Offshore vs. Onshore Wind Turbines: Which Is Best?
 Topic: differences between onshore and offshore wind |  Read Time: 8 mins |
 Landowner type:Independent landowners | Institutional landowners | Professional advisers | Site Operator |  Energy:Offshore wind | Onshore wind |
23rd August 2024Are you looking for a detailed rundown on offshore vs. onshore wind turbines? Whether you’re interested in the main differences between the turbine types or simply want to figure out the advantages and disadvantages of each, this article will explain everything you need to know.
Although you may be familiar with offshore and onshore wind turbines, have you ever wondered how they differ? Well, I’m here to tell you everything you need to know.
This blog post will explore the key differences between offshore and onshore wind turbines. I’ll look at their benefits and drawbacks to reveal which option might be best suited for specific locations and situations.
What Is Onshore Wind Energy?
Onshore wind energy is power generated by wind turbines that are located on land.
You’ll typically find onshore wind turbines in less-populated rural areas. Not only are average wind speeds usually higher in these areas, but there are fewer buildings around to disrupt the flow of wind.
Onshore turbines have been around in some form since 1887 when Professor James Blyth used a small one to generate electricity in Scotland.
Commercial wind power was only truly realised in 1991 when the Delabole Wind Farm burst onto the scene. These days, there are more than 1,500 operational onshore wind farms across Great Britain, which generate a total of 34.7 terawatt hours a year.
What Is Offshore Wind Energy?
Offshore wind power is energy taken from the force of winds that are out at sea (so these turbines are not land-based).
The winds produced offshore tend to be much faster, as they’re blowing across the sea with no obstacles to intercept them. Generally, offshore turbines are larger than onshore turbines. They’re also built with hardier materials to withstand the often brutal wind speeds.
Space isn’t typically an issue with offshore turbines, meaning you can make a dedicated wind farm with turbines spread across a vast ocean area. Each turbine is usually fixed to the seafloor with a strong foundation, and developers prioritise using extremely strong steel foundations to mitigate damage and reduce the need for maintenance.
The UK is home to the largest offshore wind farm in the world as of 2023. Hornsea 2 is the brainchild of Danish firm Ørsted and is tucked around 89 kilometres off the coast of Yorkshire. It boasts a whopping 1,320 MW capacity and houses 165 turbines that generate enough energy to power 1.4 million homes.
What Are the Differences Between Offshore and Onshore Wind Turbines?
Size
The main difference between offshore and onshore wind turbines is their size.
The average capacity of an onshore turbine is between 2.5 to 3 MW, with a height of around 94 metres and blades clocking in at around 50 metres long.
By comparison, offshore wind turbine blades can be as long as 150 metres, with an impressive turbine height of up to 260 metres. So an offshore turbine is almost 3.5 times larger than an onshore turbine.
Offshore turbines’ capacity is normally around the 8 to 12 MW mark. But remember that the output will always depend on the turbine height, blade length and wind speeds around the area.
Location
As mentioned earlier, the highly tensile steel used for offshore turbines can cost a pretty penny. However, onshore turbines don’t face the same harsh factors as offshore ones. So, they can be constructed with easier-to-find materials.
Tensile strength of steel
The material developers use for the foundation of offshore turbines depends entirely on their depth. Some wind farms can’t rely on large steel piles or lattices because the water is incredibly deep, and the pressure of the water would degrade these materials over time.
To address this issue, several companies are using floating platforms called spar buoys to support turbines above the sea floor.
If offshore turbines use steel, it’s usually of a higher tensile strength than developers would use for onshore turbines. As well as being stronger, the chemical composition of this steel is also less resistant to corrosion, giving it the power to withstand the harsh environment out at sea.
Onshore turbines are also built from high-grade steel, which is usually more flexible than the varieties used at sea. Like offshore turbines, the average onshore turbine’s material makeup also includes fibreglass resin, iron or cast iron, copper and aluminium.
Advantages and Disadvantages of Onshore and Offshore Wind Turbines
Now that I’ve covered what sets onshore and offshore wind turbines apart, let’s examine their advantages and disadvantages.
Advantages of onshore wind turbines
Less expensive to build and maintain
Onshore wind turbines are typically far cheaper to build and maintain than offshore wind turbines. This is partly because they’re more accessible, but the infrastructure developers use to construct the turbines is usually more affordable.
As mentioned earlier, the highly tensile steel used for offshore turbines can cost a pretty penny. However, as onshore turbines don’t face the same harsh factors as offshore ones, they can be constructed with easier-to-find materials.
But it’s not just the materials that boost the cost of constructing offshore turbines. Building out at sea requires a lot of specialist labour and machinery. As a result, many companies charge a premium due to the more dangerous work.
Developers can build them quickly
New wind farms can take a while to construct. This timeline includes getting planning permission and having fully functional turbines on a plot of land.
In my experience, the overall process takes between three years and eight months. This timeline runs from receiving planning permission to getting the turbines up and running. Of course, you may find a project with lead times that are far less or greater than this figure, but this is a great ballpark to work with.
Onshore wind turbines can also quickly connect to the Grid, while offshore turbines use complex undersea cables to transmit energy.
Offshore wind farms are a complete labour of love, which may put certain developers off. They can take an incredible seven to 11 years to build, and construction times may be even longer if there are supply-side delays.
Lead to local jobs
One of the major winning points in the offshore vs. onshore wind turbines debate is that onshore wind often leads to local jobs. The UK needs 400,000 jobs in the energy sector to reach net zero by 2050. More onshore wind vacancies will shift us closer to that figure.
It’s worth noting that these additional jobs can come in several different forms, including:
- Passive income for landowners leasing their acreage
- Construction jobs
- Supply-side jobs relating to materials
- Site operator work
- Developer work
This list isn’t exhaustive, but the economic value of onshore wind goes far beyond the energy production process.
Disadvantages of onshore wind turbines
Variable wind speeds that cause intermittent generation
One of the main disadvantages of onshore wind turbines is that wind speeds around the UK can be relatively variable. Although average wind speeds in the country are somewhat stable, extreme dips in wind speed can cause significant issues regarding output.
While this isn’t necessarily a huge problem, achieving consistent power generation can be challenging. And for developers (and landowners on variable payment arrangements) who rely on certainty, investing in onshore wind can sometimes feel like a gamble.
Impacts on people and nature
Opinions on wind farms can vary across the country. While some people dislike the appearance of turbines in the landscape, 80 per cent of people in the UK actually support onshore wind energy.
But while onshore wind power impacts humans, it also impacts bird and bat mortality. When birds or bats are in soaring flight, they’re extremely vulnerable to colliding with turbines.
Aside from mortality, biologists around Finland have found that 70 per cent of animals can be displaced from their homes if developers choose to erect turbines near their habitats. A valid Wildlife Impact Assessment can mitigate the overall impact, but there will always be residual fallout for wildlife.
But studies have shown that birds’ wings can adapt to the increased movement of turbine blades from up to 120 metres away, giving them ample time to avoid a collision.
Advantages of offshore wind turbines
Wind speeds are higher, which leads to greater outputs
Wind speeds are generally far higher out at sea, which makes offshore turbines a clear winner in the generation subsection of the offshore vs. onshore wind turbines debate.
In 2023, the average onshore wind speed in the UK was around 4.29 m/s (9.60 mph). Comparatively, offshore wind speeds are usually around 8.90 m/s (19.91 mph).When you add the higher wind speeds to the greater potential capacity of the larger turbines at sea, it’s easy to see why they generally produce more reliable energy.
Generally unaffected by ecology restrictions
I’ve already established that onshore wind turbines can majorly affect local wildlife. As a result, finding an adequate location for these turbines is often extremely difficult.
But offshore turbines have little visual impact and are far away from local ecosystems, making them easier to place.
This isn’t to say that developers don’t need to consider local marine life. However, as long as plans consider local fisheries, there should be minimal pushback.
Disadvantages of offshore wind turbines
More expensive
The typical offshore wind turbine costs approximately £4.49 million per MW to build and maintain – a colossal figure.
Considering these turbines have an average capacity of 8 to 12 MW, you’re looking at anywhere from £35.92 million to £53.88 million per turbine. A commercial wind turbine with a capacity of 3.5 MW can cost around £3.13 million – a considerable difference for developers.
Challenging to maintain
A combination of high-speed winds and severe currents at sea makes offshore wind farms tricky to access. These conditions can damage infrastructure, and developers will need to hire highly skilled workers to maintain the complicated technology inside the turbines.
Although cost is one consideration, these access difficulties also mean that maintenance takes time. From the time it takes to reach the turbines to the long hours spent figuring out issues and solutions, it can be an arduous process.
So, Who Wins in the Offshore vs. Onshore Wind Turbines Debate?
There’s no strict correct answer about which turbine is better than the other. Each turbine type has its unique benefits and drawbacks when it comes to generating energy.
Generally, offshore wind turbines are a better option for reliable energy generation. But they’re not a great choice if you’re looking for something easy to maintain or access.
On the other hand, onshore wind turbines are slightly less reliable (due to lower wind speeds inland). But they’re cheaper, easier to manage and often benefit the local community.
So each type of wind turbine has its pros and cons. The only question is, which turbine is right for your investment?
If you want to place turbines on your land, contact the team at Lumify Energy. We’re experts in onshore wind and will gladly guide you through the process of placing turbines on your land.
From dealing with developers to checking over lease agreements, we’ll ensure you get off to the best start.
