Wind turbines generate electricity by rotating when the wind blows on them. There are a number of different types of turbine, but by far the most common type is the 3-bladed horizontal axis turbine that is used for grid-scale electricity generation, both on-shore and off-shore, and it is these turbines that we shall consider.
First, we shall look at the advantages and disadvantages of off-shore compared to on-shore wind turbines.
Off-shore Wind Turbines
Off-shore wind turbines are built on the sea, and present more difficult engineering challenges, both in transporting the turbine sections to the site, and assembling them on the site. A large, specially designed ship called a Wind Turbine Installation Vessel (WTIV) has to be used to transport all the mast sections, turbine blades and nacelle (the nacelle is the ‘head’ of the turbine to which the blades are attached). These WTIVs have cranes permanently attached to them, and are then used as a platform from which the turbines are assembled.1
All off-shore turbines have traditionally had their foundations in the sea bed. Current diving technology allows turbine foundations to be laid in sea depths of up to about 40m deep, which means they can be sited up to about 30km from shore (depending on how steeply the sea bed falls away).
However, in September 2021, the world’s first floating wind farm became operational off the east coast of Scotland, UK2. Because these turbines do not need to have foundations going all the way down to the sea bed, this technology will allow wind farms to be built further off-shore, where wind speeds are consistently higher, thereby generating more power.
Having wind turbines off-shore is an advantage because:
- The average wind speeds are higher over the sea compared to over land, improving their cost effectiveness due to higher power output
- They are far away from homes and places of work and recreation, so do not cause distress to people who find them visually unappealing
- They do not take up valuable land space - As wind turbines are spaced far apart
Having wind turbines off-shore is a disadvantage because:
- A special WTIV has to be used to transport and assemble the turbine, increasing construction costs –and there are only 137 of these vessels in the whole world (as of October 2020)3 most of which are not large enough for the latest high-power wind turbines
- Carrying out routine maintenance and repairs on the turbines is more costly because getting to them is more difficult
- Sites have to be carefully chosen so as not to disrupt shipping lanes
- Undersea cables have to be laid to supply the generated electricity back to the mainland
On-shore Wind Turbines
On-shore wind turbines are built on the land, and so transportation and installation of the turbines is much easier and cheaper, using vehicles and cranes that are much more readily available than a WTIV.
Building regulations in most countries dictate that wind turbines cannot be installed too close to where people live or work, so finding on-shore sites that are sufficiently far away from housing / populated areas is difficult in smaller countries.
So while a turbine itself does not take up too much land, it is necessary to consider the fact that a lot of land around it is made unusable for housing etc.
Having wind turbines on-shore is an advantage because:
- Access to the site is much easier and cheaper, lowering the cost of installation, maintenance and repair
Having wind turbines on-shore is a disadvantage because:
- Average wind speeds over land is lower than over the sea, so the turbines don’t generate as much power
- Some people find them displeasing to look at
- They take up land and restrict how the land around them can be used
Next, we shall examine advantages and disadvantages of wind turbines in general, compared to traditional coal fired electricity generation plants.
Advantages of Wind Energy Over Coal
1. Cost - Generating electricity from wind costs half as much as generating electricity from coal
Due to increasing investment and technological innovations in the manufacture of wind turbines over the last decade, it is now much cheaper to generate electricity from wind than coal. A study4 by BloombergNEF in April 2020 shows that on-shore wind turbines operate at a Levelised Cost Of Electricity (LCOE) of $44 per megawatt-hour (MWh). To generate electricity from coal fired power plants costs twice as much (LCOE of $88/MWh), according to an IEA fuel report5 from December 2020.
2. Pollution – Generating electricity from wind creates far less greenhouse gas emissions
Carbon dioxide (CO2) is a greenhouse gas. There is overwhelming agreement amongst the scientific community that global warming is being driven primarily by greenhouse gas emissions produced by human activities6.
Studies have been carried out that examine how much CO2 is emitted over the whole-of-life cycle of coal power plants and wind turbines (including manufacture and construction). These studies show that burning coal to generate electricity emits 980g of CO2 for each kWh of electricity generated7 - this is about 80 times higher than the amount of CO2 emitted by wind turbines, which emit between 11-14g of CO2 per kWh over their lifetime.8
3. Availability of fuel – Wind will always be available, coal is finite
The wind will keep blowing as long as the sun keeps shining (which, according to scientists at NASA, is about another 5 billion years9). However, coal and all other fossil fuels will run out much sooner than that. A study by scientists at Stanford University shows that if we continue using coal at the rate we are, the world has enough to last until around 2090 – about 70 years from now.10 After that, there will be no more coal, ever – it will all be gone. Some of us reading this will still be alive when this happens.
Disadvantages of Wind Over Coal
1. Predictability – if the wind doesn’t blow, wind turbines don’t generate
Coal power plants generate electricity for as long as you keep shovelling coal into them. But wind turbines need wind to generate electricity - if there isn’t enough wind to blow the turbine, it cannot generate electricity. Weather forecasts can’t predict wind with enough accuracy to determine in advance how much power is going to be available from any particular wind farm. This causes complications in the management of the national electricity grid. If the output from a wind farm drops unexpectedly, power will be needed to be generated elsewhere on the grid to compensate.
2. Harm to birds – turbines can disrupt bird populations
Both on-shore and off-shore turbines can have a detrimental effect on birds in three ways – disturbance, habitat loss and collisions, according to the UK’s Royal Society for the Protection of Birds (RSBP).11
Not all wind farms disrupt bird populations, but some on-shore wind farms have been poorly sited on land that is important for some birds of prey, for example the Altamont Pass Wind Farm in California. While hunting for prey, birds that fly through the ‘swept area’ of a wind turbine (the circular space marked out by the three rotating turbine blades) run the risk of being struck, injuring or killing them. A 2009 study shows that by replacing older wind turbines with fewer, more powerful turbines at the Altamont Pass site could reduce bird deaths by up to 65%.12
There are also mitigations that can be taken to reduce fatalities of marine birds at off-shore wind farms too. Sea birds tend to fly less than 40m above the surface of the sea, so larger turbines which have a lowest blade swept point that is higher than 40m will mean “you may not have a measurable impact [on marine bird fatalities] at all”, according to the UK director and vice-president of Niras, an international engineering consultancy.13