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Photovoltaic modules

"Do bear in mind: No one has ever scientifically proved solar energy inefficient or non-economical. If such a scientific research had been conducted, I would be eager to learn more about it."

Monocrystaline module, Solar-fabrik AG Polycrystalline module, Solar-fabrik AG Bifacial modules - Poulek Solar Co.Ltd Transparent module, Sunways AG

Photovoltaic modules
(source/copyright: Solar-fabrik AG pictures 1,2 from left to the right - Poulek Solar Co.Ltd. picture 3 - Sunways AG picture 4)

In photovoltaic (solar) module light energy converts into electricity. A photovoltaic module is the basic element of each photovoltaic system. It consists of many jointly connected solar cells. According to the solar cell technology we distinguish monocrystalline, polycrystalline and amorphous solar modules. Detailed description on solar cell technologies you will find in the technologies section. Most commercial crystalline modules consist of 36 or of 72 cells. Solar cells are connected and placed between a tedlar plate on the bottom and a tempered glass on the top. Placed between the solar cells and the glass there is a thin usualy EVA foil. Solar cells are interconnected with thin contacts on the upper side of the semiconductor material, which can be seen as a metal net on the solar cells. The net must be as thin as possible allowing a disturbance free incidence photon stream. Usually a module is framed with an aluminium frame, occasionally with a stainless steel or with a plastic frame. Special flexible modules are designed for use on boats that can be walked upon without causing any damage to the modules. The typical crystalline modules power ranges from several W to up to 200 W/module. Some producers produce preassembled panels with several 100 Wp. Over its estimated life a photovoltaic module will produce much more electricity then used in it's production and a 100 W module will prevent the emission of over two tones of CO2.

 

Photovoltaic modules - features and applications

Module construction

Photovoltaic module consists of transparent front side, encapsulated solar cells and backside. As front side material (superstrate) usualy low-iron, tempered glass is used. For some special module types some other front side materials are used like DuPont™ Tefzel® or non-tempered glass for example.

You may also learn more about some front- and backside materials used in photovoltaic modules if you visit DuPont™ web site.

Required mechanical characteristics (impact resistance etc.) and module qualification procedures are defined in international standards, for details please see standards section.

Backside is usualy non transparent, most common used material is PVF (registered trade mark - Tedlar®). Transparent back side is also possible - transparent back side materials are often used in modules that are integrated into buildings envelope (facade or roof), see also BIPV section.

Between glass and back side solar cells encapsulated with encapsulation material are placed. Many different materials can be used for encapsulation but two most often used materails are EVA (ethylene-vinyl-acetate) and PVB (polyvinyl-butiral). PVB is also used in safety windscreens in automotive industry. It is used as encapsulation material in transparent modules. EVA is used for encapsulation of cells in standard modules.


Technical data

The most important module parameters include a short circuit current, an open circuit voltage and a nominal voltage at 1000 W/m2 solar radiation, current and rated power at 1000 W/m2 solar radiation value. Module parameters are measured at standard test conditions (STC) - solar radiation 1000 W/m2, air mass (AM) 1,5 and temperature 25oC. The following parameters can usualy be found in module datasheets:

Peak power - Wp
Open cirquit voltage - Voc
Short cirquit current - Isc
Voltage at maximum power - Vmp
Current at maximum power - Imp
Current at battery operating voltage - I
Nominal operating cell temperature (NOCT) - oC
Wind loading of surface pressure - N/m2 (km/h)
Impact resistance - mm  at km/h
Maximum system voltage - Vmax
Storage and operating temperature - oC

 

Monocrystalline solar module   Polycrystalline solar module

Photovoltaic modules with monocrystaline solar cells - left
(Source/copyright IEA PVPS Task2)

Modules with polycristalline solar cells - right
(photo: Denis Lenardic)


Module efficiency

Commercial crystalline photovoltaic modules efficiency typically ranges from 10 to 13 %. However, you must be aware, that the solar cell efficiency doesn’t equal the module efficiency. The module efficiency is usually 1 to 3 % lower than the solar cell efficiency due to glass reflection, frame shadowing, higher temperatures etc. Table 1 represent some features of different solar module types. Amorphous modules have the lowest price, yet their lifetime is short and their efficiency is up to 8 % only.


Temperature coefficients

All electrical parameters of solar module depends on temperature. The most common temperature coefficients that are usualy available in module data sheets are (typical values are valid for crystalline silicon solar cells):

α (Isc) typical values between +0.03%/K and +0.1%/K
β (Voc) typical values between -0.33%/K and -0.40%/K
γ (Pmpp) typical values between -0.40%/K and -0.50%/K.
 

Values are important in design stage of PV system and they should be considered as important parameters related to the PV system design.


Additional information

How to choose wire crossection for interconnection of photovoltaic modules?

If you are interested in solar trackers, bifacial trackers, trough concentrators systems then please proceed to trackers and concentrators page.



Photovoltaic module I-U characteristics

Photovoltaic module power

Solar module characteristics


Transparent solar modules

Transparent crystalline solar modules are produced with transparent Tedlar back side, on the other side is transpareny by amorphous modules usualy achieved by microperforation of the modules. With special production procedure polycristalline semitransparent solar cells can also be produced.
 

Transparent solar module   Transparent solar cell - Sunways AG

Transparent solar module - left, and transparent solar cell - right
(source/copyright: Sunways AG).

Flexible solar modules

Front and back side of flexible modules, with crystalline solar cells, are most often produced from plastic materials like plexiglas® or makrolon® for example. Between front and back side encapsulated cells are located. Flexible solar modules can be produced with transparent or with opaque back side. Back side in different colours is also an option. Makrolon is one of the most common plastic materials used. Learn more how useful makrolon is (german language only)...

Amorphous flexible modules are also available. Most often metal substrate is used - modules can be used as roof or facade cover.

Solar modules related web sites

 

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Module mounting structures

 

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Photovoltaic module testing institutions

 

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Literature and more information

pdf Agro, S.C., Tucker, R.T.: Development of New Low-Cost, High-Performance, PV Module Encapsulant/Packaging Materials; 29th IEEE PV Specialists Conference New Orleans, Louisiana May 20-24, 2002 (281 kB)
pdf Osterwald, C.R., Anderberg, A., Rummel, S., Ottoson, L.: Degradation Analysis of Weathered Crystalline-Silicon PV Modules; Specialized Technology Resources, Inc. Enfield, Connecticut; March 2004, NREL/SR-520-35683 (595 kB)
pdf Webmaster's choice King, D.L., Quintana, M.A., Kratochvil, J.A., Ellibee, D.E., HansenMeyer, B.R.: Photovoltaic Module Performance and Durability Following Long-Term Field Exposure; Sandia National Laboratories, Albuquerque, NM, (448 kB).
pdf Webmaster's choice Measuring Photovoltaic Cell I-V Characteristics with the Model 2420 3A SourceMeter® Instrument.