Photovoltaic Cell Photovoltaic PV

2.2.1 Photovoltaic Cell

Photovoltaic cell is also known as solar cell. It is not work during darkness and usually is made from semiconductor material such as silicon. When the photovoltaic cell exposed to sun, the photons in form of light are converted into electrons. The photons that flow through the PN junction in solar cell randomly strike the atom and give energy to the outer electron that make the electron can break freely from the atom. The photons in the process are converted to electron movement are called electric energy [2]. Photovoltaic cell is a simplest component of a photovoltaic module that can generate very small current. A photovoltaic cell usually represented as an equivalent single diode model. Figure 2.1 show single diode model of photovoltaic cell. Figure 2.1: Single diode model of PV cell [3] A practical photovoltaic cell is deemed to be current source with a parallel forward diode [4]. This model contain a current source � �ℎ with a parallel forward diode, a parallel resistance � �ℎ and a series resistance � � . Series resistance, � � represent the resistance inside PV cell. Forward current � � that flow through the diode is view as dark current or diode current. Parallel resistance � �ℎ is mainly cause by the surface leakage current along the edge of a PV cell. The net current of a photovoltaic cell can be represent as � = � �� − � � − � � . The relation between current and voltage of photovoltaic cell can be express in equations 2.1 and 2.2. � = � �� − � � − � � 2.1 � = � �� − � � �exp � �� + �� � ��� � − 1 � − � + �� � � �ℎ 2.2 Where, � �� : current generated by the incident light � � : diode current � � : current through shunt resistor � � : leakage current of diode � : electron charge 1.6 × 10 −19 � � : Boltzmann constant 1.38 × 10 −23 �� � : ideality factor that varies between 1.0 to 1.5 Equation 2.1 and 2.2 can be representing by applied Kirchoff’s current law to the circuit. The V-I characteristic of PV module when assuming that � � is negligible and � �ℎ is infinite is shown in Figure 2.2. Figure 2.2: V-I Characteristic by assuming � � is negligible and � �� is infinite[4] Leakage current of diode or diode saturation current,� � can be expressed by Equation 2.3. � � = � �,� � � � � � 3 ��� � �� � �� � 1 � � − 1 ��� 2.3 Where, � � : band energy gap of the semiconductor � � : nominal temperature 298 Kelvin The nominal saturation current, � �,� can be expressed by the following equation. � �,� = � �� ��� �� �� �� � � − 1 2.4 Where, � �� : short circuit current of the PV module � �� : open circuit voltage of the PV module � � : thermal voltage that can be defined as, � � = � � ���

2.2.2 Photovoltaic Module