Renewable Energy - Volume 2: Wave, Geothermal, and Bioenergy: Definitions, Developments, Applications, Case Studies, and Modelling and Simulation

Renewable Energy - Volume 2: Wave, Geothermal, and Bioenergy: Definitions, Developments, Applications, Case Studies, and Modelling and Simulation is the next volume in this comprehensive resource for those wanting an extensive reference on these specialized technologies. Providing a structured approach to the emerging technologies and advances in implementation of Geothermal and Biofuels systems, this reference addresses geothermal and biofuel coverage in a logical and accessible arrangement. From definitions to developments in technology and applications, to case studies, modelling examples and lifecycle analysis, this book considers the most requested and desirable practical elements of geothermal and biofuel technologies from an applied perspective.

This coordinated approach allows for stand alone, accessible and functioning chapters dedicated to particular energy sources. This is a suitable reference for students and post-doctoral research fellows working on projects related to renewable energy, sustainability and energy system design.

• Includes in-depth and up-to-date explanations for the latest developments in Marine, Geothermal and Biofuels
• Uniquely thematically arranged with structured content, for accessible and usable reference material
• Extensively illustrated and supported by multimedia components, including short videos and slide shows for greater examples and case studies

• Language: English
• Publisher: Academic Press
• Release date: Oct 8, 2023
• ISBN: 9780323952125

Book preview

Section 1

Wave energy

Outline

Chapter 1.1 Introduction and definition of wave energy

Chapter 1.2 Recent progress in wave energy

Chapter 1.3 Wave energy extraction technologies

Chapter 1.4 Case studies of wave energy

Chapter 1.5 Strengths, weaknesses, opportunities, and threats analysis of wave energy

Chapter 1.6 Modeling and simulation of wave energy

Chapter 1.1

Introduction and definition of wave energy

Tabbi Wilberforce¹, Enas Taha Sayed², ³, Mohammad Ali Abdelkareem³, ⁴, Montaser Mahmoud⁴ and Abdul Ghani Olabi⁵,    ¹Mechanical Engineering and Design, Aston University, School of Engineering and Applied Science, Birmingham, United Kingdom,    ²Center for Advanced Materials Research, University of Sharjah, Sharjah, United Arab Emirates,    ³Chemical Engineering Department, Minia University, El- Minia, Egypt,    ⁴Sustainable Energy and Power Systems Research Centre, RISE, University of Sharjah, Sharjah, United Arab Emirates,    ⁵Sustainable Energy and Power Systems Research Centre, University of Sharjah, Sharjah, United Arab Emirates

Abstract

Harnessing energy from the ocean is becoming increasingly important as the world shifts toward renewable energy sources to meet growing energy demands while reducing greenhouse gas emissions. The ocean’s energy is abundant and infinite, making it an attractive source for power production. One of the most promising ways to harness energy from the ocean is through wave energy converters, which convert the kinetic energy of ocean waves into electricity. There are various types of wave energy converters being researched globally to improve the performance of existing concepts. The aim of this study is to present the main concept of wave energy and its related aspects. The chapter presents the advantages and disadvantages of wave energy and highlights the factors impeding its commercialization. The study also evaluates various technologies captured in literature and their technological approaches. Despite the promise of wave energy converters, there are several challenges that need to be addressed before they can be widely commercialized. One of the biggest challenges is the high cost of construction and maintenance, which makes wave energy more expensive than other forms of renewable energy. Another challenge is the variability of wave energy, which can affect the reliability and consistency of power generation.

Keywords

Wave energy; renewable energy; converters; ocean energy

1.1.1 Introduction

Renewable energy is currently gaining more popularity, with the goal of completely replacing fossil fuels in the near future. The diversity in the types of renewables makes their usage applicable all over the globe, as they are available in the form of solar [1], wind [2], hydro [3], geothermal [4], biomass [5], and wave energy [6]. Increasing the utilization of these sources is fortunately leading to a reduction in the impact of energy systems on the environment and climate change [7,8]. Therefore it can be noticed that renewables have been incorporated into various types of systems, including electricity generation [9], heating [10], cooling [11], transportation [12], and hydrogen production [13].

A renewable energy source with enormous promise that is still mostly untapped is wave energy. Compared with wind energy, sea waves have a higher energy density, better forecasting, and less fluctuation [14]. It is due to the fact that the first wind- driven waves extend far beyond the area where the original storm originated and remain longer as they disperse. Although wave energy might increase the penetration of renewable energy sources and reduce intermittency, the industry is young, and its commercialization is low compared with other sources of energy, such as wind or solar [15]. Wave energy converter (WEC) papers number over a thousand, yet only a few have advanced to manufacturing, much less comprehensive testing [16]. Despite efforts being made to enhance the use of renewable energy sources as well as create sustainable systems, it is anticipated that global energy usage will spike by over 25% by 2040 [17]. It is also projected that electricity demand will go up by 65%. The majority of this energy demand is likely to come from lower-middle-income countries. Offshore winds combine with the ocean’s surface to create waves. As a result, huge waves that reach the beach have traveled quite far while losing relatively little energy [18]. Other sustainable energy sources have lower power densities compared with wave as well as tidal energy, with an average wave farm producing 2–3 kW/m² compared with wind farms’ maximum of 0.6 kW/m². Furthermore, due to the inconsistent and unpredictable nature of alternative types such as wind and solar, generation is only feasible in the United Kingdom for 20%–30% of the time. Despite the diversity of this resource and the complexity of its extraction, wave energy may be captured up to 90% [19]. A proven wave energy device idea that will play a significant role in the development of wave energy is the oscillating water column (OWC). The literature has a thorough evaluation of the OWC and existing connected equipment [20].

The International Energy Agency built a model known as Energy Technology Perspectives (ETP), aiming to develop advanced analysis of the global energy system by combining energy supply and demand analysis [21]. The ETP scenarios, which are projected to take place until 2050, explicitly mention the average global rise in degrees centigrade (DS) as a result of anthropogenic climate change. According to the 2 DS scenario, there is at least a 50% chance of limiting the normal temperature increase to 2°C. The 4 DS scenario assumes a 3.7°C temperature rise and takes into account energy and climate measures that are currently being planned or assessed. In the 6 DS scenario, no additional GHG reduction measures are planned beyond current policy measures, which could lead to a 60% increase in annual energy and process-related CO2 emissions and a 5.5°C temperature increase. Fig. 1.1.1A depicts the anticipated generation amount from ocean energy for each of these three situations. Generally, the outlook for ocean energy is more promising, with 52 TWh expected to be produced under 6 DS, 92 TWh under 4 DS, and 144 TWh under 2 DS by 2040. The total installed ocean energy output will have grown to 37 GW under 6 DS, 71 GW under 4 DS, and 178 GW under 6 DS by 2050, from about 1 GW in 2013 to that point. Despite this, in all three cases, the share of ocean energy in overall renewable power production is less than 1%. This estimate projects a combined potential of 236 GW of wave energy and 101 GW of tidal stream by the year 2050 (see Fig. 1.1.1B).

Figure 1.1.1 The expected (A) electricity generation from ocean energy and (B) installed capacity of tidal and wave energies [22]. (Open access).

This chapter consists of six sections, including this section (introduction). The next section presents an overview of wave energy. Sections 1.1.3 and 1.1.4 show the principle and steps involved in capturing the energy from ocean waves. The main challenges faced by this sector are presented in Section 1.1.5 and are divided based on the issues related to the capacity, dependability, and environment. The conclusions are finally summarized in Section 1.1.6.

1.1.2 Overview of wave energy resource

The ocean possesses a high amount of energy, usually in the form of ocean currents and osmotic as well as tidal and thermal energy [16]. The theoretical energy composition of the oceans is summarized in Table 1.1.1. As depicted in Table 1.1.1, it can be observed that wave energy comes with several merits, which includes being a source of large energy reserves coupled with wider distribution [25]. It has also been reported that energy harnessed from the ocean is flexible. The energy is however suitable for marine buoys, lighthouse, and large-scale grid sources of harnessing energy [26].

Table 1.1.1

Wave energy generation is predominant in United States, China, and India. In the past few years, these countries have been at the forefront of harnessing energy from the ocean in terms of structural development [27]. Other companies aside from those being championed by these government bodies are also involved in the investigation of various stages of wave energy system deployment [28]. There are several designs of WECs with different shapes and structures based on their specific applications, and there are several patents in excess of 1000 to buttress this position [29]. Information in relation to the development of wave energy can be traced to the 1970s [30]. A study on OPERAWEC explored various ranges of operation for a novel WEC [31]. A study into the development of future generator control concluded that novel nonlinear as well as intelligent control systems are being studied for developing wave energy technologies. Various types of power take off (PTO) systems coupled with their merits and demerits have also been explored in the literature and discussed. Hybrid systems were considered as the most ideal for future PTO systems [32,33]. Fatigue design factor impact on the development of the converter has equally been reported to ensure that the WEC is reliable.

1.1.3 Harnessing energy from waves

Due to the consistent changes in the state of the sea, coupled with changes in the season, monitoring the movement of the ocean is quite challenging. Eq. (1) therefore denotes a numerical representation of wave motion that is not regular [34–36].

Equation (1)

The wave surface elevation is denoted as Equation The direction of the wave is Equation . The time taken for the entire process is Equation , while the total partial waves is captured as Equation . Equation is the amplitude, while the frequency is Equation , and the phase angle is represented as Equation . The movement of the ocean can be deduced from Eq. (1) as explained earlier. Generally, the installations of WECs can be classified based on the site, which can be offshore, near shore, or onshore, as depicted in Fig. 1.1.2. In this figure, percentages of the peak wave power are used to indicate the average and exploitable quantities. As the wave trough would be close to touching the seafloor, onshore refers to coastal areas where the water level is between 10 and 15 m, and the highest wave height can reach up to 7.8 m. The nearshore has moderate ocean zones with a maximum depth of 15–25 m. It can be categorized as deep water, moderate water, or shallow water, depending on the level of the water [37–39].

Figure 1.1.2 The variation of wave power based on the installation location [37]. (Open access).

The wind velocity is what basically creates the wavelength, the swell, which is one of the terminologies used in wave energy, is simply a phenomenon where, at far distances, waves of the sea show a regular shape. Water particles produced by wind travel on circular paths, with the radius increasing near the top but declining as it descends. The wave creation and correct dispersion are caused by this interaction of circular motion. The classification of wave energy is generally dependent on the working approach, where the system is installed, the forms of power being harnessed, as well as the structural requirements of the overall system. The entire process is quite complex due to the working depths and sea conditions where the entire system is being harnessed. Wave energy production medium is today classified into three main approaches, namely the oscillating body type, the OWC type, and the overtopping methods [30].

1.1.4 Steps involved in harnessing wave energy

The overall processes that come with wave energy conversion are basically depicted in Fig. 1.1.3. These processes involved the primary energy conversion processes. The primary energy conversion approach includes a transition from wave energy to mechanical energy, then to pneumatic or potential energy. The second phase of the process involves changing the energy that is absorbed into mechanical energy with the aid of PTO systems [35]. The three-stage energy conversion devices are progressive and connected to one another above. It is vital to maximize conversion efficiency between various levels to increase wave energy conversion’s total power generating efficiency.

Figure 1.1.3 Wave energy conversion processes [40]. With permission number 5507630518501.

The features of ocean waves are unpredictable as well as erratic [41]. A body possesses 6 DOF classified as heave, surge, sway, yaw, pitch, as well as roll, as depicted in Fig. 1.1.4. The oscillating buoy power production technique employs the body to perform heave, pitch, or roll motions under wave stimulation to drive the PTO device, hence stimulating the generator to create energy. This method considers the continuity of power generation.

Figure 1.1.4 Oscillating body concept [40]. With permission number 5507630518501.

WECs are designed to use various types of PTO approaches for transforming energy. There are also those designed for producing specific electric energy. In the case of PTO concepts, mechanical gear is one type of system often used for oscillating bodies. Due to their flexible transmission, some research studies recommend the usage of the hydraulic and pneumatic systems. The energy storage for these device is also stable, and they are associated with higher torque [42]. Using either the liquid or air concept can help in converting wave energy into electrical energy. This phenomenon is capable of improving power quality as well as the accumulated wave energy at lower wave speeds. The direct drive approach relies on the undulating movement of the waves in the generation of electricity through a vertical motion [43].

The OWC WEC is made up of an OWC section that supplies wave energy in the form of pneumatic energy to a PTO system as well as a PTO unit that supplies pneumatic energy in the form of electric power (see Fig. 1.1.5). To curtail the overtopping of the waves, it has been reported that the structure of the OWC WEC can be slanted to reduce the impact of turbulence [45]. The PTO for these types of WECs is made up of turbines, generators as well as power converters. The turbine shaft power, as well as the pneumatic power that is available but expressed as a percentage, is the turbine efficiency. The total performance of the PTO system is largely dependent on the performance of the turbines. It is usually required that the performance of the generator as well as the power converter is higherthan that of the turbine system. Controlling the PTO system is one of the key parameters that can help increase the turbine efficiency of a WEC.

Figure 1.1.5 Oscillating water column [44]. (Open access).

Even though the reliability of the turbine system is a crucial factor in PTO efficiency, angular speed control is dependent on the power converter. As a result, the power converter’s load control has a direct impact on the efficiency of the turbine. Despite the turbine system generator’s inertia, wave energy has a high degree of unpredictability, making load regulation of the power converter crucial. Turbine efficiency is therefore subject to angular speed, which is dependent on the power converter’s ability to manage load. An example of the OWC WEC is the Spar Buoy depicted in Fig. 1.1.6. There is also the multioscillating water column technology as depicted in Fig. 1.1.7 where the OWC units are attached together in terms of the structure, airflow as well as the PTOs.

Figure 1.1.6 Spar Buoy oscillating water column [46]. With permission number 5507650024865.

Figure 1.1.7 (A) Oscillating water column in array, (B) segmented and (C) modular [47]. With permission number 5507650348549.

Bringing water up into a reservoir where energy is turned into mechanical energy by a turbine and subsequently electrical energy by a generator is the basis of the wave overtopping idea depicted in Fig. 1.1.8. The reservoir’s water level is raised by the wave-breaking action such that it is high compared with the surface of the water.

Figure 1.1.8 Wave overtopping concept [48]. With permission number 5507650558111.

The waves break as they begin to experience a decrease in water depth as they get closer to the beach. Fig. 1.1.9 depicts a new concept that functions using the concept of overtopping. This is called the Wave Dragon [49]. The physical design of this gadget indicates increased capacity for harnessing energy as well as its capability as a wave terminator gadget [50]. Three primary structural components were used to build this device: a ramp, a pair of reflectors, and a water reservoir, as depicted in Fig. 1.1.9.

Figure 1.1.9 Wave dragon device. (http://tpeenergiedelamer.blogspot.com/p/houlomotrice.html).

The development of the Aqua Buoy point absorber WEC can be traced to 2000 [51]. With the point absorbers, extracting energy originates from the oscillatory motion of a single body in reaction to a frame that is fixed. Hydraulic cylinders are fixed to a body capable of floating. The movement of the float because of heave results in the cylinders driving the hydraulic motor, which in turn engages the generator [52].

Depending on the type, they are usually made up of a buoy, an accelerating tube, a piston, as well as a hose pump. There is contraction of the hose pump due to the movement of the buoy upward and downward. This phenomenon results in equal amounts of expansion due to the relative motion of the tube and the piston. The sea water is therefore pumped to the turbine via the hose pump, which in effect causes a movement of the generator, thereby producing power. The Power Buoy, developed by American Ocean Power Technologies in 2005, functions using this principle. Today there are the Archimedes wave pendulum and the wave bob [53].

Christopher Cockrell, a British inventor, initially presented the idea of an attenuator WEC in the 1870s. He later created the Cockrell raft, a wave power system [53]. The converter is made up of rafts that are able to float on the water surface. Because of the angular displacement caused by wave undulation between nearby rafts, a hydraulic system constructed between them powers a generator to generate electricity. As depicted in Fig. 1.1.10, the attenuator is designed to operate in parallel to the direction of the wave. Energy is absorbed as the waves move around the device [54].

Figure 1.1.10 (A) Attenuator wave energy converter. (B) Terminator wave energy converter. (C) Point absorber [54]. With permission number 5507650719065.

The buoy of the terminator WEC has a larger dimension as well as a primary axis that is parallel to the direction of waves, allowing it to collect wave energy from a wider range of wave sizes. It comes with higher energy generating performance when compared with other oscillating buoys. The Oyster terminator WECs were developed in 2001 [50]. The Oyster is designed to be positioned nearer to the seabed and attached to cylinders. The motion of the waves via the oyster causes the buoyancy of the pendulum to swing, resulting in the hydraulic cylinder transporting higher-pressure water to the shore as well as propelling the hydroelectric generators in producing power. The Bio WAVE terminator WECs were developed in 2009 [55]. As depicted in Fig. 1.1.11, the converter is positioned close to the seabed. The converter is positioned close to the seabed. To create energy, a pendulum body may swing back and forth with waves, as well as spin around a vertical axis to follow the waves’ direction.

Figure 1.1.11 Oyster wave energy converter [49]. With permission number 5510090790279.

1.1.5 Challenges associated with evaluating wave energy converter performance

From the discussions highlighted in the previous sections, it can be deduced that there are several technical methods, designs, etc., for various WEC technologies [40]. The commercialization of these technologies is rather slow than expected due to the technology being between TRL 1 and 2. Capacity in the capture of energy, cost, dependability of concept, users’ perceptions, and the environmental impact of these technologies are major issues impeding their accelerated commercialization.

1.1.5.1 Capacity in the capture of energy

When WEC is being evaluated, how energy is captured, distributed, and generated all contribute to the coefficient of energy conversion. It is determined that Multidegree Freedom WECs account for the greatest coefficient, while the attenuator accounts for the least coefficient. In the absence of defined cost information for activities (manufacturing, operating, as well as installing), it is very challenging to analyze the costs. Nonetheless, it should be mentioned that multidegree freedom WEC is responsible for the greatest technological expense. The point absorber, terminator, and overtopping types are then placed after it, accordingly. The introduction of wave energy will reduce the overreliance on conventional renewable energy technologies such as solar and wind.

1.1.5.2 Dependability of concept

Material as well as structural design has been shown to affect WEC dependability. Due to the increased risk of corrosion in maritime conditions, materials used have significant impact on the converter efficiency. Hence, it is important to use high-strength as well as anticorrosion materials. Due to complicated transmission systems coupled with a number of components in saltwater, converter dependability might be significantly lowered in terms of structural designs. As there are fewer pieces in saltwater, OWC as well as overtopping systems is more reliable. Yet, due to the complexity of the multidegree of freedom WEC structure, this accounts for its low dependability.

1.1.5.3 Zero harmful environmental impact

The degree of low carbon footprint is the main motivating reason for this energy source. This technique has little environmental impact when compared with the effects brought on by the usage of fossil fuels. However, there are some significant repercussions that can be anticipated, which are related to the environment, streams, and fish. The most ecologically friendly gadget is the multidegree of freedom WEC, which is subsequently followed by the point absorber and terminator.

1.1.6 Conclusions

The present study highlighted the current state of wave energy technological concepts and devices used in the present day in harnessing energy from the ocean. Various types of WECs were discussed based on their operating principles and system configuration. A brief overview of PTO was also summarized in the present study. Similarly, an evaluation of the existing wave power production medium in terms of performance, cost, how the energy is harnessed, dependability, and environmental issues was critically discussed. According to the study, there are three major approaches to producing power based on how energy is used. These were categorized into OWCs, overtopping, and the buoy concept. Despite the technological advancements made, there is still room for improvement in terms of reducing the overall cost of the technology. This will basically imply that further research work be conducted within this field to clearly improve the systemic performance from the design point of view and the operating mechanisms. The present information is aimed at providing the academic community with the needed information in terms of wave energy converting devices and their technological readiness level to influence decision-making by policymakers and industrial players in the renewable energy industry.

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