Solar Tracking system:
three main types of the solar tracker drives divided based on the type of the
sensing, drive, and the positioning system that they incorporate. The three
Open Loop Trackers.
A compressed gas fluid is used
in the passive tracker in two canisters in the east and west of the tracker in
order to move it. The mechanism
is depending on the direction of the sunlight that falls on the gas container.
If one side is heated other side piston rises and create a gas pressure,
causing the panel to move and tilt over the sunny side until it gets to
an equilibrium position. This system doesn’t require any controller, and needs
Motors, actuators, and gears are
used in the active tracking system to locate the solar tracker to be
perpendicular to the sun. It use light sensors to track the sunlight and
measure the light intensity to point the required position and use it as a
input data for the microcontroller to monitor the motors and actuators to
adjust the location of the solar panel.
Open Loop Trackers:
This type use the pre recorded
information in a particular site to determine the sun’s position instead of the
main components of the solar tracking system consist of three main parts:
• Four Light
Dependent Resistor (LDR)
• Servo Motors
as main controller.
Block diagram of Solar tracking
system using LDR
LDRs are also named as photo resistors or photo conductors; it is a
light controlled variable resistor which is made of a high resistance
semiconductor that applies the principle of photoconductivity. As the incident
light intensity increase the resistance of the photo resistors decrease. It can
be applied in light and dark activated switching circuits, and light sensitive
detector circuits. LDRs are very effective and useful sensors especially in the
dark, it has a very high resistance normally as high as thousands Mega ohms
(M?), but it have a low resistance in the light. The Light Dependent Resistor
(LDR) is mainly used in this project to sense the sunlight and track the sun,
and provides the arduino with the analog input.
The table below shows the behavior of Light Dependent Resistor with the
light intensity change.
LIGHT INTENSITY LDR OUTPUT (V)
The LDR’s have
a simple structure; which
is made of cadmium sulfide (CdS) and gallium arsenide (GaAs).
and Electronic symbol
The LDR used with the Arduino:
Clockwise to increase the sensitivity towards the
Anticlockwise to decrease the sensitivity towards
the light intensity.
We built a solar tracker
using four LDRs that have a cylindrical shade. The design of the solar sensing
device is shown in figure (no. of fig). The sensing system is attached with the
photovoltaic panel, where the South- North LDRs and the East-West LDRs are used
to detect the azimuth motion and the elevation motion of the solar panel, the
main principle of the light sensors is based on the shadow. As the sun change
its direction the solar sensing system track the movement of the sunlight, if
the solar panel is not perpendicular to the sun, the shadow will cover one or
two light sensors. As a result, a light intensity difference is created to be
received by the solar sensing system.
system with a four quadrant LDR sensor.
The concept of using four LDRs:
Concept of using four
LDRs for sensing is illustrated in figure (no. of fig), which shows the
interconnection of the closed loop tracking system. The main aim of the solar
tracker is to arrange the solar panel location to track and follow the sun
location as closely as possible. The system consists of LDR sensors,
differential amplifier, and a comparator. In the tracking process, the light
sensors measure the intensity of the sunlight as an input signal. So, when the
four LDRs have the same light intensity, the system is said to be in the stable
position. But when the sun moves from south to north or from east to west, the
level of the light intensity falling on each LDR is change, and a voltage
divider is used to calibrate this change into voltage. The unbalance in the
voltage levels are amplified and then create a feedback error voltage, which is
proportional to the difference between the solar panel position and the
sunlight position. At this time a built in comparator of the microcontroller
compares the error voltage. If the output voltage goes high, the servo motor is
activated, so as to change the rotation angle of the solar panel to face the
sun and track the sunlight.
Block diagram of the
solar tracking system.
The four LDRs measure the sunlight intensity from four
various locations, where the south, north, east, and west LDRs are produce the
sensing voltages Vs, Vn, Ve, and Vw respectively. Figure (no. of fig)
represents the working algorithms of the system.
Feedback Error Voltage:
electronic circuit for creating feedback error voltage is shown in figure(no.
As it can be
seen, when the corresponding LDR is shadowed the output voltage from the
voltage divider will be lower. So, if one LDR sense the light more than the
other which will be shadowed, the difference voltage between them will be
amplified by the differential amplifier.
The feedback error voltage can be
can then be rearranged as:
If the east LDR is shaded, Vw > Ve and Vwe >
0, and the same for Vs and Vn.