The increasing popularity of renewable sources of energy, in the energy deficient world has made a remarkable contribution in shortening the energy gap up to a certain extent. The awareness regarding global warming, CO2 emissions (greenhouse gases), peaking of most oil reserves and impending climate change are critically driving the adoption of solar photo voltaic as a sustainable renewable and eco friendly alternative. Solar panels are the most favorite among the entire renewable sources, because of the abundance of solar energy and its free and easy availability. In India with about 300 clear sunny days in a year, the daily average solar energy incident over India varies from 4 to 7 kWh/m2 with about 1500–2000 sunshine hours per year, depending upon location. While installing the PV panels appropriate installation design such as orientation, exposure, sun tracers to maximise solar insolation can potentially ensure sustained yield (electricity). However, the panels are vulnerable to often overlooked, on site omnipresent practicalities such as deposition of dust, bird droppings and water stains which significantly degrade the efficiency of the solar installations. Dust is a lesser acknowledged factor responsible for decreasing the efficiency of PV installations. As we know solar panels are left under open sky in dusty environment. When not cleaned for a long duration of time (from few days to many months), the dust gets accumulated on the front surface of the panels which block the direct incident light from the sun. Thus it is significantly important to clean the panels at regular intervals of time for maintaining a constant efficiency of the panels.
Figure 1: Dust accumulated Solar Cooker (Photo Courtesy- Gujarat Institute of Solar Energy (GISE), Gandhinagar)
Figure 2: Dust prone solar water heater (Photo Courtesy- Gujarat Institute of Solar Energy (GISE), Gandhinagar)
Figure 3: Dust laden PV panel (Photo Courtesy – Gujarat Institute of Solar Energy (GISE), Gandhinagar)
Experiment on Effect of Dust on PV Panels
According to an experiment conducted on a PV panel to study the effect of dust for time duration of 8 weeks in the month of January to February. The radiation measured was during the peak solar insolation hours from 11AM to 2PM. The power output per hour initially was 1.98kWh and at the end of 8th week it was 1.49kWh, the total loss in power was of 0.49kW in duration of 1 hour. If we consider the losses to be steady taking an assumption of same operating environment throughout the year, this power loss can range up to 4,292.4kW (approx.) for 1 year. The amount of this loss is approximately equal to 4,292.4*4.34 Rs, if we consider the tariff rate of solar energy per unit as 4.34Rs. Thus this experiment leads to the conclusion that a regular cleaning of the installed panel can help us to save the power losses to a great extent, which otherwise if neglected can result into a huge monetary loss.
Figure 4: Table showing the experiment results of dust affecting the power output of PV panel
Fig.5 Graph showing the experiment results Power Output (kWh) vs. Time (Week)
Design & Development of the Cleaning Mechanism
Solar Panels are generally cleaned by human interference but it is quite tedious as well as time consuming and ultimately is not much effective. Hence, designing and developing an automated system for cleaning the panels is significantly imperative to be implemented. The figure below shows the block diagram of the proposed mechanism. The components highlighted in the diagram are micro controller (L293D-ARDUINO), DC Motor with a motor driver, solid state relay, RTC (real time clock). L293D is a typical Motor driver or Motor Driver IC which allows DC motor to drive on either direction. L293D is a 16-pin IC which can control a set of two DC motors simultaneously in any direction. It means that we can control two DC motor with a single L293D IC. Dual H-bridge Motor Driver integrated circuit (IC). It works on the concept of H-bridge. H-bridge is a circuit which allows the voltage to be flown in either direction. As we know voltage needs to change its direction for being able to rotate the motor in clockwise or anticlockwise direction, Hence H-bridge ICs are ideal for driving a DC motor. In a single L293D chip there are two h-Bridge circuit inside the IC which can rotate two dc motor independently. Due its size it is very much used in robotic application for controlling DC motors.
When supply is given to the micro controller it drives the motor with the help of the motor driver circuit. The motor starts rotating in the forward and backward direction as commanded by the micro controller using rack & pinion linear mechanism. The micro controller is a timer based and can be programmed as per the desired interval of time required for cleaning. Therefore it is mandatory to determine the amount of dust which will be accumulated on the panels at a specific location prior installing the system and according to the site survey results the interval for cleaning the module can also be programmed or changed. The cleaning interval can also vary with respect to the seasons along with the geographic locations.
Fig. 6 Block Diagram of the cleaning mechanism
Design of the system using the software Proteus
Figure 7 shows 3 switches called HOME, MIDDLE AND EXTREME. These three switches indicate the portions of the PV Panel to be cleaned. HOME and EXTREME stands for the two edges of the PV panel and MIDDLE indicates the intermediate part of the panel. The IC L293D Arduino is programmed and connected to these 3 switches which act as an input to it. L293D is a typical Motor driver or Motor Driver IC which allows DC motor to drive on either direction. L293D is a 16-pin IC which can control a set of two DC motors simultaneously in any direction. It means that we can control two DC motor with a single L293D IC. The pins numbered from A0 to A5 are the analog pins whereas pins 0 to 13 are the digital pins. The switches HOME, MIDDLE & EXTREME are connected to the analog inputs of the Arduino i.e. A0, A1, A2 respectively. The digital pin no 8 and 9 of the Arduino are acting as the input to the motor driver. The pin 8 & 9 are given to the pin no. 2 and 7 of the motor driver circuit and the output pins of motor driver i.e. pin no.3 and 6 is given to the motor. The PROTEUS simulation is provided mainly to understand the motor mechanism. When pin no. 8 of two inputs is made HIGH and another is LOW pin no. 9 then the motor will run in forward direction (i.e. from HOME to EXTREME). If the delay is given for some seconds then the motor will stop automatically without giving any command and if both the pins are made LOW then the motor will force stop. Now if the inputs are reversed i.e. pin no.8 is LOW and pin no.9 is HIGH then the motor will rotate in reverse direction (i.e. EXTREME to HOME).
Figure 7: PROTEUS Simulation of the cleaning mechanism
Figure 8: 3D Model of the cleaning mechanism
The 3 D model (Fig.8) shows the schematic of the actual model. The model is designed with rack and pinion gears which are used to convert rotation into linear motion. The flat, toothed part is the rack and the gear is the pinion. A piston coaxial to the rack provides hydraulic assistance force, and an open centered rotary valve controls the assist level. A rack and pinion gears system is composed of two gears. The normal round gear is the pinion gear and the straight or flat gear is the rack. The rack has teeth cut into it and they mesh with the teeth of the pinion gear. A ring and pinion gear is the differential’s critical point of power transfer. A ring and pinion gear set is one of the simplest performance modifications that can be performed on a vehicle. The most common reason to change ring and pinion ratios from the original equipment is to retain power when bigger tires are put on a vehicle. The torque can be increased by a ratio change when there is enhanced pulling or higher take off power from a dead start. A well designed mechanism such as the rack and pinion gears save effort and time. Rack and pinion gears provide a less mechanical advantage than other mechanisms, but greater feedback and steering sensation. A rack and pinion gear gives a positive motion especially compared to the friction drive of a wheel in tarmac. The rack and pinion is also used in railway, a central rack between the two rails engages with a pinion on the engine allowing a train to be pulled up very steep slopes. Rack and pinions gears are commonly used in the steering system of cars to convert the rotary motion of the steering wheel to the side to side motion in the wheels. The steering wheel rotates a gear which engages the rack. As the gear turns, it slides the rack either to the right or left, depending on which way the wheel is turned. Rack and pinion gears are also used in some scales to turn the dial that displays a weight. This rack & pinion is driven by the supply which it is connected to the sprinkler. The sprinkler sprinkles the water on the panels which is cleaned by the brushes moving on the panels. The water for the sprinkler is drawn from a water reservoir but if this system is installed at canal top solar plants then no added water reservoir is required as it can draw water from the canal for cleaning purpose.
Figure 9: Actual connections of the Arduino with the motor driver
Thus, the system developed is very easy to install, it can be used for standalone PV systems. It is fully automated which saves time and human labour. The motor can be driven from the PV panel supply as well which results in power saving. The system can be programmed as per the location of the PV panels, in terms of interval of time of cleaning needed. At the end it would be concluded that don’t let the dirty panels contribute to the power loss and economic loss, which may act as a hindrance in the expected contribution in the development and growth of India in long run.
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