# How much wind is needed for a small wind turbine?

## Background

three-phase project began in fall 2012 on the Bearspaw Operations Workplace Centre site to see what options we have to harness the power of the wind and sun on City of Calgary work sites.

When comparing wind turbine sizes, industry definitions generally describe a "large" wind turbine as over 50 kilowatts (kW) in size and any turbine 50 kW and under as a "small" wind turbine.

The average Calgary household uses about 7,200 kilowatt hours (kWh) of electricity per year.

## How fast does the wind need to be to generate electricity?

Certain small wind turbine models (50 kW) are effective at generating electricity with relatively low wind speeds.

Wind speed is averaged over a year to get a consistent measurement.

Wind speed within a preferred range can produce a significant amount of electricity with certain small wind turbine models.

About 14 to 22 kilometres per hour (4 to 6 metres per second) is generally the preferred wind speed.

The wind speed when wind turbines start producing electricity is called cut-in wind speed. Depending on the model, the cut-in wind speed for small wind turbines varies from 9 to 16 kilometres per hour (2.5 to 4.5 metres per second); being 12 kilometres per hour (3.5 metres per second) the most common.

The Beaufort Wind Force Scale helps explain wind speed:

• A "gentle breeze" that causes leaves and small twigs to be constantly moving has wind between 12 and 19 kilometres per hour.
• A "moderate breeze" that causes dust and loose paper to be raised and small branches begin to move has wind between 20 and 28 kilometres per hour.

## How much electricity can a small wind turbine produce?

With consistent wind of between 14 and 22 kilometres per hour:

• Some small (50 kW) wind turbines could produce anywhere from about 60,000 to 170,000 kilowatt hours annually.
• This is enough electricity to power between 8 and 23 houses for a whole year.

## A slight difference in wind speed makes a big difference in electricity

Even slight differences in wind speed can greatly improve electricity generation.

For example, winds at about 14 kilometres per hour produce about half the electricity as winds at about 18 kilometres per hour.

 Wind speed   (annual average) Electricity production   (estimate for 50 kW wind turbines effective at low wind speeds) 14.4 kilometres per hour   Same as 4 metres per second 62,500 kilowatt hours   (enough to power about 8 average Calgary households for a year) 18 kilometres per hour   Same as 5 metres per second 114,900 kilowatt hours   (enough to power about 16 average Calgary households for a year) 21.6 kilometres per hour   Same as 6 metres per second 168,000 kilowatt hours   (enough to power about 23 average Calgary households for a year)

## How much wind is “enough” for Bearspaw OWC?

To generate enough electricity for a small wind turbine to significantly offset current electricity usage on site, a wind speed of about 18 kilometres per hour over a year is preferred. This assumes the small (50 kW) wind turbine model is the type that is effective at generating electricity with relatively low wind speeds.

The wind speed at which some small wind turbines start producing electricity (cut-in wind speed) is 12 Kilometres per hour (3.5 metres per second).

Winds between 12 and 19 kilometres per hour (3.5 to 5.5 metres per second) are defined as a "gentle breeze” on the Beaufort Wind Force Scale.

## How much wind is there in Northwest Calgary?

Part of the research is to gather existing information on wind speed in the area.

• The Canadian Wind Energy Atlas calculated the annual average (mean) wind speed in Northwest Calgary as 21.2 kilometres per hour (5.92 metres per second).
• This measurement was taken 50 metres up from ground level in the postal code T3L 2V3. It is useful to know the wind speed at 50 metres high because this is the approximate maximum height for small wind turbines.