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Balan­cing Group

In the energy industry – in other words on the elec­tri­ci­ty market – elec­tri­ci­ty custo­mers and elec­tri­ci­ty sup­pliers are grouped in so-called balan­cing groups. Such groups are virtual energy accounts in which the elec­tri­ci­ty feed-in rates of an area for all end custo­mers and those respon­si­ble for the balan­cing group can be read. These accounts are the respon­si­bi­li­ty of Trans­mis­si­on System Ope­ra­tors (TSOs).

BoS Com­pon­ents

BoS” means “Balance of Systems”. This refers to all secon­da­ry com­pon­ents of a pho­to­vol­taic system in running order, except for the solar panels and the inver­ters. The BoS mainly includes the sub­st­ruc­tu­re, elec­tri­ci­ty cables and other necessa­ry hardware for the instal­la­ti­on of a roof-mounted or free-field solar system.

Coef­fi­ci­ent of Per­for­mance

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.

Com­mer­ci­al 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

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.

Data Logger

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 of Solar Elec­tri­ci­ty

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.

EEG (Erneuerbare-Energien-Gesetz , Rene­wa­ble Energy Sources Act)

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.

Feed-In Meter

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.

Feed-In Tariff

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.

Free-Field System

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.

Green Waste

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.

Grid Feed-In

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.

(Elec­tri­ci­ty) Grid Ope­ra­tors

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.

Grid Security Manage­ment

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.

In-Feed manage­ment


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.

Kilowatt-hour (kWh = 1,000 watts per hour output)

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

Main­ten­an­ce of PV Systems

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.

Module Cleaning

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.

MWp / kWp (megawatt peak / kilowatt peak)

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).

Ope­ra­ti­on of Pho­to­vol­taic Systems

Orientation/Azimuth Angle

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.

Per­for­mance Ratio (PR)

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.

Pho­to­vol­taics (PV)

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.

Photovoltaic/Solar Module

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)

Remote Control System

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.

Ripple Control Receiver

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).

Rooftop System (Pho­to­vol­taic)

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.

Tech­ni­cal Manage­ment

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.

Thin Film Solar Cells

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.

Tilt Angle

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.