Solar Panels – Photovoltaic, Thermal Collector, Solar Hot Water Panel

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Solar Panels


From Wikipedia


A photovoltaic module is composed of individual PV cells. This crystalline silicon module one has an aluminium frame and glass on the front.In the field of photovoltaics, a photovoltaic module is a packaged interconnected assembly of photovoltaic cells, also known as solar cells. An installation of photovoltaic modules or panels is known as a photovoltaic array. Photovoltaic cells typically require protection from the environment. For cost and practicality reasons a number of cells are connected electrically and packaged in a photovoltaic module, while a collection of these modules that are mechanically fastened together, wired, and designed to be a field-installable unit, usually with a glass covering and a frame and backing made of metal, plastic or fiberglass, are known as a photovoltaic panel or simply solar panel. A photovoltaic installation typically includes an array of photovoltaic modules or panels, an inverter, batteries (for off grid) and interconnected wiring.




1 Theory and construction

2 Crystalline silicon modules

3 Rigid thin-film modules

4 Flexible thin-film modules

5 External Links

6 See also


Theory and construction


Crystalline silicon and gallium arsenide are typical choices of materials for solar cells. Gallium arsenide crystals are grown especially for photovoltaic use, while silicon crystals are available in less-expensive standard ingots. These ingots are produced mainly for consumption in the microelectronics industry. Polycrystalline silicon has lower conversion efficiency but also lower cost.


During the manufacturing process, crystalline silicon ingots are sliced into wafer-thin disks, polished to remove slicing damage, dopants are introduced into the soup, and metallic conductors are deposited onto each surface: a thin grid on the sun-facing side and usually a flat sheet on the other.[1] Solar panels are constructed of these cells cut into appropriate shapes, protected from radiation and handling damage on the front surface by bonding on a cover glass, and cemented onto a substrate (either a rigid panel or a flexible blanket). Electrical connections are made in series to achieve a desired output voltage and/or in parallel to provide a desired amount of current source capability. The cement and the substrate must be thermally conductive, because the cells heat up from absorbing infrared energy that is not converted to electricity. Since cell heating reduces the operating efficiency it is desirable to minimize the heating. The resulting assemblies are called solar or photovoltaic panels.


Depending on construction the photovoltaic can cover a range of frequencies of light and can produce electricity from them, but cannot cover the entire solar spectrum. Hence much of incident sunlight energy is wasted when used for solar panels, although they can give far higher efficiencies if illuminated with monochromatic light. Some more advanced multispectrum photovoltaic arrays have several different cells tuned to different frequency ranges. This can raise the solar efficiency by several times, but can be far more expensive to produce.


Crystalline silicon modules


The most common design of modules contains cells connected using conductive ribbons into one or more 'strings'. The strings are sandwiched between a solar glass frontside and a flexible and durable polymer backsheet, using a polymeric encapsulant. The encapsulant is melted and crosslinked in a vacuum laminator. The strings are electrically terminated into a junction box usually glued to the back of the module. A frame made of aluminium profile is fitted around the edges.


1. Cells connected to make string 

2. encapsulant film ready 

3. ready for lamination. Note ribbons terminating 2 strings

4. after lamination 

5. Aluminium profiles added to make the frame


Rigid thin-film modules


In rigid thin film modules, the cell is created directly on a glass substrate or superstrate, and the electrical connections are created in situ, a so called "monolithic integration". The substrate or superstrate is laminated with an encapsulant to a front or back sheet.


The main cell technologies in this category are CdTe, amorphous silicon, micromorphous silicon (alone or tandem), or CIGS (or variant).


Flexible thin-film modules


Flexible thin film cells are created by depositing the photoactive layer and other necessary layers on a flexible substrate. If the substrate is an insulator (e.g. polyester or polyimide film) then monolithic integration can be used. If a conductor then monolithic integration cannot be used, and another technique for electrical connection used. The cells are converted to a module by lamination to a transparent colourless fluoropolymer on the front side (typically ETFE or FEP) and a polymer suitable for bonding to the final substrate on the other side. The only commercially available (in MW quantities) in a flexible module is amorphous silicon triple junction (from Unisolar)


Solar thermal collector - From Wikipedia


A solar thermal collector is a solar collector specifically intended to collect heat: that is, to absorb sunlight to provide heat. Although the term may be applied to simple solar hot water panels, it is usually used to denote more complex installations. There are various types of thermal collectors, such as solar parabolic, solar trough and solar towers. These type of collectors are generally used in solar power plants where solar heat is used to generate electricity by heating water to produce steam and driving a turbine connected to the electrical generator.




1 Types

1.1 Flat plate

1.2 Evacuated Tube

1.3 Pool or Unglazed

1.4 Air

1.5 Box type

1.6 Parabolic trough

1.7 Parabolic dish

1.8 Power tower

2 Advantages

3 Disadvantages

4 See also

5 References




Flat plate and box-type collectors are typically used in domestic and light industry applications. Parabolic troughs, dishes and towers are used almost exclusively in solar power generating stations or for research purposes.


Flat plate


Solar thermal system for water heating - these are deployed on flat roof.This is the most common type of solar thermal collector, and is usually used as a solar hot water panel to generate solar hot water. A weatherproofed, insulated box containing a black metal absorber sheet with built in pipes is placed in the path of sunlight. Solar energy heats up water in the pipes causing it to circulate through the system by natural convection. The water is usually passed to a storage tank located above the collector. This passive solar water heating system is generally used in hotels and homes in sunny climates such as those found in southern Europe.


For these purposes, the general practice is to use flat-plate solar energy or evacuated tube collectors with a fixed orientation (position). The highest efficiency with a fixed flat-plate collector or evacuated tube collector is obtained if it faces toward the sun and slopes at an angle to the horizon equal to the latitude plus about 10 degrees. Solar collectors fall into two general categories: nonconcentrating and concentrating.


In the nonconcentrating type, the collector area (i.e. the area that intercepts the solar radiation) is the same as the absorber area (i.e., the area absorbing the radiation).


There are many flat-plate collector designs but generally all consist of (1) a flat-plate absorber, which intercepts and absorbs the solar energy, (2) a transparent cover(s) that allows solar energy to pass through but reduces heat loss from the absorber, (3) a heat-transport fluid (air or water) flowing through tubes to remove heat from the absorber, and (4) a heat insulating backing. One flat plate collector is designed to be evacuated, to prevent heat loss.


The most effective use of collectors is with a sealed heat exchange system, rather than having the potable water flow through the collectors. A mixture of water and propylene glycol (which is used in the food industry) can be used as a heat exchange fluid to protect against freeze damage, up to a temperature that depends on the proportion of propylene glycol in the mixture.


Evacuated Tube


Evacuated (or vacuum) tubes panel.These collectors have multiple evacuated glass tubes which heat up solar absorbers and, ultimately, solar working fluid (water or an antifreeze mix -- typically propylene glycol) in order to heat domestic hot water, or for hydronic space heating. The evacuated tubes minimize the re-radiation of infrared energy from the collectors, allowing them to reach considerably higher temperatures than most flat-plate collectors. For this reason they can perform well in colder conditions. The advantage is largely lost in warmer climates, except in those cases where very hot water is desirable, for example commercial process water. The high temperatures that can occur may require special system design to avoid or mitigate overheating conditions. A further advantage this design has over the flat-plate type is that the constant profile of the round tube means that the collector is always perpendicular to the sun's rays and therefore the energy absorbed is approximately constant over the course of a day.


Pool or Unglazed


This type of collector is much like a flat-plate collector, except that it has no glazing/transparent cover. It is used extensively for pool heating, as it works quite well when the desired output temperature is near the ambient temperature (that is, when it's warm outside). As the ambient temperature gets cooler, these collectors become extremely ineffective.




These collectors heat air directly, almost always for space heating. They are also used for pre-heating make-up air in commercial and industrial HVAC systems


Box type


A common solar cooker is a box type collector. It is a metal box open from top, and insulated from sides with an equally sized mirror hinged to it (like a simple box with a mirror attached to the underside of the cover).


Parabolic trough


Parabolic troughThis type of collector is generally used in solar power plants. A trough-shaped parabolic reflector is used to concentrate sunlight on an insulated tube (Dewar tube) or heat pipe, placed at the focal point, containing coolant which transfers heat from the collectors to the boilers in the power station.


Parabolic dish


Solar Parabolic dishIt is the most powerful type of collector which concentrates sunlight at a single, focal point, via one or more parabolic dishes -- arranged in a similar fashion to a reflecting telescope focuses starlight, or a dish antenna focuses radio waves. This geometry may be used in solar furnaces and solar power plants.


There are two key phenomenena to understand in order to comprehend the design of a parabolic dish. One is that the shape of a parabola is defined such that incoming rays which are parallel to the dish's axis will be reflected toward the focus, no matter where on the dish they arrive. The second key is that the light rays from the sun arriving at the earth's surface are almost completely parallel. So if dish can be aligned with its axis pointing at the sun, the incoming radiation will almost all be reflected towards the focal point of the dish -- most losses are due to imperfections in the parabolic shape and imperfect reflection.


Losses due to atmosphere between the dish and its focal point are minimal, as the dish is generally designed specifically to be small enough that this factor is insignificant on a clear, sunny day. Compare this though with some other designs, and you will see that this could be an important factor, and if the local weather is hazy, or foggy, it may reduce the efficiency of a parabolic dish significantly.


In some power plant designs, a stirling engine coupled to a dynamo, is placed at the focus of the dish, which absorbs the heat of the incident solar radiation, and converts it into electricity. See Knowing Parabolic Concentrators and Concentrating Solar power overview


Power tower


A power tower is a large tower surrounded by small rotating (tracking) mirrors called heliostats. These mirrors align themselves and focus sunlight on the receiver at the top of tower, collected heat is transferred to a power station below.




Very high temperatures reached. High temperatures are suitable for electricity generation using conventional methods like steam turbine or some direct high temperature chemical reaction.


Good efficiency. By concentrating sunlight current systems can get better efficiency than simple solar cells.


A larger area can be covered by using relatively inexpensive mirrors rather than using expensive solar cells.


Concentrated light can be redirected to a suitable location via optical fiber cable. For example illuminating buildings, like here (Hybrid Solar Lighting).




Concentrating systems require dual axis sun tracking to maintain Sunlight focus at the collector.

Inability to provide power in diffused light conditions. Solar Cells are able to provide some output even if the sky becomes little bit cloudy, but power output from concentrating systems drop drastically in cloudy conditions as diffused light cannot be concentrated passively.


See also


Selective surface

Solar collector

Solar oven



Solar hot water panel - From Wikipedia


A solar hot water panel is a solar water heater that uses the sun's energy to heat a fluid, which is used to transfer the heat to a heat storage vessel. In the home, for example, potable water would be heated and then stored in a hot water tank. Flat-plate solar-thermal collectors are usually placed on the roof, and have an absorber plate to which fluid circulation tubes are attached. The absorber, usually coated with a dark selective surface, assures the conversion of the sun's radiation into heat, while fluid circulating through the tubes carries the heat away where it can be used or stored. The heated fluid is pumped to a heat exchanger, which is a coil in the storage vessel or an external heat exchanger where it gives off its heat and is then circulated back to the panel to be reheated. Fluid circulation can be assisted by means of a mechanical pump (which itself could be powered by photovoltaic cell), or (where mounting conditions allow) by allowing convection to circulate the fluid to the storage vessel mounted higher in the circuit, also known as a thermosiphon.



Solar trickle charger 1 Watt solar panel (Skyline Solar, UK)

Pool Solar Panels (source page)

Monocrystal Solar Panels (source page)


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