Photovoltaic-Glossary

The coefficient of performance is the ratio between sun irradiance and the actual electricity generated. A deteriorated coefficient of performance can have different reasons (e.g. dirt, module failure). The causes of deterioration in performance are examined in the context of the technical management.

The commercial management of a solar park covers the commercial administration of the business operation of a photovoltaic system. The individual tasks of commercial management include, among others: controlling, accounting, financial accounting, performance and contract monitoring, claim management and the overall coordination of all project participants. The commercial management takes over as “caretaker” the business aspects of a PV project company.

Crystalline solar cells are made from very pure crystal-based silicon. We distinguish between monocrystalline and multicrystalline or polycrystalline cells. In the manufacturing process, the silicon is cut into thin slices (wafers). Depending on the crystalline structure, they may be either monocrystalline or polycrystalline solar cells. Compared to thin film solar cells, crystalline solar cells are more expensive but also achieve much higher efficiency.

The data logger is a stationary data storing device that stores inverter data and ensures a steady operational control of the photovoltaic system over longer periods of time.

Direct marketing is the sale of electricity – from renewable energy sources – to the electricity exchange or to end customers (e.g. large grid operators). According to the Renewable Energy Sources Act (EEG) “green electricity” is traded on the exchange on an equal footing with classically generated electricity and is thus available at the same market price. The legislator has introduced a promotion of direct marketing with the market premium model.

The “Act on Granting Priority to Renewable Energies” is a part of the comprehensive policy package to achieve the objectives of climate protection, among them, a 21% CO2-reduction by 2012 and also the reduction of the dependence on fossil and nuclear fuels. With its fixed remuneration rates (see also feed-in tariff) for the different renewable energy technologies, the EEG sets a high degree of investment security. The EEG was copied by more than 50 countries and regions worldwide.

Since the implementation of the EEG, equipping grid-connected solar systems with a feed-in meter is compulsory. In addition to the usual consumption meter, this device measures the electricity fed into the public grid.

The use of renewable energies is encouraged by means of the feed-in tariff specified in the Renewable Energy Sources Act. The amount of the remuneration depends on the technology and scale used. Thus, for example, the feed-in tariff for a small PV rooftop system is higher than for a large PV electricity plant. The feed-in tariff is determined for 20 years after commissioning, which leads to high investment security. The amount due is established by a by a feed-in meter; the invoice is billed to the responsible grid operator, or credited directly by the grid operator.

A (photovoltaic) free-field system (abbreviated PVF) is “mounted” on a flat, open area. It is a fixed, permanently installed system in which a substructure allows orienting the photovoltaic modules at an appropriate angle (called azimuth angle) to the sun.

Regular mowing of grass (and other vegetation such as shrubs), both between the solar modules and in the rest of the solar farm area avoids shading on the modules and prevents efficiency loss. Mowing can be done using mowers or by means of professional sheep grazing.

Photovoltaic systems in Germany are connected mainly to the public grid and feed electricity mostly into the distribution system. The direct current generated in the PV modules is converted by the inverter into alternating current, so that it can be fed into the AC grid.

In the German electricity grid, Transmission System Operators (TSOs) are responsible for the transport of electricity within the high voltage grid. In Germany there are four Transmission System Operators: Amprion, EnBW, Tennet and 50 Hertz, each of them responsible for a regional grid. Distribution system operators (DSOs) are responsible for the operational management of the grids for retail upply, primarily in the medium and low voltage range. Solar system electricity feed-in is mostly at distribution level. The remuneration due for the feed-in tariff is the responsibility of distribution system operators in these cases.

Describes the temporary reduction in the electricity supply of the solar system. The process is necessary, among other reasons, when an overload of the grid’s capacity in the regional area is imminent. PV systems larger than 100 kWp participate since 1 July 2012 in the NSM and can – depending on the situation – be throttled down to 60%, 30% or 0% of their rated capacity. Optimal grid utilisation is guaranteed by this NSM method, emergency shutdowns also being prevented. The control of the systems is usually performed by the distribution grid operator via remote systems or ripple control receivers.

See Grid Security Management (NSM).

The direct current generated by the solar cells is converted into grid-compliant AC electricity by the inverter. It is the link between the solar modules and the electricity grid.

Physical unit used to measure the electricity produced by an electricity plant (in this case a solar system).

Regular maintenance of a PV system is required to keep a constant high level of system performance. Among others, the following check-ups and measures can be carried out during maintenance (included in our performance and maintenance tasks): visual inspection of modules and frames, inverter operation check-up and replacement of worn materials (e.g. filter mats), measurement of electricity voltage curves using professional measuring technology, check-up of connectors, clamps, and control cabinets.

Dirt and debris can significantly reduce the output of a PV system. The income loss is caused by a similar effect as shading. The performance of the PV modules can be increased under certain circumstances through regular cleaning.

In the energy industry, the output of solar electricity plants is measured in megawatts peak/kilowatts peak. The abbreviation “p” comes from the English language and means “p”. In the case of photovoltaic modules and systems, the value refers to the rated output, i.e. the output measured under standardised test conditions (25° C module temperature and irradiance of 1000 W/m²).

See Commercial Management and Technical Management of PV systems

The horizontal orientation of the photovoltaic modules also plays an important role in feed-in tariffs. They reach their highest value when south-oriented. However, in cases of slight deviation from the optimal angle, the profitability of the energy output is not affected significantly.

The performance ratio is an important parameter for evaluating the actual performance of a photovoltaic system and for comparing different photovoltaic systems. The performance ratio is the ratio between the actual and the desired yield of the system under ideal environmental conditions. Local irradiance values are required for the determination of the performance ratio, for example, collected through irradiance sensors, a pyranometer or satellite data.

The term photovoltaics describes the conversion of solar radiation into electrical energy. All solar systems are based on the principle of the photoelectric effect in which a direct current is generated by the input of light. The output depends on the orientation of the modules, the intensity of the sun and the module type.

A photovoltaic module is composed of a plurality of mutually connected solar cells which are enclosed by two plastic sheets or panes of glass protected from harmful influences such as rain and dirt. They are the generator forming the core of a solar system, since the current is generated in them. (see also photovoltaics)

The remote control system, part of the grid security management system (NSM), has a similar function as the ripple control receiver. In contrast to the ripple control receiver, the remote control system allows transmission of grid information between the switch systems of the solar system and a grid control centre.

The ripple control technology is used for remote control of solar systems. The means of transmission however is not the electricity grid, but a long-wave radio channel. In particular, this technique is used in feed-in management (or by the NSM).

In this type of installation of solar electricity generators, the modules are mounted on the roof with steel/aluminium/stainless steel fixtures at a distance of 5-15 cm. This variant is often found in the private sector. Factory roofs, barn roofs and roofs of commercial buildings are also suitable for the installation of photovoltaic Systems.

The technical management includes general maintenance (see maintenance) and repair of all technical components of a solar farm such as solar modules, inverters, data loggers, etc. Other technical management services may include system monitoring, green waste, module cleaning and creating technical reports.

In addition to crystalline solar cells, thin-film solar cells are the most common type of module. A thin layer is formed by the application of photoactive semiconductors on a carrier material (e.g. stainless steel foil or glass). Positive aspects of this coating process are relatively low production costs, high shape flexibility and less susceptibility to shading. However, their efficiency compared with silicon solar cells used in crystalline solar cells is lower.

The tilt angle is measured between the horizontal plane and the solar modules. This setting is important in first place for sun irradiance and the associated efficiency of the solar system throughout the day. An angle of 30° is considered optimum. In second place, the effect of “free of charge” cleaning by rain starting at an angle of 15° is guaranteed.