Energy is the prime factor for the development of a nation. An enormous amount of energy is extracted, distributed, converted, and consumed in the global society daily. Eighty-five per cent of energy production is dependent on fossil fuels. The resources of the fossil fuels are limited and their use results in global warming due to emission of greenhouse gases (GHGs). To provide a sustainable power production and continuous power resources for the future generations, there is a growing demand for energy from renewable sources, such as solar, wind, geothermal, and ocean tidal waves. Renewable energy (RE) sources are the best-proven sources of energy. Solar energy is one of the most abundant resources of RE. Energy from sun is perceptibly environmentally advantageous in all respects. There are many different ways of generating electricity from the sun’s energy. The most popular are photovoltaic (PV) panels, where silicon solar cells convert solar radiation to electricity. Keeping the PV-panels perpendicular to the sun’s radiation maximizes the output. The systems that are utilized for this movement are called solar trackers. The solar trackers are also required for concentrating solar power applications to function. The power incident on a photovoltaic (PV) module depends not only on the power contained in the sunlight, but also on the angle between the module and the sun. When the absorbing surface and sunlight are perpendicular to each other, the power density on the surface is equal to that of the sunlight (in other words, the power density will always be at its maximum when the PV module is perpendicular to the sun). However, as the angle between the sun and a fixed surface is continually changing, the power density on a fixed PV module is less than that of the incident sunlight. The amount of solar radiation incident on a tilted module surface is the component of the incident solar radiation which is perpendicular to the module surface.

Development and Simulation of the Prototype

The overall solar tracking system consists of a mechanism that enables the PV panels to follow or track the sun. The mechanical structure consists of one servo motor that drives the mechanism, LDR sensors for measuring light intensity, and a programmable microcontroller responsible for giving electric signals to the motors in accordance to the sun angle in order to achieve solar tracking (keeping the PV panel perpendicular to the sunlight). Based on the system requirement tilt angle is provided of 25° angle southwards. The feedback control system operation is based on servo mechanism principles and the controller is responsible for the solar tracker motion. The controller coding and servo mechanism is simulated in PROTEOUS 7. In summary, this article presents the simulation and development of a prototype of a single axis automatic solar tracking system using servo mechanism. The simulation for servo mechanism using PROTEUS 7.0 is described thereafter. This is followed by the description of the development of a proposed solar tracking system.

The mechanism of the discussed system deals with the open loop tracking system in which sensors detect the higher light intensity. The motor actuates in the direction where sunlight is more. Such type of tracking mechanism is called servo mechanism and is also known as real-time tracking. It was resolved that real-time tracking would be necessary to follow the sun effectively so that no external data would be required in operation. The open-loop type is simpler and cheaper but it could not compensate for disturbances in the system and has low accuracy. On the other hand for the closed-loop tracking, the sun trackers usually sense the direct solar radiation falling on a photo-sensor as a feedback signal to ensure that the solar collector is tracking the sun all times and keep the solar collector at a right angle to the sun’s rays for getting maximum solar insolation. The closed-loop tracking mechanism can overcome the issues related to (cloudy, rainy) weather conditions using AC antenna motors, and power electronic control circuit to convert DC into AC. However, it causes more losses in the system.

Since the PV module has nonlinear characteristics, it is necessary to model it for the design and simulation of PV system applications. Recently, a number of powerful componentbased electronics simulation software package have become popular in the design and development of power electronics applications. It is difficult to simulate and analyse in the generic modelling of the PV power system. To test the operation logic code there is one more software to simulate the servo mechanism, that is, PROTEUS 7. Generally, most of the parameters are given in manufacturer’s specifications but sometimes some parameters (such as ideality factor, series resistance, etc.) may not be given and may change due to ageing and other environmental factors. Hence, it is necessary to develop relations to find these parameters.

Simulation for Servo Mechanism

The working of microcontroller and servo is first simulated in PROTEUS 7.0 software (Figure 1). The servo mechanism of the solar tracker is first simulated in the software to determine whether the code generated for servo controlling is correct. This provides the working of servo mechanism before actual implementation.

Solar Tracking System Description

Development of the tracking system was carried out through the following two major steps which were as follows:

ƒ Mechanical structure design ƒ Control system design

Mechanical structure:

The structure of the prototype was prepared using CAD Solid Works 2013 to check the free movement of panel in east–west direction. Realization was accomplished at the workshop of renewable energy engineering department. Figure 2 shows the design prepared for tracking system.

Control system:

This can be understood in two parts. First one works with active components which controls the system automation. The second one is to prepare circuit using passive components for charge controller, voltage regulation, and connections of all components.

The active components required are as follows:

• Light-dependent resistor (LDR): It is the light-depending resisters that have a particular property that they can detect lightning intensity in which they have been stored. The cell resistance falls with increasing light intensity. The sensitivity of a photo detector is the relationship between the light falling on the device and the resulting output signal. In the case of a photocell, one is dealing with the relationship between the incident light and the corresponding resistance of the cell.
• Microcontroller: The microcontroller is the brain of the tracker, and it controls the tracking system. Basically, it receives input from the sensors, specifying the position of the sun and in response, it sends signal to the motors that are connected to the solar panel to move to the panel to the position of the sun in which optimum solar rays could be received. The microcontroller is made up of software and hardware components. The software component is basically the computer programmes that decode the input signals and sends out appropriate signal in response to the inputs to control the tracking system. It is connected to the sensors and motors. The hardware executes the command. It requires 5 V DC.
• Servo motor: Servomotors are handy and practical in today’s robotic and mechatronic systems as they provide a high level of accuracy, are simple to wire up, and relatively simple to control. They are also more applicable for certain applications than standard DC motors as they are position controlled rather than rotation controlled. A good application for servomotors is a sun tracking system for solar panels. The system requires a fairly high positional accuracy, therefore, servomotors are ideal for the job. The motor used here requires 4.8 V and an operating speed of 0.18 sec/60° at no load.
• Battery: The tracker needs a power source to keep it running due to the irregularity of the power received from the solar panel. A 6 V and 4.5 Amp rechargeable battery is used; the battery as it is connected to the tracking system is also connected to the output of the solar panel to keep it charging. Figure 3 shows the working of controlling components.

Conclusion

In the proposed design and operation of the solar tracker system, the sun was not constantly tracked based on the irradiation. This helps to prevent unnecessary energy to be consumed by the devices and the system stops moving when the night falls. Simulation result shows that the codes generated for servo controlling are working accordingly. The developed system was also tested for performance evaluation.

It was observed that at 15.00 hours, tilted tracking gave 1.27 W of power gain in comparison to the fixed one. The complete calculated data for 12 hours are given in Table 1.

Where, ηf=fixed system efficiency, ηt=Tracking system efficiency, ηt*=Tracking at latitude angle efficiency.

Efficiency Gain = ηt – ηf = 5.63- 3.64=1.99% Efficiency Gain* = ηt * – ηf = 6.32- 3.64=2.68% Efficiency Gain* = ηt ** – ηf = 8.43- 3.64=4.79%

An energy efficiency gain of 44.25 per cent relative to the fixed system was obtained. Results showed viability of the tracking strategy. Hence, it can be concluded that tracking system with a location-specific tilt can give better efficiency. The proposed control structure provides the flexibility to accommodate different weather conditions.

Source: IOSR Journal of Electrical and Electronics Engineering (IOSR-JEEE). Courtesy: Er. Khyati Vyas, Chemtrols Solar Pvt. Ltd, Mumbai, India; Email: khyati.vyas@ chemtrolssolar.com