1.1. Energy transition and pathways to achieve net zero

Energy transition must involve decarbonization of the economy, and the backbone of a modern economy is energy. A practical way to achieve the net zero target is to run the country mostly on electricity where possible, producing energy from renewable sources without burning much fossil fuel. Ideally, one should have an entirely clean energy-based system through a mix of renewable, sustainable and low-carbon sources, and this is technologically feasible.

1.2. Wind power

Wind power is of course a well-established renewable energy technology and has the potential to tackle many current technological and societal challenges such as sustainable energy sources and air pollution reduction. Wind power has been used for centuries for sailing ships, sawing wood, grinding grains, and moreover it is one of the oldest sources of ‘machine’ power. The invention of wind-powered sawmills by Dutchman Cornelis Corneliszoon van Uitgeest in the late 16th century helped Holland increase ship production through automated wood-cutting, outcompeting their European rivals who were relying on slow manual processes. Figure 1a shows a windmill from Holland used for sawing wood. Modern-day wind power is harvested through wind farms, either onshore or offshore. Offshore wind farm has plenty of advantages due to scalability, higher energy generation, faster construction and reduced time to get planning permission.

Figure 1. Wind energy generation (16th century) and modern day (21st century).

Offshore wind farms provide new, carbon-free, generation assets that are now rapidly scaling in the EU, East Asia, and while more slowly, the United States is joining this push with a 2030 target of 30 GW (Figure 1b). These turbines convert the kinetic energy of wind into electrical energy, which can be used to power homes and businesses. Offshore wind farms can also be larger than onshore ones, as the wind is often stronger and more consistent over the ocean. Additionally, they do not take up land space and can have less visual impact on the surrounding area. By using renewable energy sources like wind power, the offshore wind farm can help reduce greenhouse gas emissions and decrease dependence on fossil fuels.

A typical offshore wind farm can generate 1 GW of power, approximately equivalent to two standard nuclear power plants (NPP). A typical wind turbine can produce 10–18 MW of power, and therefore 1 GW of offshore wind farm power involves installing 60–100 offshore turbines. Figure 1 compares 16th-century windmills with modern-day wind power.

Figure 2 shows a schematic of offshore farm with the main components: energy generation assets (wind turbines) and transmission assets (substations and the electric cables) that feed the national grid. A typical wind turbine comprises three rotor blades, a nacelle, a rotor hub, a tower and foundation. The main raw materials for manufacturing the turbines are steel (typically 66–79%), glass fibre/carbon fibre and plastic (11–16%), iron/cast iron (5–12%), copper (1%), aluminium (1–2%). Table 1 summarizes the materials inventory used for wind power generation. Currently, 85–90% of the materials used in wind power generation can be recycled. Recycling of blades is currently a challenge due to the composite nature and they are often repurposed to construct roofs, bike sheds, foot bridges and so forth There are other ideas for blade recycling through energy recovery where blades are shredded and can be used as fuel in cement kilns or power plants to generate heat or electricity.

Figure 2. Schematic of a wind farm.

Table 1. Materials used for the construction of wind farm

Figure 3 shows a wind resource map showing the wind speed along the coast based on the study conducted by the World Bank. Average wind speeds (WS) over 7 m/s are considered to constitute a financially viable project. Figure 4 shows power curve for six turbines, which shows the energy production corresponding to wind speeds. It is clear that wind turbine produces the maximum power at wind speed of about 12 m/s.

Figure 3. Global offshore wind speeds (World Bank Initiative, 2020).

Figure 4. Power curve.

International Energy Agency (IEA, 2019) in their special report showed that offshore wind can generate 11 times more electricity than the world needs. There are a few more similar studies such as Possner and Caldeira (Reference Possner and Caldeira2017) where it is shown that offshore wind farm of the size of India in North Atlantic can produce enough electricity to power the world. Essentially, the untapped potential of offshore wind is vast. Based on IEA assessments, offshore wind could potentially generate a whopping 420,000 terawatt-hours of electricity globally per year while the entire world consumed 23,000 terawatt-hours of electricity in 2018.

1.3. Innovation in wind turbines

Figure 5 shows the evolution of wind turbines over the past 20 years, and this is clearly due to innovation. The turbine rated power increased by 10 times in a span of circa 20 years. In other words, one machine can produce 10 times more electricity (i.e. 2–20 MW) and can also operate in different extreme conditions. These machines are smart in the sense that the turbine can turn horizontally towards or away (known as yaw control) from the wind in order to maximize energy production. The blades are also designed to twist (pitch control) during the operation for better performance/energy generation as well as during extreme wind condition (i.e. hurricane/typhoon) to avoid damages.

Figure 5. Nameplate capacity innovation in wind turbines.

1.4. Aside: Oldest, largest and a smart machine

Wind power has an established track record for centuries and is the oldest source of ‘machine’ power which fits the definition of a machine (namely a piece of equipment with several moving parts that uses wind power to carry out a particular type of work such as sawing wood). It can also be said that offshore wind turbine machines are also the largest moving machines. A typical 10 MW turbine will have three 80-m-long blades and each weighing circa 35 tonnes turning at average of 8–10 RPM. As mentioned in the previous section, the machine carries out control operation through yaw action or pitch to maximize power production.

2.1. Origin of wind resources

Simply put, wind will blow as long as the sun is shining. The ultimate source of energy responsible for the creation of wind is the sun. Sun bombards the surface of the earth with radiation energy leading to a continuous warming. Out of this energy, the largest amount is sent back to space and only a small amount is transformed into heat energy. Due to the shape of the earth and having different materials (water and land), its surface is not heated evenly resulting in the equator getting more energy than the poles. As a result, there is a continuous heat transfer from the equator to the poles.

The atmospheric air consists of nitrogen and oxygen and they expand when heated and contract when cooled. Solar radiation causes the air to get warmer and lighter and less dense than cold air. This also results in the rise of warm air to higher altitudes and the creation of areas with lower atmospheric pressure, where the air is warmer. Due to the variance in pressure, the air will move from a high-pressure to a lower-pressure area, in an attempt to reach equilibrium, thus causing wind.

Wind is essentially atmospheric air in motion and is very complex; see Figure 6. At 30° and 60° latitude, there is a major change in atmospheric pressure creating zones of high and low pressure, respectively. The air circulation within these zones is known as cells and the major winds thus created as trade winds. Due to the diurnal motion of the earth, the wind deflects to the right in the northern hemisphere and to the left in the southern one, leading to a spiral movement of the air mass; this phenomenon is known as the Coriolis Effect. Figure 6 describes the mechanism of the above global wind system. In addition to this global wind system, there are localized influences as well and are mostly related to the terrain of an area and its proximity to water bodies. For further details, see Letcher (Reference Letcher2023).

Figure 6. Global circulation of wind.

2.1.1. Storage of wind power: Battery

The power curves in Figure 4 show that a turbine can generate power from a wind speed starting from as low as 4 m/s and reach the rated power at about 12 m/s. It is often argued that wind does not blow all the time, and when you need power, there may not be the desired wind. Also, when the wind is blowing at optimum speed, there may not be the need for the power. To combat these problems, technologists have developed systems that can store the excess electrical power generated by wind in batteries, optimizing it with the grid.

The combination of offshore wind and storage technologies, such as batteries, will become important to secure grid stability. Figure 7 shows a schematic of battery storage. For example, the Japanese wind farm Ishikari Offshore Wind project located around 3 km off the coast of Hokkaido will comprise 112 MW of wind power generation from 14 Siemens Gamesa 8 MW wind turbines and will be paired with the 100 MW/180 MWh BESS (battery energy storage system). However, such technologies often need rare earth metals for battery production, which needs unsustainable extensive mining and effects of commodity trading (similar to oil and gas trading). The next section shows another technology (dispatchable fuel) that may address some of the above challenges.

Figure 7. Combining offshore wind with battery storage.

2.2. Hydrogen production using offshore wind: The Japanese ‘Jidai’ concept

The 2011 Fukushima Daiichi NPP disaster was a watershed moment in the history of mankind; see Bhattacharya and Goda (Reference Bhattacharya and Goda2016). Following the disaster, many countries such as Germany and Japan reduced their reliance on nuclear power and compensated with fossil fuels and renewables. Within the framework of global warming, and among others such as energy security, Japan aims to become a carbon-free country through a ‘hydrogen society’. The main idea is to generate hydrogen from water through renewable energy sources such as wind, solar and hydroelectricity. Japan named it the Jidai concept. Similar attempts are also ongoing in major European economies. These attempts have been boosted by other technology developments such as the invention of hydrogen-powered cars, trains, ships and even aircrafts.

The Jidai concept shown in Figure 8 is a four-step process: (a) seawater is desalinated; (b) electrolysis is used to produce hydrogen and oxygen from water; (c) hydrogen gas is compressed to 700 bar to reduce storage volume; and finally (d) high-pressure hydrogen gas is stored in a module-based tank system that can be used in fuel cells or via direct combustion.

Figure 8. Green hydrogen: An application of offshore wind.

Ongoing studies demonstrate that a 100% hydrogen gas network is equally as safe as the currently popular natural gas. It is worth noting that burning natural gas to heat homes and businesses accounts for approximately a third of the UK’s carbon emissions. Hydrogen-powered commuter trains are available, and it has been reported in New Civil Engineer that 30% of the UK rail fleet could be suitable for running hydrogen-powered trains (Ibbetson, Reference Ibbetson2019; Bhattacharya et al., Reference Bhattacharya, Fthenakis and Kammen2021). In summary, wind power has the potential to carry the transition to low carbon energy, transforming the fossil fuel energy landscape to a more sustainable energy future.

3.1. Case study: Performance of near-shore wind farm during 2011 Tohoku earthquake

A devastating earthquake of moment magnitude 9.0 struck the Tohoku and Kanto regions of Japan on 11 March 2011 at 2:46 PM, which also triggered a tsunami; see Figure 9 for the location of the earthquake and the operating wind farms. The earthquake and the tsunami caused effects such as liquefaction, economic loss, loss of life, damage to national infrastructures but very little damage to the wind farms. Extensive damage was also caused by the massive tsunami in many cities and towns along the coast. Figure 10 shows photographs of a wind farm at Kamisu (Hasaki) after the earthquake, and Figure 11 shows the collapse of a pile-supported building at Onagawa where for the first time the world saw complete uprooting of piled foundations. At many locations (e.g. Natori, Oofunato and Onagawa), tsunami heights exceeded 10 m, and sea walls and other coastal defence systems failed to prevent the disaster.

Figure 9. Details of the 2011 Tohoku earthquake and locations of the wind farms.

Figure 10. Photograph of the Kamisu (Hasaki) wind farm following the 2011 Tohoku earthquake.

Figure 11. Collapse of the pile-supported building following the same 2011 Tohoku earthquake.

The earthquake and its associated effects (i.e. tsunami) also initiated the crisis of the Fukushima Dai-ichi NPP. The tsunami, which arrived around 50 minutes following the initial earthquake, was 14 m high which overwhelmed the 10-m-high sea walls, flooding the emergency generator rooms and causing a power failure to the active cooling system.

Limited emergency battery power ran out and subsequently led to the reactor heating up and the subsequent meltdown leading to the release of harmful radioactive material to the surrounding environment. Power failure also meant that many of the safety control systems were not operational. The release of radioactive materials caused a large-scale evacuation of over 300,000 people and the clean-up costs are expected to be of the order of tens of billions of dollars. On the other hand, following/during the earthquake the wind turbines were automatically shut down (like all escalators or lifts), and following an inspection, they were restarted.

3.1.2. Forward outlook

If there had been more offshore wind turbines operating, the disaster may have been averted or the scale of damages could have certainly been reduced. The wind turbines could have run the emergency cooling system and prevented the reactor meltdown. Figure 12 shows schematically the proposed additional backup system to enhance resilience of offshore wind farm system. A study has been conducted by Kolli et al. (Reference Kolli, Dammala, Bhattacharya, Fan, Wang and Cui2023) to show the application of such a system for an NPP in India.

Figure 12. Proposition of additional backup power for resilience of NPP.

4.1. LCOE

LCOE is a metric used to assess the cost of generating electricity from a particular energy source over its entire lifespan. It is a standardized way to compare the cost of different energy technologies. The LCOE takes into account all the costs associated with a specific energy project, including the initial investment, operational and maintenance costs, fuel costs (if applicable and is zero for wind) and the expected energy output over the project’s lifetime. These costs are then spread out over the expected energy production to calculate the levelized cost. LCOE allows for a fair comparison of different energy sources, such as solar, wind, coal, natural gas and nuclear power. By considering the lifetime costs and energy output, it provides a more comprehensive understanding of the economic viability and competitiveness of different energy options. Figure 14 shows the global trend in LCOE of offshore wind, following Machiridza and Bhattacharya (Reference Machiridza, Bhattacharya and Letcher2023), and this clearly shows a descending trend. For the UK, the reduction of cost is remarkable: LCOE for offshore wind reduced from £160/MWh to £44.00/MWh from the latest round of auction. In contrast, the negotiated strike price for nuclear energy from Hinkley Point C in the UK is £92.50; see UK Government (2016). Figure 15 shows the LCOE for various forms of energy.

Figure 14. LCOE of offshore wind.

Figure 15. Comparison of LCOE for various forms of energy.

The massive cost reduction is achieved by utilizing efficiently the inherent advantages of offshore wind and, at the same time, minimizing the cost disadvantages. Wind farm sites are selected further offshore and often in deeper waters to get best wind resource (faster and consistent) and avoid fishing and shipping channels. Good wind resources enhance electricity generation and thereby revenue. Further cost reduction is achieved through the optimization of key components by broadening the global supply chain as well as installation and maintenance activities. The construction process of offshore wind farm can be expedited with minimum disruption to the lives and livelihood of an economy using the sea routes and taking advantage of global supply chain. Figure 16 shows a wind farm construction using marine vessels. By contrast, an onshore wind farm construction suffers from disruption as can be noted from Figure 17 where one blade for 2.75 MW turbine is being transported. For example, for a UK wind farm, it is possible to have the steel tower and foundations fabricated in Singapore or South Korea and the turbines assembled in Germany.

Figure 16. Construction of offshore wind farm.

Figure 17. Transportation of blades (58.7 m long for GE 2.75–120 wind turbines) to Muirhall Onshore Wind Farm, South Lanarkshire (Photo credit: https://www.collett.co.uk/muirhall-wind-farm/).