Hello Everyone I think this thread is a necessary read for anyone interested in using wind power I know its a little long winded but there is a lot of information you need to understand when considering wind power.

Part 1

Principles of Micro and Small Wind Turbines

• Wind as Energy Source: Micro and small turbines harness wind, a renewable resource driven by solar-induced air movement, for decentralized power (e.g., homes, farms, off-grid systems).

• Kinetic to Electrical Conversion: Blades rotate to convert wind’s kinetic energy into electricity via a generator, often direct-drive in micro turbines for simplicity and reduced losses.

• Key Components: Blades (1.5–8 m diameter), rotor, nacelle (housing generator), tower (9–30 m), and often a tail fin for yaw in micro turbines. Blades use fiberglass, carbon fiber, composites, or high-quality polymers.

• Swept Area Determines Power: Power scales with the rotor’s swept area (A = πR²). Larger blade diameters capture more wind energy (e.g., doubling diameter from 2 m to 4 m quadruples swept area from ~3.14 m² to ~12.56 m², boosting power).

• Blade Diameter vs. Surface Area: Blade diameter (swept area) is critical because:

  • Power Scaling: Power is proportional to swept area (P = ½ρAV³Cp, ρ ~1.225 kg/m³), not blade surface area. Larger diameters maximize energy capture.

  • Aerodynamic Efficiency: Thin, airfoil-shaped blades optimize lift-to-drag ratio, unlike broad blades that increase drag and weight without proportional power gains.

  • Example: A 3 m diameter turbine (~7 m²) at 8 m/s yields ~400 W (Cp = 0.35), while wider blades (same diameter) reduce efficiency due to drag.

• Blade Rigidity and Efficiency:

  • Role of Rigidity: Rigid blades maintain their aerodynamic profile, minimizing deformity (bending, twisting, fluttering) that disrupts airflow and lowers the power coefficient (Cp).

  • Impact of Deformity: Flexible blades deform at high wind speeds (>8 m/s), reducing Cp by 5–15% (e.g., from 0.35 to 0.3, lowering output from ~400 W to ~340 W for a 3 m diameter turbine at 8 m/s).

  • Materials: Carbon fiber, fiberglass, or reinforced composites ensure rigidity. Low-cost plastic blades in some Chinese turbines deform, reducing Cp and output.

  • Swept Area Synergy: Rigid blades ensure the full swept area contributes to power capture.

• Power Coefficient (Cp) and Betz Law:

  • Power Coefficient (Cp): Cp is the ratio of power extracted by the turbine to the total power available in the wind (P_turbine / ½ρAV³), measuring efficiency. Typical values: 0.3–0.4 for well-designed micro/small HAWTs, 0.11–0.25 for VAWTs, and 0.2–0.3 for low-cost Chinese turbines with flexible blades.

    • Factors Affecting Cp: Blade design (airfoil shape, rigidity), tip speed ratio (TSR ~4–7 for HAWTs), pitch control, and site turbulence.

    • Example: A 2.6 m diameter turbine (~5.3 m²) at 8 m/s with Cp = 0.38 produces ~550 W, while Cp = 0.2 (flexible blades, turbulent site) yields ~290 W.

  • Betz Law: States that no turbine can capture more than 59.3% (Cp = 0.593) of wind’s kinetic energy, as some energy must remain to carry air away. Real-world turbines achieve 50–70% of this limit due to aerodynamic and mechanical losses.

    • Implications: Maximizing Cp requires rigid blades, optimized TSR, and low-turbulence sites. Flexible blades or poor sites significantly lower Cp, far below the Betz limit.

• Large Diameter, Low RPM Generators:

  • Description: Axial flux or permanent magnet generators with large rotor diameters produce power at low RPMs (100–300 RPM vs. 500–1000 RPM), reducing wind speed needed for rated power (8–10 m/s vs. 12–15 m/s).

  • Impact: A 2.6 m diameter turbine (~5.3 m²) yields ~400–700 W at 8 m/s (Cp ~0.35–0.38), vs. ~200–400 W with high-RPM generators. Rigid blades ensure consistent torque.

  • Advantages: Usable power at 8 m/s, lower noise (3–5 dB(A)), and reduced wear, maximizing swept area benefits.

  • Disadvantages: Higher cost (20–40% more) and weight.

• Wind Speed Dependency: Power scales with V³, making 8 m/s productive. Cut-in speeds (~4 m/s) yield minimal power; 6–8 m/s is optimal. Rigid blades and high Cp maintain efficiency.

• Site Selection and Topography:

  • Importance: Site location determines wind speed, consistency, and turbulence, directly affecting Cp and output.

  • Topography Impact:

    • Open, Elevated Sites: Hills, ridges, or open fields maximize wind speed (5.5–8 m/s) and laminar flow, boosting Cp (0.35–0.4) and output (1000–2000 kWh/year for a 2.6 m diameter turbine).

    • Valleys or Forested Areas: Low wind speeds (<4 m/s) and turbulence reduce Cp (0.2–0.25) and output (<500 kWh/year).

    • Coastal Areas: High, consistent winds (7–10 m/s) optimize Cp and output but require corrosion-resistant materials.

  • Structures and Obstacles:

    • Turbulence from Buildings/Trees: Obstacles within 150–300 m reduce wind speed by 20–50% and Cp (e.g., from 0.35 to 0.25), lowering output (e.g., ~300 W vs. 400 W at 8 m/s for 3 m diameter).

    • Tower Height: Towers 9–10 m above obstacles within 150 m access cleaner winds, increasing Cp and output by 30–50%.

    • Urban Environments: High turbulence makes urban sites unsuitable, especially for micro turbines with small swept areas.

  • Site Assessment: Use wind maps, anemometers, or historical data to confirm >5.5 m/s and low turbulence intensity (<0.2). Poor sites negate swept area, rigidity, and Cp benefits.

• Myth of Roof-Mounted Turbines:

  • Myth: Small turbines (1–2 m diameter) on rooftops can power homes due to ease of installation.

  • Reality: Roof-mounted turbines are ineffective because:

    • Turbulence: Roofs experience turbulent boundary layers (wind speeds 20–50% lower, turbulence intensity >0.3), reducing Cp (0.2–0.25) and output (e.g., ~20–40 W for 1 m diameter at 8 m/s).

    • Vibration and Noise: Vibrations amplify noise (50–60 dB(A) indoors) and cause structural fatigue. Flexible blades worsen vibrations, lowering Cp.

    • Low Swept Area: Small swept areas (<3.14 m²) produce minimal power in turbulent winds (<100 kWh/year vs. 300 kWh/year in open sites).

    • Structural Risks: High wind loads risk damage, especially with flexible blades.

    • Chinese Turbine Context: Low-cost models (e.g., 400 W rated, 1 m diameter) yield 10–30 W at 6 m/s, with high noise (50–55 dB(A)) and low Cp (0.2).

    • Exception: Tall buildings (>30 m) in high-wind areas with rigid-blade, low RPM turbines may produce ~100–200 W at 8 m/s, but costs outweigh benefits vs. solar.

  • Recommendation: Use pole-mounted turbines in open, elevated sites with tall towers (15–30 m).

• Myth of Small Turbines Killing Birds:

  • Myth: Small wind turbines are significant threats to bird populations, frequently killing birds through blade collisions.

  • Reality: The impact of micro and small turbines on birds is minimal compared to other human-related threats:

    • Low Collision Risk: Small turbines have smaller swept areas (0.785–38.5 m²) and lower blade tip speeds (30–50 m/s vs. 70–100 m/s for large turbines), reducing collision risks. Studies (e.g., National Renewable Energy Laboratory, 2016) show small turbines cause negligible bird mortality (0.01–0.1 birds/turbine/year) compared to large wind farms (1–5 birds/turbine/year).

    • Site-Specific Factors: Bird mortality is higher in migratory corridors or near habitats with high bird activity (e.g., wetlands). Proper site selection (avoiding flyways) minimizes impacts.

    • Comparison to Other Threats: Buildings (600–1000 million bird deaths/year in the U.S.), power lines (130–230 million), and cats (1.3–4 billion) cause far greater bird mortality than small turbines (estimated <10,000 deaths/year globally).

    • Design Mitigations: Rigid blades and low RPM generators reduce blade visibility issues (blurring at high speeds), and some turbines use visible blade patterns or slower rotation to deter birds.

    • Chinese Turbine Context: Low-cost models with flexible blades may vibrate or flutter, potentially startling birds but not significantly increasing collisions. Poorly sited rooftop turbines in urban areas may pose slightly higher risks due to proximity to bird populations, but data remains limited.

  • Recommendation: Conduct site-specific environmental assessments and avoid installing turbines in sensitive bird habitats. Small turbines are generally low-risk for wildlife when properly sited.

• Grid/Off-Grid Integration: Turbines connect to grids via inverters or power off-grid systems. Poor sites reduce output, hindering grid compatibility.

• Environmental and Noise Considerations: Low emissions, but noise (aerodynamic and mechanical) requires careful siting, influenced by blade rigidity, RPM control, and site turbulence. Bird impacts are minimal with proper siting.

• Maintenance and Durability: Lifespan ~20 years with maintenance. Rigid blades withstand high winds, using furling or pitching for overspeed protection. Turbulent sites increase wear on flexible blades.

• Myths About Small Plastic Chinese Turbines:

  • Myth: High Rated Power = High Output: Many claim 400 W for 1–2 m diameters but deliver ~40–80 W at 8 m/s due to flexible blades (Cp ~0.2–0.3), poor site suitability, and low-quality electronics.

  • Myth: Plastic Blades Are Inadequate: Low-grade plastic blades deform, reducing Cp (20–30% less output), but high-quality polymers can be rigid and effective.

  • Myth: Low Cut-In Speeds = Efficiency: Cut-in at 2–3 m/s produces negligible power (<10 W). Output at 8 m/s depends on swept area, rigidity, Cp, and site.

  • Myth: All Are Junk: Some use rigid blades and low RPM generators, but many have flexible blades, low Cp, and short lifespans, especially in turbulent sites like rooftops.

  • Reality: Suitable for low-power needs in high-wind, open sites but not cost-effective for significant energy, particularly in urban or roof-mounted setups.

Continued

Part 2

Fixed Bladed vs. Mechanical Variable Pitch (RPM-Limiting) Systems

Fixed Bladed Systems

• Description: Blades are fixed at a set angle, optimized for 8–12 m/s. Common in micro turbines (<1 kW, 1–3 m diameter) for simplicity.

• Operation with Low RPM Generators, Blade Rigidity, and Site:

  • Blades rotate proportional to wind speed, limited by furling or stall regulation.

  • Low RPM generators yield 400–600 W at 8 m/s for a 2.6 m diameter turbine (5.3 m², Cp ~0.35) in open sites vs. ~200–300 W in turbulent sites (Cp ~0.25).

  • Rigid Blades: Maintain Cp ~0.35–0.4. Flexible blades drop Cp to ~0.2–0.3, reducing output (e.g., ~300 W vs. 400 W for 3 m diameter).

  • Poor Sites (e.g., Rooftops): Turbulence lowers Cp and output (~100–200 W for 2.6 m diameter) and increases noise/vibrations.

  • Bird Impact: Minimal risk (0.01–0.1 birds/turbine/year), but turbulent urban sites may slightly increase collisions due to erratic bird behavior.

• Noise Characteristics:

  • At 8 m/s in open sites with low RPM generators and rigid blades: ~40–42 dB(A) at 10 m.

  • At 12 m/s: RPMs rise (400–600 RPM), causing noise (50–60 dB(A)). Flexible blades add 2–5 dB(A).

  • In turbulent sites: Noise ~45–55 dB(A) at 8 m/s.

• Advantages:

  • Simplicity and Cost: Fewer parts reduce costs.

  • Low RPM Benefits: Usable power at 8 m/s with lower noise in open sites.

  • Rigid Blade Efficiency: Maintains high Cp, maximizing swept area benefits.

• Disadvantages:

  • Noise in High Winds/Turbulent Sites: High RPMs and flexible blades increase noise (50–60 dB(A) at 12 m/s, 45–55 dB(A) in turbulent sites).

  • Overspeed Risk: Flexible blades in turbulent sites lower Cp and increase wear.

  • Site Sensitivity: Poor sites drastically reduce Cp and output.

Mechanical Variable Pitch (RPM-Limiting) Systems

• Description: Blades pivot to adjust pitch via governors or springs, limiting RPMs in high winds. Used in small turbines (1–10 kW, 2.6–7 m diameter).

• Operation with Low RPM Generators, Blade Rigidity, and Site:

  • At 8 m/s, blades optimize lift (~500–700 W for 2.6 m diameter, Cp ~0.38) in open sites vs. ~300–400 W in turbulent sites (Cp ~0.28).

  • In high winds (>12 m/s), blades feather, capping RPMs (200–300 RPM).

  • Rigid Blades: Maintain Cp ~0.38–0.42. Flexible blades reduce Cp to ~0.28–0.33.

  • Poor Sites: Pitch adjustment mitigates turbulence losses better than fixed systems.

  • Bird Impact: Low RPMs and pitch control reduce blade visibility issues, further minimizing collision risk (negligible, <0.01 birds/turbine/year in open sites).

• Noise Characteristics:

  • At 8 m/s in open sites with low RPM generators and rigid blades: ~38–40 dB(A).

  • At 12 m/s: Noise 40–50 dB(A). Flexible blades add ~1–3 dB(A).

  • In turbulent sites: Noise ~42–50 dB(A) at 8 m/s.

• Advantages:

  • Superior Noise Reduction: Low RPM generators and rigid blades minimize noise, ideal for residential areas.

  • Higher Efficiency: Pitch optimization and rigid blades boost Cp (10–20% more kWh/year).

  • Site Adaptability: Maintains higher Cp in moderately turbulent sites.

  • Swept Area Synergy: Maximizes large diameter benefits.

  • Bird Safety: Lower RPMs reduce collision risk slightly more than fixed systems.

• Disadvantages:

  • Cost and Complexity: Pitch mechanisms and large generators increase costs (30–50% more).

  • Maintenance: Pitch systems and rigid blades require inspection.

Part 3

Noise, Blade Rigidity, Low RPM Generators

• Fixed Bladed with Low RPM Generators and Rigid Blades:

  • At 8 m/s in open sites: Noise ~40–42 dB(A), Cp ~0.35–0.4, bird impact negligible.

  • At 12 m/s: Noise 50–60 dB(A). Flexible blades lower Cp to ~0.2–0.3, add 2–5 dB(A).

  • In turbulent sites: Noise ~45–55 dB(A), Cp ~0.2–0.25, slightly higher bird risk in urban areas.

• Variable Pitch with Low RPM Generators and Rigid Blades:

  • At 8 m/s in open sites: Noise ~38–40 dB(A), Cp ~0.38–0.42, bird impact negligible.

  • At 12 m/s: Noise 40–50 dB(A). Flexible blades lower Cp to ~0.28–0.33, add ~1–3 dB(A).

  • In turbulent sites: Noise ~42–50 dB(A), Cp ~0.25–0.3, minimal bird risk.

• Blade Rigidity Benefit: Maintains high Cp and reduces noise (1–7 dB(A)) by minimizing vibrations.

• Low RPM Generator Benefit: Lowers noise (3–5 dB(A)) and supports high Cp at 8 m/s, slightly reducing bird collision risk.

• Site Impact: Turbulent sites lower Cp (0.2–0.25), increase noise (5–10 dB(A)), and may slightly elevate bird risk in urban settings.

• Chinese Turbine Context: Flexible blades and high-RPM generators yield low Cp (~0.2–0.3), high noise (45–55 dB(A)), and poor output in turbulent sites. Bird impact is minimal but may be slightly higher in urban rooftop installations.

Realistic Power Output at 8 m/s

Using P = ½ρAV³Cp (ρ ~1.225 kg/m³, Cp = 0.3–0.4 for HAWTs, 0.11–0.25 for VAWTs):

• Fixed Bladed with Low RPM Generators and Rigid Blades:

  • Open Site:

    • 1 m diameter (~0.785 m²): ~40–70 W (Cp ~0.32). Noise ~40–42 dB(A).

    • 2.6 m diameter (~5.3 m²): ~400–700 W (Cp ~0.36). Noise ~41–43 dB(A).

    • 7 m diameter (~38.5 m²): ~2.5–4.5 kW (Cp ~0.4). Noise ~43–47 dB(A).

  • Turbulent Site (e.g., Rooftop): Cp ~0.2–0.25, output ~20–50 W (1 m), ~200–400 W (2.6 m), ~1–2 kW (7 m). Noise ~45–55 dB(A).

  • Flexible Blades: Cp ~0.2–0.3, output ~30–50 W (1 m), ~300–500 W (2.6 m), noise ~43–48 dB(A) in open sites.

  • Bird Impact: Negligible (<0.01–0.1 birds/turbine/year), slightly higher in urban turbulent sites.

• Variable Pitch with Low RPM Generators and Rigid Blades:

  • Open Site:

    • 1 m diameter: ~45–80 W (Cp ~0.34, rare). Noise ~38–40 dB(A).

    • 2.6 m diameter: ~450–800 W (Cp ~0.38). Noise ~39–41 dB(A).

    • 7 m diameter: ~3–5 kW (Cp ~0.42). Noise ~41–45 dB(A).

  • Turbulent Site: Cp ~0.25–0.3, output ~30–60 W (1 m), ~300–500 W (2.6 m), ~1.5–3 kW (7 m). Noise ~42–50 dB(A).

  • Flexible Blades: Cp ~0.28–0.33, output ~35–60 W (1 m), ~350–600 W (2.6 m), noise ~41–46 dB(A) in open sites.

  • Bird Impact: Negligible, lower than fixed systems due to slower RPMs.

• VAWTs (Fixed, High-RPM Common):

  • Open Site: 200–400 W for 3 m diameter (7 m², Cp ~0.11–0.25). Noise ~45–50 dB(A).

  • Turbulent Site: ~100–200 W- Turbulent Site: ~100–200 W, noise ~50–55 dB(A).

  • Low RPM and rigid blades: ~250–450 W, Cp ~0.15–0.27, noise ~43–48 dB(A) in open sites.

  • Bird Impact: Slightly higher than HAWTs due to complex motion, but still negligible (<0.1 birds/turbine/year).

• Chinese Turbines (Fixed, High-RPM, Flexible Blades):

  • Open Site: 1 m diameter “400 W” yields ~40–80 W (Cp ~0.2–0.3), noise ~45–50 dB(A).

  • Turbulent Site: ~10–30 W, noise ~50–55 dB(A).

  • With low RPM generators and rigid blades: ~50–100 W, Cp ~0.25–0.32, noise ~42–45 dB(A) in open sites.

  • Bird Impact: Negligible, but urban rooftop installations may pose minimal risk due to bird proximity.

Good day. I would so much like to get in touch with a knowledgeable guy better still an expert in the field

of the Savonius turbine. I designed a Savonius and my key word was not it must be cheap. My

key words was " It must be Efficient and reliable and no shortcuts taken and all the problems of the

Savonius must be addressed. I achieved at least 90% of it. I have build a very rugged model that can

be tested. Swept area is 0.6 x 0.9 meter. I want to invite all the experts and interested people to

come and evaluate the design and maybe we can create an interest group.

I am from Claremont Pretoria.

Hennie Stander

0725621591