How to Build a Solar Fan-Assisted Cone TLUD
This guide shows how to build a solar fan-assisted cone TLUD for biomass like converting coffee husk into high-quality biochar using locally available materials. The design is low-cost, off-grid, and optimized for clean combustion, higher char yield, and consistent performance with variable husk quality.
Materials and Tools
Materials
- 200-liter steel drum
- Mild steel sheet for cone and grate
- Small steel pipe (air inlet)
- Small steel cylinder (25 cm diameter)
- 12-volt DC fan or blower
- 100-watt solar panel
- Basic wiring and switch
- Welding rods
Tools
- Angle grinder
- Welding machine
- Drill
- Measuring tape
- Compass or improvised pivot (nail + string)
Step 1: Prepare the Drum
- Take a 200-liter steel drum.
- Cut off and remove the top lid completely.
- Measure 10–15 cm from the bottom and cut around the drum.
- You now have a short cylindrical section with both ends open.
Step 2: Make the Cone
Drawing the cone layout
- Lay a steel sheet flat.
Mark a center pivot point.
Draw two concentric arcs:
- Outer radius: 60.56 cm
- Inner radius: 26.56 cm
From the center, mark a sector angle of 169.41 degrees (or measure 179.07 cm along the outer arc).
Draw the two radial edges.
Cutting and forming
6. Cut along both arcs and the two radial lines.
7. Roll the sheet so:
- Inner arc becomes a 25 cm opening
- Outer arc becomes a 57 cm opening
- Weld the radial edges together to form the cone.
Step 3: Attach the Cone
- Weld the wide opening of the cone to the bottom of the drum section.
- Ensure the cone is centered and sealed properly.
Step 4: Build the Lower Air Chamber
Make a small steel cylinder:
- Height: ~20 cm
- Diameter: 25 cm
Weld a circular steel plate to close one side.
Weld the open side of this cylinder to the bottom opening of the cone.
Step 5: Add the Air Inlet
- Cut a 6 cm diameter hole on the side of the small cylinder.
- Weld an angled steel pipe (15–20 cm long) to this hole.
- This pipe will connect to the fan or blower.
Step 6: Make the Grate
- Cut a circular steel plate, 25 cm diameter.
- Drill holes 5–7 mm in diameter.
- Space holes 1–2 cm apart evenly.
- Place this grate above the air chamber to support the fuel.
Step 7: Fan and Solar Setup
- Connect a 12-volt fan to the air inlet pipe.
- Power the fan using a 100-watt solar panel.
- Include a simple switch or airflow bypass for adjustment.
- Adjust airflow by allowing excess air to escape from the upper inlet pipe.
Step 8: Operation Tips
- Use clean, dry coffee husk.
- Ignite from the top.
- Adjust airflow carefully:
- Too little air → smoke, slow burn
- Too much air → lower char yield
- Allow the unit to cool fully before removing char.
Final Notes
- This cone-based TLUD design was developed after field comparison with a standard flat-bottom drum TLUD, which showed lower char yield, incomplete carbonization at the base, and higher sensitivity to airflow. The internal cone improves airflow distribution, increases biochar yield, and reduces smoke while remaining low-cost and locally buildable.
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