SOLAR TECH EXPLAINED
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of note: in some parts of the world PV solar cells are referred to as 'solar batteries'. These terms are interchangeable.
- atomic #14,
- 8th most common element in the universe,
- 2nd most abundant element (after Oxygen) in the earths crust (25.7%)
- pure silicon in crystalline form is rare in nature,
- sand=silicon dioxide,
- combine silicon dioxide with carbon in a furnace at 1900C,
- result is molten Metallurgical Silicon, 98% pure
- Float-Zone Silicon-purification technique for ultra-pure silicon needed for high power electronic devices.
- purify via various methods, Siemens Reactor the most common, to a few ppm of impurities, to get SGS-Solar Grade Silicon,
- SGS + Czochralski Process = Poly Crystalline ingot/boule.
- see Jetion Holdings-website for good process explanation of how to slice ingots into wafers, (wafer thickness: get more PV power per ingot, but wafers more fragile)
- build Solar Cell,
- build Photovoltaic Module
- install on roof
- See Also:
- How Stuff Works- Solar Cell
- animation of cell production on Q-Cells website.
- 2007 new development:
- Dirty Silicon-metallurgical silicon upgraded by coaxing impurities to the borders via chemical, physical, or magnetic means, resulting in PV grade silicon. Invented by Eicke Weber while at UC Berkeley.
- (from above article-electrical grade silicon is +99.99999% pure and costs $150-$250/kg (2007) with 70,000 tons made worldwide, whereas upgraded metallurgical silicon is 99% pure, costs $20-50/kg and 1.2 million tons made per year (2007 #'s).
- CaliSolar, solar start-up.
- Q-Cells and see-Elkem Solar jv to market solar cells in 2008.
- 2007 new development:
- 3D Solar Cells-Big Sun, nano towers.
PV- Amorphous vs Mono/Multi/Poly Crystalline
- Thin Film- instead of using ingots/wafers uses vapour deposition onto glass, plastic, steel, etc.
- can be silicon vapour (Silane gas) or other chemicals
- Thin Film- flex plastic backed products that roll up into a roll. slightly lower efficiency, faster production, new products possible.
- differs from the solid (very thin + fragile) nature of wafer based PV in that the photo-electric converting chemicals (Silane gas) are applied as a vapour.
- this allows the 'thin film' to be applied to glass, steel, etc or to flexible backing materials like plastic.
- conversion efficiency is in general not as high as PV wafers.
- following is a rough, and not necessarily totally correct, expansion of the thin-film info.
- note that nano tech is also refered to as thin-film, but is thin on a totally different scale of 'thinness' ie nano scale.
- Silicon Thin Film
- a-Si Amorphous Thin Film- see-Unisolar
- Crystalline Thin Film -on glass.
- BIPV- Building Integrated PV, thin film vapour deposition on glass, roofing tiles, etc. most BIPV is a-Si or CIGS vapour deposition.
- Konarka Technologies Inc-tech allows solar panels to be made on plastic sheets.
- REC, largest maker of Silane gas
- String Ribbon thin film (see Evergreen, +EverQ with Q-Cells)
- TCO-Transparent Conductive Oxide process, unique to see-Oerlikon Corporation AG
- CVD Chemical Vapour Deposition Thin Film - (non-Silicon Thin Film)
- Vapour deposition production methods. technical, not dependent on silicon supply, potentially faster and cheaper per MW than wafers.
- 3D Solar Cells-silicon wafer base, vapour deposition of carbon nanotubes, molecular beam epitaxy coated with CdTe, CdS, or other such, topped by a thin coating of indium tin oxide.
- multi-junction cells:
- CdS-Cadmium(II) Sulfide
- CdTe-Cadmium Telluride. (see First Solar with excellent write-up)
- CIGS-Copper Indium Gallium di-Selinide. see-Shell, Honda, Daystar, Nanosolar, Miasole, Wurth, Ascent Solar
- CIS Copper Indium di-Selinide. se Miasol, CIS Solar, Showa-Shell Sekiyu
- GaAs-Gallium-Arsenide, has higher saturated electron mobility, allowing it to function at frequencies in excess of 250GHz, expensive, powers robots Spirit and Opportunity on Mars see-CPV (below). GaAs ingots made using Bridgeman Technique also GaAs thin film
- InGaP/InGaAs/Ge see-Sharp Corporation (36.5% efficiency)
- II-V, III-V, etc, two/three/five junction cells (the more junctions, the more tech, the more cost, but higher efficiency can be had). The II-V or III-V refers to rows in the Periodic Table that the specific chemicals of the multi-junction come from and not the number of junctions.
CPV- Concentrated PV
- CPV- Concentrated PV, PhotoVoltaic- (general term). Used for power plants and space exploration.
- CPV used with GaAs-Gallium-Arsenide, has higher saturated electron mobility, allowing it to function at frequencies in excess of 250GHz, expensive but more efficient than silicon at high 'sun' concentrations, powers robots Spirit and Opportunity on Mars.
- Solar Concentrators- report
- Solar Systems-Australian Company has built three CPV systems, total 720kW, now building 154MW system
- Tracking the Sun-REA story on CSP
Other Tech Links of Interest
- Quantum Dot research-hot electrons and semiconductor nanocrystals.
- Timeline of Solar History
- glosary- from Q-Cells website
- links to solar motors
- story about Gruner Anlegen
- low efficiency=10% or less, mid=10 to 16%, high=lab only, up to 40% or more.
- of note: unlike the dot.com tech of the '90s, a new version of solar technology does not relegate the previous tech to the dustbin. Different technologies are best for different uses and new technologies create new uses. example amorphous solar has a lower voltage/temperature coefficient than crystalline solar, also is used in applications where low efficiency and low price works such as solar calculators; crystalline ingots, wafers, cells for PV modules; thin film amorphous for BIPV roofing material, RV battery chargers; thin film CIGS for BIPV glass; GaAs for outer space etc.