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Solar Panels - The Theory and Uses

Discussion in 'Renewable Energy' started by bryan1, Jun 23, 2009.

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  1. bryan1

    bryan1 Well-Known Member

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    SOLAR PANELS (version 0.01)



    A solar cell, or photovoltaic cell, is a semiconductor device consisting of a large-area p-n junction diode, which in the presence of sunlight is capable of generating usable electrical energy. This conversion is called the photovoltaic effect, which commonly shortened to PV.

    Crystalline silicon and gallium arsenide are typical choices of materials for solar cells. Gallium arsenide crystals are grown especially for photovoltaic use, but silicon crystals are available in less-expensive standard ingots, which are produced mainly for consumption in the microelectronic industry. Polycrystalline silicon has lower conversion efficiency but also lower cost where monocrystalline being more cost produces a greater output compared to polycrystalline.

    Crystalline ingots are sliced into wafer-thin disks then polished to remove any slicing damage, a binder or dopant is introduced into the wafers, and metallic conductors are deposited onto each surface, a thin grid of crystalline on the sun-facing side and usually a flat sheet on the otherside as the wafers are so thin they are very brittle. Solar panels are constructed of these cells and cut into appropriate shapes. The wafers are protected from radiation and handling damage on the front surface by bonding on a cover glass, and cemented onto a substrate. Electrical connections are made in series-parallel to determine total output voltage. 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. Solar panel frames are made using usually an aluminum channel to provide air space to cool the panel.



    TYPES OF SOLAR PANELS

    Solar panels are made from different types of material to form the P-N junction where some have different properties where the performance varies greatly in the sun.

    Different Cell Types

    The three main types of solar panels produced for the world market are polycrystalline,monocrystalline and amorphous. The more exotic materials like gallium arsenide (GaAs), cadmium telluride (CdTe) and copper indium selenide (CuInSeĀ²) are used in spacecraft, satellites, specialized industries.



    POLYCRYSTALLINE PV PANELS

    Polycrystalline wafers are produced by pouring liquid silicon into blocks then sawed into thin wafers. This tends to cause some cracking or defects in the wafers and the results are lower efficiency.

    MONOCRYSTALLINE PV PANELS

    Monocrystalline wafers are produced by using pure semiconductor material where pure monocrystalline rods are extracted from the molten silicon bath and then sawn precisely into wafers, this process ensures high quality wafers are produced resulting in a greater efficiency.

    AMORPHOUS PV PANELS

    Amorphous panels are produced by placing a silicon
    film onto glass or a different substrate in very thin layer ( as low as 1
    Āµm) and a common name for amorphous is 'Thin Film'. Amorphous panels are less efficient and the size of the solar panels are greater for the same wattage compared to mono and poly crystalline panels.

    Amorphous panels also come in higher voltage panels which are suited to grid-tie arrays and where mono and poly crystalline panels lose power output under clouds amorphous panels still produce power.

    SOLAR PANEL EFFICIENCY

    The efficiency of the 3 main types of solar panels do vary greatly due to the manufacturing. The claims of the efficiency of each panel can be wildly varied depending on who you talk to or where you look. The figures claimed below are to be considered a general claim as the figures were taken as an average after looking at several different sources.
    Polycrystalline Solar Panels - 13-15%

    Monocrystalline Solar Panels - 14-20%

    Amorphous Solar Panels - 10-12%


    SOLAR PANEL MOUNTING


    99% of solar panel retailers will tell you or organize an installer to mount the panels on the roof of your dwelling and say that is the best position for them. Well if the world was flat and earth didn't rotate it would be the best position. Depending where you are in the world the azimuth angle between summer and winter can be a big margin. Also the with sunrise and sunset there is a good chance you'll lose anywhere upto 3 hours of charging time.

    Solar panel trackers can be expensive or you can DIY your own, now when setup correctly you'll see a great boost on a daily basis.

    Sun trackers come in a wide array of types, most being electronic but some people have just used mechanical parts to move the panels at a very slow pace with great results. Electronic trackers can have the problem of 'hunting' where when cloudy the panels will moves in both directions trying to find the best position.

    A simple test can be done to find the correct azimuth angle for your panels, get say a 12" square wooden board and hammer a 6" nail in the centre so it's firm, now point the face of the board at the sun untill the shadow of the nail disappears. Use an angle gauge to find the azimuth angle then look at the angle of the panels on your roof. If you do this test at the summer and winter solstice you'll find just how much the sun will change between the 2 seasons.

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    Just remember any solar tracking mounting device must be built to withstand the local weather conditions as a solar panel mount coming to earth in a wild storm hurts both financially and personally.

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    SUMMARY


    As shown above different types of solar panels have different power outputs due to manufacturing. Just because Amorphous Panels have a lower claimed efficiency doesn't mean they shouldn't be considered as Amorphous panels do out perform the crystalline panels in overcast weather conditions.

    In future updates more content will be added as seen appropriate.

    Regards Bryan1








     
    Last edited: Jul 4, 2009
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