The brain power behind wind power
I’m Charlotte, I have a background in Environmental Science and I am fascinated by how wind turbines work, in particular, offshore wind farms. We’re one of the largest investors of renewable generation in Europe, and we’ve also started generating our own power too – initially with 2 turbines (which we’ve called #1 Fan and #2 Fan), and we have 30 more turbines in the pipeline - check out Tom Scott abseiling down #1 Fan.
Our interviewee, Robin O'Connell
With the Prime Minister's new plan to boost Britain’s energy security following rising global energy prices (which could see 95% of Great Britain’s electricity set to be low carbon by 2030) and his recent pledge that offshore wind farms will generate enough electricity to power every home in the UK within a decade, I wanted to know a bit more about how wind turbines actually worked. So, I decided to sit down with Robin O’Connell, the team lead for Naval Architecture at Kent (aka my brother in law), who just so happens to design floating platforms for offshore wind turbines.
Charlotte: So Robin, my first question to you is... how on earth do you secure a wind turbine in place offshore and how do you get the massive turbine parts out to sea?
Robin: This varies depending on the type of wind turbine you’re installing. The two main types of turbine foundations are fixed-bottom and floating.
On the left are ‘fixed-bottom’ turbines and on the right are ‘floating’ turbines
The UK is surrounded by a continental shelf, so we have plenty of shallow water (less than 60m), making fixed-bottom turbines a suitable option here. For fixed-bottom wind farms, the components (turbine foundation, turbine tower, nacelle, and blades) are transported to the wind farm location on an installation vessel - this is an expensive operation and depends on having calm weather conditions.
Fixed-bottom turbine installation vessel
The turbine foundations can then either be secured in place by tubular piles (steel tubes driven roughly 30m deep into the seabed by offshore cranes) or simply be heavy enough so that they can be sat on the seabed (these need a diameter of ~15m at the base). Once the foundations are secured, the offshore cranes can install the remaining turbine components. The installation vessels have ‘legs’ (see image on the right) which raise the vessel out of the water to keep it in place during the installation process.
A floating wind turbine being towed out the the wind farm
Floating turbine foundations are more suitable for deeper water, but only a few have been installed so far. For floating wind farms, most of the construction can be done at the quay side and the turbines can be towed out to the location without the need for big installation vessels or heavy lifts. The turbines float in position and then are held in place by a mooring system (made up of mooring lines, anchors and connectors) which secure them to the seabed.
We’re hoping there'll be a large increase in the number of floating turbines over the next 10 years as offshore wind moves further offshore and into deeper water.
Charlotte: I can imagine designing and installing offshore wind farms comes with many challenges?
Robin: Offshore wind farms have to operate in challenging environments and must resist very large loads from the wind and waves. You have very significant wave loading on the structure and this causes problems for both the extreme strength of the structures (a single large wave pushing over the platform) and the fatigue strength of the platform. Fatigue is where the steel is weakened by repeated cyclic loading and this comes from both the wind and the waves. The analogy which is often used is bending a paper clip backwards and forwards until it breaks.
A diagram of wave loading on a wind turbine foundation
In addition to this, there is the challenge of transporting construction and maintenance engineers to the wind farm - this is normally done by special crew transfer vessels with specially designed bows (front end), as these can push up against the boat landings and allow crew to transfer to the turbine platforms safely.
The UK is truly a world leader in offshore wind turbines and we’re beginning to export a lot of the technology that we have developed to other countries. This will start to have a big impact on the global energy mix as countries such as China adopt it in a big way (and they are starting to).
The map below shows some of Kents global offshore wind farm projects.
Charlotte: Well done to all you engineers working to overcome these complex offshore challenges! How do we get the offshore electricity into our homes?
Robin: Offshore wind farms use undersea cables in the seafloor to transmit electricity to the National Grid via a single offshore substation where the voltage is increased. Electricity is distributed from there to our homes and industries.
Charlotte: With the challenging offshore installation process covered, how do wind turbines actually work?
Robin: Turbine blades have an aerofoil shape which creates a pressure difference between the top and bottom surface at wind speeds as low as 7-11 mph. This pressure difference makes the blades rotate. This rotation powers the generator (housed in the Nacelle - the big box you see on top of the turbines), which converts the wind energy into electricity which is then transmitted to the National Grid.
The turbine's control system will rotate the Rotor Nacelle Assembly (the blades, hub and nacelle) to ensure it is pointing into the wind and generating power efficiently. Once the wind speed exceeds ~25mph, the turbine will be generating maximum power. You don’t see turbines turning in high winds (roughly 50+mph) or storms as the turbines are shut down to avoid damage.
Check out our video with Electrifying for more info!
Charlotte: And how long do they last?
Robin: They have a useful life of 20-25 years. At the end of their life, most of the structure is made of steel which can be recycled very efficiently. The turbine blades are made of composite material which can pose more of a challenge, but plants to recycle the turbine blades are currently being developed.
Charlotte: That’s great to hear that most of the structure is already recyclable! Why don’t we just build more of them? And bigger ones?
Robin: We actually are building bigger ones - 5 years ago a 5megawatt (MW) turbine with a rotor diameter of 126m was considered very large. Now we have 12MW turbines with a rotor blade diameter of 220m, and bigger ones are in the pipeline. Each is similar in height to the Shard (that’s over 1,000 feet tall).
There are already over 11,000 wind turbines in the UK (producing nearly a quarter of the UK's electricity), mostly onshore, but Planning Permission and Local Authorities do restrict turbine locations, so we can’t put them up everywhere and anywhere.
Charlotte: That makes sense. Octopus Energy Generation recently invested in Simply Blue Holdings, which is an Irish renewables developer specialising in floating offshore wind farms. Tell us more about the advantages of engaging in this technological field.
Robin: There are many benefits to offshore farms, including;
- The wind is more consistent, so the full potential of the turbines can be met.
- There’s a lot more space available and so there is minimal disruption to human activity.
- Ships and large floating cranes are able to transport and install the turbine components. These are huge, so it is not so easy to transport them around by road.
- The impact on animals and birdlife is lower offshore (as long as the locations are carefully considered). However, their installation can affect marine life, especially sensitive mammals like whales and dolphins so the way they’re installed, the locations they’re installed in and the times of year they’re installed need to be carefully considered and managed.
Charlotte: As we know, climate change and fossil fuels have an irreversible effect on the environment and living species, so with careful planning, wind farms are definitely friendlier to our natural world. Why can’t we just ditch the ‘dirty’ fuels and run off 100% renewables right now?
Robin: As we don’t currently have enough renewable energy capacity to run off renewables alone (or the infrastructure in place to cope with intermittent energy supply), the UK electricity system relies on a mix of ‘firm’ and ‘intermittent’ sources of power. Renewable energy is intermittent because it’s not always windy and the sun doesn’t always shine. Recently there have been periods of a few weeks at a time where the UK used no coal to generate electricity for the grid. This may not sound that exciting, but 2019 was the first time the UK achieved this since the start of the industrial revolution.
We also currently need fossil fuels for transportation, aviation, shipping, and heating. There are studies ongoing at the moment which are looking at using offshore wind energy to generate Green Hydrogen which can be used as an environmentally friendly replacement (check out how Octopus Energy does green power).
Charlotte: That makes sense - Octopus are also trying to help drive the movement to electric heating and transportation through heat pumps and electric vehicles. How can we move to a 100% renewable grid?
Robin: There are 3 key things being developed that would help us move to a 100% renewable grid;
Storing energy: There are methods for storing renewable energy such as pumping water up a hill when excess energy is available (i.e. at night) and using it to drive turbines when extra capacity is required, but these are limited. Other options being investigated include using wind energy to generate hydrogen. The hydrogen can then be stored and used to generate electricity as and when it is needed.
Creating a constant supply: The UK is investigating other ways of generating green electricity such as tidal (where tide causes the blades to turn). Tidal energy is still intermittent as water must be flowing for energy to be produced, and at high/low tide the flow of water slows down to a standstill. However, one big advantage is that it’s completely predictable. High and low tides also vary around the country, so you can have some tidal turbines on one side of the country which aren’t generating any electricity but this could be balanced out by tidal turbines which are generating on the other side of the country.
Changing consumer patterns: Reducing the daily peak energy demand will help the grid cope with intermittent renewable energy supply. I’ll let you discuss how Octopus are taking big steps towards achieving this.
Charlotte: Yes, we’re working towards changing consumption patterns by rewarding customers for using energy when renewables are most abundant, and reducing consumption during daily ‘peaks’ in demand that renewable generators struggle to meet. Some examples include the launch of Powerloop and the Big Switch On. But as we’re on the topic of turbines, let's take a closer look at how our windy-tariff Fan Club is helping the drive to a 100% renewable, smart flexible grid. Fan Club is the UK’s first energy tariff to give customers living near to our turbines the benefits of local renewable energy production in real-time. By providing mega discounts to energy prices when the wind blows, this tariff rewards customers for shifting their energy use to when their turbines are generating energy.
Charlotte: Finally Robin, out of total curiosity - is there a particular reason why turbines are always white?
Robin: There are 3 reasons; One is to prevent accidents - pilots can see white turbines clearly against the sea/grass/landscape. Two is to reduce the need for maintenance - white reflects the sun, so therefore the metal turbine doesn’t absorb the heat which would impact its state and need for maintenance. And three is to reduce cost - white paint is simply cheaper than pigmented paints.
As gutted as we are that we can’t turn all our turbines pink, we’ve found some creative ways to get around it with light projections, check them out.
A big thank you to Robin for letting me borrow his engineering brain power for this blog - a crate of Octopus IPA is on its way to say thank you!
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