IntroductionThe rise in the usage of non-renewable energy resources and fossil fuels has lead the world to a stage where the main governments want to develop strategies and policies that show they take care about the global warming and CO2 emissions. That is the example of the European Union, where each country has assumed a goal to complete by 2020 [1] and charges would apply to those that cannot achieve this objective. The energy consumption can be divided into three main uses, electricity, transport and energyheating [2] being transport the main source of fuel consumption that need research to find better ways to power vehicles and systems. According to P.E. Hodgson, fossil fuels are expected to reach a peak production level in 2018 and after that fall in the subsequent years. Otherwise, based on the supply and demand principle, the prices of this resource will rise as the production level decreases coming to a critical level by 2060, when fossil fuels are expected to become a very bad option to power the world [3]. Then other alternatives need to be evaluated and taken into account for replacing these fuels. When talking about replacing fossil fuels, there are some points that need to be addressed first in order to get a stable point in the supply chain for renewable energy resources. This is the example of the policies that favor the generation of green energy in some countries where the consumer is awarded a tax reduction for preferring energy from renewable resources or the companies responsible for electrical distribution receive bonuses according to the percentage of green energy they supply. Nowadays, the prices for renewable energy are higher than conventional generation systems because green energy requires complex systems to integrate themselves into the current grid and make it safe. Some research and design stages are still required for integrate some renewable resources like off-shore wind power, solar photovoltaics and wave power, but it has to be said that the current state is mature and currently used mainly in niche and showcase applications [4]. The prediction of renewable energy availability is a highly appreciated factor that can be crucial when selecting between one system and other, thats why the use of the sun and the solar thermal and photovoltaics is often preferred in some places of the earth. The study of the movement of the sun and the huge studies (data available) done by every country about the irradiation in that particular place of the world, make this form of energy easy to address and study. The photovoltaics panels (PV) are devices that harness the impact of the sun light on their surfaces by exciting electrons in the internal materials (silicon and others) and create a voltage difference between the ends of the these panels, generating a current and providing a reliable source of electricity that can be only affected by the weather conditions such as clouds or rain. One particular difference between photovoltaics and other sources is that photovoltaics make the DC available instantly due to the internal characteristics of the generation without needing a converter to use in equipment, but in most cases this DC are converted in AC and then for final usage is DC. The earth moves in relation to the sun describing a trajectory that can be described by the Keplers laws of planetary motion, this means that the solar incidence in one point at certain time of the day wont be the same at a different time that day, consequently, there is a need to know where the highest energy vector is pointing at certain time. For energy generation, in most cases, a PV panel is placed in a fixed or manually operated way which causes that from the overall energy ready to be collected, just the part that concurs in that place is taken. This has been done and applied based on the thought that more energy and time would be needed to harness the part of energy is being lost and this has led to inefficient solar systems that dont reach its full potential by trying to avoid a little higher investment. Sometimes, the way how this issue is solved is by installing a micro-controller that simulates the movement of the sun according to the equations mentioned, this means that a 3 axes system is needed, and then energy to power these 3 motors is taken from the overall benefit of the system. A need is then created to develop a model able to sense the irradiation of the sun, harness it in its strongest points, and avoid possible errors introduced by applying the formulas for sun movement, in other words, o achieve something more empirical rather to improve the theoretical model (without throwing away the theoretical needs).A solar tracking panel is a PV panel that fills the need for harness the strongest points of concentration while following the sun and converting its energy into electricity. The advantage of this system as it has been mentioned is the increase in the energy efficiency and the availability to harness more power while trying to reach the full potential of the equipment. It works by measuring some points of irradiation and comparing them with others, based on this comparison it moves towards the best energy-position. Several research studies have been made in this field and important advances are already built such as the combination of the theoretical and the empirical model in a 2-axes tracker done by Tung-Sheng Zhan and Whei-Min Lin [5]. More advanced studies on this field will lead to an almost perfect efficiency-improved model that suits the condition of the weather and harness perfectly the sun in its place, in the other hand, its application in further sun-applications such as solar-thermal, where the main panels are directed toward a point of concentration and the energy is used to heat water for electricity generation.In order to enhance the efficiency of the system, the panel can be mounted on a car. The advantage of this system is that it would provide more time exposure to the sun light depending on the surroundings of this device, and how far can it go while increasing the efficiency depending on the precision of the tracking module and devices used for this purpose. Tuton Chandra Mallick et al [6] studied the solar-tracking robotic car topic in their research paper called A Design & Implementation of a Single Axis Solar Tracker with Diffuse Reflector. Their system worked in the way that the vehicle will move on that direction where the sensor detects maximum intensity of light, giving the system an efficiency rise of up to 7% compared with the fixed panel. The applications of this system can vary depending on what the final user wants, maybe this wouldnt be suitable for concentrating plants as the space is reduced and the panels are expected to be fixed, but in automated systems the tracking device and its relative-movement program would be significantly important when generating the electricity needed. Taking the recent use of the Solar Impulse Airplane [7] and placing a tracker in it would provide extra capacity for its operation and emergency needs in case of bad weather in some points of the earth, charging batteries in mobile robots such as lawn mowers would take less time by activating its tracking function. ApplicationMost of the solar panels that can be seen in some buildings are placed in a fixed position in the top of the buildings reducing the efficiency and wasting valuable sunlight during the morning or the afternoon because the movement of the sun. This means that a single solar panel placed with this arrange, may take most of the energy during the mornings and be almost useless in afternoons. There is another option that taking this into account, put solar panels in both sides, increasing the initial costs of the project and the future maintenance costs while trying to join the two sources of energy and placing them into one device. What has been done in this project, assuming a rooftop with triangular shape (or a surface where the panel can be placed easily), is to place a single solar panel that is able to change its position based on the amount of energy available to harness, this means that the device will have the arrange described in figure 1.Figure 1. Arrange of the Top Tracker

An infinite-position device would take all possible sun light (from the area viewpoint), but the main purpose of this experiment is to calculate the variation of the efficiency and power output of this arrange compared to the complete fixed one.The prototype was built using some LEGO components as shown in figure 2.Figure 2. LEGO Structure

As shown, the device is composed by: LDR (Light-dependent Resistor) x 3. Stepper motor to improve the precision of the move x 1. Mini solar panel x1. LEGO structureThe results given by this experiment are shown in table 1.Table 1. Fixed Panel vs. Tracking Panel

The controller used in this experiment was the arduino-one. Another approach in the research of this topic is the one done by mounting the panel into a car and looking for harnessing the maximum amount of useful sunlight. The floor device is always looking to move in the direction that suits better with the electricity generation. A complete application of this technology in some smart homes would mean that the overall amount of energy produced would increase and the potential of the device may be achieved. A little con about this idea is the fact that it may require a little maintenance extra-effort. Figure 6. Shows the complete tracking device.Figure 6. Car-mounted Tracking Device

This device has an important feature, the collision avoider. This is an ultrasonic sensor placed in the direction of the movement; this technology has been largely applied by some domestic robots, such as lawn mowers or house cleaners [8].A car with a panel mounted was built and the parts shown represent a design effort and thought. The sensors are placed in their specific place in order to achieve what the project is looking for: efficiency. As a conclusion, it can be said that the efficiency of the technology used to take advantage of the sunlight will, as it name claims it, on the sunlight and every effort made to ensure that the light go directly to the panel is a considerable advantage.It is important to recognize, at this stage, that investment in renewable energy should have a quantitative aspect, as well as a qualitative one, in other words, the decision about investing in a certain project should take into account not only the economic benefit, but its advantages in the investigation and efforts for taking the first step in some paths for the green energy race.

Conclusion A new way for placing solar panels was shown in this report, 3 positions were used for harnessing the energy provided by the sun and this approach resulted more efficient than the fixed one, making the arrange viable for using in the buildings that want to generate some green energy. A robot sun-tracker was design and built using the describe systems and the analysis yielded that a considerable amount of efficiency raise can be achieved by using tracking techniques. The solar panel was placed in a tracking device that work with sunlight sensors that drive the motors to accomplish a condition in the way that the panel is normal to the sun light. This arrangement is widely known and used in the solar electricity generation. As could be shown, the solar panel follows the sun trace in an effective way and the results are favorable and encourage the use of tracking schemes for solar energy.Two approaches were made for the fixed panels and tracking panels showing the technology used and details about each device, where the LDR sensors take almost the most important place. The important variable to measure is the power output, where it could be seen that the tracking panel was superior to the fixed one by almost 1 mW. It is obvious that applying tracking techniques will increase the energy consumption because the energy needed to power the motors, but according to some investigations, this energy is small compared to the generated by the system and the tracker is still more efficient than the fixed arrange.The variables of voltage and current could be analyzed for comparing the types of solar panels and some materials discussion, which is not the objective of this project.It was shown that making a tracking panel is not waste of energy and resources as it was thought at some points of the research in this field, but a good extra-effort to make in order to guarantee the best efficiency. There are several applications of the Tracking Car that include its use in smart houses and offices, mobile self-powered robots as the example mentioned and the now-common drone. As a recommendation, precise parts (such a smaller-step stepper motor ) and appropriate coding can become an energy-efficiency trigger, not to mention the overall efficiency of the solar panel, which is a matter of several studies because its efficiency has not reached a desirable value (not even 20% in some cases). This lead to the financial analysis of what the project wants and what it requires.

References1. House of Lords, UK, 2008. Report. The Economics of Renewable Energy, 1, 6.The House of Lords is an organization located in the UK that provides information about important matters to the country. In their economic affairs committee, they discuss about the economics of renewable energy by analyzing the different types (ocean, solar, biomass) and what are the following steps to achieve the established goals.In page number 6, they state the goals established by the European commission that says, The EU is committed to a binding target that 20% of its energy consumption should be from renewable sources by 2020. This topic is taken further by analyzing how much of this total have to be achieved by each country, in example, they say The expected UK target implies a dash from 1.8% renewable energy now to a near-tenfold increase in 12 years.2. House of Lords, UK, 2008. Report. The Economics of Renewable Energy, 1, 11.When analyzing the demand of energy consumption in page number 11, they divide the main uses of energy into heat, electricity, land transport, and aviation and clarify that only 1% of the heat and transport energy comes from renewable resources. This fact is important because it points the urgency of developing new technologies to use in this field and decrease the usage of fossil fuels necessary for now to power vehicles. 3. Ecotricity. 2015. The End of Fossil Fuels. [ONLINE] Available at: https://www.ecotricity.co.uk/our-green-energy/energy-independence/the-end-of-fossil-fuels. [Accessed 07 June 15].This paper discuss the past, present and future of fossil fuels from a negative viewpoint by stating, fossil fuels will be gone forever and letting clear that its only a matter of time for the world to run out of this kind of fuels. Another analysis is carried out when analyzing the risks of keeping the usage of gas and coal and saying that it will only make the world more dependable of them without looking for other options before 2088.4. House of Lords, UK, 2008. Report. The Economics of Renewable Energy, 1, 78.The report shows a table describing where each type of renewable energy is, what can be achieved, what is holding it back from full success and what needs to be done. For solar photovoltaics, they say that the main causes for slow-growing are high capital cost, lack of skilled installers, competition for raw materials that result in high cost, and lack of information and accreditation schemes. It is important to recognize that the first thing to be done is research and design into manufacturing, point that this report try to advance in. Other important steps to take are skills development and research into materials.5. Zhan, TSZ, 2013. Design and Implementation of the Dual-axis Solar Tracking System. 2013 IEEE 37th Annual Computer Software and Applications Conference, 1, 1.The robot designed by them uses the theoretical Keplers equations to calculate the angles (latitude and azimuth). This information is translated into commands to drive DC motors that rotate the panel and once is in the expected position, the feedback from the sunlight sensors provide the information to drive the motors.This experiment uses 2 axes, meaning that the system can move right-left and up-down to properly track the light as described. This experiment had a result of an increase in the overall efficiency of 17%-25% for sunny days and 8%-11% in cloudy days (compared to the fixed arrange)6. Tuton, C.M, et al (2014). A Design & Implementation of a Single Axis Solar Tracker with Diffuse Reflector. In The 9th International Forum on Strategic Technology. Bangladesh, October 21-23, 2014. Chittagong, Bangladesh: Premier University. 3This project compares three sets of data obtained by different means but using a single-axis solar-tracking system that consist in a robot that follows the sunlight in order to harness the most possible. This report integrates the control systems and the hardware design for the tracker while explaining which way is the most efficient to install the sunlight sensors and a possible way to wire them. Control schemes are provided as a guidance.7. Solar Impulse RTW. 2015. Solar Impulse. [ONLINE] Available at: http://www.solarimpulse.com/?utm_source=site&utm_medium=header&utm_content=corporate&utm_campaign=home. [Accessed 03 June 15]This is a project that tries to take an airplane all around the world just solar-powering it. The airplane took off from Abu Dhabi and is now in a city of Japan. The project reflects all the advances that have been reached in the solar renewable energy and represents a breakthrough that is expected to encourage more people into the investigation and involvement in this field.8. iRobot Roomba. 2015. Vacuum cleaning robot. [ONLINE] Available at: http://www.irobot.com/For-the-Home/Vacuum-Cleaning/Roomba.aspx. [Accessed 07 June 15].This commercial robot sweeps the house automatically by creating cleaning circuits. The device integrates a series of sensors and processors that can detect what areas havent been cleaned and when obstacles such as walls, chairs, tables, etc. are in front of the robot adapting it to the house where it is used in.

Literature ReviewAlthough solar energy is considered to be in a developed phase, the literature available tends to focus on the basic important topics: materials selection for panel, control schemes for harnessing the most energy, number of axis to maximize the efficiency, and tracking options available. Gan, GY, 2014. Research on Solar Tracking Composite Control. TokyoThe goals of the authors is to explain a genetics based algorithm to improve the control applied to heliostats in solar-thermal plants. There are two basis methods for controlling the movement of the panels, the theoretical sun-movement dependant, where the rotation of the panel depends on the Keplers equations, and the sunlight-measurement dependant, where the closed loop circuit uses sunlight sensors to provide feedback to a microcontroller and this one controls the rotation of the panel. Authors say that the first one lacks on precision and self-control because the movement is fixed meaning that the system is relying on equations that may not take into account the weather conditions, i.e. if there are clouds or its raining and the second one requires a lot of initial costs since several photodiodes or sensors are to be installed in each panel to make it light-dependable. The authors suggest that there has to be an algorithm that can overcome those inefficiencies and explain the basis of the assumption (based on genetics) by saying that the solar thermal power plant is a population where heliostat angles survive on through collection compared with individuals, reproduction, and development. The amount of the energy that the tower is absorbing is the factor that affect the evolution of populations, the most-optimum focusing heliostat angle survives and GA (genetics algorithm) eliminates the others. In the design process, for this paper they come up with two improved control schemes. The first is the theoretical combined with the genetic algorithm (what they call Dichotomy combined with local area algorithm-D-LAGA) and the second one is the fit control scheme combined with genetic algorithm (GA-OFCS). The fit control scheme is an approach where each heliostat fitness is described as the energy being supplied to the tower from that specific device making it the strongest one. The developing stage of these algorithms includes some equations and theoretical approaches, but the report lacks on programming and construction details, what microprocessor was used, which sensors were placed and where, etc. As a conclusion, the paper shows that the efficiency of D-LAGA increases about 34.8% and GA-OFCS increases approximately 31.5% compared to fixed position generation. Statistics say that original composite control method efficiency increases about 33% to 35% compared to fixed-type power generation, what be assumed as that the original composite control is enough efficiency improvement but the fact that just some heliostats need sunlight sensors make the current paper a very good option for controlling the devices from the financial viewpoint.Another system control approach, but for photovoltaic panels is discussed in the next review. Mashohor, S, 2008. Evaluation of Genetic Algorithm based Solar Tracking System for Photovoltaics Panel. MalaysiaIn this work, the GA is proposed to give a solution to the little inefficiencies the two explained control methods have. The system described is a PV panel using 2 axis to locate itself in an ideal direction to harness the most quantity of energy from the sun. It is assumed that the system will require just one calibration, right after its installation, and after that, the algorithm will start looking for the best values of power generated and position itself. For this experiment to be carried out, a simulator is used, but details about its name or function are not provided.The position method relies in the fact that the tilt and azimuth angle are both ranged from 0 to 180 degrees, then certain position is a combination of those parameters. If the algorithm wants to find the best local, it has 180x180=32400 places to find it, fact that the authors describe as suitable for GA to explore. Its assumed that the maximum power value is 10 W (generated into a Look-Up table). Although this paper represents a good advance in the solar energy technology-development, the application for the current work is just how the variables of a system (sunlight values, motors placement, etc.) can be put together into a software in a way that it avoid control and programming inefficiencies. Haryanti, M, 2014. Development of Two Axis Solar Tracking Using Five Photodiodes. Electrical Power, Electronics, Communications, Controls, and Informatics SeminarThe paper describes how a solar tracking system was designed and built using an arrange of one panel, two axes of movement and five photodiodes to track the movement of the sun and make the system more efficient. The axes of movement are south-north and east-west. The actuators are one linear actuator and one conventional motor. The experiment uses five different sensors pointing at different directions as shown in the figure.

The purpose of the placement of the four external sensors is to monitor the sunlight from those directions and the fifth one in the middle is responsible for facing the panel up to the sun direction. The objectives of this work are to build the solar PV system and to apply a tracking scheme to it when using an artificial light with intensity similar to day light. It is considered important for this project because it shows the components necessary to build the system, such as the sensors (photodiodes to make it cheaper), holding frame, control and logical system, etc. In addition, it gives the experiment results showing the time response for the actuators and explain how it could be improved in the future. The work also shows a table that represents the energy loss due to the angle difference between the sun and the solar panel; it says that loss can go up to 65.8% when the angle difference is 80. The electronic components used in this paper are also a basis to study in order to understand the basic requirements. In example, authors used a microcontroller Atmega32 to control all components, having the values for the 5 different voltages, they are compared with the database of angles that are stored in the microcontroller. The actuators are going to turn on only if the elevation angle is more than 15 or if the azimuth angle is more than 7.81 and they are going to be activated until the panel face itself perpendicular to the sun. In order to control the movement of the actuators, the system function in this way: when the system is turned on, the program starts to run and the sensors are hit by the sunlight, the voltage is measured on each one and the program waits until all voltages are greater than 0.1 V (user experience). After that, the system compares the voltages of the sensors, if the sum of voltages 2 and 4 is greater than the sum of the other two, the lineal actuator turns on until a set point is achieved and activates timer on 1 hour in order to verify the new conditions in one hour. If not, the rotator turns on until the correspondent set point and activates a timer on 30 days, time in which new conditions have to be verified. This control scheme makes the sensor calibration the most important part of the experiment in order to avoid errors and inefficiencies. This is overcame by saving the data in the controllers memory and comparing it with the data obtained in every days operation. The experiment also measured the response time of the system to a new voltage value. The sensor in the middle is responsible for the movement of the system, if there is a high voltage difference, it means that the panel is placed far from where it is supposed to be, and then more time is required for it to position itself. Experimental results yields that for a 0.25 V value on that sensor, the response time was approximately 9 seconds, but for 2.5 V was almost 2 seconds. The authors conclude by saying that this system has a 5% of error in the tracking design (compared with theoretical approach). As a comment, it would have been valuable to show the power generated by the system and the area and materials of the panel because the voltage doesnt show significant information regarding the electricity generation.

Afarulrazi, A.B, 2011. Solar Tracker Robot using Microcontroller. 1. Malaysia: University Tun Hussein OnnThis paper is related more to the design of the tracking architecture and construction of the system and provides a good practical background to build similar systems because it shows the wiring diagrams (although there is one servomotor missing) and the final robot built. The proposed approach is a 2-axis tracker that relies on the signal of two LDR (Light Dependent Resistors) to provide information about where the panel is and where it needs to be. For knowing the current position of the robot, a digital compass is used. This compass provides the position information that will be compared with the LDR data and the microprocessor will correct the error. The microprocessor used is a PIC16F877A, the programming software is MPLAB IDE v8.30 and Fluke 1750 power quality recorder was used. The project uses three servomotors and a driver servo motor. One servomotor is used to move and position the LDRs. The arrange of the LDRs is a perpendicular one, assuming that when both LDRs are receiving the same amount of light, the position is correct (normal to the sun beam) and the microprocessor should assume that position to control the other three servo motors. Explanation of the sensors placement choice is shown in the following figure:

The authors split the robot in two parts: tracker and base. The servomotor for the LDRs is in the tracker and the other three are in the base. Limit switches are also used to prevent the robot to drive the panel to undesirable places, hitting objects or damaging itself.In the first placement, the robot will be placed heading to the north, meaning that the compass angle is 0 and the panel will track the light from east to west. If the north placement start to be inefficient due to the solar movement, the microprocessor runs a software that reads the current position of the tracker and if the angle from 1 up to 180 degrees, the microprocessor turns the servomotors counter clock wise, but if the angle is from 181 to 359, the servomotors are activated clockwise. The collected data belongs to the conditions on 22 March from 9 a.m. to 4 p.m. in Malaysia. Although is a highly valuable feature that the report includes all the information about voltage, current and power lectures for the panel and resistance for different conditions of the LDRs, it has to be taken into account that this data cannot be used to design or assess other devices in different places of the world at different days and hours. However, its suggested that every country collect that kind of data in order to encourage the investigation on solar energy.Finally, the authors show the comparing graph of the power generated by the fixed system and the tracking system, yielding that the power can increase up to 19.72% using the tracking device. The authors may have made a mistake by comparing the fixed system and the tracking system just with the energy generated, it means, they didnt take into account the energy used to power the servomotors as the equations in page 49 suggest.The report lacks on information about how the driver servomotor was controlled and which logical approaches were used, because the only information given is that when the LDRs are in a shadow, that driver is activated until they are illuminated again, but it doesnt mention what happens if the tracker is not able to find an illuminated spot. From first sight, seems that using 4 motors would consume more electricity than expected, making the overall efficiency decrease, this report could be changing precision for efficiency, meaning that maybe less precise devices may have a higher efficiency. It would have been useful to mention the area of the panel used in order to get more practical data about the amount of energy that can be harnessed with certain amount of area, fact that is almost crucial when evaluating a project financially. In addition, the cost of making the robot (base, sensors, compass, microprocessor, etc.) could have serve as guide to future researchers when evaluating the initial investment. Mahmood, O.T, (2013). Programmable Logic Controller Based Design and Implementation of Multiple Axes Solar Tracking System. In The First International Conference of Electrical, Communication, Computer, Power and Control Engineering. Iraq, December 17-18, 2013. Hawija: Dept. of Electrical TechnologiesThe present work represents a theoretical-empirical approach to the tracking issue since it uses the solar-movement equations to drive a solar panel with the help of a Siemens LOGO! Programmable Logic Controller (PLC). The project was about designing, building and evaluating the system and its performance using two axis, one for vertically daily tracking and horizontal seasonal tracking, while comparing the tracking option to the fixed one. The project differentiates itself from the rest in the fact that it doesnt use sunlight sensors to add precision to the tracking task, it relies entirely in the theoretical equations. At first, the author describe the process of construction of solar cells from the theoretical viewpoint but not making a selection of materials or dimensions. The author mentions and discuss the benefits of the tracking techniques available and select the open loop one based on the assumption that a PLC can run and execute the entire tasks (controlling the motors, running the programs, etc.) without human intervention and taking into account that sunlight sensors can have errors during dusty and rainy days. A complete study of the basic earth-sun angles is carried out in order to understand how the PLC is going to know where to move the panel, explaining the concepts of latitude, hour angle, declination angle, etc. and their application into the tracking system. The calculation of the angles was made using Matlab 7.11 by introducing the equations in the software and plotting them for a specific day and time. From Matlab, the results are taken to the PLC and stored there making it run using various hourly, daily, monthly, and yearly timers. This means that if the PLC reads that today is the day 30th of June, it will change the program the next day. PLC operation only needs to run the specified programs and to provide the output signals to the motors, this is why the system is called open loop, because it doesnt need a feedback. In order to make the control of the panel easy, the DC motors are able to run clock and counter clockwise. The PLC program is done by using Soft Comfort software (manufacturer software to configure the device) in a computer; this program is sent to the PLC memory later. The program is configured in a four parts block; the parts are forward horizontal daily tracking per one month, backward horizontal daily tracking, forward vertical daily tracking per one month and backward vertical daily tracking per one month. According to the description, the system operation is as follows:1. Initialization of the system.2. Calculation of the required sun angles for vertical and horizontal axis.3. Set the time of the blocks in the PLC according to the required position.4. Sending command from the yearly and weekly timers to the motors. 4*. At the sunrise, start the horizontal tracking by sending the signal to the motor. 5. At the sunset, the motors receive a signal to go to the position required for the next day.* The steps happen at the same timeThe results obtained during the 20th of April at 34 latitude apparently show that the power obtained with the tracking device was 38% higher than the obtained with the fixed one, but again, the paper doesnt show if the author took the power to generate the motors into account. It would have been useful to show the area of the panel and the cost of the project in the report for the reasons discussed earlier. The usage of a PLC in this kind of devices make them robust and reliable. Further studies would have to be done in order to assess the need of that robust system, it means, that maybe a microprocessor such as an arduino one would have been cheaper and enough to run that kind of software.The work is highly useful since it gives the coding necessary to program the PLC in a KOP language. Another useful feature is that it explains the basic literature of the main problem (tracking the sun) and takes the project step by step to make it more understandable while showing how easy is to build such a system. Kassem, A, 2011. A Microcontroller-Based Multi-Function Solar Tracking System. Lebanon: Notre Dame University Louaize.This work can be considered a highly practical one since it explains how the control and the hardware of the tracking system was made. The project aims were to design and build the complete solar energy tracker and to compare the results with the fixed ones regarding the efficiency. One important issue that the report overcomes is the powering of the system, the designed tracker has its own battery and all elements are powered by the electricity produced. This represents an advantage compared to previous discussed works that didnt mention that and can be assumed that the power for the motors and sensors is provided with the use of an external source. The tracker uses the sunlight tracking approach where 3 photo resistors are placed on the panel in order to provide the feedback signal to the closed loop control. The actuators are stepper motors and they receive the signal from a microcontroller that processes the signals of the sensors and provides information about where is more efficient to move the panel to. The operation of the tracker is configured as follows:1. Place the panel in the initial position (0, 0, 0)2. Using the photo resistors, the maximum value of sun light is found and saved3. At this point, the current is measured4. If the value of the current is less than a threshold value, the system waits 30 minutes and goes to the step 2; but if the value is greater, it goes to step 5.5. The tracker turns the panel 3.5 left and the current is measured again, if the current is greater than the actual one, the panel rotates until it finds the maximum value; but if its not greater, it turns right and repeat the same process. 6. If the tracker finds a maximum current point, it turns the other stepper motor in order to find the maximum current in the Z axis and wait 45 minutes.7. Store the coordinates found.At the end, the process from point 2 is repeated.Its not pointed why the times 30 and 45 minutes are used for waiting and not other values.The paper comes up with the conclusion that the tracking efficiency is about 64% greater compared to the fixed arrange and table the current values for different hours in the day. A good feature of this tracker is that it has a LCD screen to read what is happening in the system and those data can be transmitted to control a remote system. Author doesnt mention the place and the data when the data was taken. As discussed these are important parameters to measure the effectiveness of the experiment because what can be considered good results in certain place, could be poor results in another one.In page 2, the author mentions that a raise of 95% of efficiency in the electricity generation can be expected in comparison with the fixed arrange. As known, such improvement is not actually possible and that comment could have been a writing mistake. In page number 3, it is mentioned that system consumes little power but the value of the power is not given and could have been a very good reference for future research.As a comment, a conventionality should be applied, since different projects name the process variables with different names, i.e., sometimes the axes are called West-East, XY, depending on what the author wants with the project. This can confuse the researchers in this field. Its proposed the usage of XYZ worldwide, where X is the east-west direction, Y is the north-south and Z is the vertical coordinate. Fei, Y, (2012). Design of the Solar-driven Module on Modular Mobile Robot. In 19th International Conference on Mechatronics and Machine Vision in Practice (M2VIP). New Zealand, 28-30 th Nov, 2012. Auckland: University Auckland. 4.A tracking robot is designed under the scheme of the usage of LDR sensors. The system has 2 degrees of freedom and uses a control system based on the signal from 25 LDRs to move the two motors. It has to be taken into account that the system doesnt intent to generate electricity, the report cares more about the construction and the tracking capabilities than the current or voltage results, since no power generation results are provided. A flashlight is used to assess the robot abilities to track the light and the authors describe the system as efficient to track the sun but results about how quickly the system responds to a change in the position of the light source are not shown.Authors explain what components were used and the purpose of each one. Wiring and control diagrams are provided in order to understand the system better and to encourage the research in this field. This work can be taken as an investigation in the half of the tracking devices, since it discuss just the tracking of the light without caring about electricity generated. This may lead to the situation that diffuse radiation may not be taken into account in some places where it is highly important since the tracker is just looking for the sun, but not looking for the energy concentration points, so, for complementing this work in the energy generation field, frequent measures should be carried out to fin those points.