Assessment of the locational potential

of floating offshore wind energy in South Africa

Kubiat Umoh1*, Abbas Hasan1, Amangeldi Kenjegaliev1 and Ayman Al‑Qattan2

Abstract

Expanding floating wind into new markets could support emission reduction targets in several national contexts.

It furthers the need for adequate assessments to gain a full understanding of the technology’s potential in future

markets. South Africa is a prime case study as it has seen limited industry and policy developments despite its huge

technical potential for floating offshore wind (FOW). This paper assessed the locational potential of floating wind

in South Africa through a three-phased approach that evaluated the key technical drivers/barriers of the technology,

conducted a Geographic Information System analysis (GIS) using ArcMap 10.8 to exclude unsuitable sites based

on a predetermined exclusion criteria (including marine protected zones, underwater cables, major oil and gas deposits,

etc.), and estimated the total harvestable capacity in the feasible sites. The study found that 2% (246,105.4 km2)

of South Africa’s entire Exclusive Economic Zone (EEZ) is suitable for hosting floating wind turbines, with a potential

to generate a maximum of 142.61 GW of floating wind power. Although the Western Cape province holds the highest

potential (80.52 GW) for floating wind in the country, the Eastern Cape region, with a locational potential of 20.04

GW, is considered most suitable for early-stage developments due to the availability of grid connection points, limited

marine traffic, and proximity to appropriate port facilities. Future work can conduct techno-economic assessments

to evaluate the technical and economic implications of developing floating wind in distinct sites in the country’s EEZ.

Keywords Floating wind, Offshore wind, Technical potential, Locational potential, GIS, South Africa

Introduction

Floating offshore wind turbines (FOWT) can unlock

greater wind power generation in deeper and more distant

waters, due to the presence of stronger and more

stable mean wind speeds (Hannon et al., 2019). As

opposed to bottom-fixed structures, where foundations

like jackets, gravity-based structures and monopiles

are utilised for turbine-tower mounting (IRENA,

2016), FOWT utilises floaters (such as tension-leg platform

[TLP], semi-submersible, and spar-buoy), along

with a station-keeping system (including moorings and

anchors), for turbine mounting in water depths greater

than 50 m (EWEA, 2013). Amidst the numerous floater

typologies currently under development, the major floating

foundations include tension-leg platform (TLP),

barge, semi-submersible, and spar (as displayed in Fig. 1)

(Carbon Trust, 2015). The technology could facilitate

better capacity factors and play a key role in the energy

transition, as 80% of global offshore wind resources are

in deeper waters (i.e. in water depths greater than fifty

metres) (Wind Europe, 2017). In recent times, there has

been an increased level of activity in the floating wind

market, as the sector heads for full commercialisation

around 2030 (GWEC, 2019). With more than 100 MW

of capacity currently installed, the commercialisation of

this technology will see it play a major part in the global

energy mix with a projected

Review

Floating Offshore Wind Turbines: Current Status and

Future Prospects

Mohammad Barooni 1,†, Turaj Ashuri 2 , Deniz Velioglu Sogut 1,*,†, Stephen Wood 1

and Shiva Ghaderpour Taleghani 3

1 Ocean Engineering and Marine Sciences, Florida Institute of Technology, Melbourne, FL 32901, USA

2 College of Engineering and Engineering Technology, Kennesaw State University, Kennesaw, GA 30144, USA

3 School of Arts and Communication, Florida Institute of Technology, Melbourne, FL 32901, USA

* Correspondence: [email protected]

† These authors contributed equally to this work.

Abstract: Offshore wind energy is a sustainable renewable energy source that is acquired by harnessing

the force of the wind offshore, where the absence of obstructions allows the wind to travel

at higher and more steady speeds. Offshore wind has recently grown in popularity because wind

energy is more powerful offshore than on land. Prior to the development of floating structures,

wind turbines could not be deployed in particularly deep or complicated seabed locations since

they were dependent on fixed structures. With the advent of floating structures, which are moored

to the seabed using flexible anchors, chains, or steel cables, wind turbines can now be placed far

offshore. The deployment of floating wind turbines in deep waters is encouraged by several benefits,

including steadier winds, less visual impact, and flexible acoustic noise requirements. A thorough

understanding of the physics underlying the dynamic response of the floating offshore wind turbines,

as well as various design principles and analysis methods, is necessary to fully compete with

traditional energy sources such as fossil fuels. The present work offers a comprehensive review of

the most recent state-of-the-art developments in the offshore wind turbine technology, including

aerodynamics, hydromechanics, mooring, ice, and inertial loads. The existing design concepts and

numerical models used to simulate the complex wind turbine dynamics are also presented, and their

capabilities and limitations are discussed in detail.

Keywords: wind energy; offshore wind turbine; numerical models; design concepts

1. Introduction

Global warming and climate pattern changes are some major consequences of the

human activities that are caused by the overuse of fossil fuels [1]. Renewable energy, on

the other hand, has the capability of decreasing greenhouse gas emissions by providing

a sustainable and clean energy resource [2,3]. Based on the statistical data from the International

Energy Agency (IEA), the renewable energy market share is growing steadily, in

which wind power takes up 36% of the total growth [4]. Offshore wind is advantageous

among the various forms of renewable energy since it can produce large amounts of electricity

[5]. Over 6000 MW of new offshore wind energy installations were made worldwide

in 2021, following the construction of 5618 MW in 2020 (Figure 1). By the end of 2021, the

capacity increased to 39,006 MW, thanks to the more than 200 active projects. Annual new

installations are expected to surpass the milestones of 20 GW by 2025 and 40 GW in 2030,

with a compound average annual growth rate (ACAGR) of over 30% up to 2025 and 12.7%

until the end of the decade [6].

The world’s first offshore wind turbine was installed in 1990 in Nogersund, Sweden.

The Netherlands, Sweden, Denmark, and the UK have established a number of offshore

wind power demonstration projects over the past two decades, which were funded mainly

by the governments and research organizations [7].

Energies 2023, 16, 2. https://doi.org/10.3390/en16010002 https://www.mdpi.com/journal/energies

Energies 2023, 16, 2 2 of 28

(a)

(b)

Figure 1. Global cumulative offshore wind energy deployment and annual capacity trends through

2021 [8]. (a) Cumulative installed wind energy trends for countries with the highest record in the

past two decades. (b) Annual new installation trends for countries with the highest record in the past

two decades.

The vast majority of operational offshore wind turbines are mounted on bottom-fixed

substructures, such as monopile, jacket, tripod, and gravity base substructures, which are

positioned in shallow to intermediate sea depths of up to 50 m. Although wind resources are

significant in locations with sea depths over 50 m, fixed-bottom offshore wind turbines do

not have an economic justification for their use in energy extraction at these depths [9]. With

the advent of floating structures, however, wind turbines can now be placed far offshore.

The deployment of floating wind turbines in deep waters has several advantages, such as

steadier winds, less visual impact, and flexible acoustic noise requirements. In recent years,

various types of floating offshore wind turbines (FOWTs) with different support platforms,

anchoring and mooring configurations have been proposed and investigated. The designs

have benefited from the floating support structure concepts employed by the oil and gas

offshore industry, such as semisubmersibles, tension leg platforms (TLPs), and spar-buoys.

Energies 2023, 16, 2 3 of 28

In 2008, Blue H Technologies deployed a tension leg platform (TLP) with an 80 kW

rated capacity 21.3 km off the coast of Apulia, Italy, as the first floating wind turbine trial [10].

In 2009, the Norwegian State Oil Company, Statoil, installed HyWind, a 2.3 MW wind

turbine equipped with a spar-type support platform, which was the world’s first floating

offshore wind turbine on theMWscale [11]. In 2011, the 2MWturbine-equippedWindFloat,

designed by Principle Power Inc., was deployed 4 km off the coast of Aguçadoura, Portugal,

at a 45 m depth [10].

Onshore wind turbines have recently improved their economic viability relative to the

conventional energy sources [12,13]. This achievement was made possible by a number of

developments, including improved control systems [14–16], larger wind turbines [17,18],

higher fidelity models [19,20], the collective installation of wind turbines called wind

farms [21–23], improved energy loss recovery [24–26], and more optimized designs [27,28].

The construction of offshore wind turbines, however, is more expensive and capitalintensive

than that of onshore wind turbines. Additionally, costs may change based on

factors such as the distance from the coast, the sea conditions, and more [29]. In general, the

tower and foundation of an offshore wind turbine are approximately 20% and three times

more costly than their onshore counterparts, respectively [30]. For offshore wind platforms

with fixed bottoms, the most expensive component is the turbine itself, contributing about

31.8% to the overall expense, while the assembly and installation is 19.3%, followed by

the construction of foundation and substructure at 14.7% [31]. On the other hand, for the

FOWTs, the wind turbine and installation and assembly take up about 22.1% and 11.1% of

the total cost, respectively, with the foundation and substructure being the most expensive

components at 36.2% [31]. Of course, the ratios mentioned above may change with the

industrial development of the offshore wind turbines in the future.

Compared to fixed-bottom offshore and onshore wind turbines, the overall cost of

FOWTs is significantly greater due to the high cost of floating offshore support structures.

However, the most densely populated areas across the world are along the coasts where

FOWTs are a better alternative than onshore wind turbines [32,33]. Therefore, many of the

concerns that are related to onshore wind turbines such as visual and noise distractions can

be avoided by placing the wind turbines far offshore [34,35].

Stronger and more consistent winds also promote offshore wind energy, which results

in higher energy yield and lighter loads on the rotor and nacelle assemblies. [36]. In shallow

to intermediate water depths, where wind resources are substantial, the installation of fixedbottom

offshore wind turbines is more practical and cost-effective than floating platforms.

However, the countries that border the Atlantic Ocean, including the United States, Japan,

and west European nations, have limited coastal territorial waters that are less than 50 m

deep. As a result, there has been a considerable interest in floating offshore wind turbines

(FOWTs) over the past ten years [9].

The current study provides a thorough overview of advances in FOWT technology

from the perspective of design concepts, loading, and analysis tools and presents the future

prospects for the floating offshore wind industry.

2. Design Concepts for Floating OffshoreWind Turbines

FOWTs are among the concepts that can efficiently and economically capture energy

from deep-water offshore wind resources [37,38]. A wind turbine mounted on a floating

foundation is part of the FOWT idea, which enables the production of power in deep waters

where bottom-fixed wind turbines are not economically feasible. Different floating wind

turbine concepts are shown in Figure 2.

Several FOWT designs have been developed on barge, spar, TLP, and semisubmersible

foundations [39]. Every FOWT