Industrial Visit Report
Solar plant
G.Sri Venkat Sai Raj
06-Mar-19
Introduction
The students of Electrical and Electronics Engineering of Vaagdevi College of Engineering
went on an industrial visit to Solar power plant of Mahindra_Susten Private Limited on 6 th of
march 2019. During the visit we have been shown the working of solar panel, Inverter,
transformer and the control of the entire system.
Details about the site:
Site Location : Wadekothapally
Plant capacity : 42 MW
Types of Modules : Poly silicon and Thin film
Total no. of modules : 1, 70,000
Inverters : GE & SMA
No. of Inverters : 40
Area : 141 Hectares (350 acres)
Transformers : 2.2 MVA (10 nos.)
Switch yard : 33KV/132KV
Power transformer : 31.5MVA (2 nos.)
Types of solar panels
As said by the field engineer at the solar plant, there are 3 main types of solar panels used.
1.Monocrystalline Thick blue Very efficient High cost
(~99%)
2.Polycrystalline Blue Average efficiency Medium cost
3.Thin film Black Poor efficiency Medium cost
At the site we use both poly as well as thin film type, in which some of the poly-Si has the
tracking system available.
How do Photovoltaic cells work?
Photovoltaic cell coverts the light energy into electrical energy. Some materials exhibit a
property known as the photoelectric effect that causes them to absorb the photons from light
and release the electrons. When these free electrons are passed through the conductor and
captured they result in the electricity.
Solar Panel
The panel used here has 72 cells (12 X6) built in, each cell producing the voltage of 0.5V and on
the whole each panel results in 36V DC output. As this small voltage can’t be fed to inverter we
go for strings. Group of 21 panels is called and OFF-STRING and 2 of them is called a STRING.
Each off string produces 8A of current and a string gives 16A. The positive of the panel can be
seen in silver where the negative is grey. All the panels in a string are connected by MC4 (multi
connect 4mm2 ) cable. Each panel has a diode box, which has 3 diodes in it to ensure
unidirectional flow. It was said that incase of burnout of diode the box shows a white patch
indicating a damage. Each panel weighs at an around 23 Kg and the dimensions be 1972 X 992 X
40 mm. The manufacturer of the panel is
“Hanwha Solar”- a Chinese company.
Connecting Box
Group of 16 strings (max) are connected to a
combiner box which gives input to the
Inverter panel. The combiner box has
protection as well as isolation equipment in
it. The isolation switch is opened during
maintenance or any replacing of panels.
Surge protecting devices (SPD’s) are used to
avoid the surge currents to reach the inverter
cabinet. The 4002 mm cable is used for
carrying the output from the combiner box to IC pad and these cables are passed underground
here.
Tracking system
Firstly, tracking might be of two kinds 1) Dual axis
tracking_ which gives all four directions movement 2)
Single axis tracking _ only two directions of movement.
Here in the site we can see single axis.
A special tracking system is used here for the tilting of the
solar panels according to sun direction, similar to that of a
sunflower. MSAT (Mahindra Solar Azimuth Tracking) is the
device used here which has the actuator, tilt sensor and a preprogrammed control board. For
every 5 lines of strings there is separate solar panel for tilt operation, it has 24V DC motor built
in which aids the hydraulic system. The range of tracking is from 1350 to 2250, which is 450 in
both of the directions. The system adjusts the panels for 20 of angle for every 10 minutes.
IC Pad
The plant has 10 IC pads i.e. the inverter and the transformer unit collectively. Each IC
pad has 4 inverters. Here there are two types of inverters used, made by GE and SMA. Ones by
GE have effective cooling and need for periodic maintenance in form of replacing the coolant
where as the SMA has no such issues. IGBT is the switch used in inverter. Each inverter has two
cabins. One for the inverter itself and other for protecting and communicating devices. As per
the day of visit the total generation on that day and till date by the particular inverter is 4,854
MWh and 2,977 GWh respectively. The minimum input for each inverter to get started is in the
range of 650 - 850 V. After the inverter its fed to a Step Up Transformer to give a output of
33KV.
Control room and SCADA
It has all the devices which monitor the status of inverter, MSAT devices and the tap
changes of power transformer .All the information gathered that control panel is fed to
Mumbai using FOTE technology for supervisory. The control room also has the SCADA system to
monitor the outputs of each inverter and to see the present capacity of the line to which the
synchronism of generated power has to be done.
Substation
As usual the substation started with sight of Lightening arrester and surge protection devices
and ended with the power transformer.
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