Solar-Powered Glass Tumbler for Cape Maclear, Malawi

Design, Maintenance, Operation, and Results

DOI

Contributors

1 Introduction

Cape Maclear is a rural Malawian town located within a UNESCO World Heritage Site, which has attracted a lot of tourism and growth in the last 20 years. This has led to a unique waste challenge: an abundance of non-returnable glass bottles that are not part of a deposit system. As shown in Figure 1, this broken glass creates sharp fragments that pose significant injury risks to residents, tourists, and wildlife.

Figure 1: Accumulation of broken glass on the beach

Because industrial recycling is not economically or technically feasible in this location, this project utilizes glass tumbling to grind away sharp edges. This process produces smooth “sea glass,” which is safe for reuse in construction, landscaping, and jewelry. The transformation from sharp fragments to smooth glass is illustrated in Figure 2.

Figure 2: Glass fragments before and after the tumbling process

2 Tumbler Overview

The machine is a standalone, solar-powered rotating drum system designed to process batches of glass. An overview of the full assembly can be seen in Figure 3.

Figure 3: Overview of the glass tumbler assembly

The system operates through five core stages:

  1. Solar Harvesting: A 260 W solar panel generates DC electricity from sunlight.
  2. Power Regulation: An electronics box containing a DC-DC converter and PWM motor controller stabilizes the variable solar voltage to a consistent 24 V.
  3. Mechanical Drive: A 350 W 24 V DC motor converts electrical energy into rotational motion.
  4. Power Transmission: A bicycle chain and sprocket system transmits torque to a shaft attached to the rear of the drum.
  5. Rotating Drum: A 19 kg LPG cylinder serves as the tumbling vessel.

2.1 Key Specifications

  • Capacity: The drum has a volume of 38.5 l and can processes 20 kg of glass per batch (typically requiring 8–10 hours of tumbling for the best finish). It operates with the drum being around half-full.
  • Operating Speed: The drum is typically run at 40 RPM but can reach speeds up to 57 RPM.
  • Direct Solar (Battery-Free) Design: The system operates without a battery buffer, making the motor’s performance directly dependent on real-time solar irradiance. When sunlight is abundant, the tumbler maintains its preset operating speed. If irradiance drops—due to cloud cover, panel shading, or a suboptimal angle of inclination—the system slows down accordingly.

3 Part List

The total cost to manufacture the system is approximately $581.10. A detailed breakdown of the components, specifications, and procurement origins is provided in the table below.

Item Specification Origin Qty Unit (\() | Total (\))
Drivetrain 56.50
DC Motor 350 W CH 1 48.00 48.00
Sprocket Bicycle 410, 48T MW 1 5.30 5.30
Chain 1/2” x 1/8” x 114 L MW 1 3.20 3.20
Electronics 123.00
DC-DC Converter 50 A, 1000 W CH 1 41.00 41.00
PWM Controller 10 – 55 V CH 1 22.00 22.00
Circuit Breakers 25 A CH 3 9.00 27.00
Ring Ferrules 3, 4, 5 mm ID CH 20 0.13 2.50
Fuses 10 A CH 2 0.25 0.50
Tachometer Model BC 120 CH 1 20.00 20.00
Volt/Amp Meter 0–100 V, 50 A CH 2 5.00 10.00
Finishing 85.10
Enclosure 350 mm x 250 mm x 200 mm MW 1 6.70 6.70
Motor Cover 460 mm x 350 mm x 250 mm MW 1 6.60 6.60
Lid Seal 10 mm x 12 mm CH 1 16.00 16.00
Surface Treat. 2K Paint/Red Oxide MW 1 55.80 55.80
Housing 222.80
Gas Cylinder 19 kg (300 mm ID) MW 1 78.90 78.90
Steel Beam (L) 80 mm x 40 mm x 2 mm (6 m) MW 1 44.50 44.50
Steel Beam (S) 30 mm x 30 mm x 2 mm (6 m) MW 1 23.70 23.70
Steel Sheet 460 mm x 200 mm x 5 mm MW 1 9.20 9.20
Bearings 25 mm ID CH 1 0.00 0.00
Shaft 25 mm OD CH 1 0.00 0.00
Steel Offcuts Various Dimensions MW 1 8.90 8.90
Castor Wheels Ø 100 mm MW 2 2.10 4.20
Small Wheel 50 mm x 19 mm CH 1 4.00 4.00
Toggle Clamp 150 kg Capacity CH 4 5.00 20.00
Lid Metal 400 mm x 400 mm x 3 mm MW 1 7.90 7.90
Fasteners M6, M8, M10 MW 1 10.30 10.30
Welding Rods Ø 2.5 mm MW 1 11.20 11.20
Solar PV 93.70
Solar Panel 260 W MW 1 69.70 69.70
Connectors MC4 Standard CH 6 4.00 24.00
GRAND TOTAL $581.10

COO Key: MW = Malawi (Local Procurement), CH = Switzerland (Imported)