor and has measurement uncertainties smaller than 3%.
The rated power is the maximum power that a solar module or PV system can produce under standard test conditions (STC) and is measured in watts peak (Wp).
Reference cells are used to calibrate solar cells and ensure better production of PV modules. They are usually the same material as solar cells. The measurement uncertainty of irradiance measurements with reference cells is higher than with pyranometers, but they are also less expensive.
As part of the NSM, the telecontrol system has a similar function to the ripple control receiver. Unlike the ripple control receiver, the telecontrol system also enables the transmission of network information between switchgear in solar installations and other devices.
In this installation of solar power generators, the modules are fixed at a distance of about 5-15 cm above the roof with steel/aluminum/stainless steel fixtures. This variant is often used in the private sector. Hall roofs, barn roofs and roofs of commercial buildings can benefit from a photovoltaic system.
In ground-mounted PV systems, one row of modules can be shaded by the row of modules in front of it, especially in the winter months. This can also happen when the sun is at its highest. The reduced yields in winter are taken into account in the system design, so fluctuations are not to be feared. On the contrary, these are compensated by correspondingly higher yields in the very high-yield summer months. In other words, you see an average profit over all seasons. The diffuse radiation prevailing in winter makes the negative effect of row shading almost negligible.
“Snailtrails” is a term used to describe the visual change in printed conductive traces on solar modules in crystalline solar cells. These are the corrosion marks on the silver contacts of the modules that occur when there is a micro hairline crack in the cell. The term is derived from the appearance of the lines on PV modules that are obvious during visual inspection.
A solar cadastre records the energy potential of the roof surface. Roof orientation, pitch and shading are taken into account in the energy efficiency analysis.
The Standard Test Conditions (STC) are the conditions under which a solar module is tested. These include 1000 W/m² irradiation, 25°C cell temperature and an air mass of 1.5.
Technical operation management usually includes maintenance (see also maintenance) and repair of technical components of a solar park such as solar modules, inverters, data loggers, etc. Further technical operation management services may include plant monitoring, green cutting, module cleaning and the preparation of technical reports.
With the help of thermal imaging cameras and a few other quality checks, you can continuously perform your system quality control during operation. This allows you to detect any defects as they arise, without any loss of yield.
Thin-film solar modules are the most common type of module alongside crystalline solar cells. They are manufactured by applying photoactive semiconductors to carrier materials such as stainless steel or glass. This forms a thin layer. The advantages of this coating process are relatively low production costs and high flexibility. Solar cells with such a coating are also less susceptible to shading. However, the efficiency is lower compared to silicon cells used in crystalline solar cells.
The angle between the horizontal plane and the solar modules is called the tilt angle. The tilt is an attempt to allow as much sunlight as possible to fall on the PV module to achieve the best possible yield. The optimum tilt angle depends on the location of the solar array and the average position of the sun (azimuth).
A transformer is used to convert the voltage in the solar modules to a voltage suitable for feeding into the power grid. It usually consists of two or more coils / windings, usually wound from insulated copper wire. The coils are located on a common magnetic core. A transformer converts an AC input voltage applied to one of the coils into an AC output voltage that can be tapped at the other coil. The AC input voltage and the output voltage are related by the ratio of the number of coils. More turns for a coil means a higher input strength. A higher input voltage on one coil also means a higher generated output voltage.
As common sources of energy, solar and wind power have been described as volatile because they provide energy at different times of the day and during bad weather. Fossil fuel plants are an example of a more stable source because the output is much more predictable.
The voltage in an electric field indicates how much energy is required to move a charge in it. The voltage expresses the specific working capacity of the field at a given charge and is given in the unit volt.