Introduction

Solar distillation is a sustainable and environmentally friendly method of producing clean water using solar energy. However, conventional solar stills often operate at lower efficiencies because they remain fixed and cannot continuously utilize the maximum available solar radiation throughout the day.

The primary objective of this project is to develop a solar still capable of automatic sun tracking. By continuously aligning the system with the Sun, greater solar energy can be captured, resulting in higher water temperatures, increased evaporation rates, and improved distilled water production.

System Concept

The proposed system combines a solar still with a parabolic trough solar concentrator.

The parabolic reflector concentrates incoming solar radiation onto a focal line, increasing the thermal energy available to the solar still. Higher temperatures promote faster evaporation of water, thereby improving the overall productivity of the distillation process.

To ensure maximum solar energy collection throughout the day, the concentrator must continuously face the Sun. Therefore, the development of a smooth and reliable tracking mechanism became a key part of the project.

Working Principle

The system consists of two major components:

1. Parabolic Trough Solar Concentrator
2. Solar Still Unit

The parabolic trough reflector concentrates incoming solar radiation onto a focal line where the receiver is placed. Heat collected at the receiver is transferred to the water inside the solar still, increasing its temperature and accelerating evaporation.

The generated water vapor rises and condenses on the cooler transparent cover of the still. The condensed droplets then flow into a collection channel and are collected as distilled water.

Disassembly and Structural Assessment

To improve the existing design, the entire structure was disassembled and carefully inspected. This process helped identify mechanical limitations and areas requiring modification before implementing the tracking mechanism.

The assessment revealed that the rotational support arrangement required improvement to achieve smooth movement. The disassembly process also provided an opportunity to strengthen structural members, improve alignment, and redesign critical mounting points.

Redesign of the Rotating Structure

To overcome the friction problem, the original rotational arrangement was removed and redesigned.

The modified system involved:

• Welding mounting bolts onto the reflector support structure.
• Installing pillow block bearings on the structure.
• Passing a steel pipe through the bearings to act as the rotational shaft.
• Mounting the shaft securely onto the base frame.

This new arrangement provided proper support to the reflector while allowing smooth rotational movement with significantly reduced friction.

Redesign of the Rotating Structure

Several transmission mechanisms were evaluated for automating the solar parabolic trough, including direct gear drive, chain drive, and cable-driven systems. Considering fabrication simplicity, cost, ease of maintenance, and positioning accuracy, a belt-driven winding mechanism was selected.

In the proposed design, a belt is attached to both ends of the parabolic trough. The two free ends of the belt are wound in opposite directions around a drum mounted on the shaft of a stepper motor. During operation, the stepper motor simultaneously winds one side of the belt while unwinding the opposite side. This creates equal and opposite tensile forces that rotate the parabolic trough about its central axis. The transmission arrangement enables smooth bidirectional rotation while maintaining continuous belt tension.

The stepper motor is mounted at the base of the supporting frame to reduce the load on the rotating structure and simplify maintenance. The belt connecting the motor drum and the parabolic trough is inclined at approximately 45° with respect to the horizontal plane, allowing the motor to be positioned conveniently within the support structure while transmitting the required motion to the collector.

Since the parabolic trough is balanced about its rotation axis, the motor is primarily required to overcome bearing friction, transmission losses, and external disturbances such as wind rather than continuously supporting the collector weight. This significantly reduces the motor torque requirement.

Experimental Torque Evaluation

To estimate the torque required for rotating the collector, an experimental test was conducted.

A 2 kg mass was suspended at one end of the parabolic trough at a distance of 1.1 m from the rotation axis. The applied load was sufficient to rotate the balanced collector, indicating the maximum torque required to initiate rotation.

The applied force is$$F=mg$$where

• $m=2$m=2 kg
• $g=9.81\;m/s^2$

Hence,$$F=2\times9.81=19.62\;N$$

The corresponding torque about the rotation axis is$$\tau=F\times L$$where

• $L=1.1\;m$

Therefore,$$\tau=19.62\times1.1$$$$\tau=21.58\;N\cdot m$$$$\tau\approx220\;kg\cdot cm$$This value represents the experimentally determined torque required to rotate the collector.

Motor Torque Calculation

The selected transmission mechanism uses a winding drum mounted on the motor shaft.

The design parameters are

• Drum radius = 25 mm = 0.025 m
• Belt inclination = 45°

Because the belt is inclined at 45°, only the component of belt tension perpendicular to the lever arm contributes to rotation.

The required belt tension is calculated as$$T=\frac{\tau}{L\sin45^\circ}$$

Substituting the known values,$$T=\frac{21.58}{1.1\times0.707}$$$$T=27.75\;N$$

The required motor torque is therefore$$\tau_{motor}=T\times r$$

where

• $r=0.025\;m$r=0.025m

Hence,$$\tau_{motor}=27.75\times0.025$$$$\tau_{motor}=0.694\;N\cdot m$$

Converting into kg·cm,$$0.694\times10.197$$$$\tau_{motor}=7.08\;kg\cdot cm$$

Safety Factor

Although the calculated motor torque is approximately 7.1 kg·cm, the actual operating conditions include

• bearing friction,
• belt friction,
• belt elasticity,
• wind loading,
• starting and stopping inertia,
• manufacturing tolerances.

Therefore, a safety factor of 3 was adopted.

The required motor torque becomes$$\tau_{required}=7.08\times3$$$$\tau_{required}=21.24\;kg\cdot cm$$

13/07/2026 – 20/07/2026

Motor Selection, Control System Development, and Initial Testing

Based on the torque analysis and the experimental evaluation, an appropriate NEMA 23 stepper motor was selected to satisfy the calculated torque requirement for the solar tracking mechanism. The motor was chosen with an adequate safety margin to compensate for frictional losses, transmission inefficiencies, and external disturbances such as wind.

After selecting the motor, the mechanical transmission system was assembled and the initial prototype was fabricated. The stepper motor was integrated with the winding drum mechanism, where a belt attached to both ends of the parabolic trough is simultaneously wound and unwound to rotate the collector about its central axis.

The electrical system was then developed by interfacing the stepper motor with the ESP32 microcontroller through a suitable stepper motor driver. Initial testing was carried out to verify the communication between the microcontroller and the motor driver, evaluate the motor’s rotational performance, and ensure smooth bidirectional movement of the parabolic trough. The prototype successfully demonstrated controlled angular movement of the collector according to the commanded position.

Following the successful hardware integration, the focus shifted to the development of the solar tracking algorithm. An astronomical position algorithm was studied to determine the Sun’s position using date, time, latitude, and longitude. The algorithm calculates the solar azimuth and elevation angles corresponding to the geographical location and current time.

Based on the calculated solar position, the control software continuously determines the desired orientation of the parabolic trough and commands the stepper motor to adjust the collector angle accordingly. This enables the collector to remain aligned with the Sun throughout the day, ensuring that the maximum possible solar radiation is concentrated at the focal point of the parabolic trough, thereby improving the thermal efficiency of the solar cooker.

The developed system combines the mechanical transmission mechanism, stepper motor control, and real-time solar position calculations to achieve fully automatic and accurate solar tracking. Further work includes long-term outdoor testing, optimization of the tracking algorithm, and evaluation of the system’s thermal performance under varying environmental conditions.

21/07/2026 – 27/07/2026

Initial experiments were conducted to evaluate the rotational performance of the parabolic dish and verify the synchronization between the microcontroller, motor driver, and stepper motor. The tests confirmed that the motor successfully rotated the collector according to the commanded tracking angle. However, during continuous operation, it was observed that the belt gradually lost tension as the dish rotated. This reduction in belt tension caused the belt to slip and partially disengage from the winding drum, resulting in inaccurate positioning and unreliable control of the parabolic trough.

To overcome this issue, the transmission mechanism was redesigned by incorporating two idler pulleys into the belt path. The idler pulleys maintain constant belt tension throughout the entire range of motion while increasing the belt’s contact with the winding drum. This modification prevents belt slippage, ensures continuous engagement between the belt and the drum, and improves the transmission of motion from the stepper motor to the parabolic dish.

Following the redesign, the modified transmission system was reassembled and tested. The improved mechanism demonstrated smooth and reliable bidirectional rotation of the parabolic trough, with the dish accurately following the angular commands generated by the control algorithm. The addition of the idler pulleys significantly enhanced the stability, positioning accuracy, and overall reliability of the automatic solar tracking system, making the mechanism suitable for extended outdoor operation.