Wind Power

The wind is the oldest source of power harnessed by mankind. Sailing ships have been in use for at least 7,500 years whilst the first ever windmill to power a machine was built in Greece during the first century AD.

Throughout the middle ages, windmills were used for grinding corn into flour and pumping water for irrigation. Later on, they began to be used for sawing timber and for grinding spices, tobacco, dyes and cocoa. In the latter half of the 19th Century, water pumping windmills became popular in the United States, allowing vast tracts of otherwise inhospitable land to be farmed. Around six million water-pumping windmills were built in the United States between 1850 and 1950.

Harnessing the power of the wind is an important part of mankind’s history. With the creation of wind turbines for electricity generation, it is as relevant and important today as it has always been. Wind is one of the most promising sources of renewable energy sources for electricity production, particularly in colder climates where electricity demand is higher in the seasons when wind energy is at its peak.

Wind power has a number of benefits for electricity production: it’s environmentally friendly, with the carbon footprint associated with the production, assembly and installation of the wind turbine usually recovered within a few months of production; they can be installed quickly and additional turbines can be added to a wind farm quickly if demand rises. Wind turbines are extremely reliable, requiring minimal maintenance and servicing.

Of course, there are disadvantages as well. The wind blows when it wants to, not when we want it, which means that matching supply with demand is more difficult. From a national viewpoint, this is not as great a problem as it once was: improved forecasting has enabled power management planning to accurately predict wind energy volumes one day in advance, allowing wind power to be more easily integrated into the mix of power generation sources. As wind turbines are installed across the country, a lull in wind in one area may be compensated by higher winds elsewhere. Consequently, it has been found that 1,000MW of installed wind power can replace 300MW of power from a coal or gas-fired power station.

In the future, large wind farms will be combined with an energy storage system, such as creating hydrogen through electrolysis, then using fuel cells to convert the hydrogen back into electricity on demand. Combining wind power with a hydro-electric pumped storage facility, where water is pumped from a lower level to an upper reservoir when supply is greater than demand and then released when demand is higher, is also an effective way of creating a more constant power source from wind.

If you are planning a wind turbine for your own micro-generation project, you have two choices. You can either feed your power directly into the grid and not have to worry about peaks and troughs, or you can use your wind turbine to charge a bank of batteries, thereby smoothing out the peaks and troughs of supply and demand to provide your own reliable power source.

Small Wind

1kW micro wind turbine

From a micro-power perspective, small wind systems are defined as wind turbines with a peak capacity of 100kW or less. 100kW is still a substantial amount of power, capable of powering a small village. In reality, most micro-power wind projects are a fraction of this size, either providing power for one home or a rural business such as a farm, or providing an even smaller amount of power for an off-grid application in a remote location.

The physical size of a wind turbine comes as quite a shock to many people. Particularly if you were originally assuming you could install a small, unobtrusive wind turbine on the roof of your house to generate all your domestic electricity needs.

The reality is quite different. The scale and the height of even a small wind turbine means that you are going to need a fair amount of open space in order to install a wind power system. The following diagram gives some idea of the scale of different sizes of wind turbine, showing the minimum height of the wind turbine and the size of the rotor blades in comparison to the height of a six foot tall man:

Comparative sizes of small wind turbine

Anatomy of a wind turbine

Anatomy of a wind turbine

  1. The Rotor spins as it catches the wind. In small micro-power turbines, this rotor is often a fixed pitch design, optimised for a specific wind speed. In larger systems, the rotor is a variable pitch, which can adjust itself to match the speed of the wind.
  2. The aerodynamics of the Nose Cone minimise turbulence around the turbine head. On a variable pitch rotor system, the mechanics for the variable pitch are mounted inside the nose cone.
  3. The Nacelle contains the power generator, a gearbox (where used) and, on larger wind turbines, a braking system so that the rotors can be halted if wind speeds get dangerously high or for carrying out servicing.
  4. Most of the smaller wind turbines have a Tail Boom so that the turbine can face into the wind.
  5. The wind turbine needs to be able to turn to face into the wind. This is known as yawing. The Tail is used on smaller wind turbines to face the turbine into the wind. This is known as passive yawing. Larger wind turbines are turned into the wind using a motor, known as a yaw drive. This is known as active yawing.
  6. The Yaw Bearing enables the wind turbine to yaw. These are extremely specialised bearings that are capable of handling very high loads: not just the weight of the nacelle and rotor, but also the wind force on the turbine. In an active yawing system, the yaw drive is also mounted at this point.
  7. The tower can be as simple as a pole or an extremely complicated tower. Like the yaw bearing, the tower must be capable of handling very high loads and must be mounted in strong foundations. In many cases, the tower must also be capable of lowering the wind turbine to ground level for inspection and maintenance, or to protect the wind turbine in dangerously high winds.

Calculating the power of the wind

In order to calculate how much energy you can capture from the wind at your site, you first need to know the wind speed at your location. Wind speed is usually measured either as metres per second (m/s), knots (kn) or miles per hour (mph). You also need to know the direction of the prevailing winds - i.e. the direction from which the wind blows from for most of the time.

The most accurate way to do this is to measure the speed of the wind yourself over a lengthy period of time. Wind speed is measured using an anemometer. These consist of a propeller and a digital readout showing the current wind speed. They are either handheld or pole mounted. If you are looking to invest in a wind turbine system, a full wind survey is a good investment.

However, for initial evaluation, you can use an online wind database in order to identify wind speeds and directions in your region. The wind calculators on this website can provide you with a source of this information, based on aggregated NASA satellite readings. To use this database, click on the Wind Calculators option in the Renewable Resources section of this website.