Small wind turbines

New Zealand has excellent wind resources and increasing numbers of wind farms have been 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 off-grid power system.

Types of wind turbines

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).

Does it make financial sense?

If you are looking at a wind turbine for purely economic reasons, EECA strongly advises you do your sums carefully before you buy – especially if you are already connected to the electricity grid.

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. A solar electricity system is likely going to be more cost-effective than a small wind turbine.

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.

Therefore you will most likely need to remain connected to the electricity grid and electricity continues to be purchased from a retailer during times when the wind turbine does not generate enough electricity.

Some households choose to go ‘off-grid’, disconnecting from the grid entirely and purchasing batteries to provide electricity when the wind turbine is not generating enough electricity to meet demand. Although battery prices are falling, this approach won’t make economic sense for most households that are already grid-connected.

However, if you’re not connected to the grid, it can be more cost effective to install a small wind turbine (or solar electricity or micro-hydro system) as part of an off-grid power system than to pay for a connection to the electricity network (as much as $25,000 per km).

Excess wind electricity can be sold to a retailer

At times, the wind turbine may generate more electricity than can be used, allowing grid-connected households to sell electricity to an electricity retailer. The retailer buys this electricity at a ‘buy-back rate’- these vary but are lower than the amount companies charge you for electricity. This means households with a wind turbine get greater value out of using the electricity they generate themselves, rather than selling it back to a retailer.

When considering a small wind turbine, consider the buy-back rates on offer. You may need to switch from your current retailer to access a buy-back rate. The retailer offering the best buy-back rate may not necessarily charge the lowest for the electricity they sell.

Checklist for installing a small wind turbine

  • Get expert advice - SEANZ (Sustainable Electricity Association of New Zealand) is the representative body for the onsite renewable electricity generation industry. EECA recommends consumers use SEANZ members to provide advice, quotes and undertake small wind turbine installation work.
  • You may need a resource consent from your regional council.
  • You need prior approval to connect a small wind turbine to the electricity grid, so contact your lines company before you start and talk to your electricity retailer also. A small wind turbine installation expert will be able to assist with this.
  • Although you may undertake some of the work to install a small wind turbine yourself, all electrical work needs to comply with and be certified to NZ electrical standards. Your installation must comply with any local council regulations, so check with your council before going ahead.
  • Make allowances for maintenance - 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.

SEANZ website

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