New Zealand has one of the best wind resources in the world
New Zealand has one of the best wind resources in the world. While large wind farms are making the most of this, small wind turbines in the right setting are well suited to generating electricity for individual households or communities.
If you’re in a rural area with a strong and constant wind flow and no access to the electricity network, a small wind turbine might work for you. However, you are likely to need to plan for alternative back-up power.
How small wind turbines work
There are many varying designs and different types available, some more suitable to built up areas.
One of the best places for wind turbines is on towers on an exposed ridgeline where they will get smoother wind flow with a higher average speed. The wind turns the rotor blades of the turbine which then spins a shaft connected to a generator.
Rooftop-mounted or wall-mounted micro wind turbines are becoming more common. However, the wind in urban areas can be turbulent and erratic, affected by buildings, trees and other obstacles – this can result in poor energy generation. Careful siting can make a difference, but as a general rule, it is difficult to get wind power performing well in urban areas.
Because wind blows intermittently, you will need a source of back up power. Small wind turbines are usually combined with other energy generators, such as:
- Conventional petrol or diesel generators.
If your home is not connected to the grid (a stand-alone system), you will need a battery bank to store the electricity generated by the small wind turbine. If the home is connected to the local electricity network and your small wind turbine produces more power than you need, you can export the extra electricity into the grid and sell it to an electricity retailer.
How much can it generate?
Households usually use wind turbines that are smaller than 5kW. Small communities, a group of houses, or a cluster of farm buildings might use turbines that are up to 20kW in size.
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 3kW, it means it will produce 3kW of electricity per hour given a certain wind speed - the wind speed used for ratings varies between different models and manufacturers.
However, your turbine will not be exposed to this wind speed all the time – typically, turbines will only generate, on average, 10-40 per cent of their rated capacity This means that if the wind only blows consistently for two hours, your 3kW turbine will only produce about 6kWh of electricity.
Go to the EECA Energywise website to work out what generating capacity your situation might need.
Is it suitable for all properties?
Generally, small wind turbines are best suited to rural properties that are exposed to strong and consistent wind, with minimal obstructions and less chance of noise upsetting neighbours. They are most economic where there is no connection to the electricity network.
Roof mounted wind turbines are less suited to urban environments in New Zealand. Obstructions from other buildings and trees mean they won’t operate very efficiently, while potential noise and visual issues may impact very close neighbours.
Types of system
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 which can look like a giant egg beater. These are less common than horizontal-axis turbines. Vertical-axis turbines do not need 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.
Resource consents can often be required to mitigate noise and visual issues. A building consent would also typically be required – especially if the turbine is to be attached to a dwelling.
Is a wind turbine for me?
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 per hour) to operate effectively. 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.
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 to get the lines to you.
Harnessing the power of wind does not produce greenhouse gases, except for minor levels during construction and installation of turbines. However, fossil-fuelled back-up power (e.g. diesel generators) are less environmentally friendly. Alternative renewable energy generation and storage systems such as PV and batteries may reduce or even eliminate the need for fossil fuel based backup.
It is important to use an experienced supplier with a good understanding of their product. Make sure you get itemised quotes that cover all the costs involved, such as labour expenses and resource or building consents.
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.