Photovoltaic Modules

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.

Different poly- and monocrystalline modules with opaque and with black backside
(courtesy: Solar-fabrik)

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 polycarbonate or non-tempered glass for example. For flexible modules ethylene tetrafluoroethylene (ETFE) a fluorine based plastic, with high corrosion resistance and strength over a wide temperature range.is often used. Backside is usualy non transparent, most common used material is polyvinyl fluoride (PVF). 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 materials 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. Other less common encapsulation materials are thermoplastic polyurethane (TPU) and polyurethane or silicone cast resins used for example in transparent modules or other demanding applications. Required mechanical characteristics (impact resistance etc.) and module qualification procedures are defined in international standards, for details please see standards section.

TECHNICAL DATA

General electrical and mechanical properties

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 25°C. The following parameters can usualy be found in module datasheets:

Peak power	PSTC	Wp
Open cirquit voltage	Voc	V
Short cirquit current	Isc	A
Voltage at maximum power	VMPP	V
Current at maximum power	IMPP	A
Maximum system voltage	Vmax	V

TABLE 1: Electrical parameters of photovoltaic (solar) modules

Nominal operating cell temperature	NOCT	°C
Storage temperature	Tstor	°C
Short cirquit current	Isc	A
Wind loading of surface pressure	Cp	N/m2 (km/h)
Impact resistance	-	mm at km/h

TABLE 2: Non-electrical parameters of photovoltaic (solar) modules

Samples of solar modules I-V and power characteristics are presented on pictures below. Presented characteristics were calculated for solar module with following data: V_oc = 48,1 mV, I_sc = 5,8 A, I_MPP = 4,99 A, V_MPP = 59,3 V, and P_MPP temperature coefficient γ = -0,0045 %/K. Calculation algorithm presented in the book Photovoltaik Engineering (Wagner, see sources) was used.

Example of solar module I-V characteristics for different irradiation values

Example of solar module power characteristics for different irradiation values

Module efficiency

Commercial crystalline photovoltaic modules efficiency typically ranges from 12 to 15 %. 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. Amorphous modules have the lowest price, yet their lifetime is shorter and their efficiency is up to 10 % only.

Temperature coefficients

All electrical parameters of solar module depends on temperature. Values are important in design stage of PV system and they should be considered as important parameters related to the PV system design. The most common temperature coefficients that are usualy available in module data sheets are presented in table below - values are valid for crystalline Si solar modules only:

Short cirquit current	α	+0.03%/K and +0.1%/K
Open cirquit voltage	β	-0.33%/K and -0.40%/K
Maximum power (MPP)	γ	-0.40%/K and -0.50%/K

TABLE 3: Temperature coefficients of electrical parameters for Si-crystalline cells/modules

FLEXIBLE MODULES

Front and back side of crystalline Si flexible solar modules are most often produced from plastic materials like poly(methyl methacrylate) (PMMA) known also as plexiglas® or polycarbonate. For demanding applications transparent flexible modules can be produced. Amorphous Si flexible modules are also available. As modul substrate EPDM (ethylene propylene diene Monomer/M-class) synthetic rubber is used. This material can also be used in combination with bitumen what makes it a preffered choise for flat roofs.

MODULE PRICES AND ONLINE SHOPS

Market prices

pvXchange PV Price Navigator - through this hourly updated, analytical tool, you gain insight into pricing trends of more than 30 PV module brands on the European PV market. The price information is subdivided into different downstream value chain levels, ranging from factory gate to installer level. A user-friendly toolbar allows in addition for individual requests and personalisation of the Monitor.
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Solar Buzz Retail Price Environment - Solarbuzz offers the most complete pricing in the solar industry. Free monthly summary includes retail pricing data, trends and analysis.

Antaris Solar - OnLine Photovoltaic Shop.

MODULE MOUNTING STRUCTURES

Ground screws

Krinner - Ground screws for photovoltaic systems.
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DOMA-Drehfundamente - Ground screws for photovoltaic systems.
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Terrafix - Your specialist for foundation design free of concrete.
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Mounting structures

Schletter - photovoltaic array mounting structures for wide variety of applications.
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Zimmermann - open area solar mounting frames.
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Unirac - UniRac manufactures photovoltaic mounting structures for any type of solar installation.

Professional Solar Products - ProSolar has been manufacturing solar equipment longer than any other PV mounting manufacturer.

DPW Solar - we provide innovative mounting solutions for any PV solar application including commercial, industrial, government, utility and residential applications.

IronRidge - IronRidge solar mounts are relied upon every day in solar PV installations that range from small, single-use residential solar applications to some of the largest industrial solar deployments in the world.

Hopergy - Xiamen Hopergy Photovoltaic Technology specializes in the research & developing, production, sales, engineering of PV mountings, solar systems. Company provide innovative mounting solutions for any PV solar application including commercial, industrial, government, utility and residential applications.

Pole mounted array structure, Solarpark Waldpolenz, Germany during construction
(credit: pvresources)

Screws and fastening

SOLAR FASTENER EXPERT - SOLAR FASTENER EXPERT.COM was created to provide a site where Installers, Integrators, Manufacturers and Maintenance contractors could easily obtain all the Stainless Steel Fasteners needed in their projects at a single source.

Heyco - Founded in 1926 and still family owned. Heyco Products Inc. offers decades of experience in the design and manufacture of molded wire protection products and stamped electrical components to meet demanding customer application requirements.

Schäfer + Peters - Schäfer + Peters is your partner for stainless steel and anti-corrosion fasteners, DIN and standard parts such as wood screws, metric screws, tapping screws, washers, nuts and also products such as heavy-duty fastenings, safety screws and solar fastenings as well as special and drawing parts.
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HECO Schrauben - HECO-TOPIX®-T Solar made from stainless steel is the ideal fixing solution for solar panels on over-rafter-insulated roofs.
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PV ARRAY CLEANING SOLUTIONS

Solar Farm Cleaning - a patent protected technology for industrial cleaning of Solar Farms.

Lehmann - German cleaning systems.
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suncleX - suncleX offers high quality products for Photovoltaic and Solar panel cleaning.
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SOURCES AND ADDITIONAL INFORMATION

Books

	Poliskie, M.: Solar Module Packaging: Polymeric Requirements and Selection; CRC Press, 2011, ISBN 978-1439850725.
	Tiwari, G.N., Dubey, S.: Fundamentals of Photovoltaic Modules and their Applications; Royal Society of Chemistry, 2009, ISBN 978-1849730204.
	Wagner, A.: Photovoltaic Engineering, Handbuch für Planung, Entwicklung und Anwendung; Springer, 2006, ISBN 978-3-540-30732-7.

Papers

	Bittmann, E. et al.: Low concentration with polycarbonate; 23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain.
	Geurts, C.P.W., Steenbergen, R.D.J.M.: Full scale measurements of wind loads on stand-off photovoltaic systems; 5th European & African Conference on Wind Engineering, EACWE 5, Florence, Italy, 19-23 July 2009.
	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
	Osterwald, C.R. et al.: Degradation Analysis of Weathered Crystalline-Silicon PV Modules; Specialized Technology Resources, Inc. Enfield, Connecticut; March 2004, NREL/SR-520-35683
	King, D.L. et al.: Photovoltaic Module Performance and Durability Following Long-Term Field Exposure; Sandia National Laboratories, Albuquerque, NM