Small wind turbines

New Zealand has excellent wind resources and increasing numbers of wind farms are being proposed and built. Small scale and micro wind turbines are also available for homes, farms and businesses that want to generate their own wind power.

How wind turbines work

Wind turns the rotor blades of a turbine. The turbine then spins a shaft connected to a generator where electricity is generated. Wind turbines generate electricity as long as there is relatively constant wind at a reasonable speed. Most small wind turbines need an average speed of 4.5 metres per second (16 km/h).

Micro and small scale wind turbines are usually mounted on towers so they’re exposed to more consistent wind with a higher average speed. Because wind blows intermittently, small wind turbines are usually combined with other energy generators in a grid-connected or stand-alone power system.

 Grid-connected power systems

 Stand alone power systems

Types of wind turbine

Horizontal-axis turbines

Most wind turbines are horizontal-axis turbines - like the ones you see on wind farms. The turbines are mounted on a tower facing the wind. Small scale versions have tail fins to make sure the blades constantly turn towards the wind.

Vertical-axis turbines

Vertical-axis turbines are less common than horizontal-axis turbines, but have the advantage of not needing to face the wind. This is useful where the wind direction varies quickly. Some are small enough to be mounted directly onto a building, others are mounted on a pole in the ground.

Rooftop or wall-mounted turbines

Rooftop or wall-mounted micro wind turbines are a new type of turbine.

Best sites for small wind turbines

In urban areas - even on roof tops - turbines aren’t usually very successful. Winds tend to be turbulent, weak, and erratic because of obstructions such as buildings and trees. 

If you live in a rural area that is exposed to strong and consistent wind, and there is no connection to the electricity network, then it may be cost effective for you to install a small scale wind turbine. Households normally usually use micro wind turbines that are smaller than 5 kW. Small communities or groups of houses might use turbines up to 20 kW in size.

Energy output of small wind turbines

The amount of electricity a wind turbine generates depends on the wind speed and the turbine's capacity rating. If a model has a rated capacity of 1 kW, it will produce 1kWh of electricity per hour when exposed to a specific rated wind speed. This specific rated wind speed varies between different models and manufacturers, but is generally 11 to 15 metres per second. This is about 40 to 55 kilometres per hour.

Capacity ratings

In the real world a turbine will not be exposed to ideal conditions or the rated wind speed at all times. This means turbines will usually generate only 10 to 40% of their rated capacity every hour. 

To calculate how much electricity a turbine will generate in a day, multiply the rated capacity by 24 hours, then multiply it again by percentages ranging from 10 to 40:

  • a 1 kW wind turbine might generate between 2.4 kWh and 9.6 kWh a day (1 x 24 hours x 10% = 2.4 kWh/day, 1 x 24 hours x 40% = 9.6 kWh/day).

Cost to install small wind turbines

Small wind turbines generally cost between $10,000 and $15,000 per kW of rated capacity. So a 2 kW turbine could cost between $20,000 and $30,000, including the cost of installation. If you’re not connected to the grid, it can be more cost effective to install a small wind turbine as part of a stand alone system than to pay for a connection to the electricity network (as much as $25,000 per km).

The average New Zealand household uses about 8 kWh of electricity per person per day. An average family of 4 would need 3 to 13 kW ($30,000 to $195,000) worth of installed wind capacity to provide their own electricity. Even if you make significant energy efficiency improvements, a small wind turbine is unlikely to generate enough electricity to run your house on its own.

Maintenance of wind turbines

Small wind turbines generally need more ongoing maintenance than solar panels and micro-hydro systems. This is especially true if your turbine is on a very exposed site.