Solar PV Theory.pdf

# Current a i sc 02 04 06 08 01 02 03 04 05 06 01 02 03

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Current (A) I sc 0.2 0.4 0.6 0.8 0 0.1 0.2 0.3 0.4 0.5 0.6 0.1 0.2 0.3 0.4 Power (W Constant-current region (current source operation) Constant-voltage region (voltage source operation) E oc V PV cell I Electrical load 0 Voltage (V) Maximum power point (MPP)

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The Solar Panel (Photovoltaic Panel) Discussion Solar Power 1 4 Figure 2 4 . The open-circuit voltage E OC is proportional to the number of PV cells connected in series. When several PV cells of the same fabrication and size are connected in parallel to form a PV module, the open-circuit voltage E OC remains virtually the same but the short-circuit current I SC is proportional to the number of PV cells connected in parallel as shown in Figure 2 5 For instance, when 10 PV cells are connected in parallel, I SC is multiplied by 10. 0.6 V Figure 2 5 . The short-circuit current I SC is proportional to the number of parallel-connected PV cells. Electric power output The amount of electric power that a PV cell provides, depends on the point on the E-I curve at which the PV cell operates. In other words, this depends on the electrical load applied to the PV cell (in practice, this depends on the electrical load applied to the PV module or PV panel). The point on the E-I curve where the PV cell output power is maximum, is commonly referred to as the maximum power point (MPP). As Figure 23 shows, this point is located just between the constant-current and constant-voltage regions of the characteristic E-I curve. It is very important that PV panels operate as close as possible to the maximum power point in order to maximize the amount of energy produced. The amount of light incident to a PV cell (cell illumination) has a great incidence on the short-circuit current I SC but a mitigated effect on the open- circuit voltage E OC , as shown by Figure 2 6 . The short-circuit current I SC is in fact directly proportional to cell illumination while the open-circuit voltage E OC increases only a little (logarithmic relationship) with cell illumination. The output power of a PV cell is thus virtually proportional to cell illumination. 4 cells 2.4 V 36 cells × 0.6 V = 21.6 V 36 cells Adding cells in series Current (A) I SC 0 Voltage (V) 21.6 V 0.6 V for each cell 10 cells 1 cell Adding cells in parallel 1 2 10 Current (A)
The Solar Panel (Photovoltaic Panel) Discussion 15 Solar Power Cell voltage (V) Figure 2 6 . Characteristic E-I curve under various cell illumination levels. Irradiance Cell illumination is referred to as the solar irradiance when PV cells are illuminated by sunlight. Irradiance due to solar radiation is also called insolation . The global irradiance on a PV cell positioned horizontally on Earth’s surface consists of direct irradiance and diffuse irradiance. On a tilted surface, there is also a component reflected from the ground. The average ground reflection is generally about 20% of the global irradiance. Irradiance is expressed in W/m 2 (W/ft 2 ).

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• One '14
• Photovoltaics, Solar cell, PV cell, Photovoltaic module, pv module

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