In this note, I’ll dive into some of the most promising emerging technologies—Wave Energy, Tidal Energy, Salinity Gradient Power, Ocean Thermal Energy Conversion (OTEC), Parabolic Troughs (PT), and Linear Fresnel Reflectors (LFR). We’ll look at real-world case studies, explore the challenges these technologies face, and discuss what needs to happen for them to go mainstream. While these innovations hold enormous potential to contribute more to global energy demand, several technical, economic, and environmental hurdles must be overcome. Continued research and development will be key to making these solutions more efficient, affordable, and accessible for widespread adoption.
I. INTRODUCTION
There has been an increase in the utilisation of renewable energy from just 2% in 1998 to more than 24% of the worlds energy demand at the moment [1]. A contributing factor to this increased use of renewable sources of energy is the significant decrease in costs to utilise renewable energy as well as technological advancements that have made these technologies more efficient [2]. As a result, some of these technologies have become well established and more ”mainstream” as they are increasingly becoming more competitive to conventional non-renewable energy sources. These mainstream technologies include (but are not limited to) solar, Wind, and Hydro Power [3].
Another main factor that has led to a rise in the utilisation of renewable sources of energy is the increased awareness of the harmful effects of fossil fuels on the environment [4]. Therefore, there is ever increasing pressure on governments and policy makers to reduce overall carbon emission through the utilisation of renewable energy technologies. This has resulted in new developments and emerging technologies in the use of renewable sources of energy. Recent developments in renewable energy utilisation include (but are not limited to) Marine Energy, Concentrated Solar and Enhanced Geothermal [3]. Fig. 1 below shows some of the mainstream and emerging renewable energy utilisations.
Fig. 1: Mainstream and Emerging renewable energy utilisations (From [2]).
II. PROBLEM STATEMENT
There are several recent developments and emerging technologies that are providing more ways to utilise renewable sources of energy. This paper aims to provide a detailed overview on some of the significant recent developments in the utilisation of renewable sources of energy as well as to provide case studies of where some of these technologies are already being used. The challenges faced by each technology, future prospects and recommendations are also provided.
III. EMERGING RENEWABLE ENERGY UTILISATION
In this section, the state of the art of several emerging renewable energy utilisations are discussed together with specific case studies that detail how successful these technologies are.
A. Marine/Ocean Energy
Marine/Ocean energy is an extremely attractive renewable source of energy [5]. This is mainly due to the abundance of the ocean which covers about 75% of the earths surface [2]. The main advantages of Marine energy over most other forms of renewable energy is that it is predictable as well as consistent [6]. It has been observed that there is an enormous quantity of energy that is available in oceans [7]. This energy is observed in the form of waves, currents, tides and heat [3]. When these forms of energy are summed, it is estimated that the energy that is available in oceans is not only able to meet the worlds energy demand but is able to do this several times over [3]. The recent developments and technologies in extracting marine energy are discussed.
1) Wave Energy: Ocean Waves are a phenomenon that is observed on the top surface of the ocean. These waves are formed whenever wind moves over the ocean. The wind that forms these waves is generated because there is always an irregular distribution of solar energy that reaches the surface of the ocean [8]. When wind travels across the ocean surface, the friction between the wind and water results in a transfer of energy from the wind to the surface water which in-turn generates the waves [9]. The ocean waves generated contain both kinetic and potential energy [10]. Devices called wave energy converters can be used to extract some of this energy and to generate electrical energy [11]. These wave energy converters can either be onshore, offshore or near shore, depending on where these converters are located. Several techniques for wave energy converters are available such as point absorber, oscillating water column, oscillating wave surge converter and submerged pressure differential [3], [11].
Case Study: Perth Wave Energy Project (Australia): This is an offshore wave power plant development that is in Garden Island in Western Australia [12]. Construction of this plant began in September 2013 and it was connected to the grid in February 2015. The output of this plant is 5MW which is sufficient to power approximately 3500 households [13]. This particular plant makes use of ”CETO” wave energy technology which uses a Buoyant Actuator (BA) which is fully submerged in the water and is buoyant [13]. The actuator moves with the energy of the oceans waves [13]. This technology is shown below.
Fig. 2: CETO Wave technology (From [14]).
Fig. 3: CETO Wave technology installed at the Perth Wave Energy Project (From [14]).
As can be seen in Fig. 4 below, the BA is attached to a pump through a tether and the entire system is fixed to the ocean floor. When the ocean waves occur, the BA oscillates and allows the pump to extend and contract. The motion is then used to pump high pressure water which is used to turn normal hydroelectric turbines to generate electricity. The water is then returned to the ocean and this forms a closed loop system shown below.
Fig. 4: CETO Wave technology in a array in a closed loop system (From [13]).
2) Tidal Energy and Ocean Currents : Tidal energy is the kinetic energy which results from the rising and falling of ocean waves as a result of rotational and gravitational forces [15]. These forces result from the positions on the moon and the sun in relation to the earth [3]. The rising and falling of tides vertically results in water moving horizontally [2]. It is this horizontal motion of the water that forms tidal streams which can be used to turn hydrokinetic turbines and generate electricity. A major advantage of tidal energy is that the size and occurrence of these tides is highly predictable and is usually not affected by climate changes [16], [15] . Tidal current energy converters are used to convert tidal energy to electrical energy and can be classified into Twin Turbine Horizontal Axis Device, Cross-flow device and Vertical axis device as shown in Fig 5 Below.
Fig. 5: Classification of Common Tidal Current Energy Converters (From [3]).
Ocean currents have the same concept as tidal currents but are formed deeper in the open-ocean as compared to near shore tidal currents [17]. The major difference is that Ocean currents are unidirectional while tidal is bidirectional. The main drawback of tidal energy is that it is location specific, however it shows massive potential. Another main challenge with implementing Tidal plants is the cost as they require high capital investment. Several challenges are also encountered when attempting to repair this equipment as it is located under water and may be deeper in the open-ocean [3]. Another challenge encountered is in the transmission of this energy inland as there is usually large distances.
Case Study: Sihwa Lake Project (South Korea): The Sihwa Lake project that is located in the west coast of South Korea is the worlds largest tidal power station. This location is ideal as it has a large tidal range. In 1994, the artificial Sihwa Lake was originally constructed in an attempt to provide flood mitigation and to also provide a reliable source of irrigation water. Unfortunately, because tides were not occurring anymore since natural tides were cut off, the water quality deteriorated significantly. In order to improve seawater circulation, the seawalls sluice was to be periodically opened. Fig. 6 below shows a Schematic of the turbo-generator used and the Sluice gate. A Tidal power plant was then also constructed to take advantage of the moving water [18].
Fig. 6: Schematic of the Turbo-generator used and the Sluice gate (From [18] ).
The Sihwa power plant shown in Fig. 7 below generates power twice a day at high tide. It consists of ten 25.4MW turbines and therefore has a capacity of 254 MW. This is enough to supply half a million people with electricity. That is 552 GWh hours of electricity.
Fig. 7: Sihwa Tidal Power Plant (From [19]).
3) Salinity Gradients: Salinity Gradient Power is the energy that is created when there is a difference in the concentration of salt in two liquids. In order to make use of this energy, a power plant can be located at the junction between a sea and a river. It is at this junction that a difference in concentration can be observed [20]. Alternatively, a plant can be located where waste water treatment occurs since pure and salty water can be found when desalination occurs [2]. The main two techniques that are used to extract this energy are pressure-retarded osmosis and reversed electro dialysis (RED). Pressure-retarded osmosis seeks to make use of osmotic power which can be captured across a semi-permeable membrane. It is estimated that this technology has massive potential and can yield up to 1650 TWh/yr [3]. The main challenge is implementing this technology is the cost of installing a plant. The permeable membrane is currently an expensive resource that has limited the utilisation of this technology [2]. Case Study: Statkraft Osmotic Power Plant (Norway): This plant owned by Statkraft is a prototype plant that uses osmotic technology shown in Fig. 8 below . This prototype plant has a capacity to generate about 10kW of electricity [21].
Fig. 8: Osmotic Power plant working principle (From [21]).
Unfortunately in 2013, it was announced that the Statkraft was not going to continue with the project and the main plant has not been built. Fig. 9 below shows the prototype plant.
Fig. 9: Statkraft Osmotic Power plant prototype in Norway (From [21]).
4) Ocean thermal Energy Conversion (OTEC) : Ocean thermal Energy Conversion takes advantage of the differences in temperatures between waters at different depths of the ocean [22]. The difference in temperature is generally caused by solar energy. Thermal energy from the suns rays is absorbed into the top layer of oceans [3]. As a result the top water has a higher temperature than deep sea water (800-1000m depth). A temperature difference of at least 20°C is required for the technology to be effective. Three techniques are mainly used by OTEC plants, these are; open-cycle which uses sea water as the working fluid, closed cycle which uses ammonia or propane as the working fluid and Hybrid cycle which is a combination of the open and closed cycle technologies [2]. The basic concept is to make use of the working fluid eg ammonia, and heat it using the surface water. The vapour produced is then used to turn turbines and generate electricity [22]. The cold water form deep in the ocean is then used to cool the ammonia back to liquid level before it is heated again. The potential of OTEC is considered to be the largest in marine energy however, the main challenge in utilising this technology is cost of the electricity generated [2]. Case Study: Makai Ocean Thermal Energy Conversion (OTEC) Power Plant (Hawaii): The Hawaii OTEC plant is a closed loop plant which has been successfully connected to the United States electric grid. This facility is the biggest of its kind at the moment and produces 100kW of electrical power which can power 120 homes. Fig. 10 below shows the working principle of this plant described above. The Makai OTEC plant in Hawaii is shown in Fig. 11 below.
Fig. 10: Working Principle of the Makai OTEC plant in Hawaii (From [21]).
Fig. 11: Makai OTEC plant in Hawaii (From [21]).
B. Concentrated Solar Power/ Photovoltaics
Concentrated solar power is a technique of using the heat produced by solar irradiation and concentrating it to a small area in order to produce electricity. Morros or lenses are used in this technique to reflect sunlight to a particular location where the receiver is situated [23], [24]. The main advantage of CSP is that it can generate electricity even when it is cloudy and has significantly higher capacity than regular solar technology. The solar collector is used to convert the solar radiation captured into heat energy. This heat can then be converted to electricity by making use of turbines [2]. The major CSP technologies and a description of the technique are given in Fig. 12 below.
Fig. 12: Major Concentrated Solar Power Technologies (From [2]).
1) Parabolic Trough: The majority of the projects that make use of Concentrated Solar power technology make use of the parabolic trough technology. That is because it has the lowest risk in CSP and is the most mature. In this technique, heat receivers are placed on the focal line of parabolic mirrors [24]. A special coating is put on these receivers to increase energy absorption. A liquid such as oil or molten salt is used to transfer the heat from this focal point to a steam generator to produce steam which in-turn produces electricity. Thermal storage units are sometimes used to store heat for generating electricity when the sun is no longer available [25]. Fig. 13 below shows the working principle of parabolic Troughs.
Fig. 13: Working principle of parabolic Troughs (From [24]).
Case Study: Kathu Concentrated Solar Power Plant (South Africa): This CSP plant is located in the Northern Cape Province of South Africa and has a installed capacity on 100MW. It was constructed in May of 2016 and commissioned in 2019. It is estimated to have a lifetime of 30 years. This plant also includes heat storage which allows for 4.5 hours of thermal energy storage [26]. Fig. 14 below shows the Kathu Concentrated Solar Power Plant.
Fig. 14: Kathu Conentrated Solar Power Plant (From [26]).
2) Linear Fresnel Reflectors: The working principle of Linear Fresnel Reflectors (LFR) is very similar to that of the Parabolic trough described above. However, in LFR, a series of long flat and slightly curved mirrors are used [24]. In order for the reflected ray to hit the target, different angels are used on the mirrors depending onthe position of the mirrir.Each mirror is optimised individually. Fig. 15 below shows this principle.
Fig. 15: Linear Fresnel Reflectors working Principle (From [24]).
The main advantage is the simplicity of the technology as compared to the Parabolic Trough technology described above. The installation and operation costs are also significantly lower. These systems also produce steam directly as they use water as the heat transfer liquid. However the performance of this technology is not as high as that of PT [2] . Case Study: LFR for Liddell Power Station (Australia): A 5MW Linear Fresnel reflector technology Power station is used to supplement the coal fired Lindell power station in order to reduce carbon emissions from the plant. The energy produced by this technology is mainly used to power Liddell Power Station [27]. Fig. 16 shows some of the Reflectors used.
Fig. 16: Linear Fresnel Reflectors used by Liddell Power Station (Australia) (From [27]).
IV. FUTURE RECOMMENDATIONS
There are still several hurdles that need to be addressed before the emerging technologies discussed above can reach their fullest potential and maturity. This has resulted in only a small portion of the available energy being utilised. However, the potential of this energy is large and it is capable of single handedly providing more than enough clean and renewable energy required [3]. It is recommended that more research is done to reduce the costs of these technologies as this is the main barrier to their utilisations. It is also recommended that policy makers and governments should encourage the development of these technologies through funding in order for them to quickly reach maturity. Some other drawbacks of Marine energy usage also need to be addressed. For instance, the effect of these technologies on marine life needs to be investigated further and addressed. Another challenge is that the marine energy extraction equipment may result in a reduction in opportunities for recreation therefore affecting industries such as tourism [2]. It is recommended that these challenges are looked into while these technologies are still emerging as changes may be harder to make once they reach maturity.
With regard to Concentrated Solar Power, the potential of these technologies is also large. The main barrier in the rapid expansion of these technologies is the economics. It is recommended that more research should be conducted to find cheaper alternatives to the materials that are used. It is also recommended to use cheaper liquids for heat transfer. It is also recommended to use mature technologies that are already being implemented in fossil fuel plants to reduce costs such as water cooling technology.
V. CONCLUSION
Through the study conducted on emerging technologies and recent developments in renewable energy utilisation, it can be concluded that is indeed possible for renewable sources of energy to contribute more to the global energy demand and that the possibility of using 100% renewable energy is indeed attainable. However, There are several technical, economic, social and environmental challenges that need to be addressed when attempting to utilise renewable energy sources by using these new technologies. It is recommended that research should be conducted so that the cost of these technologies may be reduced and therefore resulting in more widespread usage.
REFERENCES
[1] Josee Goldemberg. World energy assessment : energy and the challenge of sustainability. United Nations Development Programme, New York, NY, 2018.
[2] Akhtar Hussain, Syed Muhammad Arif, and Muhammad Aslam. Emerging renewable and sustainable energy technologies: State of the art. Renewable and Sustainable Energy Reviews, 71:12–28, 2017.
[3] Tabbi Wilberforce, Zaki El Hassan, A. Durrant, J. Thompson, Bassel Soudan, and A.G. Olabi. Overview of ocean power technology. Energy, 175:165–181, 2019.
[4] P. Swain, S. Jagadish, and K. N. S. Uma Mahesh. Integration of renewable sources of energy into power grid. In 2017 IEEE Region 10 Symposium (TENSYMP), pages 1–5, 2017.
[5] J. Lawrence, J. Sedgwick, H. Jeffrey, and I. Bryden. An overview of the u.k. marine energy sector. Proceedings of the IEEE, 101(4):876–890, 2013.
[6] Joao Cruz. Ocean wave energy : current status and future prepectives [i.e. perspectives. Springer, Berlin, 2008.
[7] S. J. Couch, A. R. Wallace, and I. G. Bryden. Overview of the supergen marine energy research program. In 2007 International Conference on Clean Electrical Power, pages 312–314, 2007.
[8] H. Titah-Benbouzid and M. Benbouzid. Ocean wave energy extraction: Up-to-date technologies review and evaluation. In 2014 International Power Electronics and Application Conference and Exposition, pages 338–342, 2014.
[9] Assessing the Global Wave Energy Potential, volume 29th International Conference on Ocean, Offshore and Arctic Engineering: Volume 3 of International Conference on Offshore Mechanics and Arctic Engineering, 06 2010.
[10] MA Mueller. Electrical generators for direct drive wave energy converters. IEE Proceedings-generation, transmission and distribution, 149(4):446–456, 2002.
[11] R. Dinzi, H. Hutagalung, and F. Fahmi. Feasibility study of ocean wave energy for wave power plant at sibolga-tapanuli tengah. In 2017 International Conference on Control, Electronics, Renewable Energy and Communications (ICCREC), pages 111–115, 2017.
[12] Mark A. Hemer, Richard Manasseh, Kathleen L. McInnes, Irene Penesis, and Tracey Pitman. Perspectives on a way forward for ocean renewable energy in australia. Renewable Energy, 127:733–745, 2018.
[13] Jonathan Fievez. Perth wave energy project design and construction update. ´ SaltKraft pure Energy, 1:1, April 2014. https://www.sut.org/wp-content/uploads/2014/08/Jonathan-Fi
[14] Jasmina. Carnegie receives ceto 6 design completion grant. Australian Manufacturing, 116:1, December 2016. https://www.australianmanufacturing.com.au/42565/carnegiereceives-ceto-6-design-completion-grant.
[15] R. Rosli and E. Dimla. A review of tidal current energy resource assessment: Current status and trend. In 2018 5th International Conference on Renewable Energy: Generation and Applications (ICREGA), pages 34–40, 2018.
[16] ASEJHWMTPJT-M Lewis. Ocean energy dalam ipcc special report on renewable energy sources and climate change mitigation, 2011.
[17] Andreas Uihlein and Davide Magagna. Wave and tidal current energy – a review of the current state of research beyond technology. Renewable and Sustainable Energy Reviews, 58:1070–1081, 2016.
[18] Young Ho Bae, Kyeong Ok Kim, and Byung Ho Choi. Lake sihwa tidal power plant project. Ocean Engineering, 37(5):454–463, 2010.
[19] Technology case study: Sihwa lake tidal power station. international htdropower association, page 1, August 2016. https://www.hydropower.org/blog/technology-case-study-sihwalake-tidal-power-station.
[20] A. T. Jones and W. Finley. Recent development in salinity gradient power. In Oceans 2003. Celebrating the Past … Teaming Toward the Future (IEEE Cat. No.03CH37492), volume 4, pages 2284–2287 Vol.4, 2003.
[21] Crown princess of norway to open the world’s first osmotic power plant. SaltKraft pure Energy, page 1, August 2009. http://www.statkraft.no.
[22] A. Hossain, A. Azhim, A. B. Jaafar, M. N. Musa, S. A. Zaki, and D. N. Fazreen. Ocean thermal energy conversion: The promise of a clean future. In 2013 IEEE Conference on Clean Energy and Technology (CEAT), pages 23–26, 2013.
[23] Z. Chen, J. M. Guerrero, and F. Blaabjerg. A review of the state of the art of power electronics for wind turbines. IEEE Transactions on Power Electronics, 24(8):1859–1875, 2009.
[24] Paul Breeze. Chapter 4 – parabolic trough and fresnel reflector solar power plants. In Paul Breeze, editor, Solar Power Generation, pages 25–34. Academic Press, 2016.
[25] Toshiyuki Sueyoshi and Mika Goto. Comparison among three groups of solar thermal power stations by data envelopment analysis. Energies, 12(13), 2019.
[26] Jose Santamarta. The kathu concentrated solar power plant was officially inaugurated in ´ south africa. Reve Energy, 1:1, April 2019. https://www.evwind.es/2019/04/11/the-kathuconcentrated-solar-power-plant-was-officially-inaugurated-in-south-africa/66740.
[27] Stela world. Ste/csp technologies, linear fresnel reflector. Stela, 1:1, April 2019. http://www.stelaworld.org/linear-fresnel-reflectors/.