Article by Christian Haen

In a world with an ever-increasing energy demand, which is mostly met by non-renewable energy sources such as coal, oil, or gas [1], alternatives to common renewable energy generation technologies are required to secure sustainable access to electricity as well as mitigate the major impact of the energy sector on climate [2]. This is especially true for fast-growing countries like India, which wants to achieve its NDC target as posed by the Paris agreement. Commonly, technologies that are considered in the efforts to shift to renewable energy generation are solar cells, wind, and nuclear power. But there are many more additional potential energy sources, some completely new and some as improvements on existing technologies. In the following, I aim to highlight a small selection of such technologies, albeit I will focus more on their actual advantages and applications instead of the in-depth physics behind them (which are provided in more detail in the included sources).

First, I want to mention a development in one of the most widespread renewable energy sources: solar cells. In India specifically, the output power of solar cells is quickly increasing [3] with much higher goals planned to be reached in the near future [4]. Commonly produced solar cells consist mainly of silicon, an inorganic semiconductor that captures incoming sunlight which “produces” free electrons in the silicon to be available as electric current. While it is relatively efficient with an energy conversion efficiency of generally between 20%-25% [5], their production process is costly and the mining of silicon can have severe environmental impacts, including in India [6]. A relatively new research branch aims to improve upon this by using organic solar cells. Organic refers to their composition of molecules that mainly consist of carbon and hydrogen, which take over the role of silicon to convert light into electricity. They are cheaper to produce, flexible and durable, and since their main components are readily and abundantly available, can be produced with a much lower environmental impact [7]. On the other hand, one of the major downsides of organic solar cells at the moment is their low efficiency ranging from 5% to a recently achieved record of 17.3% [8].

The next energy generation method I want to discuss is a relatively unknown one called Blue Energy, its name stemming from its simple main component: water. Blue Energy uses the salinity difference between salt and freshwater, as appearing at the estuary of a river, to produce energy with a potential yield greater than conventional hydro power plants [9]. The basic underlying principle is one called osmotic pressure, describing a pressure between a solution and a pure solvent separated by a membrane through which just the solvent can pass into the solution, in this case, unsalted water and salt-containing seawater. When separated through such a membrane, the freshwater attempts to flow through the membrane into the seawater to equalize the salinity difference between both fluids. If the seawater is kept in an enclosed container, its volume and pressure increases as the freshwater flows into it irreversibly, a process which can then be turned into electric energy via a turbine [10]. Besides its relative simplicity, this process also has a huge advantage due to its high energy efficiency of 91% [11].

Many other methods to use the salinity gradient exist, for example ones using the fact that a saline solution contains many electrically charged particles called ion, while freshwater doesnot (in relevant quantities). This difference can be exploited to generate electrical energy e.g. by charging and discharging an electrical condensator [12]. Many methods are still the topic of active research, but some applications are already implemented. Examples include a prototype power plant by Statkraft in Norway, which expects to generate 10 kW [13], or a plan to generate Blue Energy in indian estuaries [14], where a large coastline and an abundance of rivers provide ample opportunities.

Lastly, and maybe most importantly, is the technology of nuclear fusion. For the last decades, nuclear power comprised an increasing share of the world’s energy production [1], although this is purely done by the process known as nuclear fission: Heavy, radioactive atoms, commonly uranium isotopes, are split to result in multiple lighter atoms. The start and end products have a mass difference, which is, according to Einsteins’ famous equation E=mc² , converted into energy. This results into the release of vast amounts of energy due to the much larger energy scales of nuclear bindings (through something called the strong force), whose differences between original atoms and end products govern the energy released, compared to, e.g., chemical processes (oil, coal etc.), which are based on weaker electromagnetic forces. The fission process itself is completely carbon neutral, yet problems concerning hazardous radioactive waste products have to be considered. Due to the large decay time of this waste, they have to be stored for potentially thousands of years, making efficient storage solutions imperative. Additionally, the risk of safety measures in nuclear fission plants failing, causing an uncontrolled chain reaction and consequent explosion, is always present, although slim.

Now, the inverse to fission is also possible: light atoms, such as hydrogen, can be fused into heavier atoms, for example helium when fusing hydrogen, a process that is actually powering our sun. Due to the much larger difference in binding energy between hydrogen (and its isotopes) and helium, an even larger amount of four times the energy produced via fission can be released [15]. Apart from that, fusion has another advantage over current fission technology: It creates only short lived radioactive waste due to different products in the fusion process. Furthermore, a meltdown is impossible since without the precise conditions needed in a fusion reactor to create the hot plasma to induce fusion, it quickly cools off and is physically unable to perform nuclear reactions [15].

The only current problem is to actually build a fusion power plant capable of generating more energy than is put into it. Many protoype power plants to perform fundamental research into this topic are built worldwide, most notably the international project ITER in France [16], with major partnering nations, including, the EU, USA, China, Russion, Japan, and India who has a 9.1% contribution share to the project [17]. Although efforts and research in constructing an energy producing fusion power plant have been undertaken for decades without producing a net energy output, groundbreaking research such as this is hard to put into a time frame, and plans, for example for ITER, still estimate more than a decade to fulfill such a goal [18]. Still, progress is being made, and additional efforts to produce energy via fusion are planned, as seen in a recent 10 year roadmap of U.S. fusion scientists [19]. Overall, achieving fusion has the potential to solve many of today’s energy related problems.

All of these technologies can help mitigate the current energy and climate crisis, but their success rests on the backs of thousands of dedicated scientists and engineers, requiring strong and urgent support from states around the world to further develop and implement them, as well as the public to accept these new developments. I sincerely hope that this article can help shine some light on some of the less well known and/or obscure renewable technologies, thereby increasing the public awareness.

References:

1. https://ourworldindata.org/grapher/global-primary-energy?time=earliest..latest
2. https://archive.ipcc.ch/pdf/assessment-report/ar5/syr/SYR_AR5_FINAL_full_wcover.pdf
3. https://ourworldindata.org/energy/country/india?country=~IND
4. https://mnre.gov.in/img/documents/uploads/0ce0bba7b9f24b32aed4d89265d6b067.pdf
5. Battaglia, Corsin & Cuevas, Andres & De Wolf, Stefaan. (2016). High-efficiency Crystalline Silicon Solar Cells: Status and Perspectives. Energy Environ. Sci.. 9. 10.1039/C5EE03380B
6. Ashutosh, Mishra. (2015). Impact of silica mining on environment. Journal of Geography and Regional Planning. 8. 150-156. 10.5897/JGRP2015.0495
7. Askari, Mohammad. (2014). Comparison of Organic Solar Cells and Inorganic Solar Cells. International Journal of Renewable and Sustainable Energy. 3. 10.11648/j.ijrse.20140303.12
8. Meng, Lingxian & Zhang, Yamin & Wan, Xiangjian & Li, Chenxi & Zhang, Xin & Wang, Yanbo & Ke, Xin & Xiao, Zuo & Ding, Liming & Xia, Ruoxi & Yip, Hin-Lap & Cao, Yong & Chen, Yongsheng. (2018). Organic and solution-processed tandem solar cells with 17.3% efficiency. Science. 361. 10.1126/science.aat2612
9. PATTLE, R. Production of Electric Power by mixing Fresh and Salt Water in the Hydroelectric Pile. Nature174, 660 (1954). https://doi.org/10.1038/174660a0
10. Jan W. Post, Joost Veerman, Hubertus V.M. Hamelers, Gerrit J.W. Euverink, Sybrand J. Metz, Kitty Nymeijer, Cees J.N. Buisman, Salinity-gradient power: Evaluation of pressure-retarded osmosis and reverse electrodialysis, Journal of Membrane Science, Volume 288, Issues 1–2, 2007
11. Ngai Yin Yip and Menachem Elimelech Environmental Science & Technology 2012 46 (9), 5230-5239 DOI: 10.1021/es300060m
12. Brogioli, Doriano. (2009). Extracting Renewable Energy from a Salinity Difference Using a Capacitor. Physical review letters. 103. 058501.10.1103/PhysRevLett.103.058501
13. https://www.power-technology.com/projects/statkraft-osmotic/
14. https://economictimes.indiatimes.com/news/science/iit-madras-working-on-tech-to- produce-power-from-estuaries/articleshow/70699029.cms
15. https://www.iter.org/sci/Fusion
16. https://www.iter.org
17. https://www.iter.org/proj/Countries
18. https://www.iter.org/sci/Goals
19. https://science.sciencemag.org/content/362/6421/1343