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Various roofs with photovoltaic systems in Oberstdorf
Globally cumulative photovoltaic power

Under photovoltaic or PV is the direct conversion of light energy , usually from sunlight into electrical energy by means of solar cells . It has been used in space travel since 1958, after which it was used to supply energy to individual electrical devices such as pocket calculators or parking ticket machines . By far the most important area of ​​application today is grid-connected electricity generation, primarily on roof surfaces and as an open-space system to replace conventional power plants.

The term is derived from the Greek word for “light” (φῶς, phos, in the genitive: φωτός, photos) as well as from the unit for electrical voltage , the volt (after Alessandro Volta ). Photovoltaics is a sub-area of solar technology that includes other technical uses of solar energy.

At the end of 2018, photovoltaic systems with an output of more than 500 GW were installed worldwide . Between 1998 and 2015, the worldwide installed photovoltaic capacity increased with an average growth rate of 38% per year. According to a paper published in Science in 2019, it is expected that the installed capacity will reach around 10,000 GW by 2030 and 30,000 to 70,000 GW by 2050. In 2014, the global market share of crystalline silicon cells was around 90%. Forecasts assume that silicon cells will remain the dominant photovoltaic technology in the long term and, together with wind turbines, will be the “workhorses” of the energy transition .

Photovoltaics has long been considered the most expensive form of electricity generation using renewable energies ; a view that has now become obsolete due to the significant cost reductions in the system components. From 2011 to 2017, the cost of generating electricity from photovoltaics fell by almost 75%.

In the USA, remuneration of less than 5 US cents / kWh (4.2 Euro cents / kWh) is common for solar parks (as of 2017); At this point in time, under favorable circumstances, similar values ​​were also possible in other countries. In several countries, record values ​​of 3 US cents / kWh (2.5 euro cents / kWh) were achieved in tenders. In 2020, several solar parks were awarded for which the remuneration is well below 2 US cents / kWh. As of April 2020, the cheapest bid awarded is 1.35 US cents / kWh (1.14 ct / kWh) for a solar park in Abu Dhabi . In Germany, too, the electricity production costs of newly built large-scale photovoltaic systems have been lower than for all other fossil or renewable energies since 2018.

As early as 2014, the electricity production costs of photovoltaics in certain regions of the world were at the same level or even lower than those of fossil fuel competitors. Including storage, which is necessary when photovoltaics make up a high proportion of the electricity mix , the costs at that time were even higher than for fossil power plants. However, even at this point in time, solar power would have been competitive if the external costs of fossil power generation (i.e. damage to the environment , the climate and health ) had been taken into account; in fact, they were only partially internalized .

History of photovoltaics

Photovoltaic system tracking the position of the sun in Berlin-Adlershof
Sales of solar systems in Ouagadougou , Burkina Faso

Photovoltaics is based on the ability of certain materials to convert light directly into electricity. The photoelectric effect was discovered in 1839 by the French physicist Alexandre Edmond Becquerel . This was then further researched, with Albert Einstein in particular, with his work on light quantum theory published in 1905 , having a large share in this research, for which he was awarded the Nobel Prize in Physics in 1921 . 1954 succeeded, the first silicon solar cells with efficiencies up to produce to 6% of. The first technical application was found in 1955 in the power supply of telephone amplifiers. Photovoltaics found widespread use in light meters for photography.

Photovoltaic cells have been used in satellite technology since the late 1950s; Vanguard 1 was the first satellite with solar cells to be launched into orbit on March 17, 1958 and remained in operation until 1964. In the 1960s and 1970s, space demand led to advances in the development of photovoltaic cells, while photovoltaic systems on earth were only used for certain island systems.

Triggered by the oil crisis of 1973/74 and later intensified by the nuclear accidents in Harrisburg and Chernobyl , however, a rethinking of energy supply began. Since the late 1980s, photovoltaics has been intensively researched in the USA, Japan and Germany; later, financial subsidies were added in many countries around the world in order to stimulate the market and make the technology cheaper by means of economies of scale. As a result of these efforts, the worldwide installed capacity rose from 700 MWp in 2000 to 177 GWp in 2014 and continues to grow.


Usually the spelling photovoltaics and the abbreviation PV are used. Since the German spelling reform , the spelling photovoltaic has been the new main form and photovoltaic is still a permitted alternative spelling. In the German-speaking world , the alternative spelling photovoltaics is the most common variant. The spelling PV is also common in international parlance. For technical fields, the notation in standardization (here also photovoltaics ) is an essential criterion for the notation to be used.

technical basics

The photoelectric effect of solar cells is used for energy conversion , which in turn are connected to so-called solar modules . The electricity generated can be used directly, fed into power grids or stored in accumulators . Before being fed into AC - grids generated is direct current of a inverter converted. The system of solar modules and the other components (inverter, power line) is called a photovoltaic system.

Working principle

Photovoltaic operating principle using the example of a silicon solar cell (for explanations of the digits, see text)

Photovoltaic functional principle using the example of a silicon solar cell. Silicon is a semiconductor . The special feature of semiconductors is that the energy supplied (e.g. in the form of light or electromagnetic radiation ) can generate free charge carriers in them.

  1. The upper silicon layer is negatively doped with electron donors (electron donors - e.g. phosphorus atoms). There are too many electrons here (n-layer).
  2. The lower silicon layer is interspersed with electron acceptors (e.g. boron atoms) - positively doped. There are too few electrons here, i.e. too many defects or holes (p-layer).
  3. In the boundary area between the two layers, the excess electrons from the electron donors loosely bind to the defects in the electron acceptors (they occupy the defects in the valence band ) and form a neutral zone ( pn junction ).
  4. Since there is a lack of electrons at the top and a lack of defects at the bottom, a constant electrical field is created between the upper and lower contact surfaces .
  5. Photons (light quanta, "sun rays") get into the transition layer.
  6. Photons with a sufficient amount of energy transfer their energy in the neutral zone to the loosely bound electrons in the valence band of the electron acceptors. This releases these electrons from their bond and lifts them into the conduction band . Many of these free charge carriers (electron-hole pairs) disappear again after a short time through recombination . Some charge carriers drift - moved by the electric field - to the contacts in the similarly doped zones (see above); ie the electrons are separated from the holes, the electrons drift upwards, the holes downwards. A voltage and a usable current arise as long as further photons continuously generate free charge carriers.
  7. The “electron” current flows through the “external circuit ” to the lower contact surface of the cell and recombines there with the holes left behind.

Nominal power and yield

Radiation atlas based on satellite data from 1991–1993
Solar radiation potential in Europe

The nominal output of photovoltaic systems is often given in the notation W p ( watt peak ) or kW p and relates to the output under test conditions that roughly correspond to the maximum solar radiation in Germany. The test conditions are used to standardize and compare different solar modules. The electrical values ​​of the components are given in data sheets. It is measured at 25 ° C module temperature, 1000 W / m² irradiance and an air mass (abbreviated to AM from English air mass ) of 1.5. These standard test conditions (mostly abbreviated to STC from English standard test conditions ) were established as an international standard. If these conditions cannot be met during testing, the nominal power must be calculated from the given test conditions.

For comparison: The radiation strength of the sun in near-earth space ( solar constant ) averages 1367 W / m². (About 75% of this energy arrives on the ground in clear weather.)

The decisive factor for the dimensioning and amortization of a photovoltaic system is, in addition to the peak performance, above all the annual yield, i.e. the amount of electrical energy obtained. The radiation energy fluctuates depending on the day, the season and the weather. For example, a solar system in Germany can have a yield up to ten times higher in July than in December. Up-to-date feed-in data with a high temporal resolution for the years from 2011 onwards are freely accessible on the Internet.

The yield per year is measured in watt hours (Wh) or kilowatt hours (kWh). The location and orientation of the modules as well as shading have a significant influence on the yield, whereby in Central Europe roof pitches of 30 - 40 ° and orientation to the south deliver the highest yield. Oriented to the maximum height of the sun (midday sun), in Germany with a permanent installation (without tracking) the optimal inclination in the south of the country should be approx. 32 °, in the north approx. 37 °. In practice, a slightly higher angle of inclination is recommended, as the system is then optimally aligned twice a day (in the morning and in the afternoon) and twice a year (in May and July). For this reason, such orientations are usually chosen for open-space systems. Although the average solar height distributed over the year and thus the theoretically optimal inclination for each degree of latitude can be precisely calculated, the actual irradiation along a degree of latitude is different due to various, mostly terrain-dependent factors (e.g. shading or special local weather conditions). Since the system-dependent effectiveness with regard to the angle of irradiation is different, the optimal alignment must be determined in each individual case for the location and the system. In these energetic investigations, the location-related global radiation is determined, which, in addition to direct solar radiation, also includes diffuse radiation incident via scattering (e.g. clouds) or reflection (e.g. nearby house walls or the ground) .

The specific yield is defined as watt hours per installed nominal power (Wh / W p or kWh / kW p ) per time period and enables the simple comparison of systems of different sizes. In Germany, with a reasonably optimally designed, permanently installed system per module area with 1 kW p , an annual yield of around 1,000 kWh can be expected, with the values ​​fluctuating between around 900 kWh in northern Germany and 1150 kWh in southern Germany.

Assembly systems

On-roof / in-roof installation

House roof with photovoltaic system for electricity and solar collectors for hot water generation

With the mounting systems, a distinction is made between on-roof systems and in-roof systems. In the case of an on-roof system for sloping house roofs, the photovoltaic system is attached to the roof with the help of a mounting frame. This type of installation is most often chosen because it is the easiest to implement for existing roofs.

In an in-roof system, a photovoltaic system is integrated into the roof skin and takes on its functions such as roof tightness and weather protection. Advantages of such systems are the visually more attractive appearance and the saving of a roof covering, so that the higher installation costs can often be compensated for.

In addition to tiled roofs , on -roof installation is also suitable for sheet metal roofs, slate roofs or corrugated sheets. If the roof pitch is too flat, special hooks can compensate for this to a certain extent. The installation of an on-roof system is usually easier and cheaper than that of an in-roof system. A roof-top system also ensures that the solar modules are adequately ventilated . The fastening materials must be weatherproof.

Another form is flat roof mounting. Since flat roofs are not or only slightly inclined, the modules are angled between 6 and 13 ° by the mounting system. An east-west slope is also often used to achieve a greater use of space. In order not to damage the roof cladding , the mounting system is fastened with ballast if the load is sufficient.

The in-roof system is suitable for roof renovations and new buildings, but is not possible for all roofs. Tile roofs do not allow in-roof installation, sheet metal roofs or bitumen roofs. The shape of the roof is also decisive. The in-roof installation is only suitable for sufficiently large pitched roofs with a favorable orientation to the sun path. In-roof systems generally require greater angles of inclination than on-roof systems in order to enable sufficient rainwater to run off. In-roof systems form a closed surface with the rest of the roof covering and are therefore more attractive from an aesthetic point of view. In addition, an in-roof system has a higher mechanical stability against snow and wind loads. The cooling of the modules is, however, less efficient than with the roof-top system, which reduces the performance and the yield somewhat. A temperature higher by 1 ° C reduces the module output by approx. 0.5%.

Open space assembly

When it comes to the assembly systems for open-space systems, a distinction is made between fixed elevation and tracking systems. In the case of fixed elevation, a steel or aluminum frame is anchored in the ground by ramming or screwed onto concrete blocks, depending on the subsurface; the angle of the modules is no longer changed after assembly.

Tracking systems follow the course of the sun to ensure that the modules are always optimally aligned. This increases the yield, but also increases the investment costs and the operating costs for maintenance and the energy required for tracking. A distinction is made between single-axis tracking - either only horizontally (the panel follows the position of the sun from sunrise to sunset from east to west.) Or only vertically (the south-facing panel rotates depending on the height of the sun above the horizon.) And the two-axis tracking - horizontal and vertical. This increases the yields compared to fixed elevation: in Central European latitudes by about 20% with only single-axis tracking and by over 30% with two-axis tracking.

Another form of open-space installation is floating installation on water, with the modules being installed on plastic floating bodies. However, the yield increases due to the cooling effect of the water. The investment costs are 20-25% higher than with conventional assembly. The Fraunhofer Institute estimates the potential for floating PV systems alone on 25% of the areas destroyed by lignite mining at 55 GWp if they are flooded.

In 2020, a system with vertical modules was put into operation in Baden-Württemberg .


So far, the majority of photovoltaic systems worldwide have been based on silicon technology. In addition, various thin-film technologies were able to gain market share. Other semiconductors such as cadmium telluride or gallium arsenide are also used . Layers of different semiconductors are used in so-called tandem solar cells .

The development of solar modules based on perovskite is judged to be very promising due to their inexpensive manufacture . The cells can be made much thinner than silicon cells. So far, however, the problem has been the short shelf life.

Another research goal is the development of organic solar cells . Together with partners, the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg has succeeded in producing an inexpensive organic solar cell on flexible film.


Worldwide usage potential

Worldwide PV installation in watts per inhabitant (2016).
  •  none or unknown
  •  00-0< 010 watts per inhabitant
  •  > 010–100 watts per inhabitant
  •  > 100–200 watts per inhabitant
  •  > 200–400 watts per inhabitant
  •  000–> 400 watts per inhabitant
  • The solar energy  hitting the earth's atmosphere amounts to 1.56 · 10 18 kWh annually, which corresponds to almost 12,000 times the primary energy consumption of mankind in 2005 (1.33 · 10 14  kWh / year). About half of this energy reaches the earth's surface, which means that it can potentially be used for photovoltaic energy generation. According to a study published in the journal Nature Energy in 2017 , photovoltaics can technically and economically cover approx. 30–50% of global electricity demand by 2050 and thus become the dominant type of electricity generation. It has already been taken into account that at this point in time the energy system will be more electricity-intensive than it is now, so that photovoltaics could then also contribute to a considerable decarbonization of other sectors such as the transport sector or industrial energy consumption by means of sector coupling .

    The level of irradiation depends on the geographic location: near the equator , for example in Kenya , India , Indonesia , Australia or Colombia , the electricity production costs are lower than in Central Europe due to the high irradiance . In addition, the energy yield at the equator fluctuates much less over the course of the year than at higher latitudes (fairly constant seasonal sun positions and times between sunrise and sunset ).

    Sales development

    Actual development of the photovoltaic expansion in comparison with the IEA prognoses 2002–2016

    By the end of 2017, photovoltaic systems with a capacity of approx. More than 500 GW had been installed worldwide. The IEA expects a further increase to around 400 to 500 GWp by 2020. By the end of 2015, a total of 229 GW of solar power had been installed worldwide. In China alone, more than 7 GW of new PV capacity was installed in the first quarter of 2016. The total installed capacity in Europe is 100 GW. Between 1998 and 2015, the world's installed photovoltaic capacity grew by an average of 38% per year. This was significantly stronger than most of the growth scenarios assumed. The actual growth rates have historically been underestimated not only by the International Energy Agency , but also by the IPCC , the German Advisory Council on Global Change and Greenpeace .

    Photovoltaic installation worldwide
    year 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019
    GWp installed (rounded) 5 7th 9 16 23 40 71 101 139 177 227.1 302.1 402 500 627
    GWp expansion 1.4 1.5 2.5 6.7 7.4 17.1 30.2 30.0 38.4 37.2 50.1 75 98 98 127

    The construction of new plants continues for several reasons:

    • the module prices have fallen significantly
    • the general level of prices for electricity is moving towards the state subsidized prices
    • most countries in the world operate a low interest rate policy (see financial crisis from 2007 ); therefore investors prefer this low-risk investment option with a relatively high return.

    The following tables provide an overview of the development of the installed nominal output of photovoltaic systems in the European Union from 2005 to 2019.

    Installed nominal PV power in the EU in MW p
    No. States 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019
    1 Germany 1.910 2,743 3,846 6,019 9,959 17,370 25.094 32,703 36,402 38,408 39,763 41,340 42,339 45,277 49,016
    2 Italy 46.3 50 120 458 1,157 3,484 12,783 16,152 18,065 18,622 18,924 19,274 19,682 20,107 20,864
    3 Great Britain 10.9 14.3 18.1 22.5 29.6 76.9 978 1,708 2,782 5,380 8,918 11,562 12,783 13,054 13,616
    4th France 26.3 33.9 46.7 104 335 1,197 2,949 4,085 4,625 5,699 6,579 7.164 8,610 9,466 10,576
    5 Spain 57.6 175 734 3,421 3,438 3,859 4,322 4,603 4,766 4,872 4,921 4,801 4,725 4,751 9.233
    6th Netherlands 50.8 52.7 53.3 57.2 67.5 88.0 146 365 739 1,048 1.405 2,040 2,903 4,300 6,924
    7th Belgium 2.1 4.2 21.5 70.9 374 1,037 2,051 2,768 3,040 3,140 3,228 3,425 3,610 4,254 4,531
    8th Greece 5.4 6.7 9.2 18.5 55.0 205 631 1,543 2,586 2,603 2,613 2,603 2,605 2,651 2,794
    9 Czech Republic 0.5 0.8 4.0 54.7 463 1,959 1.913 2,022 2,064 2,068 2,083 2,047 2,069 2,049 2,100
    10 Austria 24 25.6 27.7 32.4 52.6 95.5 187 422 631 785 935 1,077 1,269 1,433 1,661
    11 Romania 0.2 0.3 0.5 0.6 1.9 3.5 49.3 1,022 1,293 1,325 1,371 1,374 1,377 1,386
    12 Poland 0.3 0.4 0.6 1.0 1.4 1.8 2.2 3.6 4.2 29.9 86.9 195 287 486 1.317
    13 Hungary 0.2 0.3 0.4 0.5 0.7 1.8 2.7 12.3 34.9 77.7 138 288 344 754 1,277
    14th Denmark 2.7 2.9 3.1 3.3 4.7 7.1 16.7 376 572 602 783 858 906 1.002 1,080
    15th Bulgaria 0.1 0.1 1.4 5.7 32.3 212 915 1,019 1,020 1,021 1,032 1,036 1,036 1,065
    16 Portugal 3 3.4 17.9 68.0 102 131 161 228 303 423 460 470 585 671 907
    17th Sweden 4.2 4.9 6.2 7.9 8.8 11.4 15.7 24.1 43.2 79.4 130 153 244 424 698
    18th Slovakia <0.1 <0.1 <0.1 <0.1 0.2 174 487 543 588 590 545 545 528 531 472
    19th Slovenia 0.2 0.4 1.0 2.0 9.0 45.5 100 222 248 256 257 259 247 256 222
    20th Finland 4th 4.5 5.1 5.6 7.6 9.6 11.2 11.2 11.2 11.2 74 125 14.7 20th 215
    21st Malta <0.1 0.1 0.1 0.2 1.5 3.8 6.6 18.7 28.2 54.8 73.2 82 122 131 150.6
    22nd Luxembourg 23.6 23.7 23.9 24.6 26.4 29.5 40.7 76.7 95 110 125 122 132 134 140.6
    23 Cyprus 0.5 1.0 1.3 2.2 3.3 6.2 10.1 17.2 34.8 64.8 110 113 69.5 55 128.7
    24 Estonia <0.1 <0.1 <0.1 <0.1 0.1 0.2 0.2 0.2 0.2 4.1 10 31.9 107
    25th Lithuania <0.1 <0.1 <0.1 0.1 0.1 0.1 0.1 6.2 68.1 68.1 74 125 73.1 80 83
    26th Croatia 20.0 34.2 50 60 61 44.8 69
    27 Ireland 0.3 0.4 0.4 0.4 0.6 0.7 0.7 0.9 1 1.1 2.1 5.1 16 29 36
    28 Latvia <0.1 <0.1 <0.1 <0.1 <0.1 1.5 1.5 1.5 1.5 1.5 1.5 2 3
    EU28 2.172 3,148 4,940 10,376 16,103 29,828 52.126 68,882 79,794 86,674 94,568 100,935 106,726 114,549 130,670

    Due to the sharp drop in module prices in the wake of cheap imports from China, the German and European solar industries have got into a crisis. Numerous manufacturers filed for bankruptcy. In May 2013, the EU Commission imposed punitive tariffs on China, as this country sells for below production costs due to enormous government subsidies ( dumping ). The punitive tariffs are controversial in the industry and among environmental associations. At the end of July, China and the EU agreed on a minimum price of 56 ct / W p and an annual maximum delivery volume of 7 GW.

    Fields of application

    Part of a solar cell wing of the
    Juno spacecraft

    In addition to generating electricity to feed into the grid, photovoltaics are also used for mobile applications and applications without a connection to a power grid, so-called island systems. The direct current can also be used directly here. Battery-backed direct current networks are therefore the most common. In addition to satellites , solar vehicles or solar planes , which often get all of their energy from solar cells, everyday facilities such as weekend houses, solar lights , electric pasture fences , parking ticket machines or pocket calculators are also supplied by solar cells.

    Island systems with an inverter can also supply AC consumers. In many countries without a nationwide power grid , photovoltaics is a way of generating electricity more cheaply than z. B. with a diesel generator .

    The integration of photovoltaic systems and solar batteries into existing island networks is also a way of significantly reducing the costs of energy production.

    Double use of space

    With inclined PV modules, a meadow below can be used as a sheep pasture .

    Photovoltaics is compatible with a - mostly fenced - water or well protection area .

    Romande Energie is experimenting with floating PV modules in the Lac des Toules reservoir at an altitude of 1,810 m .

    PV modules can serve as a roof for bicycle parking systems, public transport shelters or part of a soundproof wall.

    Partially permeable PV elements in front of glass facades bring about a desired reduction in the solar heat effect in the room through penumbra.

    PV modules can also be used to clad a facade.


    Thermography on a photovoltaic system / detection of faulty cell

    The efficiency is the ratio between the currently generated electrical power and the radiated light power. The higher it is, the smaller the area can be kept for the system. In terms of efficiency, it is important to note which system is being considered (individual solar cell, solar panel or module, the entire system with inverter or charge controller and batteries and cabling). The yield from solar modules is also temperature-dependent. For example, the output of a monocrystalline silicon module changes by −0.4% per ° C, with a temperature increase of 25 ° C the output decreases by approx. 10%. A combination of solar cells and thermal solar collectors , so-called hybrid collectors , increases the overall efficiency through the additional thermal use, and can improve the electrical efficiency due to the cooling of the solar cells by the thermal collectors.

    Efficiency of various solar systems (elements) according to Quaschning (as of 2018)
    Cell material Maximum cell efficiency in the laboratory Maximum efficiency (series production) Typical module efficiency Space requirement per kWp
    Monocrystalline silicon 25.8% 24% 19% 5.3 m²
    polycrystalline silicon 22.3% 20% 17% 5.9 m²
    Amorphous silicon 14.0% 8th % 6% 16.7 m²
    CIS / CIGS 22.6% 16% 15% 6.7 m²
    CdTe 22.1% 17% 16% 6.3 m²
    concentrator cell A1 46.0% 40% 30% 3.3 m²

    A1 Based on the photovoltaically active area. The area for capturing light is larger.

    The efficiency levels that can be achieved with solar cells are determined under standardized conditions and differ depending on the cell technology used. The mean value of the nominal efficiency of wafer-based PV modules was around 16% in 2014 (after the year of market launch), for thin-film modules it is around 6–11%. A table of the efficiencies of individual cell technologies can be found here . Multi-junction solar cells with concentrators achieve particularly high levels of efficiency; here in the laboratory efficiency levels of up to approx. 46% have already been achieved. By combining solar cells of different spectral sensitivity, which are optically and electrically arranged one behind the other, in tandem or triple connection, the efficiency has been increased, especially with amorphous silicon. However, with such a series connection, the cell with the lowest current always limits the total current of the overall arrangement. Alternatively, the parallel connection of the optically arranged solar cells in a duo connection for thin-film cells made of a-Si on the front glass and CIS on the rear glass was demonstrated.

    One advantage of this technology is that the solar radiation can be concentrated on a small solar cell, which is the most expensive part of a photovoltaic system, with simple and inexpensive optical devices. On the other hand, it is disadvantageous that concentrating systems are dependent on tracking systems and a cooling device for the cells because of the bundling of light.

    Today's solar modules do not absorb part of the sunlight, but reflect it on their surface. Therefore, they are usually equipped with an anti-reflective layer, which already greatly reduces the reflection. Black silicon almost completely avoids these reflections.

    Performance ratio

    The performance ratio (PR) - often also called quality factor (Q) - is the quotient of the actual useful yield of a system and its target yield. The “target yield” is calculated from the radiated energy on the module surface and the nominal module efficiency; it describes the amount of energy that the system would harvest if operated under standard test conditions (STC) and at 100% inverter efficiency.

    In real terms, the module efficiency is below the nominal efficiency compared to the STC even with unshaded systems due to heating, lower irradiation, etc.; In addition, the line and inverter losses are also deducted from the target yield. The target yield is thus a theoretical calculation variable under STC. The performance ratio is always an annual average. For example, the PR on cold days is above average and decreases especially at higher temperatures and in the morning and evening when the sun shines on the modules at a more acute angle.

    The performance ratio rose significantly with the development of photovoltaic technology: from 50–75% in the late 1980s to 70–80% in the 1990s to more than 80% around 2010. For Germany, a median of 84 % determined in 2010, values ​​of over 90% are considered possible in the future. Quaschning gives lower values ​​with an average of 75%. Accordingly, good systems can achieve values ​​of over 80%, but values ​​below 60% are also possible with very poor systems, with inverter failures or long-term shadowing then often being the cause.

    Pollution and cleaning

    As on any surface outdoors (comparable to windows, walls, roofs, cars, etc.), different substances can also settle on photovoltaic systems . These include, for example, leaves and needles, sticky organic secretions from lice, pollen and seeds, soot from heaters and engines, sand, dust (e.g. feed dust from agriculture), growth of pioneering plants such as lichens, algae and mosses, and bird droppings.

    In systems with an angle of inclination of 30 °, soiling is low; here the losses are around 2–3%. On the other hand, dirt has a greater effect at shallow angles of attack, where dirt can cause losses of up to 10%. In the case of systems on animal stalls on farms, higher losses are also possible if dirt from ventilation shafts is deposited on the system. In these cases, cleaning at regular intervals makes sense.

    The state of the art for cleaning is the use of fully desalinated water ( demineralized water ) in order to avoid limescale stains. Water-bearing telescopic poles are used as a further aid for cleaning. Cleaning should be carried out without scratching the module surface. In addition, modules should not be entered at all and roofs should only be entered with suitable safety precautions.

    The contamination can also be determined with a thermal imaging camera . Soiled areas on the modules are warmer than clean areas when exposed to sunlight.

    Integration into the energy system

    Photovoltaics is an energy technology whose energy generation, depending on the weather, cannot be considered a base load on its own . In order to be able to guarantee a predictable, secure energy supply, photovoltaics must therefore be combined with other base-load generators, energy storage systems , sector coupling technologies or the like. While fossil-fuel power plants are currently playing this role in many countries, other options are needed in fully renewable energy supply systems. In the medium to long term, it is therefore considered necessary to set up an energy storage infrastructure, a distinction being made between short-term storage facilities such as pumped storage power plants, batteries, etc. and long-term storage facilities such as power-to-gas . With the latter technology, a storage gas ( hydrogen or methane ) is generated in phases of high green electricity production, which can be converted back into electricity when there is little green electricity production. In addition, there are also base-load renewable energies such as biomass power plants and geothermal power plants that can compensate for fluctuations. However, their potential is very limited in Germany. Intelligent power grids are also helpful, as they allow consumers with load shifting potential, such as heat pump heating systems , e-cars , refrigerators, etc., to be fed primarily with high levels of generation from renewable energies. In 2018, for example, Volker Quaschning explained how, for example, controllable refrigerators in an intelligent power grid with high solar power feed-in could cool down more deeply than usual, and then get by without power for a while, while heat pumps produce heat in advance. A combination of wind and solar energy as well as a supraregional exchange of electricity can enable further balancing effects, which, like the options mentioned above, can reduce storage requirements.

    Fluctuation in supply

    The generation of solar power is subject to a typical daily and annual cycle, superimposed by weather influences. These can be predicted fairly reliably by observing the weather ( see meteorology ).

    In spring and summer in particular, solar power can be used around noon to cover part of the medium load - but only if the weather permits (no cloudy sky). In autumn and winter (especially in the months of November to January) the PV systems in the regions from the poles up to about 45 degrees of latitude generate only little electricity due to the short duration of sunshine and the low position of the sun. Since a particularly large amount of electricity is then required for heating and lighting, a particularly large amount of capacities from other energy sources must be available. However, wind turbines deliver more electricity in winter than in summer, so that photovoltaics and wind energy complement each other very well. In order to compensate for the statistically predictable daily, weather and annual fluctuations, storage options and switchable loads for consumption adjustment (smart switching in conjunction with smart metering ) are also required.

    Up-to-date feed-in data (for Germany) for the years from 2011 onwards are freely accessible on the Internet.


    With a decentralized power supply through many small photovoltaic systems (PVA) in the power range of a few 10 kW, the source and consumer are close to one another; there are then hardly any transmission losses and the power generated practically does not leave the low-voltage range (as of 2009). The PVA operator feeds the power not consumed into the low-voltage network . A further substantial expansion of photovoltaics will result in regional surpluses that have to be transported to other regions via the power grid or stored for night-time use.

    Energy storage

    In stand-alone systems, the energy gained is buffered in storage systems, usually accumulators. The significantly more frequent network systems feed the electricity generated directly into the network, where it is used immediately. In this way, photovoltaics become part of the electricity mix . Storage systems are being used more and more frequently in small PV systems to increase the self-consumption rate. The electricity production costs from storage systems of small PV systems are between 16.34 - 47.34 cents / kWh. With electricity production costs below the end customer electricity price of 29 cents / kWh, there is a saving of up to 10 kWp tax-free electricity from the storage system compared to the use of mains electricity.

    Island system

    Parking ticket machine as a photovoltaic island system

    With stand-alone systems, the differences between consumption and the power supply of the photovoltaic system must be compensated for by energy storage B. to operate consumers at night or when there is insufficient sunlight. The storage usually takes place via a DC voltage intermediate circuit with accumulators, which can supply consumers as required. In addition to lead batteries , newer battery technologies with better efficiency such as lithium titanate batteries are also used. The usual AC mains voltage can be generated from the intermediate circuit voltage by means of an inverter.

    Island systems are used, for example, in remote locations for which a direct connection to the public network is uneconomical. In addition, autonomous photovoltaic systems also enable the electrification of individual buildings (such as schools or the like) or settlements in “developing countries” where there is no nationwide public power supply network. Systems of this type are already more economical than diesel generators in many non-electrified regions of the world, although subsidies for diesel have often hindered its spread.

    Compound system

    In the case of smaller systems, all available power or power above self-consumption is fed into the network. If it is missing (e.g. at night), consumers obtain their power from other producers via the network. In the case of larger photovoltaic systems, feed-in regulation via remote control is required, with the help of which the feed-in power can be reduced if the stability of the supply network requires it. In the case of systems in an interconnected network, local energy storage can be dispensed with, since the different consumption and supply capacities are balanced out via the interconnected network, usually by means of conventional power plants. In the case of high proportions of solar power that can no longer be balanced with conventional power plants, further integration measures are necessary to guarantee security of supply.

    A number of Power-to-X technologies can be used for this. In addition to storage, these are in particular flexibility measures such as For example, the use of power-to-heat , vehicle-to-grid or the use of intelligent networks that control certain consumers (e.g. cooling systems, hot water boilers, but also washing machines and dishwashers) in such a way that they are automatically switched on at peak generation become. For reasons of efficiency, preference should initially be given to flexibilization; for higher proportions, storage power plants must also be used, whereby short-term storage is initially sufficient and long-term storage such as power-to-gas should only be used for very high proportions of variable renewable energies .

    Security of supply

    Despite the fluctuating supply, the output from photovoltaics (which can be forecast about 24 hours in advance using weather forecasts) is available much more reliably than that of a single large power plant. A failure or a planned shutdown of a large power plant has a stronger impact on the power grid than the failure of a single photovoltaic system. With a large number of photovoltaic systems, the feed-in reliability is extremely high compared to a single large system.

    In order to protect against failure of large power generators, power plant operators must keep reserve power ready. In the case of photovoltaics, this is not necessary when the weather conditions are stable, since all PV systems are never under revision or repair at the same time. However, if there is a high proportion of decentralized small-scale photovoltaic systems, the network operator must centrally control the load distribution.

    During the cold spell in Europe in 2012, photovoltaics supported the grid. In January / February 2012 it fed in between 1.3 and 10 GW of power at midday peak. Due to the high electricity consumption due to winter, France had to import approx. 7–8% of its electricity requirements, while Germany exported.


    Economic consideration

    Solar power causes less environmental damage than energy from fossil fuels or nuclear power and thus lowers the external costs of energy generation (see also external costs for electricity production costs ).

    In 2011, the cost of avoiding CO 2 emissions through photovoltaics was € 320 per tonne of CO 2 , which is more expensive than other renewable energy sources. In contrast, the cost of energy saving (e.g. through building insulation) was € 45 per tonne of CO 2 or less and in some cases could even generate financial benefits. However, due to the strong cost reduction of photovoltaics, the avoidance costs of a rooftop system in Germany have fallen to around € 17–70 per tonne of CO 2 , which means that solar power generation is cheaper than the cost of damage caused by climate change, which is estimated at € 80 per tonne of CO 2 . In sunnier regions of the world, advantages of up to approx. € 380 per ton of avoided CO 2 emissions are achieved.

    How much CO 2 emissions can actually be avoided by photovoltaics also depends on the coordination of the EEG with the EU emissions trading system; also on the form of energy used to manufacture the modules.

    Business consideration

    Acquisition costs and payback period

    The acquisition costs of a PV system consist of material costs such as modules, inverters, mounting system and components for the wiring and the grid connection. In addition, there are costs for installation and connection to the grid. The modules have the largest share of the costs with 40–50%. Depending on the size of the PV system, the grid connection can make up a large part of the investment. In the case of small roof systems up to 30 KWp, the house is required to be connected to the mains by law; in the case of higher outputs, in order not to overload the low- voltage network, it can be fed into the medium-voltage network, which incurs additional costs for laying cables and a transformer or special inverter at the network connection.

    The system costs differ depending on the type of installation and the amount of installed power (as of 2018).

    • PV roof small systems (5 - 15 kWp): 1200 - 1400 € / KWp
    • Large PV roof systems (100 - 1000 kWp): 800 - 1000 € / KWp
    • PV open space (from 2 MWp): 600 - 800 € / KWp

    In addition to the modules, this price also includes the inverter, installation and grid connection.

    A system installed in Germany delivers an annual yield of around 700 to 1100 kWh, depending on its location and orientation, and requires 6.5 to 7.5 m² of surface area per kW p output for roof installation .

    The amortization depends on many factors: the time of commissioning, the amount of sunlight, the module area, the orientation and inclination of the system and the amount of external financing. The long-term and reliable support through the feed-in tariffs of the German EEG was a decisive factor for the strong cost reductions of photovoltaics.

    Electricity generation costs

    German electricity generation costs (LCoE) for renewable energies and conventional power plants in 2018.
    Between 2008 and 2015, the electricity production costs of photovoltaic systems in the USA fell by 54% (small systems) and 64% (solar parks).
    Electricity generation costs of photovoltaic systems in cents / kilowatt hour at the time of installation
    Investment / income per kW p 700 kWh / a 800 kWh / a 900 kWh / a 1000 kWh / a 1100 kWh / a 1500 kWh / a 2000 kWh / a
    € 200 / kW p 6.8 5.9 5.3 4.7 4.3 3.2 2.4
    400 € / kW p 8.4 7.4 6.5 5.9 5.3 3.9 2.9
    600 € / kW p 10.0 8.8 7.8 7.0 6.4 4.7 3.5
    800 € / kW p 11.7 10.2 9.1 8.2 7.4 5.5 4.1
    1000 € / kW p 13.3 11.7 10.4 9.3 8.5 6.2 4.7
    1200 € / kW p 15.0 13.1 11.6 10.5 9.5 7.0 5.2
    1400 € / kW p 16.6 14.5 12.9 11.6 10.6 7.8 5.8
    1600 € / kW p 18.3 16.0 14.2 12.8 11.6 8.5 6.4
    1800 € / kW p 19.9 17.4 15.5 13.9 12.7 9.3 7.0
    2000 € / kW p 21.5 18.8 16.7 15.1 13.7 10.0 7.5

    Photovoltaics has long been considered the most expensive form of electricity generation using renewable energies. This has now changed due to the sharp drop in prices, so that photovoltaics are now competitive with other regenerative and conventional types of electricity generation. In some parts of the world, PV systems are now being installed without any funding. The specific electricity production costs depend on the respective conditions. In the USA z. B. Payments of less than 5 US cents / kWh (4.2 Euro cents / kWh) are common. Similar values ​​are held to be economically feasible for other countries, if the radiation and financing conditions are favorable. In the case of the cheapest solar projects as of 2017, electricity generation costs of 3 US cents / kWh (2.5 euro cents / kWh) were achieved in tenders or these values ​​were slightly undercut even without subsidies.

    Due to the mass production , the prices of the solar modules are falling ; since 1980 the module costs have fallen by 10% per year; a trend that is likely to continue. As of 2017, the cost of generating electricity from photovoltaics has fallen by almost 75% within 7 years. According to Swansons Law , the price of solar modules falls by 20% when the output is doubled.

    Newly built large photovoltaic systems have been the cheapest power plants in Germany since 2018 (see table on the right). In the third quarter of 2013, the electricity production costs were between 7.8 and 14.2 ct / kWh or 0.09 and 0.14 $ / kWh. The LCOE of photovoltaic systems was already at the same level as the LCOE of new nuclear power plants such as Hinkley Point C with projected costs of $ 0.14 / kWh in 2023. A direct comparison is difficult, however, as there are a number of others Factors such as the weather-dependent production of photovoltaics, the final storage and the insurance of the systems must be taken into account.

    In January 2014, grid parity was achieved in at least 19 markets ; the profitability for end users is supported by a large number of analysis data. The German Institute for Economic Research (DIW) notes that the cost of photovoltaics has so far decreased much faster than expected recently. In a recent report by the EU Commission, it was assumed that the cost of capital "is already in part below the values ​​that the Commission expects for 2050".

    Until the beginning of 2016 , the cheapest solar park in the world was a system in Dubai , which receives a feed-in tariff of 6 US cents / kWh (as of 2014). In August 2016, this record was clearly undercut in a tender in Chile . There, electricity production costs for a 120 MWp solar park were 2.91 US cents / kWh (2.46 ct / kWh), which, according to Bloomberg LP, is the lowest electricity production costs ever achieved in a power plant project worldwide. By 2020 these values ​​halved again. In April 2020, a bidder in the Al Dhafra solar park was awarded the contract who had agreed to build the 2 GW solar park for a fee of 1.35 US cents / kWh (1.14 ct / kWh). Previously, other projects with less than 2 US cents / kWh had already been awarded.

    The International Organization for Renewable Energy (IRENA) forecast in 2016 that the cost of solar power will fall by up to 59 percent by 2025. The report cited the reasons for expansion of production, more efficient supply chains and technical improvements.

    Module prices

    Spot market price index in euros per kW p (net) of photovoltaic modules (wholesale price) (change compared to previous year)
    Module type Crystalline Thin film
    origin Germany China, SE Asia Japan CdS / CdTe a-Si µ-Si
    Jul 2007 ≈ 3250 ≈ 3000 ≈ 3220 ≈ 2350 ≈ 2350
    Jan 2009 3190 2950 3160 2100 2210
    Jan 2010 2030 (−36%) 1550 (−47%) 1910 (−40%) 1610 (−23%) - 1380 (−38%)
    Jan 2011 1710 (−16%) 1470 (−5%) 1630 (−15%) 1250 (−22%) 1080 1260 (−9%)
    Jan 2012 1070 (−37%) 790 (−46%) 1050 (−36%) 680 (−46%) 600 (−44%) 760 (−40%)
    Jan 2013 780 (−27%) 530 (−33%) 830 (−21%) 560 (−18%) 420 (−30%) 520 (−32%)
    origin Germany China Japan, Korea SO-Asia, Taiwan
    Jan 2014 690 (−13%) 580 (+ 9%) 700 (−19%) 530
    Jan 2015 600 (−13%) 540 (−7%) 610 (−13%) 460 (−13%)
    Jan 2016 590 (−2%) 560 (+ 4%) 660 (+ 8%) 480 (+ 4%)
    Jan 2017 480 (−19%) 490 (−13%) 570 (−14%) 400 (−17%)
    Crystalline modules
    Module type High efficiency All black mainstream Low cost Trend since
    Aug 2017 510 (−9%) 510 (+ 0%) 420 (−5%) 290 (+ 0%) Jan 2017
    Dec 2017 500 (−11%) 490 (−4%) 380 (−14%) 270 (−7%) Jan 2017
    Jan 2018 480 (−14%) 470 (−8%) 370 (−16%) 260 (−10%) Jan 2017
    Jun 2018 420 (−13%) 440 (−6%) 330 (−11%) 240 (−8%) Jan 2018
    Aug 2018 380 (−21%) 400 (−15%) 310 (−16%) 230 (−12%) Jan 2018
    Nov 2018 360 (−25%) 360 (−23%) 270 (−27%) 200 (−23%) Jan 2018
    Jul 2019 330 (−5.7%) 340 (−5.6%) 270 (± 0%) 200 (+ 11.1%) Jan 2019
    Nov 2019 320 (−8.6%) 340 (−5.6%) 250 (−7.4%) 190 (+ 5.6%) Jan 2019
    Jan 2020 320 (−8.6%) 330 (−8.3%) 250 (−7.4%) 170 (−5.6%) Jan 2019

    The module prices have fallen sharply in recent years, driven by economies of scale, technological developments, normalization of solar silicon price and by building excess capacity and competition among manufacturers. The average price development since January 2009 by type and origin is shown in the table opposite.

    As a result of the market stimulation through feed-in tariffs in Germany, Italy and a number of other countries, there was a drastic decrease in the cost of module prices, which went from 6 to 7 USD / watt in 2000 to 4 $ / watt in 2006 and 0.4 $ / watt declined in 2016. In 2018, the global average module prices were already below $ 0.25 / watt. Historically, module prices have fallen by 22.5% for every doubling of installed capacity over the past 40 years.

    The further price development depends on the development of demand as well as on technical developments. The low prices for thin-film systems are partly put into perspective for the finished system due to the lower efficiency and higher installation costs for systems with the same output. The prices given are not end customer prices.

    Further development

    Overall, the photovoltaic market is still growing strongly (around 40% annually). Forecasts of the electricity production costs in Germany come to values ​​for small PV roof systems (5 - 15 kWp) between 4.20 - 6.72 cents / kWh for the year 2035. For free-standing systems, values ​​of 2.16 - 3.94 cents / kWh are assumed. The system prices per installed kilowatt drop below 400 € / kWp for free-standing systems and between 700 - 815 € / kWp for small systems.

    At locations with high solar radiation over 1450 Wh / (m² · a), the electricity production costs for ground-mounted systems could fall below 2 cents / kWh in 2035.


    Since 2012, the electricity production costs in Germany have been below the household electricity price, which means that grid parity has been achieved.

    At the end of 2018, 46.0 GW of net electrical output were installed. In their publication from 2010 to 2020, the management consultancy Roland Berger and Prognos AG considered an expansion to 70 GW to be realistic. Under the theoretical assumption that electrical energy could be stored without loss, a total of around 690 GW would have to be installed with an average annual yield of 900 kWh per kW p for an energy supply exclusively with photovoltaics.

    United States

    In June 2014, Barclays downgraded bonds from US electricity suppliers because of competition from the combination of photovoltaics and energy storage, which leads to increased self-consumption . This could change the electricity supplier's business model. Barclays wrote: “We expect falling prices for decentralized photovoltaic systems and private electricity storage systems to break through the status quo in the next few years.” And it continues: “In the more than 100-year history of electricity suppliers there have been not yet a competitive alternative to mains electricity. We are convinced that photovoltaics and storage can transform the system in the next ten years. "

    In the summer of 2014, the investment bank Lazard, based in New York, published a study on the current levelized costs of photovoltaics in the USA compared to conventional power generators. The cheapest large photovoltaic power plants can produce electricity at $ 60 per MWh. The mean value of such large power plants is currently USD 72 per MWh and the upper limit is USD 86 per MWh. In comparison, coal-fired power plants are between $ 66 and $ 151 per MWh, and nuclear power is $ 124 per MWh. Small rooftop photovoltaic systems are still at 126 to 265 USD per MWh, which, however, can do without electricity transport costs. Onshore wind turbines range from $ 37 to $ 81 per MWh. According to the study, the electricity suppliers see a disadvantage in the volatility of solar and wind power. The study sees one solution in batteries as storage (see battery storage power plant ), which are still expensive, however.

    Environmental impact


    The environmental impacts of silicon technology and thin-film technology are typical of semiconductor manufacturing, with the corresponding chemical and energy-intensive steps. The pure silicon production in silicon technology is decisive due to the high energy consumption and the occurrence of secondary substances. Up to 19 kg of secondary substances are produced for 1 kg of high-purity silicon. Since high-purity silicon is mostly produced by supplier companies, the selection of suppliers and their production method from an environmental point of view is decisive for the environmental balance of a module. In a study in 2014, the carbon dioxide footprint of a photovoltaic module manufactured in China and installed in Europe for power generation was also without taking into account the energy required for transport due to the greater use of non-regenerative energy in China, in particular from the conversion of coal into electricity, twice as large as when using a photovoltaic module manufactured in Europe.

    With thin-film technology, cleaning the process chambers is a sensitive issue. Some of the climate-damaging substances nitrogen trifluoride and sulfur hexafluoride are used here. When using heavy metals such as CdTe technology, it is argued that there is a short energy payback time on a life cycle basis.


    In 2011, the Bavarian State Office for the Environment confirmed that CdTe solar modules pose no danger to people or the environment in the event of a fire.

    Thanks to the fact that it is absolutely emission-free during operation, photovoltaics have very low external costs . While these are around 6 to 8 ct / kWh for electricity generation from hard coal and lignite, they are only around 1 ct / kWh for photovoltaics (year 2000). This is the result of a report by the German Aerospace Center and the Fraunhofer Institute for Systems and Innovation Research . For comparison, the value of 0.18 ct / kWh of external costs for solar thermal power plants also mentioned there.

    Greenhouse gas balance

    Even if there are no CO 2e emissions in operation , photovoltaic systems cannot yet be manufactured, transported and installed CO 2e- free. As of 2013, the calculated CO 2e emissions from photovoltaic systems are between 10.5 and 50 g CO 2e / kWh, depending on the technology and location , with averages in the range 35 to 45 g CO 2e / kWh. A more recent study from 2015 determined average values ​​of 29.2 g / kWh. These emissions are caused by the burning of fossil fuels, especially during the manufacture of solar systems. With the further expansion of renewable energies in the course of the global transformation to sustainable energy sources, the greenhouse gas balance will automatically improve. The technological learning curve also results in lower emissions . Historically, emissions fell by 14% for every doubling of installed capacity (as of 2015).

    According to a holistic comparison by the Ruhr University Bochum in 2007, the CO 2e emissions from photovoltaics were still 50–100 g / kWh, with the modules used and the location being decisive. In comparison, it was 750–1200 g / kWh for coal -fired power plants , 400–550 g / kWh for combined cycle gas power plants , 10–40 g / kWh for wind energy and hydropower, and 10–30 g / kWh for nuclear energy ( without final storage), and for solar thermal in Africa at 10-14 g / kWh.

    Energetic amortization

    The energetic amortization time of photovoltaic systems is the period in which the photovoltaic system has delivered the same amount of energy that is required during its entire life cycle; for production, transport, construction, operation and dismantling or recycling .

    In 2011 it was between 0.75 and 3.5 years, depending on the location and the photovoltaic technology used. CdTe modules performed best with values ​​of 0.75 to 2.1 years, while modules made of amorphous silicon were above average with 1.8 to 3.5 years. Mono- and multicrystalline systems as well as systems based on CIS were around 1.5 to 2.7 years. The study assumed 30 years for modules based on crystalline silicon cells and 20 to 25 years for thin-film modules as the service life, and 15 years for the service life of the inverters. By 2020, an energy payback time of 0.5 years or less was seen as achievable for southern European systems based on crystalline silicon.

    When used in Germany, the energy required in 2011 to manufacture a photovoltaic system was recovered in solar cells in around two years. Under irradiation conditions typical for Germany, the harvest factor is at least 10; a further improvement is likely. The lifespan is estimated at 20 to 30 years. As a rule, the manufacturers give performance guarantees for the modules for 25 years. The energy-intensive part of solar cells can be recycled 4 to 5 times.

    Land consumption

    PV systems are mainly installed on existing roofs and over traffic areas, which does not require any additional space. On the other hand, open-air systems in the form of solar parks take up additional space, with already pre-loaded areas such as B. Conversion areas (from military, economic, traffic or residential use), areas along motorways and railway lines (in a 110 m strip), areas that are designated as commercial or industrial areas or sealed areas (former landfills , parking lots, etc.) are used become. If photovoltaic systems are set up on agricultural land, which is currently not subsidized in Germany, there may be competition for use. Here, however, it must be taken into account that solar parks have a multiple higher energy yield compared to bioenergy generation on the same area. Solar parks provide around 25 to 65 times as much electricity per unit area as energy crops .

    In Germany, more than 200 GW of photovoltaic capacity can be installed on roof and facade surfaces; on fallow arable land u. over 1000 GW are possible. This means that there is a potential of more than 1000 GW for photovoltaics in Germany, with which far more than 1000 TWh of electrical energy could be produced per year; significantly more than the current German electricity demand. However, since this would produce large surpluses, especially in the lunchtime hours of sunny days, and enormous storage capacities would have to be built up, such a strong expansion of just one technology does not make sense and the combination with other renewable energies is much more practical. If you wanted to cover all of Germany's current primary energy needs with photovoltaics, i. H. approx. 3800 TWh, this would require approx. 5% of the area of ​​Germany. The problem here is the strongly fluctuating generation with the seasons and during the day, so that an energy system based exclusively on solar power is implausible . For a completely regenerative energy supply in Germany a mix of different renewable energies is required, with wind energy having the greatest potential , followed by photovoltaics.

    Solar radiation balance of PV modules

    Depending on the material, different amounts of solar radiation are reflected. The different degrees of reflection (the albedo ) also have an impact on the global climate - also known as ice-albedo feedback . When highly reflective areas of snow and ice at the poles and in Greenland get smaller, more solar radiation is absorbed by the earth's surface and the greenhouse effect is intensified.

    An efficiency of the PV modules of 18% and the reflected portion of solar radiation results in an albedo of approx. 20%, which is even an improvement compared to asphalt with 15% and has no disadvantageous effect compared to lawns with 20% albedo . The generated PV electricity replaces electricity from combustion power plants, which also reduces the release of CO 2 .

    Recycling of PV modules

    So far, the only recycling plant (specialized pilot plant) for crystalline photovoltaic modules in Europe is running in Freiberg, Saxony. The company Sunicon GmbH (formerly Solar Material), a subsidiary of SolarWorld, achieved a mass-related recycling rate for modules there in 2008 of an average of 75% with a capacity of approx. 1200 tons per year. The amount of waste from PV modules in the EU in 2008 was 3,500 tons / year. A capacity of around 20,000 tons per year is planned through extensive automation.

    The solar industry founded the PV CYCLE association as a joint initiative in 2007 to set up a voluntary, EU-wide, comprehensive recycling system. In the EU, an increasing number of 130,000 t of disused modules are expected per year by 2030. As a reaction to the overall unsatisfactory development, solar modules have also been subject to an amendment to the electronic waste directive since January 24, 2012. For the PV industry, the amendment provides that 85 percent of the solar modules sold must be collected and 80 percent recycled. By 2014 all EU-27 member states should implement the regulation in national law. The aim is to make manufacturers responsible for providing structures for recycling. The separation of the modules from other electrical devices is preferred. Existing collection and recycling structures are also to be expanded.

    State treatment

    The generation of electricity by means of photovoltaics is promoted in many countries. The following is an (incomplete) list of various regulatory frameworks in individual countries.


    Funding programs

    In Germany there is a legally regulated feed-in tariff granted over a period of 20 years ; the amount is regulated in the Renewable Energy Sources Act . The feed-in tariff is degressive, so it drops by a certain percentage for new systems each year. There are also twelve other programs designed to promote the purchase of a photovoltaic system.

    At the federal level, the so-called investment allowance for photovoltaic systems in the manufacturing industry and in the area of ​​production-related services can be approved in the form of tax credits.

    In addition, the KfW development bank provides the following programs:

    • KfW - Renewable Energies - Standard
    • KfW - Kommunalkredit
    • BMU demonstration program
    • KfW - investing in municipalities.

    In contrast to the investment allowance, the funding from KfW-Förderbank is only approved as a loan and made available via the respective house bank.

    Furthermore, the following federal states have passed their own solar subsidy laws:

    • Bavaria - efficient energy generation and use in trade - (subsidy)
    • Lower Saxony - innovation support program (trade) - (loan / in exceptional cases grant)
    • North Rhine-Westphalia - "Rational use of energy, renewable energies and energy saving" - (grant)
    • Rhineland-Palatinate - energy-efficient new buildings - (grant)
    • Saarland - Future Energy Program Technology (ZEP-Tech) 2007 (demonstration / pilot project) - (grant).

    Additional funding and grants are also offered by numerous cities and municipalities, local climate protection funds and some private providers. Some of these can be combined with other funding programs.

    The Upper Bavarian city of Burghausen offers a local funding program with 50 € per 100 W p of installed power up to max. € 1,000 per system and residential building.

    Tax treatment

    With an annual turnover of up to € 17,500, the small business regulation according to § 19 UStG applies . As a small business owner, you do not have to submit a tax return, but you are also not allowed to invoice the customer with sales tax. An entrepreneur who is subject to sales tax (small businesses can opt to pay tax) is reimbursed the input tax on all investments, but has to invoice the buyer for sales tax in addition to the feed-in tariff and pay it to the tax office.

    Section 15 of the Income Tax Act applies to the income from the photovoltaic system . A possible loss reduces the tax burden if there is no hobby here . It would be a hobby if, based on the calculation based on the operating time of the system, it was found from the outset that the operation of the system does not generate any profit. Insofar as relevant return calculation programs take a tax advantage into account, this problem must be taken into account.

    Since there is an exemption of € 24,500 for business tax for natural persons and partnerships ( Section 11 (1) No. 1 GewStG ), only large investments are usually subject to business tax.

    Damping effect on electricity prices on the exchange

    PV is suitable as a supplier of peak-load electricity, as it generates the highest yields at midday at the “boiling point”, and it displaces expensive gas and coal-fired power plants from the market. Solar energy therefore dampens the exchange prices for peak electricity ( “merit order effect” ). The peak prices for electricity have fallen sharply compared to the average price in recent years, parallel to the expansion of solar energy. In summer, the previous daily peaks have largely disappeared. However, due to the faulty construction of the EEG compensation mechanism, this price-lowering effect does not reach private customers, but paradoxically increases the cost of electricity for private customers, while industry, on the other hand, benefits from the lower procurement costs on the electricity exchange.

    The price of electricity on the electricity exchange had risen continuously until 2008 and in 2008 reached the maximum of 8.279 cents / kWh. The increased use of renewable energies has put the electricity price under pressure. In the first half of 2013 the average electricity price on the electricity exchange was only 3.75 cents / kWh and for the 2014 futures market it was 3.661 cents / kWh in July 2013.


    From May 2012 to the end of 2015 , the utility company Wien Energie used a public or customer participation model to encourage people to finance 23 PV systems with a total of 9.1 MW p (as of May 10, 2016) p . The EVU pays the investors a rent.


    The Chinese government is strongly promoting the expansion of photovoltaics. The Chinese National Energy Agency recently increased its expansion targets by 30% and in 2015 overtook Germany as the largest installer of photovoltaics both in total (21.3 GW) and per capita of the population of newly installed capacity (16.3 W).


    One year after the Fukushima nuclear disaster , the Japanese government passed a law based on the German EEG. Since July 1, 2012, a feed-in tariff of 42 yen / kWh has been paid for photovoltaic systems with an output of ten kilowatts or more (around € 0.36 / kWh). This remuneration is paid for 20 years. Smaller systems up to 10 kW are only subsidized for ten years.


    On the basis of a law of November 2011, the Romanian state issues green certificates, currently six certificates per 1000 kWh by December 31, 2013. A reduction in the number of certificates was planned for 2014. The value of the green certificates is negotiated on the exchange and decreases with the amount of electricity generated from renewable energies. In February 2012, the price for a certificate was the equivalent of € 55, so that € 0.33 was paid for 1 kWh. However, the price can also drop to around half.


    In fact, there are three funding models in Switzerland: the small one-time payment (KLEIV), the large one-time payment (GREIV) and the cost-covering feed-in payment (KEV). Only KLEIV can apply for solar systems with a size of 10 to 600 m², those from 600 m² can choose between KLEIV, GREIV and KEV.

    The KLEIV and the GREIV are one-time payments that cover a maximum of 30% of the investment costs of the solar system and are paid out to the solar system owner by the Federal Office for Energy. GREIV is designed for solar systems with an output between 100 kWp and 50 MWp. Once the photovoltaic system has been put into operation, it takes about 2 years for the small one-time payment to be paid out.

    The situation of subsidies for solar systems has changed with the entry into force of the new Energy Act on January 1, 2018. For the commissioning of photovoltaic systems from January 1, 2018, the cost-covering feed-in tariff (KEV) is no longer available. Only registrations with a registration date up to June 30, 2012 will be considered.

    The funding programs are coordinated by Swissgrid.

    Sierra Leone

    In the West African state of Sierra Leone , around a quarter of the electricity generated should come from renewable energies, primarily solar energy, by the end of 2016. West Africa's largest solar park with a capacity of 6 MW is to be built near the capital Freetown . In Koindu , the city center is illuminated by solar-based street lighting at night. This has been in operation since July 2013. In addition, parts of the road to Yenga , a village on the border with Guinea and Liberia , are also illuminated by photovoltaic lighting.


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    Web links

    Wiktionary: Photovoltaic  - explanations of meanings, word origins, synonyms, translations
    Commons : Photovoltaics  - collection of images, videos and audio files

    Individual evidence

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