Robots are controlling everything. Now Robotic Solar-Panel Sun Tracking project is about the tracking and controlling the solar panels using travelling robot technology. Solar Robots help to increase the efficiency of the solar power system. For a photovoltaic solar panel, following the sun’s path across the sky raises efficiency by 30-50%. This robotic sun tracker is the latest advancement to the existing dual-axis solar tracking technology that use a costly DC motor with each of the solar panel.

Sun/Solar Tracking Technology

The main disadvantage of the solar power systems is its lower efficiency. The sun, the lighting source moves continuously whereas the solar panel is fixed to to a particular direction. And in the night time, there is a possibility that solar panels can generate a small amount of power from the moon light. Using the light source tracking technology, it is possible to track the sun or moon or any other brighter lighting sources, so that the solar panels can be turned towards the direction of light source to maximize the power output of photo-voltaic (PV) solar panels. the light source tracking technology is usually called as sun tracking system or solar tracker system, because it is mainly used for tracking the sun’s maximum solar energy during the day time.

Robotic Solar Tracking System Design


Robot Solar Tracking System

Travelling Robot Solar Tracking System that control the dual-axis of more than 200 solar panels using only one DC Motor

The objective of this project is to design and develop an Automatic Solar Tracker Robot that is capable to track maximum light intensity and control the direction of solar panels. The solar tracker system that follows the sun direction for producing maximum voltage out is mounted on the robot and the DC motors utilizes this energy for robot movement. The robot base can be controlled through computer using wireless Zigbee technology. The efficiency of the solar energy conversion can be optimized by receiving maximum light on the solar panel. The main components of the robot consist of microcontrollers, LDR sensors, DC motors and digital compass. This robot is programmed to detect sunlight by using Light Dependent Resistors (LDR). 

Normal Solar Tracker Vs Robotic Solar Tracking Systems

In large solar power grids, It is common for ground mounted PV solar panels to use solar trackers to tilt panels to follow the sun throughout the day, the use of robots for solar trackers is highly unusual. Existing solar trackers on the market are designed to hold up solar panels as well as to adjust their tilt, and commonly come with their own motors and electronics. There is generally two types of these solar trackers, single-axis and dual-axis, and dual-axis systems make finer angle adjustments and they are more expensive because they require more motors.

Robotic Solar Trackers perform dual-axis adjustments at the price of the same-sized single-axis solar trackers and enable the panels to produce up to 30 percent more electricity. Robotic Solar Tracker design essentially replaces the motors in each tracker with a robot that calibrates the optical angle for each set of solar panels and positions them accordingly.

Robotic Solar Trackers can cut total energy costs by 15% while increasing electricity generation by 30% to 40% over systems that don’t track the sun. Additionally The robots can be controlled through computer using wireless Zigbee technology.

In addition to tweaking the sun angle, the battery-powered robot, which has an on-board GPS, can gather data on the performance of panels.

Compared to normal solar tracking system, Instead of having the hardware to adjust the angle on every solar panel, Robotic Solar Tracking System has a traveling robot equipped with the motor needed to change the angle of several solar panels. The system can be installed to tilt 200 panels or be scaled up for larger solar farms.


Force Acting on aeroplane

While the airplane is propelled through the air and sufficient lift is developed to sustain it in flight, there are certain other forces acting at the same time (Fig. 3-4).Every particle of matter, including an airplane, is attracted downward toward the center of the earth by gravitational force. The amount of this force on the airplane is measured in terms of weight. To keep the airplane flying, lift must overcome the weight or gravitational force. The development of lift and thrust was explained earlier.

Another force that constantly acts on the airplane is called drag. It is the resistance created by the air particles striking and flowing around the airplane when it is moving through the air. Airplane designers are constantly trying to streamline wings, fuselages, and other parts to reduce the rearward force of drag as much as possible. The part of drag caused by form resistance and skin friction is termed parasite drag since it contributes nothing to the lift force.

A second part of the total drag force is caused by the wing’s lift. As the wing deflects air downward to produce lift, the total lift force is not exactly vertical, but is tilted slightly rearward. This means that it causes some rearward drag force. This drag is called induced drag, and is the price paid to produce lift. The larger the angle of attack, the more the lift force on the wing tilts toward the rear and the larger the induced drag becomes. To give the airplane forward motion, the thrust must overcome drag.

   In a steady flight condition (no change in speed or flightpath), the always present forces that oppose each other are also equal to each other. That is, lift equals weight, and thrust equals drag.


Another force which frequently acts on the airplane is centrifugal force. However, this force occurs only when the airplane is turning or changing the direction (horizontally or vertically) of the flightpath. Newton’s law of energy states that “a body at rest tends to remain at rest, and a body in motion tends to remain moving at the same speed and in the same direction.” Thus, to make an airplane turn from straight flight, a sideward/inward force must act on it (Fig. 3-5). The tendency of the airplane to keep moving in a straight line and outward from a turn is the result of inertia and it results in centrifugal force. Therefore, some impeding force is needed to overcome this centrifugal force so the airplane can move in the desired direction. The lift of the wings provides this counteracting force when the airplane’s wings are banked in the desired direction. This is further discussed in this chapter in the section on Turning Flight.Since the airplane is in a banked attitude during a properly executed turn, the pilot will feel the centrifugal force by increased seat pressure, rather than the feeling of being forced to the side as is experienced in a rapidly turning automobile. The amount of force (G force) felt by seat pressure depends on the rate of turn. The pilot will, however, be forced to the side of the airplane (as in an automobile) if a turn is improperly made or the airplane is made to slip or skid.

One other force which will affect the airplane during certain conditions of flight, and which will be frequently referred to in the discussions on various flight maneuvers, is torque effect or left turning tendency. It is probably one of the least understood forces that affect an airplane

Reverse Recovery Characteristics of Diode

The current in a forward-biased junction diode is made up of Majority carriers and Minority carriers. Once there is a forward current, there will be free minority carriers. A forward conducting diode whose forward current has been reduced to zero, will continue to conduct for some small time after due to minority carriers stored in the pn-junction and carriers stored in the bulk semiconductor material.

The forward current in a diode goes to zero if the diode goes from foward biased to reverse biased, or in other words V goes from +ve to -ve. According to the characteristics of a diode, ignoring the leakage current, when reverse biased there should be no reverse current once the reverse voltage does not exceed in magnitude to the breakdown voltage. However, in practice, the diode does exhibit a reverse characteristic for a short space of time due to the free carriers. These minority carriers require some finite time, the reverse recovery time, to recombine with opposite charges in order to be neutralized. This time is called the reverse recovery time.

  • Two reverse recovery characteristics exists. They are:

      1. Soft recovery
    1. Abrupt recovery

    as shown in Figure 2.3

Figure 2.3 Reverse recovery characteristics
trr = reverse recovery time, measured as the time between the initial zero crossing of the diode current to the time when this current reaches 25% of the peak reverse current.
IRR = maximum reverse current
ta = time between zero crossing and the maximum reverse current and it is due to the charge stored in the depletion region of the junction
tb = time between maximum reverse current IRR and 25% of the of the maximum reverse current IRR and is due to charge stored in the bulk semiconductor material
  • The reverse recovery time is measured from the initial zero crossing from forward conduction to reverse blocking condition of the diode current to 25% of the maximum reverse current IRR. Its magnitude depends on:

      1. junction temperature
      1. rate of fall of forward current
    1. forward current prior to commutation
From the graph it can be seen that,


 = softness factor (SF)

Reverse Recovery Charge

This is the amount of charge carriers that flow across the diode in the reverse direction due to changeover from forward conduction to reverse blocking condition. Its value is determined from the area enclosed by the path of the reverse recovery current (Recall D Q = D I D t). That is



From equations 2.6 and 2.8 we get


If tb is negligible in comparison to ta which is usually the case, then

Hence equation 2.9 becomes
Ideally diodes should not have a reverse recovery time, and it is possible to construct such a diode. However, the manufacturing cost of such a diode would be quite high for such a feature which in most cases has minor consequence

Types of Diode

Avalanche diodes

Diodes that conduct in the reverse direction when the reverse bias voltage exceeds the breakdown voltage. These are electrically very similar to Zener diodes, and are often mistakenly called Zener diodes, but break down by a different mechanism, the avalanche effect. This occurs when the reverse electric field across the p–n junction causes a wave of ionization, reminiscent of an avalanche, leading to a large current. Avalanche diodes are designed to break down at a well-defined reverse voltage without being destroyed. The difference between the avalanche diode (which has a reverse breakdown above about 6.2 V) and the Zener is that the channel length of the former exceeds the mean free path of the electrons, so there are collisions between them on the way out. The only practical difference is that the two types have temperature coefficients of opposite polarities.

Cat’s whisker or crystal diodes

These are a type of point-contact diode. The cat’s whisker diode consists of a thin or sharpened metal wire pressed against a semiconducting crystal, typicallygalena or a piece of coal. The wire forms the anode and the crystal forms the cathode. Cat’s whisker diodes were also called crystal diodes and found application in crystal radio receivers. Cat’s whisker diodes are generally obsolete, but may be available from a few manufacturers.[citation needed]

Constant current diodes

These are actually a JFET[19] with the gate shorted to the source, and function like a two-terminal current-limiter analog to the Zener diode, which is limiting voltage. They allow a current through them to rise to a certain value, and then level off at a specific value. Also called CLDsconstant-current diodesdiode-connected transistors, or current-regulating diodes.

Esaki or tunnel diodes

These have a region of operation showing negative resistance caused by quantum tunneling,[20] allowing amplification of signals and very simple bistable circuits. Due to the high carrier concentration, tunnel diodes are very fast, may be used at low (mK) temperatures, high magnetic fields, and in high radiation environments.[21] Because of these properties, they are often used in spacecraft.

Gunn diodes

These are similar to tunnel diodes in that they are made of materials such as GaAs or InP that exhibit a region of negative differential resistance. With appropriate biasing, dipole domains form and travel across the diode, allowing high frequency microwave oscillators to be built.

Light-emitting diodes (LEDs)

In a diode formed from a direct band-gap semiconductor, such as gallium arsenide, carriers that cross the junction emit photons when they recombine with the majority carrier on the other side. Depending on the material, wavelengths (or colors)[22] from the infrared to the near ultraviolet may be produced.[23] The forward potential of these diodes depends on the wavelength of the emitted photons: 2.1 V corresponds to red, 4.0 V to violet. The first LEDs were red and yellow, and higher-frequency diodes have been developed over time. All LEDs produce incoherent, narrow-spectrum light; “white” LEDs are actually combinations of three LEDs of a different color, or a blue LED with a yellow scintillator coating. LEDs can also be used as low-efficiency photodiodes in signal applications. An LED may be paired with a photodiode or phototransistor in the same package, to form an opto-isolator.

Laser diodes

When an LED-like structure is contained in a resonant cavity formed by polishing the parallel end faces, a laser can be formed. Laser diodes are commonly used in optical storage devices and for high speed optical communication.

Thermal diodes

This term is used both for conventional p–n diodes used to monitor temperature due to their varying forward voltage with temperature, and for Peltier heat pumps for thermoelectric heating and cooling. Peltier heat pumps may be made from semiconductor, though they do not have any rectifying junctions, they use the differing behaviour of charge carriers in N and P type semiconductor to move heat.


All semiconductors are subject to optical charge carrier generation. This is typically an undesired effect, so most semiconductors are packaged in light blocking material. Photodiodes are intended to sense light(photodetector), so they are packaged in materials that allow light to pass, and are usually PIN (the kind of diode most sensitive to light).[24] A photodiode can be used in solar cells, in photometry, or in optical communications. Multiple photodiodes may be packaged in a single device, either as a linear array or as a two-dimensional array. These arrays should not be confused with charge-coupled devices.

PIN diodes

A PIN diode has a central un-doped, or intrinsic, layer, forming a p-type/intrinsic/n-type structure.[25] They are used as radio frequency switches and attenuators. They are also used as large volume ionizing radiation detectors and as photodetectors. PIN diodes are also used in power electronics, as their central layer can withstand high voltages. Furthermore, the PIN structure can be found in many power semiconductor devices, such as IGBTs, power MOSFETs, and thyristors.

Schottky diodes

Schottky diodes are constructed from a metal to semiconductor contact. They have a lower forward voltage drop than p–n junction diodes. Their forward voltage drop at forward currents of about 1 mA is in the range 0.15 V to 0.45 V, which makes them useful in voltage clamping applications and prevention of transistor saturation. They can also be used as low loss rectifiers, although their reverse leakage current is in general higher than that of other diodes. Schottky diodes are majority carrier devices and so do not suffer from minority carrier storage problems that slow down many other diodes—so they have a faster reverse recovery than p–n junction diodes. They also tend to have much lower junction capacitance than p–n diodes, which provides for high switching speeds and their use in high-speed circuitry and RF devices such as switched-mode power supplymixers, and detectors.

Super barrier diodes

Super barrier diodes are rectifier diodes that incorporate the low forward voltage drop of the Schottky diode with the surge-handling capability and low reverse leakage current of a normal p–n junction diode.

Gold-doped diodes

As a dopant, gold (or platinum) acts as recombination centers, which helps a fast recombination of minority carriers. This allows the diode to operate at signal frequencies, at the expense of a higher forward voltage drop. Gold-doped diodes are faster than other p–n diodes (but not as fast as Schottky diodes). They also have less reverse-current leakage than Schottky diodes (but not as good as other p–n diodes).[26][27] A typical example is the 1N914.

Snap-off or Step recovery diodes

The term step recovery relates to the form of the reverse recovery characteristic of these devices. After a forward current has been passing in an SRD and the current is interrupted or reversed, the reverse conduction will cease very abruptly (as in a step waveform). SRDs can, therefore, provide very fast voltage transitions by the very sudden disappearance of the charge carriers.

Stabistors or Forward Reference Diodes

The term stabistor refers to a special type of diodes featuring extremely stable forward voltage characteristics. These devices are specially designed for low-voltage stabilization applications requiring a guaranteed voltage over a wide current range and highly stable over temperature.

Transient voltage suppression diode (TVS)

These are avalanche diodes designed specifically to protect other semiconductor devices from high-voltage transients.[28] Their p–n junctions have a much larger cross-sectional area than those of a normal diode, allowing them to conduct large currents to ground without sustaining damage.

Varicap or varactor diodes

These are used as voltage-controlled capacitors. These are important in PLL (phase-locked loop) and FLL (frequency-locked loop) circuits, allowing tuning circuits, such as those in television receivers, to lock quickly. They also enabled tunable oscillators in early discrete tuning of radios, where a cheap and stable, but fixed-frequency, crystal oscillator provided the reference frequency for a voltage-controlled oscillator.

Zener diodes

Diodes that can be made to conduct backward. This effect, called Zener breakdown, occurs at a precisely defined voltage, allowing the diode to be used as a precision voltage reference. In practical voltage reference circuits, Zener and switching diodes are connected in series and opposite directions to balance the temperature coefficient to near-zero. Some devices labeled as high-voltage Zener diodes are actually avalanche diodes (see above). Two (equivalent) Zeners in series and in reverse order, in the same package, constitute a transient absorber (or Transorb, a registered trademark). The Zener diode is named for Dr. Clarence Melvin Zener of Carnegie Mellon University, inventor of the device.