Solar PanelAsolar panelis a set of solar photovoltaicmoduleselectrically connected and mounted on a supporting structure. A photovoltaic module is a packaged, connected assembly ofsolar cells. The solar panel can be used as a component of a larger photovoltaic system to generate and supplyelectricityin commercial and residential applications. Each module is rated by itsDCoutput power under standard test conditions (STC), and typically ranges from 100 to 320 watts. Theefficiencyof a module determines the area of a module given the same rated output - an 8% efficient 230 watt module will have twice the area of a 16% efficient 230 watt module. A single solar module can produce only a limited amount of power; most installations contain multiple modules. Aphotovoltaic systemtypically includes a panel or an array of solar modules, aninverter, and sometimes abatteryand/orsolar trackerand interconnection wiring.

A solar photovoltaic module is composed of individual PV cells. This crystalline-silicon module has an aluminium frame and glass on the front.Solar Cell A solar cell (also called a photovoltaic cell) is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect. It is a form of photoelectric cell (in that its electrical characteristicse.g. current, voltage, or resistancevary when light is incident upon it) which, when exposed to light, can generate and support an electric current without being attached to any external voltage source, but do require an external load for power consumption.The term "photovoltaic" comes from the Greek (phs) meaning "light", and from "volt", the unit of electro-motive force, the volt, which in turn comes from the last name of the Italian physicist Alessandro Volta, inventor of the battery (electrochemical cell). The term "photo-voltaic" has been in use in English since 1849

Asolar cellmade from amonocrystalline siliconwaferwith itscontact gridmade frombusbars(the larger strips) and fingers (the smaller ones)The operation of a photovoltaic (PV) cell requires 3 basic attributes:1. The absorption of light, generating eitherelectron-holepairs orexcitons.2. The separation of charge carriers of opposite types.3. The separate extraction of those carriers to an external circuit.In contrast, asolar thermal collectorsupplies heat by absorbing sunlight, for the purpose of either direct heating or indirect electrical power generation. "Photoelectrolytic cell" (photoelectrochemical cell), on the other hand, refers either to a type of photovoltaic cell (like that developed byA.E. Becquereland moderndye-sensitized solar cells), or to a device that splits water directly into hydrogen and oxygen using only solar illumination.

Building block of a solar panelAssemblies of photovoltaic cells are used to make solar modules which generate electrical power from sunlight. Multiple cells in an integrated group, all oriented in one plane, constitute a solar photovoltaic panel or "solar photovoltaic module," as distinguished from a "solar thermal module" or "solar hot water panel." The electrical energy generated from solar modules, colloquially referred to as solar power, is an example of solar energy. A group of connected solar modules is called an "array."Further improvementsIn recent times, further improvements have brought production costs down under $1 a watt, with wholesale costs well under $2. "Balance of system" costs are now more than the panels themselves. Large commercial arrays can be built, as of 2010, at below $3.40 a wattfully commissioned.As the semiconductor industry moved to ever-largerboules, older equipment became available at fire-sale prices. Cells have grown in size as older equipment became available on the surplus market; ARCO Solar's original panels used cells with 2 to 4inch (50 to 100mm) diameter. Panels in the 1990s and early 2000s generally used 5inch (125mm) wafers, and since 2008 almost all new panels use 6inch (150mm) cells. The widespread introduction offlat screen televisionsin the late 1990s and early 2000s led to the wide availability of large sheets of high-quality glass, used on the front of the panels.During the 1990s, polysilicon cells became increasingly popular. These cells offer less efficiency than their monosilicon counterparts, but they are grown in large vats that greatly reduce the cost of production. By the mid-2000s, poly was dominant in the low-cost panel market, but more recently a variety of factors has pushed the higher performance mono back into widespread use.Manufacturers of wafer-based cells have responded to high silicon prices in 20042008 prices with rapid reductions in silicon consumption. In 2008, according to Jef Poortmans, director ofIMEC's organic and solar department, current cells use between eight and nine grams of silicon per watt of power generation, with wafer thicknesses in the neighborhood of 0.200mm.

Practical materialsVarious materials display varying efficiencies and have varying costs. Materials for efficient solar cells must have characteristics matched to the spectrum of available lighCrystalline silicon1. monocrystalline silicon(c-Si): often made using theCzochralski process. Single-crystal wafer cells tend to be expensive, 2. polycrystalline silicon, ormulticrystalline silicon, (poly-Si or mc-Si): made from cast square ingots large blocks of molten silicon carefully cooled and solidified. Poly-Si cells are less expensive to produce than single crystal silicon cells, but are less efficient3. ribbon silicon[29]is a type of polycrystalline silicon: it is formed by drawing flat thin films frommoltensilicon and results in a polycrystalline structure. These cells have lower efficiencies than poly-Si4. mono-like-multi silicon: Developed in the 2000s and introduced commercially around 2009, mono-like-multi, or cast-mono, uses existing polycrystalline casting chambers with small "seeds" of mono material.Thin films

Thin-film technologies reduce the amount of material required in creating the active material of solar cell.1. Cadmium telluride solar cell2. Copper indium gallium selenide3. GaAs thin film cells4. Silicon thin films Amorphous silicon(a-Si or a-Si:H) Protocrystallinesilicon or Nanocrystalline silicon(nc-Si or nc-Si:H), also called microcrystalline silicon.15.5% solar modules from MiaSol hold theflexible PV solar module efficiency record.16.1% First Solar thin-film solar Panel claim the cadmium-telluride (CdTe) photovoltaic (PV) module conversion efficiency record. Again, these are generally not used for residential applications, but I think including them helps to reinforce my key point yet again. (First Solar, a US-based company, was actually the #1 solar developer and the #2 solar module manufacturer in the world last year. Despite a relatively low 16.1% record efficiency in this category of solar panels, First Solar does very well with these relatively cheap solar modules in certain applications.)17.4% Q-Cells thin-film solar Panel hold the specific solar panel category. Thin-film solar panels are widely used, but not in residential applications. (Q-Cells was a German company, but it filed for insolvency in 2012 and was then acquired by the Korean companyHanwha.)21.5% SunPower solar Panel hold thecommercial solar module efficiency record., are also the leading solar modules in solar module yield field tests36% efficient Amonix solar modules hold theoverall solar PV module efficiency record. However, these are made with concentrator solar cells and are not used in residential applications.32.6% solar cells by junction by a Spanish solar research institute (IES) and university (UPM) These are another step down, as they are in thetwo-junction, concentrator solar cell categoryAgain, these are still far different solar cells from what are used in commercial or residential installations.

37.9% efficient solar cells by Sharp . Just a step down, these are in thetriple-junction, non-concentrator solar cell category. If this is all new to you, it might take you awhile to see the difference in the categories. The difference is that these solar cells dont use anything to concentrate the light hitting the solar cells44.7% efficient solar cells by Fraunhofer. Notably, these world-leading solar cells from Fraunhofer are in theconcentrator triple-junction solar cell category. Such solar cells are complicated and are not used in residential or commercial applications because they arebloody expensive. They are used in space applications by the likes of NASA, where a bit of extra space (or, as it may be,lessspace via extra efficiency) can make a huge difference

Reported timeline of solar cell energy conversion efficiencies (from National Renewable Energy Laboratory (USA))

Other ways for improving the efficiencyThere are many reviews that suggest many ways to improve the solar cells efficiency, consisting to incorporate lanthanide doped materials (Er3+, Yb3+, Ho3+or combination of them) on to a solar cell, taking advantage of their optical properties to convert the infrared radiation to visible light . This kind of process, calledupconversion, is a luminescence process where two low-energy infrared photons are absorbed by rare-earth ions to generate a high-energy visible photon. As example, the energy transfer upconversion process (ETU), consists in successive transfer processes between excited ions under excitation in the near infrared. Therefore, an excited ion can reach a high energetic level from which de-excites emitting a visible photon. By this way, an upconverter material could be placed below the solar cell in order to absorb the infrared light (not absorbed by the Si) and produce visible photons to excite the solar cell, enhancing its response to infrared radiation. There are many upconversion materials, but usually they are doped with lanthanide ions because they are efficient in these upconversion processes. These ions are most commonly found in the trivalent state and their rich energy level structure over a broad spectral range explains their numerous applications. Among them, the Er3+ions have been the most used. The Er3+ions absorb the solar radiation around 1.54m. Two Er3+ions that have absorbed this radiation can interact with each other through an upconversion process. The excited ion emits light above the Si bandgap that is absorbed by the solar cell and creates an additional electronhole pair that can contribute to generate current. However, the obtained efficiency of the solar cell was small. In addition, the fluoroindate glasses have shown to have very low phonon energy and they have been also proposed as suitable matrix doped with Ho3+ions in order to improve the efficiency of silicon solar cells, using upconversion processes