ekonomija

energijaW P. Part of the reason is that the lowerefficiency of CdTe (~10.5%) requireslarger panels, which require larger supportstructures.Copper Indium Diselenide solarcells (CIGS & CIS thin film solarcells)A very promising and challengingtechnology, known as a “star performer”in the laboratory with near20% conversion efficiency, is CIGSsolar cell technology based on theternary compound semi conductorsCuInSe2, CuGaSe2, CuInS2 and theiralloys. CIS is based on CuInSe crystaltechnology. Although the propertiesof these compounds are very promising,there are certain difficulties to becommercialized. The main reason isthat In and Ga are very rare elements,and nowadays research is finding away to replace indium with appropriateelement or compound.Tandem solar cells (thin filmsolar cells)Multiple-junction stacked or tandemsolar cell is a structure where severalsolar cell units with different bandgaps are stacked on top of one anotherto absorb light of different wavelength.Thus, each solar cell unit convertsappropriate part of solar radiation spectrum.With large number of stackedcell units the efficiency over 50% canbe expected in the future. Tandemstructures are produced usually withthe sequence of thin layers (films).With lens concentration of sunlight andsun-tracking devices, the efficienciesof 38% for tandem cells have beenreported. At the moment tandem cellsare used in satellite applications andthey are not presently manufactured inany significant commercial quantities.Heterojunction solar cells are tandemsolar cells introduced by the SANYOCorporation. The SANYO HIT(Heterojunction with Intrinsic Thinlayer) solar cell is made of a thin monocrystalline silicon wafer surroundedby ultra-thin amorphous silicon layersand today it is market recognized asthe industry’s leading performance andvalue product using state-of-the-artmanufacturing techniques with veryhigh conversion efficiency. Table 1.shows the cell and module efficienciesfor some SANYO solar moduleproducts.Flexible solar cellsFlexible solar cells are used in applicationssuch as: airplanes, solarvehicles, textiles, helmets, toys, andin various products with surfaces likecurves, where traditional flat solar cellmodules can not be used. Flexible celltechnology is based on conductivepolymer semi conductors, althoughtoday almost every type of solar cellcan be flexible to some extent.Silicon solar cells with Light-Trapping structures (thin filmsolar cells)Light-trapping structures (LTS) areused to improve the low absorbanceof light for the thin-film silicon solarcells. LTS are photonics devices, suchas diffractive gratings, distributedBragg reflectors, metal reflectors, etc.Light can be highly efficiently trappedinto the solar cell material, about 70%,[19], increasing significantly the solarcell conversion efficiency, by reducingreflection of the incident solar radiationfrom the cell.Dye-Sensitized solar cells (DSC)DSC are invented by M. Graetzel inthe early 1990’s and they are based onthe regenerative photo electrochemicalprocess. DSC are nano-crystallinedevices with sensitizer (dye) used tosensitize TiO2 thin film. At the verybeginning of the research with DSCefficiency was just a few percent, butat the moment their efficiency reached11%. Advanced and expensive equipment,high-temperature treatment, highvacuum conditions, and materials ofhigh purity are not required for DSCfabrications. Their cost is just 1/5 to1/3 of that for Si solar cells, so theyrepresent larger-area and low-cost solarcell alternatives. Moreover, they can bemade transparent or in desired colour,also can be made as flexible solar cells.Predictions are that by 2030, DSCwould occupy more than 1/3 of themarket share.Organic solar cellsThese cells can be molecular or polymerorganic solar cells, or flat-layersystems with organic materials havingsemi conducting properties. The possiblenumber of such stable organiccompounds (polymers) is nearly infinite.Organic cells can be produced asvery thin devices, at low-temperatureprocesses and very low cost. Efficienciesare still low, about 3-4%, however,the research interest in the organicsolar cells is growing because they offeran inexpensive solution.Although the high manufacture cost,crystalline silicon dominates the markettoday with prospects to continue soin the immediate future. Silicon (monocrystal, poly crystal, amorphous, ribbon,thin Si films, and tandem Si cells)is still occupying more than 95% ofmarket share. The market shares ofdifferent solar cell technologies areshown in Fig. 1.Away from the laboratory and technologicalsolar cell scene, PV systemdesigners offer numerous useful applications,see for example [1,20], wherethe module efficiencies, the producedsolar energy storage media, etc., areFig 1 Market shares of different solar cell technologies for 2008.Table 1 Efficiencies of the SANYO HIP solar cells and modules[062]emphasized. Sun tracking PV systemsensure the optimal operating conditionsfor solar energy conversion enablingcontinuously vertical irradiation on thesolar generator area. Concentrated PV