SOLAR PANEL EXPERIMENTS
Aim: Effect of Change in Irradiation on Solar Panels.
Theory: The photovoltaic cells (solar cells) generate electricity through a process called
photovoltaic effect. They generally comprise of a PN junction, which is formed using certain
semiconductor material. The cross-section of a general PV cell is similar to the figure below.
The electric field is created at the junction due to the negative-positive doping in the
semiconductor material. When sunlight is incident on the surface, the photon energy results
the free charge carriers. The charge carriers are separated because of the electric field and a
potential difference is generated at the external contacts. If the circuit is completed, a current
called photocurrent flows depending on the light intensity.
The solar panel simulator approximates the characteristics of a typical PV cell, through an
equivalent circuit. The equivalent circuit for a typical PV cell is given below.
Where, I = Output Current, IL = Photocurrent, Io = Diode reverse saturation current, V =
Output Voltage, Rs = Series Resistance, Rp = Parallel Resistance, q= Charge, k= Boltzmann’s
Constant, N= ideality factor, Ns = Number of cells in series, T= Solar Panel Temperature.
The ideal solar cells do not have the voltage loss and leakage currents and therefore does not
have series and parallel resistances. Using Kirchhoff’s current law on the equivalent circuit,
one can obtain:
q (V Rs I
V Rs I
I I L I o (e nkTN s
1)
RP
For an ideal solar panel, the shunt resistance is very high and series resistance is very low.
Hence, for an ideal case, third term in the equation for I is absent. The open circuit voltage
can be approximated as:
kTcell
V (ln( I L ) ln( I o ))
q
Effect of Change in Irradiation: The amount of current generated in the PV is affected by
two variables: the intensity of incident light and the wavelength of the incident rays. Each
semiconductor material shall have a limited absorption of radiation. Below this, no
electrons make the photovoltaic effect. The energy of a photon is determined by the
wavelength but not by the intensity of light, against shorter, have more energy. Increasing
light intensity increases proportionally photoelectron emission rate in the photovoltaic
material. Solar cells are usually coated with an anti- reflective material to capture the
maximum amount of radiation possible. Photons with wavelengths too high will pass through
the panel in the form of heat. Photons with a wavelength less than 1.100nm have more energy
than the required to separate the electron, the excess energy is converted to heat losses.
From the above discussion, it can be concluded that, the photocurrent increases with the
increase in irradiance. So, with the increase in irradiance the output current increases linearly,
whereas the output voltage increases logarithmically (see the equations of the output current
and voltage).
Procedure:
• Keep the temperature constant and Voc and Isc are also constant.
• Change the values of G1, G2, G3 and G4 such that G1>G2>G3>G4
Results:
Observations:
With the increase in the irradiation levels the current drawn from the panel also increases and
vice versa is also true.
References:
[1]. Renewable energy technologies - R. Ramesh, Narosa Publication.
[2]. Energy Technology – S. Rao, Parulkar
[3]. Non-conventional Energy Systems – Mittal, Wheelers Publication.
[4]. Non-Conventional Sources of Energy- G.D.Rai, Khanna Publishers
[5]. Non-Conventional Sources of Energy- B. H. Khan, TMH Publication
[6]. Renewable Energy sources And Emerging Technologies, DP. Kothari, PHI.
[7]. Hand Book of Renewable Energy Technology, Ahmed F Zooba, R C Bansal World
scientific.
[8]. Dezso Sera, Member, IEEE, Laszlo Mathe, Member, IEEE, Tamas Kerekes, Member,
IEEE, On the Perturb-and-Observe and Incremental Conductance MPPT Methods for PV
Systems, IEEE JOURNAL OF PHOTOVOLTAICS, VOL. 3, NO. 3, JULY 2013.
[9]. Trishan Esram, Student Member, IEEE, and Patrick L. Chapman, Senior Member, IEEE,
Comparison of Photovoltaic Array Maximum Power Point Tracking Techniques‖ IEEE
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