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> Solar Spectrum Challenges: Photovoltaics Issue: 2010-3 Section: Green energy



Mihai Sopronyi

Politehnica University, Bucharest, Romania


Renewable energy means the conversion of natural resources, such as sunlight, geothermal heat, wind power, wave power, which are natural, meaning they are naturally renewable – are replaced through natural processes with the passing of time. Among all types

renewable energy, the one that is from the Sun is the most significant because the incidence solar energy on the Earth’s surface in an hour is larger than the one used by the entire Earth’s population in one year; through solar panels this energy can be used for heating water, but also for electricity production; through the greenhouses, solar energy is used in agriculture, too.

A disadvantage of this technology is that not all the light spectrum emitted by Sun can be captured. An estimated calculation shows that on the surface of the Sun the density of energy is about 62MW/m2 and on the Earth’s surface arrives only about 1353 W/m2. This energy reduction is largely due to the clouds, aerosol and atmosphere molecules, but also due to the incidence angle of the Sun radiations. (fig. 2)

A solar cell is a surface composed of several layers, which converts solar energy into different forms of energy such as electricity or heat (fig. 1) Using this method of converting sunlight radiation in to electricity, solar cells are used in different technologies such as:

The concentration of solar power - instead of using fossil fuels to heat a fluid powering turbines for generating electricity, this technology uses solar power harvested by huge mirrors U shaped

Passive solar technology - the technology consists in designing buildings with large windows on the South side, walls and floors that are made of black painted materials, or having in their interior barrels with water that absorb the Sun heat during the day time and release it during the night (fig.3).


Material Color Thickness Efficiency
Amorphous silicon Red-blue, Black 0.00001 mm + glass substrate 1-3 mm 5 - 8 %
Cadmium Telluride (CdTe) Dark green, Black 0.008 mm+ glass substrate 3 mm 6 - 9 %/modul
Copper-Indium-  Diselenide (CIS) Black 0.003 mm+ glass substrate 3 mm 7,5 - 9,5 %/modul
Apex (polycrystaline Si) solar cells Blue, with AR coating, silver-grey without AR coating De la 0.03 pana la 0.1 mm 9,5 %
Hybrid silicon (HIT) solar cell Dark blue, black 0.02 mm 18 %
Monocrystaline dendritic web Si solar cells Blue, with AR coating 0.13 mm 13 %
EFG (Edge Defined Film fed Growth) Blue, with AR coating 0.28 mm 14 %
Monocrystalline Si solar cells Dark blue, black with AR(antireflexive) coating, grey without AR coating 0.3 mm 15 - 18 %
Polycrystalline Si solar cells Blue with AR coating, silver-grey without AR coating 0.3 mm 13 - 15 %
Polycrystalline transparent Si solar cells Blue with AR coating, silver-grey without AR coating 0.3 mm 10 %
Polycrystalline ribbon Si solar cells Blue, with AR coating, silver-grey without AR coating 0.3 mm 12 %


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