How Effective Are Small-Scale Vertical Axis Wind Turbines?

How Effective Are Small-Scale Vertical Axis Wind Turbines?

I’ve long been interested in renewable energy and ways to generate power at home. Small-scale vertical axis wind turbines (VAWTs) seem like an ideal option – they can be installed in urban environments and don’t require much space. But how effective are they really? In this article, I’ll explore this question in depth.

What Are Small-Scale VAWTs?

Small-scale VAWTs are wind turbines with blades that spin vertically around a vertical axis. Unlike traditional horizontal axis wind turbines (HAWTs), the turbine itself does not need to face into the wind to be effective. The vertical design allows VAWTs to capture wind from any direction.

Some key advantages of small-scale VAWTs:

  • Compact size – Require less space than HAWTs. Can be mounted on rooftops.
  • Omnidirectional – Don’t need to rotate to face the wind. Can harness wind from any direction.
  • Lower noise – Noise is directed upwards rather than outward.
  • Aesthetics – Sleek, modern designs fit into urban environments.

Typical capacities range from 1 kW to 10 kW. The turbines stand around 15-25 feet tall. Popular small-scale VAWT models include the Urban Green Energy Eclipse and the Aeolos Wind Turbine.

How Much Power Can They Produce?

The amount of power generated by a small-scale VAWT depends on several factors:

  • Wind speeds – Higher wind speeds allow the turbine blades to spin faster, generating more power. Most VAWTs reach peak power output at wind speeds of around 15-25 mph.
  • Turbine size – Larger turbines and blade spans can harness more wind energy. A 10 kW turbine will produce more power than a 2 kW model.
  • Location – Turbines mounted higher up on rooftops or towers experience stronger, less turbulent winds than those lower to the ground.

A typical 5 kW VAWT in a location with average wind speeds of 12 mph can be expected to produce around 6,500-8,000 kWh per year. This is enough to offset about 20-25% of an average household’s electricity usage.

With optimal conditions – strong prevailing winds and an elevated mounting position – a VAWT may reach 30% or higher of a household’s electricity demand. But output can also be much lower in less windy areas.

What Are The Main Factors That Impact Efficiency?

Several factors influence how efficiently a small-scale VAWT can convert wind energy into electricity:

  • Blade design – Blades with an airfoil cross-section optimized for lift can harvest more energy from the wind.
  • Solidity ratio – The ratio of blade surface area to swept area impacts torque and rotational speed.
  • Number of blades – More blades increase swept area but also drag. 2-3 blades is common.
  • Generator/inverter – High-efficiency equipment converts the mechanical power into usable AC electricity with minimal losses.
  • Tower height – Elevating the turbine even just 30 feet above the ground can expose it to faster, less turbulent winds.
  • Surrounding obstructions – Nearby buildings, trees etc. cause turbulence that decreases efficiency.

Proper siting and an optimized turbine/blade design are key to maximizing power output from a VAWT. Efficiency percentages can range from 10-40% based on these factors.

What Are The Main Challenges With Small VAWTs?

While small VAWTs have some useful advantages, there are also some particular technological and practical challenges:

  • Self-starting – The turbines need a minimum wind speed of around 8 mph to overcome inertia and start spinning from a standstill.
  • Bearing wear – The constantly changing wind direction places strain on vertical bearings.
  • Torque ripple – As blades rotate into the wind, torque output varies cyclically, placing pulsating forces on components.
  • Vibration – Unbalanced forces cause more vibration issues compared to horizontal axis turbines.
  • Guy wires – Guy cables are often needed to support and stabilize the tower; an aesthetic concern.
  • Bird/bat strikes – Vertical spinning blades pose a collision hazard for birds and bats.

These factors make VAWT systems more complex and expensive than they may initially seem. Nonetheless, through continued improvements in engineering, small VAWTs may become more viable and cost-effective.

Real-World Examples of Small VAWTs

To better understand how small VAWTs perform in real-world conditions, it’s helpful to look at some actual installations:

Case Study 1: In 2012, Aerotecture International installed a 5 kW Aeolos Savonius turbine on a warehouse roof in Chicago. Over the first 5 years, it produced an average of 7,776 kWh/year – about 18% of the building’s energy use. However, output decreased each year as blade surfaces degraded. Maintenance costs were higher than expected.

Case Study 2: An Urban Green Energy Eclipse VAWT was installed on the roof of the Pearce Institute in Govan, Scotland in 2015. With an elevated location and few nearby obstructions, the 2.5 kW turbine generates around 8,900 kWh annually – exceeding original estimates. It provides about 25% of the building’s electricity.

Case Study 3: A homeowner in Boston installed a 1 kW VAWT on a 10 foot pole mounted on his roof in 2010. Due to lower wind speeds in the area and high turbulence around the home, it has produced only 900-1,100 kWh/year – about 3% of total use. The owner found noise levels from the turbine to be intrusive.

Key Takeaways – The Potential and Limitations of Small VAWTs

In summary, small-scale VAWTs certainly hold potential advantages but have some significant limitations in real-world applications:

  • Output varies widely depending on siting, wind speeds, and surrounding conditions.
  • Maintenance costs tend to be higher than expected.
  • Maximum capacity factors of 30-40% are possible under ideal conditions.
  • More commonly capacity factors range from 10-25% of rated power.
  • Noise and vibration issues may require mitigation efforts.
  • Aesthetic concerns and permitting/zoning challenges should not be underestimated.

For most residential applications, small VAWTs seem unlikely to meet 100% of electricity needs. However, they can still be a viable complementary technology and make an impact by offsetting 20-40% of household use. Continued improvements to turbine efficiency, longevity, and cost-effectiveness will be key to making small VAWTs more mainstream.