Solar 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.

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 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.

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"deg;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
Beam irradiation Hb J/m2
Maximum system voltage Vmax V

TABLE 1: Electrical parameters of photovoltaic (solar) modules

Nominal operating cell temperature NOCT °C
Open cirquit voltage Voc V
Storage temperature Tstor °C
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: Voc = 48,1 mV, Isc = 5,8 A, IMPP = 4,99 A, VMPP = 59,3 V, and PMPP temperature coefficient γ = -0,0045 %/K. Calculation algorithm presented in the book Photovoltaik Engineering (Wagner, see sources) was used.

Module I-V characteristics, credit pvresources

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

Module power characteristics, credit pvresources

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 from +0.03%/K to +0.1%/K
Open cirquit voltage β from -0.33%/K to -0.40%/K
Maximum power (MPP) γ from -0.40%/K to -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) 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 choice for flat roofs.

Ground screws

Mounting structures

Array mounting structure, credit pvresources Array mounting structure, credit pvresources Array mounting structure, credit pvresources

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

Screws and fastening


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