• Session 1

• Eng / Ahmed Abdel Baqi.

• Photo voltaic is the concept which mean that pv cell convert sun light to electricity directly without any movable parts as traditional power stations .

Where I can install pv systems ?

first PV system installations were mounted on the roofs of private family houses.

• PV systems are increasingly being installed on all kinds of buildings , In addition, there is increasing use of other structures for photovoltaic systems (e.g. motorway noise barriers and train station platform roofs)

• The sun supplies energy in the form of radiation, without which life on Earth could not exist.

• The energy is generated in the sun's core through the fusion of hydrogen atoms into helium.

• Part of the mass of the hydrogen is converted into energy.

• In other words, the sun is an enormous nuclear fusion reactor.

• Because the sun is such a long way from the Earth, only a tiny proportion (around two-millionths) of the sun's radiation reaches the Earth's surface.

• This works out at an amount of energy of 1 x 1018 kWh/m2.

Traditional energy sources

• 1- Natural Gas.

• 2- Crude oil.

• 3- Coal.

• All these energy sources that we use in our industrial age are exhaustible.

• The amount of energy in the sunlight reaching the Earth's surface is equivalent to around 10,000 times the world's energy requirements.

• Consequently, only 0.01 per cent of the energy in sunlight would need to be harnessed to cover mankind total energy needs.

Distribution of solar radiation

• The intensity of solar radiation outside of the Earth's atmosphere depends upon the distance between the sun and the Earth.

• In the course of a year this varies between 1.47 x 108

km and 1.52 x 108 km.

• As a result, the irradiance EQ fluctuates between 1325W/m2 and 1412W/m2.

• The average value is referred to as the solar constant:

• Solar constant: EQ = 1367W/m2

Direct and diffuse radiation

• Sunlight on the Earth's surface comprises a direct portion and a diffuse portion.

• The direct radiation comes from the direction of the sun and casts strong shadows of objects.

• By contrast, diffuse radiation, which is scattered from the dome of the sky, has no defined direction.

• Depending upon the cloud conditions and the time of day (solar altitude), both the radiant power and the proportion of direct and diffuse radiation can vary greatly.

• On clear days the direct radiation accounts for the greater part of the total radiation.

• On very cloudy days (especially in winter), the insolation is almost entirely diffuse.

• In Germany, the proportion of diffuse insolation is 60 per cent and direct radiation 40 per cent over the year.

How a solar cell works

• Highly pure silicon with a high crystal quality is needed to make solar cells.

• The silicon atoms form a stable crystal lattice.

• Each silicon atom has four bonding electrons (valence electrons) in its outer shell.

• To form a stable electron configuration, in each case in the crystal lattice two electrons of neighboring atoms form an electron pair bond.

• By forming electron pair bonds with four neighbors.

• We add some impurities to the silicon (or doping atoms ).

• These atoms have one electron more (phosphorus) or one electron less (boron) than silicon in their outermost electron shell.

• In the case of phosphorus doping (n-doped), there is a surplus electron for every phosphorus atom in the lattice.

• This electron can move freely in the crystal and hence transport an electric charge.

• With boron doping (p-doped), there is a hole (missing bonding electron) for every boron atom in the lattice.

• Electrons from neighboring silicon atoms can fill this hole, creating a new hole somewhere else.

• The diffusion of charge carriers to the electrical contacts causes a voltage to be present at the solar cell.

• when light falls on the solar cell, charge carriers separate and if a load is connected, current flows.

• Losses occur at the solar cell due to recombination, reflection and shading caused by the front contacts.

• In addition, a large component of the long and short wavelength radiation energy cannot be used.

1-Mono-crystalline silicon cells

• Efficiency: 15 per cent to 18 per cent.

• Appearance: uniform.

• Color: dark blue to black

• Thickness: 0.2mm to 0.3mm.

2-Polycrystalline silicon cells:

• Efficiency: 13 per cent to 16 per cent.

• Appearance: the block casting process forms crystals with different orientations.

• Color: blue .

• Thickness: 0.24mm to 0.3mm.

3-Thin-film cell technology:

• Efficiency: 5 per cent to 7 per cent module efficiency .

• Appearance: uniform appearance.

• Color: reddish brown to blue or blue-violet.

• approximately 0.3um amorphous silicon.

4- Cadmium telluride (CdTe) cells:

• Efficiency: Per cent to 8.5-11 per cent module efficiency.

• Appearance: uniform.

• Color: reflective dark green to black.

• Thickness: 3mm substrate material (non-hardened glass) with 0.005mm coating.

5- copper indium cells

• Efficiency: 12 per cent module efficiency.

6-Gallium arsenide

• Efficiency: 32 per cent module efficiency.

Comparison between the different types

Comparison between the different types

1-Equivalent circuit diagrams of solar cells:• A solar cell consisting of p-doped and n-doped silicon material

is in principle a large scale Silicon diode, both have similar electrical properties.

• If a positive potential is present at the p-doped anode and a negative potential is present at the n doped cathode, the diode is connected in forward-biased direction.

• If the diode is connected in reverse-biased direction, current flow is prevented in this direction.

• Only starting from a high breakdown voltage does the diode become conductive, this can also lead to the destruction of the diode.

• 1-Equivalent circuit diagrams of solar cells:

• 1-Equivalent circuit diagrams of solar cells:

• When light hits the solar cell, the energy of the photons

generates free charge carriers.

• An illuminated solar cell constitutes a parallel circuit of a power source and a diode.

• The power source produces the photoelectric current (photocurrent) I p h .

• The level of this current depends upon the irradiance.

• 2- open circuit voltage :-

• The open-circuit voltage, VOC is the maximum voltage available from a solar cell, and this occurs at zero current.

• The open-circuit voltage corresponds to the amount of forward bias on the solar cell due to the bias of the solar cell junction with the light-generated current.

• 2- open circuit voltage :-• The open-circuit voltage is shown on the IV curve

below.

• 3- short circuit current :-• The short-circuit current is the current through the solar

cell when the voltage across the solar cell is zero (i.e., when the solar cell is short circuited).

• Usually written as ISC , the short-circuit current is shown on the IV curve below.

• 4- voltage-current characteristic curve (I-V curve):-

• The voltage-current characteristic curve of a PV cell is under short-circuit conditions the generated current is at the highest (Isc).

• whereas with the circuit open the voltage (Voc=open circuit voltage) is at the highest.

• Under the two above mentioned conditions the electric power produced in the cell is null.

• 5- power-voltage characteristic curve (p-V curve):-

• When the voltage increases, the produced power rises too: at first it reaches the maximum power point (Pm) and then it falls suddenly near to the no-load voltage value.

Important definitions:

• Mpp: - maximum power point. The maximum power point (MPP) value is the point on the I-V curve at which the solar cell works with maximum power.

• Impp: - current at maximum power point

• Vmpp: - voltage at maximum power point

• Voc: - open circuit voltage with crystalline cells, approximately 0.5V to 0.6V, and for amorphous cells is approximately 0.6V to 0.9V.

• Isc: - short circuit current is approximately 5 per cent to 15 per cent higher than the MPP current with crystalline standard cells (10cm x 10cm) under STC.

• FF: - fill factor it measures the quality of PV cell. If FF=1 this means the best quality of PV cell.

Standard test conditions (STC):-

• Uniform conditions are specified for determining the electrical data with which the solar cell characteristic I-V curve is then calculated.

• 1- Vertical irradiance E of 1000 W/m2.

• 2- Cell temperature T of 25°C with a tolerance of ±2°C.

• 3- Defined light spectrum (spectral distribution of the solar reference irradiance.

Environmental Factors affecting on PV modules:-

• 1-Shading and dirt:-• The effects of this shading are well known when even a

small portion of a cell, module, or array is shaded.

• 2-Temperature:-• Module output and life are also degraded by increased

temperature.

• Allowing ambient air to flow over, and if possible behind, PV modules reduces this problem, because power generated decreased by rising of temperature.

• The effect of increasing temperature on generating power from PV.

• 3-Irridiance:-

• The changes in irradiance affect the module current most of all

since the current is directly dependent upon the irradiance.

• When irradiance drops by half, the electricity generated also reduces by half.

Thank You

With my Best Wishes

Eng / Ahmed Abdel Baqi.