View source for Solar Cells and Modules


= Overview<br/> =

A solar cell or [[Photovoltaic_(PV)|photovoltaic]] (PV) cell is a semiconductor device that converts light directly into electricity by the [http://en.wikipedia.org/wiki/Photovoltaic_effect photovoltaic effect]. The most common material in solar cell production is purified [http://en.wikipedia.org/wiki/Silicon silicon] that can be applied in different ways.<br/>

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= Monocrystalline Silicon Photovoltaic (PV) Cells<br/> =

Monocrystalline silicon PV cells are made from silicon wafers that are cut from cylindrical single-crystal silicon ingots. The rotund cells have to be cut to form nearly quadratic cells, that can be easily integrated in one module. Thus, refined silicon is wasted in the cell production process. Monocrystalline silicon shows predictable and uniform behaviour, but, due to the careful and slow manufacturing processes required, it is also the most expensive type of silicon.

Modules consisting of monocrystalline silicon PV cells reach commercial efficiencies between 15 and 18 %. So far, they are the most efficient modules and, with about 85% in 2010, have the largest market share. However, other alternatives are challenging this technology.

[[File:Monocrystalline solar cell.png|thumb|center|180px|A solar cell made from a monocrystalline silicon wafer]]

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= Polycrystalline Silicon Photovoltaic (PV) Cells<br/> =

Polycrystalline or multicrystalline silicon PV cells are made from cast square ingots — large blocks of molten silicon, carefully cooled and solidified. They are less expensive to produce than monocrystalline silicon PV cells, but are marginally less efficient, with module conversion efficiencies between 13 and 16 %.

[http://pvcdrom.pveducation.org/ -> PVCDROM.org], an educational website on photovoltaics, shows the production process of polycrystalline silicon PV cells with pictures and viedeo sequences.

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[[File:Polycrystalline silicon module.jpg|thumb|center|180px|Polycrystaline PV cells laminated to backing material in a PV module]]

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= Thin Film Photovoltaic (PV) Cells<br/> =

The various thin film technologies currently being developed reduce the amount (or mass) of light absorbing material required in creating a solar cell. This can lead to reduced processing costs from that of bulk materials (in the case of silicon thin films) but also tends to reduce energy conversion efficiency (an average 6 to 12 % module efficiency).<ref name="IEA PVPS, http://www.iea-pvps.org/pv/snapshot/techproc.htm">IEA PVPS, http://www.iea-pvps.org/pv/snapshot/techproc.htm</ref>

Thin film PV cells are constructed by depositing extremely thin layers of photovoltaic semi-conductor materials onto a backing material such as glass, stainless steel or plastic. Thin film materials commercially used are [http://en.wikipedia.org/wiki/Amorphous_silicon amorphous silicon] (a-Si), [http://en.wikipedia.org/wiki/Cadmium_telluride cadmium telluride] (CdTe), and [http://en.wikipedia.org/wiki/Cadmium_telluride copper-indium-(gallium)-diselenide] (CI(G)S).<ref name="IEA PVPS, http://www.iea-pvps.org/pv/snapshot/techproc.htm">IEA PVPS, http://www.iea-pvps.org/pv/snapshot/techproc.htm</ref>



<u>Commercially available thin film modules:</u><br/>
*Are potentially cheaper to manufacture than crystalline cells
*Have a wider customer appeal as design elements due to their homogeneous appearance
*Present disadvantages, such as low-conversion efficiencies and requiring larger areas of PV arrays and more material (cables, support structures) to produce the same amount of electricity

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[[File:CdTe PV Array.jpg|thumb|center|180px|A CdTe photovoltaic array]]

= Third Generation Solar Cells<br/> =

<u>Currently there are solar cells based in different new technologies in the way to market maturity, for example the high efficiency cells:</u><br/>

<u>'''Thin film III-V solar cells:'''</u>
*nion of the semiconductors from the third and the fifth group from the periodic table.<br/>
*Efficiency of 20-25% <ref name="CIE 2011">http://www.cie.unam.mx/~rbb/Razykov_20011_PV_SolarEnergy.pdf</ref><br/>
*A variety of possible combination increasing price while increasing efficiency<br/>
*Most common connection: gallium arsenide (GaAs),
*Application: Power supply of satellites<br/>

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<u>'''Multi-stack thin film:'''</u>
*"Stacking" III-V solar cells or silicon cells
*Efficiency up to approximately 37% <ref name="CIE 2011">http://www.cie.unam.mx/~rbb/Razykov_20011_PV_SolarEnergy .pdf</ref>- Each cell absorbs a certain wavelength, and then the stack can absorb more from the solar spectrum
*The top cell material has the highest band gap and covers the highest absorption area. Underlying cells absorbs the section of the solar spectrum with smaller wavelengths.
*Series connection of the overlying cells
*Other names for mutli-stack solar cells (depending on the number of layers) are: Tandem, triple, or multiple cascade cells.

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=== Concentrator Photovolatics<br/> ===

{| cellspacing="1" cellpadding="1" border="0" style="width: 100%" class="FCK__ShowTableBorders"
|-
| 
'''Concentrator photovoltaics (CPV)''' are based on lenses or mirrors which focus direct sun light on solar cells. These cells consist of a small amount of highly efficient, but expensive, PV-material (silicon or III-V compounds, generally gallium arsenide or GaA).<br/>At present concentrating intensities vary from a factor of 2 to 100 suns (low concentration) to 1000 suns (high concentration). Commerical module efficiencies lay in the range of 20 to 25 percent, although efficiencies of 25 to 30 percent could have been achieved with gallium arsenide <ref name="EPIA11">EPIA11: http://www.epia.org/publications/photovoltaic-publications-global-market-outlook.html</ref>. An efficiency of 41,1 percent has been achieved in the laboratory by the Fraunhofer Institut für solare Energiesysteme, Germany (concentrating intensity: 450 suns) <ref name="Fraunhofer09">Fraunhofer 09: http://www.vision.fraunhofer.de/de/projekte/465.html</ref>.

In order the course of the sun Concentrator modules are mounted on a 2-axis tracking system. In case of low-concentration-PV there exist 1-axis tracking systens and less complex lenses.

| [[File:Konzentratormodul PV.jpg|thumb|180px|Concentrating module]]
|}

=== <br/>Organic Solar Cells<br/> ===

<u>'''Hybrid dye-sensitised solar cells:'''</u>

instead of semi-conductor material hybrid dye-sensitised solar cells use an organic dye for light absorption. Simple silk-screen allows cost-efficient production costs and offers different scopes for design as implementation in frontages or in advertising purposes <ref name="Jäger11">Jäger11: http://www.gtz.de/de/dokumente/giz2011-de-Potentialstudie-Marokko-PV.pdf</ref>. hybrid dye-sensitised solar cells are able to use diffuse sun light. Average efficiencies vary from 2 to 4%.



<u>'''Fully organic solar cells:'''</u>

Organic solar cells are still at an early stage of development. These cells consist of organic hydrocarbon compounds as well as a special electron structure and are able to generate electricity on foils and textiles. At present average cell efficiencies vary between 3 and 5 percent <ref name="Jäger11">Jäger11: http://www.gtz.de/de/dokumente/giz2011-de-Potentialstudie-Marokko-PV.pdf</ref>. Minor material consumption and more efficient production technologies lead to a high potential for cost-efficient production. However, there is still need for research activities as life spans are very short.

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= Solar Modules =

For almost all applications, the one-half volt produced by a single cell is inadequate. Therefore, cells are connected together in series to increase the voltage. Several of these series strings of cells may be connected together in parallel to increase the current as well.<ref name="Polar Power Inc., http://polarpowerinc.com/home.htm">Polar Power Inc., http://polarpowerinc.com/home.htm</ref>



<u>In order to use the connected cells in practical applications they must be:</u>
*protected from mechanical damage during manufacture, transport and installation and use (in particular against hail impact, wind, sand and snow loads). This is especially important for wafer-based silicon cells which are brittle.
*protected from moisture, which corrodes metal contacts and interconnects, (and for thin-film cells the transparent conductive oxide layer) thus decreasing performance and lifetime.



Therefore, the interconnected cells and their electrical connections are sandwiched between a top layer of glass or clear plastic and a lower level of plastic or plastic and metal. An outer frame is attached to increase mechanical strength, and to provide a way to mount the unit. This package is called a "module" or "panel". Typically, a module is the basic building block of photovoltaic systems.<ref name="Polar Power Inc., http://polarpowerinc.com/home.htm">Polar Power Inc., http://polarpowerinc.com/home.htm</ref>

The peak power output of a solar module depends on the number of cells connected and their size. Module performance is generally rated under '''Standard Test Conditions (STC)''' : [http://en.wikipedia.org/wiki/Irradiance irradiance] of 1,000 [http://en.wikipedia.org/wiki/W/m2 W/m²], solar [http://en.wikipedia.org/wiki/Spectrum spectrum] of [http://en.wikipedia.org/wiki/Airmass AM] 1.5 and module temperature at 25°C. Solar modules are rated in peak watts [W<sub>p</sub>] according to their output under STC. Thus, a 50 W<sub>p</sub> module can be expected to supply 50 W of power under optimal conditions. The performance is reduced by high temperatures.<ref name="Polar Power Inc., http://polarpowerinc.com/home.htm">Polar Power Inc., http://polarpowerinc.com/home.htm</ref>

Like solar cells modules can be connected in series and/or in parallel to increase the voltage and/or the current depending on the system requirements.<ref name="Polar Power Inc., http://polarpowerinc.com/home.htm">Polar Power Inc., http://polarpowerinc.com/home.htm</ref>

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= Comparison of Different Types of PV Modules =

<u>Comparison of Different Types of PV Modules</u><ref name="Solarpraxis (Hrsg.): Photovoltaik für Profis. Verkauf, Planung Montage von Solarstromanlagen, 2., vollständig überabeitete Auflage, 2009, S. 131-135.">Solarpraxis (Hrsg.): Photovoltaik für Profis. Verkauf, Planung Montage von Solarstromanlagen, 2., vollständig überabeitete Auflage, 2009, S. 131-135.</ref><ref name="EPIA11: http://www.epia.org/publications/photovoltaic-publicationsglobal- market-outlook.html">EPIA11: http://www.epia.org/publications/photovoltaic-publicationsglobal- market-outlook.html</ref>:

{| cellspacing="0" cellpadding="5" border="1" style="width: 100%"
|-
| style="background-color: rgb(204, 204, 204)" | '''Cell material'''
| style="background-color: rgb(204, 204, 204)" | '''Module efficiency'''
| style="background-color: rgb(204, 204, 204)" | '''Surface area needed for 1 kW<sub>p</sub>'''
| style="background-color: rgb(204, 204, 204)" | '''Advantages'''
| style="background-color: rgb(204, 204, 204)" | '''Disadvantages'''
|-
| Monocrystalline silicon
| 15-18 %
| 7-9 m²
| - most efficient PV modules<br/>- easily available on the market<br/>- highly standardised
| - most expensive<br/>- waste of silicon in the production process
|-
| Polycrystalline silicon
| 13-16 %
| 8-9 m²
| - less energy and time needed for production than for monocrystalline cells (= lower costs)<br/>- easily available on the market<br/>- highly standardised
| - slightly less efficient than monocrystalline silicon modules
|-
| Micromorph tandem (aµ-Si)
| 6-9 %
| 9-12 m²
| 
| - more space for the same output needed
|-
| Thin film:<br/>Copper indium diselenide (CIS)
| 10-12 %
| 9-11 m²
| - higher temperatures and shading have lower impact on performance<br/>- lower production costs
| - more space for the same output needed
|-
| Thin film:<br/>Cadmium telluride (CdTe)
| 9-11 %
| 11-13 m²
| - higher temperatures and shading have lower impact on performance<br/>- highest cost-cutting potential
| - more space for the same output needed
|-
| Thin film:<br/>Amorphus silicon (a-Si)
| 6-8 %
| 13-20 m²
| - higher temperatures and shading have lower impact on performance<br/>- less silicon needed for production
| - more space for the same output needed
|}

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<u>To compare the price of the different modules, the next database present monthly updated values:</u> [http://www.solarserver.de/service-tools/photovoltaik-preisindex.html solarserver.de]

Due to their high efficiency, market penetration and standardisation mono- and polycrystalline silicon modules are the most common modules used in [[Solar Home Systems (SHS)|solar home systems]] (SHS). However, the market share of thin film modules is growing, especially in free-standing and [[Building Integrated Photovoltaics (BIPV)|building integrated PV systems]].

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= Further Information =

*[https://energypedia.info/Portal:Solar Solar Portal on energypedia]
*Further information on PV modules in solar home systems see [[Standards for the PV Generator|standards for the PV generator]].

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= References =

<references /><br/>

[[Category:Solar]]
[[Category:Solar_Home_Systems_(SHS)]]