Windy Facts

Wind Farm Information for Pupils and Students

We receive many questions each year from people interested to learn more about wind energy and wind farms. Rather than repeating what others have set out already, we are concentrating on questions that are specific to Allt Dearg and Srondoire, or are not answered elsewhere.

You can find good information of wind energy following these links:

https://en.wikipedia.org/wiki/Wind_turbine

http://www.renewableuk.com/en/renewable-energy/wind-energy/index.cfm

Wind

Wind power is nothing new. Ancient people used wind power to sail boats across the oceans. Windmills have been used to convert the kinetic energy of wind into mechanical rotational energy to mill grains, pump water and power sawmills for over 1,000 years. The wind farm uses wind energy to generate electricity. Wind is a renewable fuel source because it comes from the heat of the sun (solar energy).

Where does wind come from?

Wind is air movement caused by the uneven heating of the earth's surface by the sun. During the day the air above the land heats up faster than the air above water like oceans and lakes. The air above the water is cooler and heavier. The uneven heating of the air is because the earth is made up of different surfaces and elevations. The warm air over the land expands and rises and the cooler air over the water rushes in to take the place of the warmer air creating winds.

How does the Wind Turbine turn Wind into Electricity?

Wind turbines work like electric fans in reverse. The wind passing through the rotor area of the turbine is slowed down, transferring its kinetic energy to the turbine blades as they rotate. The mechanical energy of the rotating blades is turned from high torque low speed, to low torque high speed rotation via the gearbox that sits between the turbine rotor and the electrical generator. The electrical generator converts the mechanical energy of the rotor into electrical energy.

How much Electricity can the Wind Turbines produce?

The smaller Allt Dearg turbines can each produce 850kW at full output, when the wind is blowing at around 30 miles per hour. That’s enough to power around 100 electric showers or 3,500 TVs. The larger Sròndoire turbines produce 2,000kW (2MW) at full output. When both Allt Dearg and Sròndoire are running at full power they produce 16,000kW (16MW), enough to power Ardrishaig, Lochgilphead and the surrounding area.

How Much Do the Wind Farms Contribute to Argyll & Bute’s Electricity Use?

Detailed electricity consumption data is published at https://www.gov.uk/government/statistical-data-sets/regional-and-local-authority-electricity-consumption-statistics-2005-to-2011

In 2013 the average annual domestic electricity consumption per Scottish household was 4,435 kWh. In Argyll household consumption was higher at 6,844 kWh, reflecting the limited availability of mains gas to heat homes. Total Domestic Electricity consumption was 280 GWh and total Non-Domestic consumption was 238 GWh. Allt Dearg produced 44 GWh in 2013, around 16% of the Domestic Electricity used in Argyll or 8% of all Electricity consumed in Argyll. With the additional output from Sròndoire, the wind farms supply about 25% of the Domestic Electricity used in Argyll.

Variable pitch and variable speed?

The wind farms’ Vestas wind turbines use variable pitch technology. This technology allows the blades to automatically feather their angle or vary their pitch to suit each wind speed, this allows the controlled extraction of the maximum energy in the wind flow. In sub-optimal wind speed conditions the pitch is tailored to derive the maximum energy potential, so in low winds the blade pitch will be “coarse” with a high blade angle (more “horizontal”). At optimal and higher wind speeds the blades are feathered to a finer pitch with less blade angle to derive a controlled amount of energy, so that the machine produces the rated power in a controlled and stable manner up to cut out wind speed.

The turbine computer controllers are adjusting pitch based on measured wind speed and turbine performance every few seconds. This system, besides maximising the wind energy derived, reduces the torque on the turbine and allows for the use of the full blade as an aerodynamic brake.

The electrical generators in Vestas wind turbines operate on the basis of variable rotation speed, providing stable generation at the grid frequency. This means that they perform as synchronous generators regarding the grid, but they allow for generation at varying speeds of rotation, whereby depending on the wind conditions the turbine's speed of rotation is the most appropriate for the maximum harnessing of wind energy. The power control system is capable of generating electricity at the 50 Hz grid frequency, across a range of generator speeds.

What keeps the Turbines from falling over?

The Allt Dearg turbine foundations are constructed of reinforced concrete discs, 13m in diameter and over 3m deep, laid on exposed bedrock and back filled with well consolidated stone and gravel ballast. The Srondoire foundations are 22m in diameter, with the base tower directly bolted to the concrete. Most importantly the turbines can regulate the amount of energy they extract from the wind, in very high winds the blades fully “feather” with a minimum profile facing the wind, this allows the majority of the wind energy to pass through the turbines. The turbine towers are hollow tapering tubes that are able to flex and bend in gusty conditions, this bending helps to absorb the wind energy across the whole structure, avoiding concentrating energy in the root where the tower meets the ground.

What are the Wind Turbine Blades made of?

The turbine blades have a complex airfoil shape to extract the maximum kinetic energy from the wind. The blades are made of a fibreglass-reinforced polyester hollow shell at the base and a wood-epoxy composite towards the tip – not dissimilar to the hull of a modern sailing boat. This construction is lightweight, and flexible enough to distort under high wind loadings.

Do the turbines get hit by lighting?

Sticking up on top of a hill ensures the turbines are regularly struck by lightning. The blades have lightning conductors located down their length that connect back to the earth network in the turbine, which in turn dissipates the lightning through the heavy copper “earth mat” buried in the ground. The lightning travelling through the blade generates significant heat which can burn or fracture the blade. The communication network between the turbines and the substation is all carried in fibre optic cables, which are well protected from lightning damage.

What’s the thing sticking up on the back of the large V80 turbine nacelles?

The V80 turbines have external oil coolers, mounted on top of the nacelles in a protective fairing. These coolers dissipate the heat generated by the mechanical losses in the gearbox and main bearings.

How are Wind Turbines positioned?

As wind passes through the turbines the flow becomes turbulent and loses energy, the turbines are set out to ensure as far as practical each turbine is exposed to “clean” air flow and wake induced losses are minimised. In practice the wind farm designer will try to keep the turbines separated by a least 6 rotor diameters from the downwind turbines, in the prevailing wind direction, and by at least 4 rotor diameters, in the prevailing cross wind direction. In practice the topography and wind resource of the site will dictate the final layout. At Allt Dearg most turbines are 5 rotor diameters apart looking west, and 3 rotor diameters apart looking north. The final “micro-sited” positions are influenced by local ground conditions to ease the construction of the access tracks and foundations. All the turbines are located on solid bedrock, avoiding areas of deep peat that are not suitable to construct foundations. The most productive turbines are those that receive the “cleanest” wind flow blowing from the south west.