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Solar PV Explained

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Solar explained
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  • Ministry of Energy and Mineral Resources

    Solar PV Explained Solar PV on Grid Training, 29-31 October 2013

    Todo Simarmata

    10/22/2013

  • Contents

    1 PV Cell ....................................................................................................................................... 2

    1.1 Energy of photon ............................................................................................................... 2

    1.1.1 The working principles of crystalline silicon PV cells.................................................... 2

    1.1.2 Current Voltage (IV) characteristic of PV Cell .............................................................. 3

    1.1.3 Irradiation and photo current ..................................................................................... 5

    1.1.4 Output power and temperature ................................................................................. 6

    2 PV Module................................................................................................................................. 8

    2.1 PV Module Structure .......................................................................................................... 8

    2.1.1 Low iron glass............................................................................................................. 8

    2.1.2 Ethyl Vinyl Acetate (EVA) ............................................................................................ 8

    2.1.3 Tedlar......................................................................................................................... 9

    2.1.4 Frame......................................................................................................................... 9

    2.1.5 PV Cells String............................................................................................................. 9

    2.1.6 Bypass Diode............................................................................................................ 10

    3 Battery .................................................................................................................................... 13

    3.1 Vented Lead Acid ............................................................................................................. 13

    3.1.1 Flat Pasted Plate Type .............................................................................................. 14

    3.1.2 Tubular Type ............................................................................................................ 15

    3.1.3 Valve Regulated Lead Acid........................................................................................ 16

    3.1.4 Lithium Ion ............................................................................................................... 18

    4 Optimum Energy Yield ............................................................................................................. 20

    4.1 PV Module Tilt and Orientation ........................................................................................ 20

    4.2 Performance Ratio ........................................................................................................... 20

    4.2.1 Actual PV production................................................................................................ 21

    4.2.2 Reference Yield ........................................................................................................ 21

    4.2.3 Performance Ratio.................................................................................................... 21

    5 Calculating Solar Energy........................................................................................................... 23

    5.1 What is solar energy?....................................................................................................... 23

    5.2 Calculating solar irradiance .............................................................................................. 23

    6 Bibliography ............................................................................................................................ 27

  • 1 PV Cell Author : Todo Simarmata

    1.1 Energy of photon

    PV cell conversion is a direct conversion from sunlight which contains of quasi particles namely

    photon into electric energy. This photon energy formulated as (Creatore, 2010):

    (1.1)

    Where :

    Eph = photon energy

    h = Plancks constant = 6.626 10 -34 joules

    v = the frequency of light

    c = the velocity of light = 2.998 108 m/s

    = the wavelength of light

    Figure 1-1-1 Solar spectrum (Creatore, 2010)

    As shown in above figure, sunlight has solar spectrum with wavelengths =0.39 m (violet) until

    =0.77 m(red). So fill-in the constant in the equation 1.1, the largest energy of photons of visible

    sunlight is 5.09e-19 Joules or 3.1790 eV (violet) and the smallest 2.58e-19 Joules or 1.6101 eV (red).

    1.1.1 The working principles of crystalline silicon PV cells

    In principle, a crystalline silicon solar cell is a semiconductor junction which has two regions. The p-

    type region is created by doping with boron and the n-type with phosphorus. The difference of these

    two region properties creates an electric field near the boundary (Creatore, 2010).

  • Figure 1-1-2 Solar cell structure (Creatore, 2010)

    Typical dimension of crystalline wafer in the market is 125x125 mm for mono crystalline with 0.3

    mm thickness and 156x156 mm for multi crystalline. There is an array of metal grid and crossways

    the busbar. Usually consists of two or three busbars.

    When a ray of light descent the surface of the n - type region, photons with energy Eph greater than

    the semiconductor band gap Eg will absorbed and generate an electron- hole pair. The

    semiconductor band gap is a minimum amount energy that is required to excite an electron from its

    bound state to participate in the conduction.

    An electron - hole pair created near the junction will experience strong electric field and be

    separated, eventually the electrons reach the n-type area and collected by the contact grid. Current

    generation occurs when electrons collected at the contact grid flow through busbar to the back

    contact via the load as depicted in figure 1.2.

    1.1.2 Current Voltage (IV) characteristic of PV Cell

    When a PV cell exposed to sunlight radiation, a photo current Iph is generated. This photo current is

    directly proportional to incident sunlight radiation to the PV cell surface. When there is no radiation

    in dark condition, PV cells works as a P-N junction diode.

    Thus, the most common model of solar PV consists of a current source to represent photo current

    parallel with the diode. The complete model is adding series resistance Rs to represent the internal

    losses and shunt resistance Rsh to represent leakage current to the ground. The simple model can be

    seen in figure 1.3

  • Figure 1-1-3 Solar cell model (Creatore, 2010)

    Current flow to the load I can be formulated as :

    (1.2)

    (1.3)

    Where,

    Id = diode current

    Is = the reverse saturation current of the diode

    q = electron charge

    K = Boltzmans constant.

    Current-voltage characteristic can be developed by measuring solar PV response to the variable load

    or current. Thus the response will be plotted from zero current which relevant to infinite resistance

    or open circuit condition to the maximum current which means zero resistance or short circuit

    condition.

    Therefore two specific parameters can be formulated as below:

    1. When the load R=0, the PV cell is in a short circuit condition, there is no current flow through

    the diode ( Id=0 ), so I = Iph or

    (1.4)

    2. When the load increasing to infinite R = , PV cell in an open circuit condition, there is no

    current flow through the load ( I=0) and all current flow through the diode, so Iph = Id and V

    open circuit can be formulated as :

  • (1.5)

    Figure 1-4 Current-Voltage characteristic

    The current-voltage characteristic of solar PV is depicted in figure 3.4. There exists a maximum

    power point which is characterized by Imp and Vmp. Maximum power point is the maximum power

    that could be delivered through resistive load and can be formulated as:

    (1.6)

    The ratio between maximum power point and the product of Voc and Isc is defined as Fill Factor:

    (1.7)

    The fill factor is a value to quantify the real I-V characteristic. A typical fill factor value of a good cell

    is above 0.7. Fill factor value is temperature dependent, as the temperature increased, the fill factor

    will diminish.

    Efficiency is defined as the ratio between the maximum power that PV cell could be harnessed and

    the incident irradiation to the PV surface. Efficiency can be formulated as:

    (1.8)

    Ga is sunlight irradiation in W/m2 and A is PV cell area.

    1.1.3 Irradiation and photo current

    The open circuit voltage as in equation 1.5, is a function of the sunlight irradiation. It increases

    logarithmically with photo current Iph which directly proportional to ambient irradiation. The short

  • circuit current as well as photo current is a linear function of the sunlight irradiation. Current voltage

    characteristic for different irradiation and temperature is depicted in figure 1.5. The short circuit

    current is slightly increased at hig

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