3.1. Global Growth in Installed Power Capacity
Figures 2 and 3 present the changes in the global installed capacity of offshore wind turbine technology as cumulative and annual. As can be seen from the figures, offshore wind power installation has overgrown since 2007. The first offshore wind power plant was established in Vindeby in eastern Denmark in 1991. The Vindeby wind farm consisted of 11 onshore turbines producing 450 kW each and a cumulative capacity of 5 MW. Since then, the Vindeby wind farm has become an influential pioneer in the European offshore wind industry. With this breakthrough, offshore wind power plants in Europe showed significant development. In the 2000s, the installation of offshore wind farms in the Southern North Sea, Baltic Sea, and the Irish Sea progressed rapidly since these seas have strong winds on average of over 8 m/s and relatively shallow water depths of less than 50 m. The cumulative installed power of offshore wind energy increased to 67 MW in 2000. In 2013, 1,567 MW offshore wind installations contributed to 11,159 MW of installed wind energy capacity. As of 2015, 3,230 turbines were installed in 84 offshore wind farms with a total power capacity of 11,027 MW in 11 European countries.
By the end of 2017, the global installed offshore wind power capacity increased to 20 GW. A 4.3 GW offshore wind farm was installed in 2018. In 2020, 90% of the global offshore wind market was represented by European companies. Fifteen new offshore wind farms started generating electricity, and nearly 6.1 GW of offshore wind capacity was installed in the world in 2020. Currently, 162 offshore wind farms are installed worldwide, and 26 offshore wind power plants are under construction. The total installed offshore wind capacity was 35.3 GW at the end of 2020. As seen in Figure 4, in 2020, cumulative capacity reached 10.2 GW in the UK, which has the world's largest offshore wind industry with the lowest costs. In addition, China, Germany, the Netherlands, Belgium, and Denmark were the countries that contributed to the increase in global installed capacity, enabling the offshore wind market to grow remarkably. Outside of Europe, China added approximately 3 GW in 2020, bringing its total installed capacity to approximately 10 GW. However, according to the International Renewable Energy Agency (IRENA), offshore wind will need to increase tenfold by 2030 to support the necessary energy sector transformation and meet the Paris Agreement goals. The total installed offshore wind power capacity is predicted to be approximately 382 GW by 2030 and approximately 2,002 GW by 2050 (Figure 5).
3.2. Turbine Capacity and Size Analysis
Due to its open and smooth sea location, ability to generate GWs quickly, and high energy output per m2, offshore wind energy is a highly viable alternative for cost-effectively powering densely populated coastal areas. Thanks to advances in installation, foundations, access, operation and system integration, and turbine technologies, it has made it possible to move into deeper waters and further offshore to achieve locations with more significant energy capacity. In the last ten years, offshore wind energy technology has attained significant maturity, has become the most advanced technology among renewable energy sources. As shown in Figure 6, wind turbines' nominal capacity and size have historically increased due to continuous and conscious research and development (R & D) processes (Quest Floating Wİnd Energy 2021). With this growth, foundation and cabling costs have been reduced, while at the same time, costs have been reduced by increasing the energy captured per MW of nominal capacity. The 15 MW turbine, which has the highest wind turbine rating globally, is scheduled to be first tested in 2022 and go into power generation in 2024.
Figure 7 shows the growth of offshore wind turbine capacity between 2000 and 2020. As can be seen from the figure, the wind turbine capacity has shown a great improvement over time. When the world’s first offshore wind power plant was built in Denmark in 1991, the turbine power capacity was just 450 kW. Since this installation, the offshore wind turbine size has grown significantly. The global average offshore wind turbine size reached 1.5 MW in 2000. In Europe in 2009, the average turbine power capacity of an offshore wind turbine was about 3 MW. The average turbine size was higher than 7.2 MW for new installations in Europe in 2019 . Global weighted average nameplate capacity increased 150% from 3 MW in 2010 to 7.5 MW in 2020. Wind farms installed in 2020 had a 10% higher wind turbine power capacity.
Figure 8 presents the change in the global weighted-average turbine size for offshore wind over time. The figure shows that rotor diameter and hub height increased in parallel with higher turbine capacity values. Growth in rotor diameter is of great importance as it causes greater energy extraction from wind turbines and more uniform power output throughout the year. Rotor diameters expanded from 112 m to 157 m in the decade from 2010 to 2019, an increase of 40%. On the other hand, hub height increased from 83 m in 2010 to 108 m in 2019, an increase of 30%. With these growing turbine sizes, wind farms grew from 83 MW in 2011 to 301 MW in 2020.
Capacity factors of the wind turbines in offshore wind power plants vary due to the technology used, wind farm configuration, and differences in meteorology between wind farm sites. Between 2010 and 2020, the global weighted average capacity factor of yearly installed offshore wind turbines varied between 35% and 45%. The capacity factor for newly established projects in 2020 ranged from 33–47%. Wind turbines with larger swept areas and higher hub heights can have more electricity collection capability and increase their capacity.
Global R&D activities in recent years have focused on manufacturing larger wind turbines, as evidenced by the practices of turbine manufacturers. For instance, the Danish wind turbine market Vestas investigates a larger offshore wind turbine with a nameplate capacity of 17 MW for future release and installation. Recent developments under consideration have shown that turbine sizes can reach 20 MW within ten or two years. Given the continued evolution of turbine size growth, capacity factors are expected to be between 36% and 58% by 2030 and 43–60% by 2050, compared to an average of 43% in 2018.
3.3. Cost Analysis
The changes in the global weighted average LCOE and TIC for offshore wind technology between 2010 and 2020 are shown in Figure 9. As seen from the figure, the global weighted-average LCOE of newly installed offshore wind turbines decreased from USD 0.162/kWh in 2010 to USD 0.084/kWh in 2020, a decrease of 48% in 10 years. On the other hand, between 2007 and 2014, the LCOE increased as projects began to shift into deeper waters. For example, it peaked at 0.180 USD/kWh in 2007 and 0.179 USD/kWh in 2008, followed by a sharp decline after 2014. The LCOE for offshore wind in the world's leading countries has decreased sharply. For example, in 2020, the lowest weighted average LCOE value was obtained in China at USD 0.084/kWh.
The global weighted average TIC of offshore wind farms has increased from approximately USD 2592/kW in 2000 to over USD 5500/kW in 2008. Between 2008 and 2015, offshore wind farm installations were carried out in areas further from shore and into deeper waters, with a global weighted average TIC of around USD 5000/kW over that period. This cost started to decline after 2015 and fell relatively quickly to 3185 USD/kW in 2020. Installation costs of offshore wind technologies peaked in 2011-2012 due to projects being located in deeper waters, farther from shore, and using more advanced technology. In contrast to onshore wind installations, offshore wind farm installations became more costly and resulted in significantly longer lead times due to the difficulties of O&M installation in harsh marine environments. Also, the project development and planning for offshore wind power plants are more complex than for onshore projects. The fact that the construction is more and takes longer increases the TICs. Due to their offshore location, these projects also have higher construction costs and grid connectivity. However, effects such as standardization of turbine and foundation designs, increased industry maturity, industrialization of production for offshore wind farm components at local centers, and a decrease in the complexity of installation practices have resulted in cost savings. Installation times and costs per unit capacity have declined due to manufacturer experience, utilize of specialized vessels planned for offshore wind studies, and increases in turbine size for a turbine that amortizes installation attempts over larger capacities than ever before. In addition to the fact that offshore wind farm installations are in deeper waters and farther offshore, there has also been a tendency towards higher hub heights, more efficient and durable blades, and higher capacity turbines. Thanks to these technological features, these turbines, which are specially designed for the offshore sector, are in a position to capture more energy. This is very important for decreasing the LCOE of offshore farms.
3.4. Farm Capacity and Installation Analysis
Figure 10 shows the change in the global weighted average wind farm capacity for offshore wind over time. The figure shows that the average wind farm capacity increased parallel with higher turbine capacity values and years. Moreover, it is evident from the figure that offshore wind farms established in Europe are slightly larger compared to the average offshore wind farm values in the world. The first large-scale offshore wind power plant started power generation in Denmark in 2002 with 160 MW. After that, globally installed offshore wind farm capacities have increased rapidly over the past two decades. In 2020, the average offshore wind farm size reached 301 MW and 325.5 MW in the world and Europe, respectively. The world's largest offshore wind power plant Hornsea 1 was installed in the UK, with a capacity of 1.12 GW.
Figure 11 shows the evolution of the number of wind turbines, and sea surface area needed to install offshore wind farms in Europe over time. Europe currently has a total of 25 GW of offshore wind installed capacity, corresponding to 5,402 wind turbines in 12 countries. The total sea surface area covered by 116 offshore wind farms is about 3,820 km2. As seen from the figure, in Europe, the number of offshore wind turbines and the sea surface area needed for offshore wind farm installation have increased over time. For example, while the number of turbines established in 2001 was 20 and the needed sea surface area was 0.3628 km2, 703 offshore wind turbines were installed on a sea surface area of 839.9 km2 in 2018. In 2020, 358 offshore wind turbines were installed on an area of 303.4 km2. In addition, it is seen that the number of turbines and the needed sea surface area increase in parallel with the increase in wind turbine capacity over time.
Figure 12 shows the evolutions of the global weighted average water depth and the distance from shore for offshore wind over time. As can be seen from the figure, offshore wind projects worldwide were established in shallow nearshore waters in the early 2000s, while they were established later in deeper waters and further offshore. At the same time, it is seen that turbine capacities increase in parallel with this development. This growth has resulted in the increased foundation, grid connection, and installation costs. This increase accelerated the total installed cost of the offshore wind turbine as designs were developed. The offshore wind farms commissioned in 2000 were approximately 6.5 km from the shore, 8 m water depths, and an average turbine power capacity of 1.6 MW. These numbers have increased significantly over time. In 2020, the average offshore turbine power capacity reached 7.5 MW, while the weighted average distance to shore and water depth increased to 29 km and 33.6 m, respectively.
3.5. Technological Growth Analysis
Over three decades of research and development, offshore wind has established itself as a cost-competitive power generation option for mature industries and governments. This has resulted in a robust offshore wind supply chain in the countries bordering the North Sea and the Baltic Sea through collaboration between European markets and experienced stakeholders. Currently, a single offshore wind turbine now has more capacity than the combined output of the world's first two offshore wind farms. With new technological advances such as floating foundations, an alternative geographic range of opportunities is paving the way by enabling offshore wind turbines to be established in deeper waters. From a technological, location-specific, and technological connectivity perspective, it appears that the key emerging trends in offshore wind are primarily the fabrication of more extensive offshore wind turbine technologies, floating foundations, use of multifaceted foundations and structures, development of combined power generation technologies, creation of offshore energy centers for sustainable and renewable energy power generation, green hydrogen production with different offshore renewable energy technologies, and airborne wind power systems.
Offshore wind turbine technology achieves higher turbine capacity factors and more stable wind power output due to less wind shear and turbulence and higher average wind speeds. This effect causes offshore wind output to have a higher value for the electrical system than onshore wind. The most common trend in the design of wind turbine technologies today is to increase turbine efficiency while reducing turbine costs. For this, the hub height and rotor sweep area of the turbines are increased. On average, if turbines' hub height and rotor swept area grow faster than their power capacity, the specific power capacity will decrease. This causes an increase in the capacity factor of the turbine. As in Europe, wind turbines in the latest offshore turbine technology models today have a larger rotor sweep area, using more wind and generating more electricity. This reduces the cost of renewable energy generation. Thus, offshore wind turbines are becoming more powerful all over the world.
Specific power is defined as a measure of the wind turbine nameplate capacity divided by the rotor swept area. Figure 13 shows the evolutions of the global weighted average capacity factor and specific power capacity for offshore wind over time. As seen from the figure, the global weighted average capacity factor and specific power capacity values for offshore wind turbines installed between 2010 and 2019 range between 35%-45% and 316W/m2-461W/m2, respectively. The specific power capacity of the annual installed wind turbines in the world decreased from 461 W/m2 in 2011 to 350 W/m2 in 2019. On the other hand, the turbine capacity factor increased from 38–42% from 2011 to 2019. Since the wind turbine’s power output is directly related to the rotor swept area, an increase in the rotor swept area results in more power output from the wind for a turbine of the same power capacity. This means that there is a decrease in the specific power capacity of the turbine. A decrease in the specific power capacity causes the turbine power output and power coefficient to increase significantly for the same wind speeds. This increase in the rotor swept area of turbines has also resulted in lower energy costs worldwide, as larger wind turbines can generally deliver electricity at a lower cost than smaller wind turbines.
As a result, the growth in turbine size results in increased wind turbine efficiency because larger turbines with larger swept areas provide higher capacity factors for the same resource quality. Technological developments that increase capacity factors and reductions in TICs, O&M costs, and capital costs have resulted in cost reductions for offshore wind farms. The larger rotor turbines have higher capacity factors because the spinning blades sweep a wider area and utilize more energy. By using taller towers to increase hub height in areas with positive wind shear, greater access to higher wind speeds was achieved, reducing wind energy costs. The growth in the rotor diameter and thus in the rotor swept area was remarkably rapid, as the wind turbines were mounted with longer blades. At the same time, there was a modest increase in the mean nameplate capacity. Results showed that the turbines with low specific power were initially designed for low wind speed sites and were increasingly installed throughout the country, even in areas with high wind speeds, because of their low cost in various wind speed regimes.
Figure 14 shows the decrease in the number of turbines per GW between 2001 and 2020 in Europe. This figure reveals that the number of turbines per GW has decreased since 2001 significantly. For example, while the number of turbines per GW of annual installed offshore turbines in 2001 was approximately 500, this value dropped to 122, decreasing by 76% in 2020. A decrease in this metric may suggest less visibility per power capacity. Figure 15 shows the change in the sea surface area needed per GW for yearly installed offshore wind farms between 2001 and 2020 in Europe. This figure shows that the area needed per GW increased from 129.19 km2 in 2002 to 236.80 km2 in 2019. However, this value has changed over the years since 2001, showing a fluctuating situation. For example, the area needed to establish a 1 GW offshore wind farm in 2020 is calculated as 103.56 km2.