Wind power 101: The science behind our largest source of renewable power

One day in early June this year saw wind energy contributing 10% to the UK’s energy mix, and we’ve welcomed some innovative wind energy projects – but how much do you know about the actual workings behind wind power?

wind power, wind energy, renewable energy, how, work

A brief history…

Wind energy was first used in windmills to mill grain in Northern Europe and later became popular in America, where small mills were used for pumping water.

By the turn of the 1900s, the first windmill for electricity generation was used to power a Scottish holiday home. Today, the installed global capacity of wind energy is estimated to be 487 GW.

Wind energy has seen such a huge jump because it has a number of advantages: the source is free, inexhaustible, environmentally friendly and cost effective.

As such, wind turbines have become a very popular way for energy companies to diversify their energy portfolios while also helping to green the electrical grid.

Read more: 14 little-known facts about wind energy

How do wind turbines work?

When we refer to wind power, what we’re talking about is the kinetic energy available in the airflow, which can be harnessed to generate electricity.

A turbine is composed of the rotor and rotor blades, which are attached to the nacelle, the hub at the top of the turbine which houses the moving parts. The internal mechanisms include a gearbox and a brake, both the low-speed and high-speed shafts, and the generator.

When wind passes over the rotor blades, they begin to rotate. This rotation turns both the low-speed and high-speed shafts. The gearbox steps up the rotational speed, and the generator begins to produce electricity.

The most common type of wind turbines that we see are Horizontal Axis Wind Turbines (HAWTs), which refers to the orientation of the rotor shaft and generator.

HAWTs rely on aerodynamically designed blades which catch the wind efficiently, but they have a theoretical limit.

The Betz Limit – named after the German physicist Albert Betz – dictates that no wind turbine will be able to convert any more than 59% of the energy contained in the wind.

There are physical limits, too. Turbines can only operate up to a certain wind speed, above which the internal mechanisms would come under stress and break. As such, the machines are self-monitoring and can shut off to prevent damage.

The physics of wind

The heating of the earth by the sun – which happens at different rates at the equator and the poles – and the rotation of the planet cause atmospheric air to move around the globe, which we experience as wind.

As air moves across the planet, it is affected by geographical and topographical features across the globe; variable terrains such as mountains and valleys, or coastal areas, are subject to their own unique wind patterns as a result of the atmospheric movement.

As long as the earth continues to rotate around the sun until the star burns out – in an estimated five billion years’ time – the planet will continue to be buffeted by winds. This means that wind will forever be a free and inexhaustible source of energy, but the energy contained within it will change depending on the terrain it crosses.

Onshore versus offshore

It’s clear that turbines are worth having, but it’s often about deciding where to put them. Whether located onshore or offshore, they come with their own advantages and disadvantages.

The biggest consideration for the placement of turbines is the wind potential of a given area; this changes across the globe.

This means that landscape features – natural ones such as hills and forests, or manmade ones such as offices and apartment blocks – can alter the airflow and the energy available within it.

With onshore wind, there are more geographical features which could limit airflow. This, combined with the fact that onshore turbines are physically smaller than their offshore counterparts, means there is generally less energy generated per turbine.

They are also controversial amongst nearby communities due to the sight- and noise pollution they cause. Turbines can also have an ecological impact, especially if placed near bird migration routes.

Wind turbine in a remote part of Scotland, Europe

Read more: How are wind turbines built?

Out at sea, however, offshore turbines are exposed to much more favourable conditions.

On the open water, wind speeds are higher, steadier, and more consistent. This is important for a few reasons: firstly, wind power increases with the cube of wind speed. This means that a doubling in the wind speed equals an increase in power output by a factor of eight, vastly increasing the amount of electricity that can be generated.

Secondly, steadier airflow means lower turbulence, which improves the longevity of turbines. Longer lifecycles mean a lower Levelized Cost of Energy (LCOE) for manufacturers; this is subsequently reflected in electricity prices for consumers.

Paul Sclavounos, a professor of Mechanical Engineering at the Massachusetts Institute of Technology (MIT), estimates that more than 75% of global energy demand is clustered around coastal areas. If those estimates are correct, it seems sensible to base electric generating turbines close to those coastal areas.

Offshore: Fixed versus floating

When it comes to offshore wind, the biggest question is whether the turbines should be fixed or floating.

The wind energy industry has focussed on turbines fixed to the seabed in (relatively) shallow waters, up to a depth of 50 metres. As such, fixed turbines are particularly widely used across Northern Europe.

Read more: Denmark’s largest offshore wind farm

However, this limits their effectiveness. As stated above, turbines on the open sea are exposed to more favourable conditions for electricity generation; pushing them further out to sea makes them more effective and efficient.

Further out to sea the waters become deeper, which is problematic because the cost of fixing turbines to the seabed quickly spirals out of control.

Due to the depth of the water, the North Sea is more suited to floating wind turbines than fixed. As such, floating turbines could become the new standard in European waters; the International Renewable Energy Agency (IRENA) has called them “game changers”.

wind farm, wind turbines, Denmark

The sector offers a great deal of promise. Because the floating turbine industry is in the early stages of development, construction costs are higher, but these will fall as the sector becomes more established.

Professor Sclavounos of MIT believes that the industry should look to offshore Oil & Gas; for years, these industries have used floating rigs to reach undersea stores of oil and gas.

In 2004 Sclavounos began working with the US National Renewable Energy Laboratory to design a floating turbine, which would rely on a tension-leg platform to secure it. Tension-leg platforms are a common feature of offshore oil platforms and are therefore a proven technology when it comes to stabilising a floating structure.

Scotland will be the home of the world’s largest prototype floating wind farm, with the construction given the green light in 2016; the Hywind project will feature five 6MW turbines. This will play a huge part in the further development of the floating wind sector, which experts have said needs to be supported independently of the traditional offshore wind sector.

Read more: Scotland gets green light for floating wind farm 

In numbers: Countries generating the most wind power

Installed capacity:

1. China (169 GW)

2. US (82 GW)

3. Germany (50 GW)

4. India (29 GW)

5. Spain (23 GW)

6. UK (15 GW)

7. France (12 GW)

8. Canada (12 GW)

9. Brazil (11 GW)

10. Italy (9 GW)

What other renewable power sources are supplying the UK? Read more in our ultimate guide to renewable energy technologies.