S-Type Vertical Axis Wind Turbine (Savonius Turbine): Simple, Reliable, and Effective for Low Wind Speeds

As renewable energy technologies diversify to meet the needs of rural areas, urban rooftops, and low-wind-speed regions, the S Vertical Axis Wind Turbine—commonly called the Savonius turbine—has emerged as a cost-effective and mechanically simple solution. Recognized for its distinctive "S" or “half-barrel” shape, the S-type turbine is ideal for small-scale applications, off-grid power, and low-maintenance energy systems.

While it’s not as efficient as lift-based wind turbines (like Darrieus or HAWTs), the Savonius turbine’s high starting torque, omnidirectional operation, and robust construction make it a dependable choice where simplicity, safety, and reliability are prioritized.

What Is an S-Type Vertical Axis Wind Turbine?

The S Vertical Axis Wind Turbine, or Savonius turbine, is a drag-based wind turbine. It uses the force of wind pushing against curved blades to generate rotation. When viewed from above, the rotor resembles the letter “S”.

This design is most effective in:

1. Low wind speed areas (2–6 m/s)
   
   

2. Rooftops, farms, boats, and remote installations
   
   

3. Systems where low noise, safety, and ease of maintenance are crucial
   
   

How Does It Work?

The S-type turbine works on the principle of differential drag. Here's how:

1. The concave (scooping) side of the blade captures more wind and creates high drag.
   
   

2. The convex (back) side deflects wind and creates less drag.
   
   

3. This difference in force between the two sides causes the rotor to turn.
   
   

4. The central vertical shaft rotates with the blades, transmitting torque to a generator or mechanical device.
   
   

✅ Key Note: Unlike lift-based turbines, which require higher speeds to function efficiently, drag-based turbines like the S-type self-start even in light winds.

Design and Construction

Basic Components:

1. Rotor Blades
   
   

   1. Usually 2 or 3 blades.
      
      

   2. Shaped like half-cylinders (like split drums or barrels).
      
      

   3. Can also use helical or spiral blades for smoother torque.
      
      

2. Vertical Shaft
   
   

   1. Transmits rotation from rotor to generator.
      
      

3. Mounting Frame or Tower
   
   

   1. Fixed structure holding the turbine above ground level or on rooftops.
      
      

4. Generator or Load System
   
   

   1. Converts mechanical energy into electrical energy or performs a task (e.g., water pumping).
      
      

Materials Used:

1. Blades: Aluminum, steel, PVC, fiberglass, or even recycled materials.
   
   

2. Shaft and supports: Galvanized steel or stainless steel.
   
   

Advantages of the S-Type VAWT

✅ Self-Starting at Low Wind Speeds

1. Operates effectively in wind speeds as low as 2 m/s.
   
   

2. No need for external power to initiate rotation.
   
   

✅ Omnidirectional Operation

1. Works regardless of wind direction—no yaw mechanism required.
   
   

✅ Simple Construction and Low Cost

1. Easy to build, even with basic tools or locally sourced materials.
   
   

✅ Safe for Urban and Public Spaces

1. Slow blade rotation makes it less dangerous to people, animals, and birds.
   
   

2. Low noise, suitable for noise-sensitive areas.
   
   

✅ Versatile Applications

1. Can power small devices directly (lights, sensors, pumps) or charge batteries.
   
   

Limitations of the S-Type VAWT

❌ Low Efficiency

1. Converts only about 10–17% of wind energy into usable power (compared to 35–45% for lift-based turbines).
   
   

2. High drag limits top speed and output.
   
   

❌ High Wind Load

1. Experiences strong lateral wind forces; requires robust support and anchoring.
   
   

❌ Not Suitable for Utility-Scale Generation

1. Not practical for megawatt-scale wind farms.
   
   

Types of Savonius Turbines

Type

Description

Notes

Classic S-Type

Two half-cylinder blades forming an "S" shape

Simple, widely used

3-Bladed Savonius

Three scoops arranged at 120°

Smoother rotation, slightly better efficiency

Helical Savonius

Spiral-shaped blades

Reduces torque ripple and vibration

Stacked Savonius

Multiple rotors on a single shaft

Increases power without increasing footprint

Applications of S-Type VAWTs

🏠 Residential and Urban Energy

1. Rooftop installations for lighting, battery charging, or supplementing solar panels.
   
   

🚜 Agricultural Use

1. Water pumping for irrigation or livestock.
   
   

2. Powering fence energizers or storage units.
   
   

🚤 Marine and Coastal Use

1. Mounted on boats or piers.
   
   

2. Performs well in gusty, variable wind environments.
   
   

🌐 Remote and Off-Grid Sites

1. Telecom towers
   
   

2. Weather stations
   
   

3. Emergency shelters
   
   

🎓 Education and Demonstration

1. Excellent for science and engineering projects due to simple construction and visual operation.
   
   

Comparison: S-Type vs. Other Wind Turbines

Feature

S-Type VAWT

H-Type VAWT

HAWT

Startup Wind Speed

Very low

Moderate

Moderate

Efficiency

Low

Medium

High

Complexity

Very low

Medium

High

Noise

Low

Low

Medium–High

Directional Sensitivity

Omnidirectional

Omnidirectional

Needs yaw control

Maintenance

Easy

Moderate

Difficult (tall towers)

Best Use Case

Small-scale, low wind

Medium-scale urban

Large-scale wind farms

Future Developments and Innovations

🔧 Hybrid Designs

1. Integration of Savonius turbines with Darrieus rotors to combine high torque and better efficiency.
   
   

🌐 IoT Integration

1. Sensors and controllers for real-time monitoring and performance optimization.
   
   

🧪 Advanced Materials

1. Lightweight composites for increased efficiency and reduced wear.
   
   

⚡ Microgrid and Hybrid Systems

1. Coupled with solar, batteries, and smart inverters to power homes or small businesses.
   
   

Do-It-Yourself (DIY) and Open-Source Potential

One of the biggest attractions of the S-type turbine is its accessibility for DIY enthusiasts, educators, and communities.

Example DIY Materials:

1. Plastic barrels
   
   

2. PVC pipes
   
   

3. Scrap metal or aluminum sheets
   
   

4. Bicycle hubs for the rotor assembly
   
   

⚠️ Always ensure balance, secure mounting, and electrical safety in DIY systems.

Conclusion

The S-type vertical axis wind turbine, or Savonius turbine, offers a compelling solution for locations where wind speed is low, maintenance must be minimal, and simplicity is key. While it lacks the efficiency of more advanced turbine designs, its strengths lie in self-starting ability, ruggedness, and ease of deployment.

For households, remote sites, educational institutions, and small farms looking to tap into the power of the wind without complexity or high cost, the S-type VAWT is a reliable, safe, and sustainable choice.