Small wind turbines
New Zealand has excellent wind resources and increasing numbers of windfarms 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.
Generally, small wind turbines are best suited to rural settings that are exposed to strong and consistent wind, and where there is no connection to the electricity network. Both these factors can help improve the economics of installing a small-scale turbine. For the same reasons, small wind turbines are less suited for use in urban areas.
Households normally usually use micro wind turbines that are smaller than 5kW. Small communities or groups of houses might use up to 20kW in size.
How wind turbines work
A wind turbine will generate electricity as long as there is relatively constant wind of a reasonable speed. Most small wind turbines need an average speed of 4.5 metres per second (16km/h) to operate effectively. Turbines can be designed for very windy places that generate more electricity than less windy sites. The downside is that turbines in windier sites may require more maintenance and have a shorter operational life.
Micro and small-scale wind turbines are usually mounted on towers so that they are exposed to more consistent wind with a higher average speed. The wind turns the rotor blades of the turbine. The turbine then spins a shaft connected to a generator where the electricity is generated.
Most wind turbines are horizontal-axis turbines - like the ones you commonly see on wind farms. These are mounted on the 'front' of the tower to face the wind. Small scale versions have tail fins to ensure the blades constantly turn to the wind. There are other designs, however, that have the blades 'behind' the tower.
Another type of wind turbine is a vertical-axis turbine. These are less common than horizontal-axis turbines. This sort has the advantage of not needing to turn to face the wind. This is useful in situations where the wind direction varies quickly. Some vertical-axis wind turbines are small enough to be mounted directly on a building. Others are pole mounted on the ground.
Rooftop or building-integrated turbines
Rooftop-mounted or wall-mounted micro wind turbines are a new, emerging type of turbine. There are many varying designs and types available. Many more are likely to become available in the future.
In urban areas, even on roof tops, turbines are typically less successful because winds tend to be turbulent, weak, and erratic due to buildings, trees and other obstructions. In some locations these effects can be mitigated through careful siting.
The capacity of small wind turbines
The amount of electricity a wind turbine generates will depend on the wind speed at the site and the turbine's capacity rating.
If a model has a rated capacity of 1 kW, it means it will produce 1 kWh 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 somewhere between 11-15 metres per second. This is about 40-55 kilometres per hour.
Actual generating rates
Although capacity ratings are a useful guide, 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 typically generate, on average, only 10-40% of their rated capacity every hour over a year.
To work out roughly how much electricity a turbine will generate on an average day, multiply the rated capacity by 24 hours, and then multiply it again by percentages ranging from 10 to 40, to reflect the typical range of wind available.
- A 1 kW wind turbine might generate between 2.4 kWh and 9.6 kWh a day on average (ie, 1 x 24 hours x 10% = 2.4 kWh/day; or 1 x 24 hours x 40% = 9.6 kWh/day)
The average New Zealand household uses about 8 kWh of electricity a day per person. Based on this an average family of four would need between 3 and 13kW (about $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. Before investing in wind generation it's more cost-effective to first minimise the amount of electricity your family consumes. This can be done by using energy efficient appliances and by using gas or other means to heat your water and home.
Things to consider before investing in a small wind turbine
How much it will cost
Small wind turbines generally cost between $10,000 and $15,000 per kW of rated capacity. So a 2kW turbine could cost between $20,000 and $30,000, including the cost of installation. For off-grid properties, however, 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, which can cost as much as $25,000 per kilometre.
The amount of maintenance it will need
Small wind turbines generally need more ongoing maintenance than solar panels and micro-hydro systems. This is especially true for turbines on very exposed sites.
Getting an experienced supplier
Ensure they have a good understanding of their product. Make sure any quote covers all the cost involved, such as labour expenses and resource consents.
A Canterbury tourist lodge uses wind to generate electricity, and sell it back into the grid - read case study
- Stand alone power systems (SAPS) are off-grid electricity generation systems that may include photovoltaics, micro wind turbines or micro hydro, batteries and a back-up generator
- Grid-connected systems are electricity generation systems that may include photovoltaics, micro wind turbines or micro hydro. They are connected to the local electricity network, and can export excess electricity, or use mains electricity as a backup
- Micro hydro for households is typically less than 5 kW
- Micro wind energy refers to the use of small wind turbines typically less than 10 kW
- Micro-generation is one form of distributed generation, which refers to local electricity generation connected to lines networks, rather than the national grid.
- More about use New Zealand's use of renewable energy including wind energy.