Generation of hydropower, a renewable source of energy, is not a difficult feat, however, making the generation process efficient and cost effective is the real challenge.
Evaluating the Efficiency of Hydropower as an Alternative Energy Source and its Effects on the Ecosystem
Dr. Raj Shah, Ms. Sharika Hoque, Mr. Stanley Zhang | Koehler Instrument Company
Introduction
Humans have been utilizing the abundance of water for thousands of years. For example, the ancient Greeks used water mills as a form of hydroelectric power to grind wheat into flour and perform other tasks. Today, hydroelectricity accounts for 73% of global renewable energy generation through three main hydropower facilities: impoundment dams, run-of-the-river dams, and pumped storage facilities. The most common type of hydroelectric power plant is an impoundment facility. This type of plant uses a dam to store river water and then releases the water into a turbine which causes it to spin. Unfortunately, dams can potentially disrupt the river ecosystems on which they are built on, but modifications can be made to limit these harmful effects.
Over the past several decades, electricity generation escalated due to rapid industrialization, modernization, and urbanization around the world. More specifically, electricity generation has increased 15-fold from 351.4 TWh in 1983 to 5347.4 TWh in 2013. The International Energy Agency predicts that by 2030 the demand for electricity will annually increase by 2.5% [1]. Renewable energy will become the primary source of energy in order to support this demand and avoid environmental problems. Generation of hydropower, a renewable source of energy, is not a difficult feat, however, making the generation process efficient and cost effective is the real challenge. In order to assess the efficiency of hydropower facilities, the electricity generation rate and water utilization rate must be evaluated.
Hydropower is an attractive form of energy because of its low carbon emission, low costs, and of course, the abundance of water. However, building a dam in a river is similar to building a roadblock in the middle of the highway; it disrupts the flow of traffic in both directions. This “roadblock” can disrupt species populations, water quality, the river food web, and the surrounding environment. Declining fish populations can result in major complications for communities that are dependent on fishing for food and income. The reservoirs can also cause floods which can force communities to relocate. Although hydropower is labeled as “renewable,” specific forms of hydropower and its effect on the ecosystem must be explored before we continue to develop more dams.
Where is hydroelectric power used?
Hydropower is the most important and widely used renewable energy source. The two main requirements for producing hydroelectricity are a constant water stream and an elevation drop. It is possible for countries all over the world to make use of hydroelectricity.
Figure 1: Hydroelectricity generation by country in 2012 [2].
China, Canada, Brazil, and the United States are the biggest hydroelectricity users in the world, and 17% of the total energy production is represented by hydroelectricity [2]. Although the majority of the energy generated in the United States comes from the use of fossil fuels and nuclear power, hydroelectricity is still an important domestic energy source. Figure 1 highlights that China is the world’s leading producer of hydroelectricity with a generation of about 900 billion kilowatt-hours in 2012. Even with all of these countries producing hydroelectricity, two-thirds of economically feasible hydro-resources remain untapped [2]. Latin America, Central Africa, India, and China have a lot of undeveloped hydro resources.
Impoundment Dams
Figure 2: Impoundment dam structure [3].
The impoundment dam is the most common hydropower facility. These dams store river water in a reservoir. This stored water can be released according to electricity demands or to maintain a constant reservoir level. The released water travels through the penstock to a turbine, where the mechanical energy is converted into electricity by a generator. The energy produced is conducted through transmission lines to areas that need electricity.
Efficiency of the Longyangxia Reservoir
In 2013, China’s hydropower capacity reached 280 GW, exceeding the cumulative value of Canada, Brazil, and the USA [1]. The Longyangxia power station is the largest reservoir in the Yellow River Basin and was selected to perform an efficiency evaluation of economic operation. The three evaluation indexes that are being observed are the relative water consumption rate (RC), the relative hydropower utilization rate (RU), and the relative hydropower utilization increasing rate (RI).
(a)
(b)
Table 1: (a) The comparison results between actual and calculated running conditions of the Longyangxia reservoir in 2001. (b) Efficiency evaluation results of economic operation in the Longyangxia power station [1].
The results in Table 1(a) show that the calculations are not a reliable source to predict the efficiency of the Longyangxia hydropower facility. The calculated final water level was 2568.95 m which exceeded the initial water level of 2565.91 m, but this observation was not observed through actual measurements. This emphasizes the need to make actual measurements to assess the efficiency of the hydropower stations. Also, according to Table 1(a) there is a surplus of water that was never predicted from the calculations. This surplus suggests that the water consumption was higher than it should have been and was not utilized effectively. Table 1(b) highlights the three important evaluation indexes previously mentioned, RC, RU, and RI. The result showed that the economic operation of this power station was not reasonable with RC > 1, RU < 1 and RI < 0 [1].
Operational changes can improve the efficiency of the Longyangxia hydropower facility. During flood seasons, the idle units should be operated accordingly, and flood control measures should be put in place to prevent surplus water. Likewise, during dry seasons, an increase in the output can improve the power generation and increase profits. The power generation and water supply should be coordinated with ecological regulations. Lastly, the reservoir water level is linked to the water resource utilization, so it deserves special attention. Although water is a plentiful resource, inefficient usage of this resource can have adverse effects on the freshwater ecosystem.
Biodiversity Concerns
Along with efficiency of the dams, the environmental concerns resulting from them must be studied as well. Freshwater ecosystems have more endangered and extinct species compared to terrestrial or other marine environments. River systems around the world are fragmented by dams which can affect fish assemblages throughout the river. Impoundment facilities contribute to the biodiversity crisis by disrupting the river ecosystem. The physical impacts of changes in freshwater ecosystems include riverine fragmentation, sediment retention, enhanced evaporation, and increased greenhouse‐gas production [4]. These impacts must be addressed when designing and developing dams.
Figure 3: (a) Percentage of surveyed lakes and impoundments that supported spiny water fleas (n = 341 sampled water bodies), zebra mussels (n = 353), rainbow smelt (n = 83), rusty crayfish (n = 567), and Eurasian watermilfoil (n = 682). (b) Comparison of the number of invaders in lakes and impoundments for the 189 water bodies sampled for the three most common invaders [4].
In addition, impoundment dams facilitate the introduction of aquatic invaders into freshwater ecosystems. Invading species are 2.4 to 300 times more likely to occur in impoundments than in natural lakes [4]. After combining information on the boating activity, water body physiochemistry, and geographical distribution of 1080 sampled water bodies (combination of natural lakes and impoundments), Figure 3(a) depicts that the invasion likelihood of impoundments exceeded that of natural lakes. The most common non‐indigenous species include zebra mussels, Eurasian watermilfoil, and rusty crayfish. According to Figure 3(b), impounds are also more likely to support multiple invaders. These findings suggest that reservoir construction and conversion of lotic to lentic water stream conditions may have promoted the spread of invasive species across the landscape.
Although dams do have a significant impact on freshwater ecosystems other environmental factors such as river size, flow and thermal regimes and land uses must be considered as well. Studies observing fish assemblages in Wisconsin rivers show a negative relationship between distance-to-dam measures and species richness and diversity. This relationship could be a result of the fishes developing a tolerance to lentic conditions [5]. Overall, this finding emphasizes the need to consider other environmental factors when judging the effects of impoundment facilities on these complex freshwater ecosystems. Furthermore, compared to natural lakes, the impoundments were 1.4 times lower in average water clarity, 2.1 times higher in conductivity, 4.3 times higher in number of boat landings, 8.7 times larger in surface area, and 44.6 times larger in watershed area [4]. Impoundments are also more likely to be accessed by humans. Nonetheless, the impoundment still had a significantly higher likelihood of invasions compared to natural lakes.
Diversion Dams
Figure 4: Diversion facility structure [6].
Diversion dams, sometimes called run-of-river dams, transport a portion of the river stream from its natural course to a powerhouse. The powerhouse contains turbines and generators to produce electricity and the water is fed back into the river. This type of facility requires substantial water flow and a large elevation drop. Unlike impoundment facilities, diversion facilities do not have large reservoirs to store water for future use, so they depend on precipitation. If the water levels of the river are depleted, then the entire facility can become inoperative. As a result, diversion facilities produce less electricity and lack consistency when compared to impoundment dams.
Optimization of Cutoff Walls
Cutoff walls are used to prevent the percolation of water through the foundation of the diversion dam. The cutoffs are sheet walls or concrete curtains that preserve the dimensions of the dam structure. The seepage water exerts an uplift pressure and may carry soil particulates with it resulting in erosion. If the thickness of the floor is insufficient, its weight would fail to resist the uplift pressure, and result in an inoperative hydraulic structure. Studies showed that cutoff walls were able to reduce the uplift force by 63% compared to a hydraulic structure without seepage control and likewise decrease the exit gradient by 79% [7]. Furthermore, it was revealed that the pressure is reduced when the inclination of the cutoff is towards the downstream side of the dam [8].
(a) (b)
Figure 5: 5(a) Comparison of the effects of the location and the angle of the cutoff wall for uplift force. 5(b)Comparison of total uplift force on the different angles of the cutoff wall to the right angled condition [7].
The effect of different angles at different positions on the uplift force was studied and the results are displayed in Figure 5. The relative positions of 0, 0.2, 0.4, 0.6, and 0.8 from the upstream end are observed at angles of 10°, 20°, 30°, 40°, 50°, and 60° for each position. According to Figure 5(a), the closer the cutoff wall is placed to the downstream end of the river and the more angled the wall is, the lower the uplift force is. This confirms that cutoff walls should be placed near the downstream heel with a large angle. Similarly, Figure 5(b) shows that when the cutoff wall is placed near the downstream heel and the angle is increasing, the percentage of total uplift force decrement decreases. The percent decrement of the uplift force will increase at higher positions and larger angles. A major decrement in seepage would occur when the cutoff wall is placed at the upstream heel and the downstream heel. When the cutoff wall moves closer to the downstream hill and the angle gets larger, the uplift force decrement percentage will increase and the total uplift force decrement percentage will decrease.
Effect of Diversion Dam Construction on Water Temperature
Although diversion facilities are often regarded as environmentally friendly due to their lack of reservoirs, the cutoff walls change the flow patterns of the river. The diversion of water causes drops in water flow and changes in water temperature which can result in declining local fish populations.
In 2013, the salmon population near diversion projects in British Columbia were studied by the Pacific Salmon Foundation. In 2016, the salmon populations dropped to its lowest level due to change in the Pacific Ocean’s water temperature [6]. The main reason for this was most likely climate change and not the run-of-river facilities, but this emphasizes the consequences of minor changes in water temperature.
(a) (b)
Figure 6: 6(a) Map of the Santo Antônio reservoir. 6(b) Depth vs. Time thermal profile before and after damming in Madeira River. The vertical black line indicates dam closure. Note that the JAT station was moved further upstream after damming [9].
Studies were done on the Santo Antonio reservoir on the Madeira River to show the effects of damming on the thermal profile. The dams created lentic conditions in the back-flooded tributaries, while the main stream maintained lotic conditions. According to Figure 6(b), the mainstream remained isothermal, while the back-flooded tributaries (JAC1, JAC2, JAT) developed thermal stratification after damming. Of the three tributary valleys, JAT was the most strongly stratified [9]. The mainstream maintained its fast water flow, while the back-flooded tributaries became lacustrine. These results demonstrate that the change in water flow of the river post damming can alter the thermal profile. As previously mentioned, the salmon population dropped to its lowest point after changes in water temperature. With that in mind, it can be assumed that the population of the species in the Madeira River were affected by the change in temperature.
Pumped Storage Facilities
(a) (b)
Figure 7: Pumped storage facility structures. 7(a) Closed loop pumped storage hydropower. 7(b) Open loop pumped storage hydropower [10].
Pumped storage facilities are another form of hydropower that functions like a battery. This system functions by pumping water from a lower elevation to a higher elevation, which increases the stored water’s potential energy. When electricity is needed, the water is released to the lower reservoir where it turns a turbine and generates electricity. Two types of pumped storage facilities exist, closed-loop and open-loop. Open-loop systems are connected to a naturally flowing water feature, while closed-loop systems require a second reservoir.
The effects of a closed loop pumped storage system are usually less severe than that of an open loop system. This is because closed looped systems are situated off-stream, minimizing aquatic and terrestrial impacts, and often have greater siting flexibility than open-loop system projects [11]. However, the geological effects of constructing two above-ground reservoirs rather than one outweighs the open loop system because it impacts the soil and groundwater more.
Enhanced-Pumped-Storage
Brazil is heavily reliant on hydroelectricity to meet the energy needs of the country. In recent years, climate change has made it difficult for the country to keep up with its energy demand. The Amazon water basin has a hydropower potential of 106 GW and if developed, it would generate 60% of Brazil’s total hydroelectric capacity [12]. However, this would create a hydropower imbalance because more than half of the capacity would generate most of its energy during wet periods. This is an unreliable form of energy because there will be a shortage of energy during dry periods. A proposed solution is watersheds with an increased storage capacity [12]. This will allow the energy generated during the wet period to be stored so it can be utilized during the dry period.
Enhanced-Pumped-Storage is another proposal to improve operation of dams and increase the energy storage capacity in Brazil. A combination of a pumped-storage site and series of dams in cascade will increase the water storage capacity and also utilize the extra capacity of the dams to pump water to an upper reservoir [12]. The pumped-storage site is located at the top of the river and this placement changes the seasonal hydroelectric power generation of the whole river. The enhanced-pumped-storage stores energy during the wet season and generates electricity during the dry season. The reservoir can also store surplus energy generated from other intermittent renewable sources like wind and solar power [12]. Overall, this type of pumped-storage facility improves the operation of dams in cascade.
Future Developments in Hydroelectricity
The increase in the human population and economic growth is tightly linked to the rising demand for electricity. From 1993 to 2010, electricity production increased by 72%. 20% of the global electricity is accounted for by renewable energy, with hydropower contributing 80% to the total share [13]. Future hydropower is being pursued in developing countries and emerging economies like Southeast Asia, South America, and Africa. In March 2014, 3,700 dams with a capacity of 1 MW were either planned or built, and these dams are predicted to increase the global hydropower capacity from 980 GW to 1,700 GW within the next 10-20 years [13].
To maintain the value and contribution of hydropower, cost-effective solutions are needed to maintain the existing hydropower facilities and assess new opportunities for hydropower energy production. The U.S. Department of Energy’s Wind and Water Power Technologies Office has a plan to evaluate future pathways for low-carbon, renewable hydropower. The U.S is working on new designs and approaches to make hydropower more competitive with other energy generation technologies. Actions like standardizing the equipment components, developing scalable structure designs, and exploring alternative hydropower design philosophies will result in lower costs, faster production, and less maintenance of the system [14].
The environmental impacts of hydropower must be considered when discussing the future development of this energy source. The re-accelerating of dams will lead to the fragmentation of 25 of the 120 large rivers, reducing the number of free-flowing large rivers by about 21% [13]. Before and after development of these dams, the flow regimes, water quality, sediment transport, habitat connectivity, fish passage and mortality, and culturally sensitive lands need to be closely monitored. Environmental stressors need to be observed with metrics and monitoring methodologies. Developers can apply the metrics to the siting, design, and post-construction monitoring phases [14].
Conclusion
Hydropower is a constantly evolving energy production system. Countries around the world are utilizing this type of renewable energy. Currently, the three types of hydroelectric generating systems are not perfect, but it is a global mission to find ways to make the process more efficient and cost effective. Operational changes such as flood control and energy storage can substantially improve the efficiency of these facilities. Large-scale improvements like developing dams in series with a pumped-storage site can also have a major impact on the overall efficiency.
Hydroelectricity is commonly viewed as a “clean” source of energy; however, the environmental effects are concerning. River systems around the world are fragmented by dams which can be detrimental to the river ecosystems. Changes in riverine fragmentation, sediment retention, enhanced evaporation, and increased greenhouse‐gas production have a major impact on fish assemblages. Although hydropower is a better alternative to fossil fuels and nuclear energy, we must consider the environmental impact it has. The environment surrounding a potential dam structure should be studied and the proper precautions should be taken when designing and constructing these facilities to protect the ecosystem.
References
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[2] Hydroelectric Power Water Use. (n.d.). Retrieved March 15, 2021, from https://www.usgs.gov/special-topic/water-science-school/science/hydroelectric-power-water-use?qt-science_center_objects=0#qt-science_center_objects
[3] Types of hydropower plants. (n.d.). Retrieved March 15, 2021, from https://www.energy.gov/eere/water/types-hydropower-plants
[4] Johnson, P., Olden, J., & Zanden, M. (2008, September 01). Dam invaders: Impoundments facilitate biological invasions into freshwaters. Retrieved March 15, 2021, from https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/070156
[5] Wang, L., Infante, D., Lyons, J., Stewart, J., & Cooper, A. (2011, May 05). Effects of dams in river networks on fish assemblages in non‐impoundment sections of rivers in Michigan and Wisconsin, USA. Retrieved March 15, 2021, from https://onlinelibrary.wiley.com/doi/full/10.1002/rra.1356
[6] Helston, C., & Farris, A. (2017, February). Run of River Power. Retrieved March 15, 2021, from http://www.energybc.ca/runofriver.html
[7] Esmat, Z., AA. Al-Delewy, A., RH. Al-Suhaili, R., MR. Alizadeh, M., S. Azizi, F., A. Azzellino, S., . . . K. Zhang, C. (2018, May 31). Multi-Objective hydraulic optimization of diversion Dam's cut-off. Retrieved March 15, 2021, from https://link.springer.com/article/10.1007/s11269-018-2015-4
[8] Mansuri, B., Salmasi, F., & Oghati, B. (2014, July 15). Effect of Location and Angle of Cutoff Wall on Uplift Pressure in Diversion Dam. Retrieved March 15, 2021, from https://link.springer.com/content/pdf/10.1007/s10706-014-9774-3.pdf
[9] Almeida, R., Hamilton, S., Rosi, E., Arantes, J., Barros, N., Boemer, G., . . . Roland, F. (2019, November 14). Limnological effects of a LARGE AMAZONIAN run-of-river dam on the main River and drowned tributary valleys. Retrieved March 15, 2021, from https://www.nature.com/articles/s41598-019-53060-1
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[11] H. (2020, April 28). New doe report on environmental effects of pumped storage hydropower. Retrieved March 15, 2021, from https://www.hydroreview.com/hydro-industry-news/new-doe-report-on-environmental-effects-of-pumped-storage-hydropower/#gref
[12] Hunt, J., Freitas, M., & Junior, A. (2014, November 07). Enhanced-Pumped-Storage: Combining Pumped-storage in a yearly storage cycle with dams in cascade in Brazil. Retrieved March 15, 2021, from https://www.sciencedirect.com/science/article/pii/S0360544214011888
[13] Zarfl, C., Lumsdon, A.E., Berlekamp, J. et al. A global boom in hydropower dam construction. Aquat Sci 77, 161–170 (2015). https://doi.org/10.1007/s00027-014-0377-0
[14] Chapter 4: A Pathway Forward. (2016). In The Hydropower Vision Roadmap (pp. 350-395). U.S. Department of Energy. doi:https://www.energy.gov/sites/prod/files/2016/10/f33/Hydropower-Vision-Chapter-4-10212016.pdf
About Dr. Raj Shah
Dr. Raj Shah is a Director at Koehler Instrument Company in New York, where he has worked for the last 25 years. He is an elected Fellow by his peers at IChemE, CMI, STLE, AIC, NLGI, INSTMC, The Energy Institute and The Royal Society of Chemistry An ASTM Eagle award recipient, Dr. Shah recently coedited the bestseller, “Fuels and Lubricants handbook”,
details of which are available at https://www.astm.org/DIGITAL_LIBRARY/MNL/SOURCE_PAGES/MNL37-2ND_foreword.pdf
A Ph.D in Chemical Engineering from The Penn State University and a Fellow from The Chartered Management Institute, London, Dr. Shah is also a Chartered Scientist with the Science Council, a Chartered Petroleum Engineer with the Energy Institute and a Chartered Engineer with the Engineering council, UK. An adjunct professor at the Dept. of Material Science and Chemical Engineering at State University of New York, Stony Brook, Raj has over 330 publications and has been active in the petroleum field for 3 decades. More information on Raj can be found at https://www.petro-online.com/news/fuel-for-thought/13/koehler-instrument-company/dr-raj-shah-director-at-koehler-instrument-company-conferred-with-multifarious-accolades/53404
About Stanley Zhang and Sharika Hoque
Stanley Zhang and Sharika Hoque are students of Chemical engineering at State University of New York, Stony Brook, where Dr. Shah the chair of the external advisory Committee in the Dept. of Material Science and Chemical Engineering.
The content & opinions in this article are the author’s and do not necessarily represent the views of AltEnergyMag
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