Technical FAQs
- Vertical versus Horizontal Turbines
- What are the dimensions?
- How tall is the mounting pole?
- What are rotor startup/shutdown speeds?
- Is it safe for Birds and Bats?
- Does the turbine make noise?
- What are the mass & loadings?
- How close can these turbines be mounted to each other?
- Can I sell electricity to the grid ?
- What safety features are there?
- Does it have accreditation?
Vertical versus Horizontal Turbines
Advantages of vertical axis wind turbines (VAWTs)
- Easier to maintain because most of their moving parts are located nearer to the ground. This is due to the vertical wind turbine's shape. The airfoils or rotor blades are connected by arms to a shaft that sits on a bearing and drives a generator below.
- As the rotor blades are vertical, a yaw device is not needed, reducing the need for this bearing and its cost and efficiency loss when tracking wind changes.
- Vertical wind turbines have a higher airfoil pitch angle, giving improved aerodynamics while decreasing drag at low and high pressures.
- Mesas, hilltops, ridgelines and passes can have higher and more powerful winds near the ground than up high because of the speed up effect of winds moving up a slope or funneling into a pass combining with the winds moving directly into the site. In these places, VAWTs placed close to the ground can produce more power than HAWTs placed higher up.
- Low installation height is useful where laws do not permit structures to be placed high.
- Smaller VAWTs, particularly modular designs which are shipped as kits and installed onsite, can be much easier to transport and install.
- May not need a free standing tower so is much less expensive and stronger in high winds that are close to the ground.
- Usually have a lower Tip-Speed ratio (particularly Savonious rotors) so less likely to break in high winds
- Ability to utilize wind from any direction without having to pitch or yaw and adjust to changes. No loss of efficiency or power collection due to wind direction change.
- Doesn’t have to shut down in high wind speeds. HAWTs which must shut down at high speeds cannot utilize the most powerful part of the wind regime, resulting in significant annual overall output decreases. Additionally, many HAWT inverters must draw grid power to re-activate after shutting down, contributing to significant annual parasitic losses over the course of a year.
Disadvantages of vertical wind turbines
- Most traditional VAWTs produce energy at only 50% of the efficiency of HAWTs in large part because of the additional drag that they have as their blades rotate into the wind. This can be overcome by using structures to funnel more and align the wind into the rotor (e.g. "stators") or the "vortex" effect of placing straight bladed VAWTs closely together. Modifications to the Helix design increases efficiency significantly, and Helix Wind turbines are only 6-7% less efficient that the most efficient HAWTs.
- There may be a height limitation to how tall a vertical wind turbine can be built and how much swept area it can have.
- A VAWT that uses guyed wires to hold it in place puts stress on the bottom bearing as all the weight of the rotor is on the bearing. Guyed wires attached to the top bearing increase downward thrust in wind gusts. Solving this problem requires a superstructure to hold a top bearing in place to eliminate the downward thrusts of gust events in guyed wired models.
Advantages of horizontal wind turbines
- Blades are to the side of the turbine's center of gravity, helping stability.
- Ability to wing warp, which gives the turbine blades the best angle of attack. Allowing the angle of attack to be remotely adjusted gives greater control, so the turbine collects the maximum amount of wind energy for the time of day and season.
- Ability to pitch the rotor blades in a storm, to minimize damage.
- Tall tower allows access to stronger wind in sites with wind shear. In some wind shear sites, every ten meters up, the wind speed can increase by 20% and the power output by 34%.
- Can be sited in forests above the treeline.
- May be self-starting.
Disadvantages of horizontal wind turbines
- HAWTs have difficulty operating in near ground, turbulent winds because their yaw and blade bearing need smoother, more laminar wind flows.
- The tall towers and long blades (up to 180 feet long) are difficult to transport on the sea and on land. Transportation can now cost 20% of equipment costs.
- Tall HAWTs are difficult to install, needing very tall and expensive cranes and skilled operators.
- Supply of HAWTs is less than demand and between 2004 and 2006, turbine prices increased up to 60%. At the end of 2006, all major manufacturers were booked up with orders through 2008.
- The FAA has raised concerns about tall HAWTs effects on radar in proximity to air force bases.
- Their height can create local opposition based on impacts to viewsheds.
- Offshore towers can be a navigation problem and must be installed in shallow seas. HAWTs can't be floated on barges.
- Downwind variants suffer from fatigue and structural failure caused by turbulence.
What are the dimensions?
Helix wind turbines currently come in two sizes, the S322 and the S594. The S322 stands about 10 feet tall and 4 feet in diameter (3.2m x 1.2m). The S594 stands about 20 feet tall and 4 feet in diameter (6.4m x 1.2m).TopHow tall is the mounting pole?
The overall height includes the mounting pole and turbine. The poles come in 5 foot increments.TopWhat are rotor startup/shutdown speeds?
The low speed Helix Wind turbine will start generating power at a little over 3.5 m/s (8 mph). It is self-starting and requires no power or input to spin up. It does not need over speed control because of its design and will continue to output power as wind increases up to 35mph. The unit will continue to spin with no damage to the system in winds as high as 80 mph (this is a sustained speed, it can withstand gusts up to 125 mph), however no additional electricity will be generated above maximum output at 35 mph due to restrictions on the inverter.TopIs it safe for Birds and Bats?
Helix Wind turbines are completely safe for wildlife because they spin at much lower speeds than horizontal turbines and appear as a solid mass rather than a sharp blurring blade that a bird or bat cannot see or detect.
TopDoes the turbine make noise?
The Helix Wind turbines are nearly silent because they operate with tip speeds close to the wind velocity. This dynamic is similar to the wind blowing around any stationary object such as a tree or house. Conventional (horizontal) wind turbines spin at up to 10 times the wind speed which causes the whistling sound that can be heard around them.
TopWhat are the mass & loadings?
The Savonious S322 weighs approximately 300lbs not including the pole structure. Each 5 feet of tower pole weighs approximately 200 lbs.
How close can these turbines be mounted to each other?
The distance between turbines depends on each individual site. Some locations with strong, consistent prevailing winds can have adjacent turbines 6 feet apart. Other settings might require them to be 30 feet apart to minimize shadowing and a reduction in power output. The optimal layout places consecutive turbines in a line perpendicular to the prevailing wind.
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