Hydroelectric Power

Hydroelectric Power: An Overview

The rapid depletion of fossil fuels combined with economic and population growth are placing a bigger strain on global energy output such that many are now looking into renewable sources of energy. While solar and wind power are two innovative solutions that have begun to gain traction among consumers in many parts of the world, the most widely-used source of renewable energy is hydroelectric power [1].

What is Hydroelectric Power?

By definition, hydroelectric power is any kind of power that takes advantage of the energy output from the physical flow of water. This category of energy includes hydroelectric dams and reservoirs, run-of-the-river turbine set-ups, pumped storage projects, tidal plants, and underground waterways. It is considered a source of renewable energy because water is seen as replenishable over time and does not consume more resources than it produces. In terms of actual economic cost, hydroelectric power is one of the cheapest methods of energy production – though initially a costly investment due to construction costs, its daily cost of operation is largely independent of labor and fuel, and if properly managed, a plant can remain in service for many decades (table 1).

Table 1: Average Power Plant Operating Expenses for Major US Investor-owned Electric Utilities [33]

Because of its initial high cost, however, the large-scale implementation of hydroelectric power often requires a significant local and regional government investment. Hydroelectric power’s dependency on water supply also means that its function is deeply tied to local climate and geography. As such, it is much more useful to separate solutions by type and geographic location than to suggest an all-around solution to fit some global mold.

Hydroelectric Dams and Reservoirs

Hydroelectric dam-and-reservoir systems are the most widely-used type of hydroelectric project. However, they are also currently under the most criticism for their adverse political, economic, and environmental effects. In a typical hydroelectric dam-and-reservoir system, either a portion of the river or the entire river’s water flow is diverted into a reservoir, which in turn feeds the water through a smaller gap in which turbines are placed (figure 1). As the water flows through this small tunnel it moves these turbines, which in turn power the attached generator through their movement, allowing the system to generate electricity. This type of structure takes advantage of natural water flow energy instead of relying on any fuel or other significant energy input, allowing the average hydroelectric dam-and-reservoir system to generate electricity at an approximate levelized cost of 2 cents per kilowatt-hour compared to coal’s 7.5 cents/kWh (figure 2).

Figure 1. Typical conventional dam-and reservoir setup [34]

Figure 2: U.S. levelized cost of electricity (cents/kWh) [40]

The primary issue with large-scale conventional hydroelectric dams, however, is that they require reservoirs to maintain a height difference between the water levels on both sides of the dam – greater differences in water level height translate to greater force of water flow, which in turn generates more energy. But installing such reservoirs irreparably alters the natural environment of the region surrounding the dam and river – entire ecosystems of marshland and neighboring lowland forests/grasslands are often submerged, leading to an enormous loss of valuable farmland and wild habitats and drastic changes in the climate of the surrounding area. As these dam and reservoir structures create large lakes they also increase the water’s rate of evaporation and humidity levels of the surrounding areas – around 7% of the total amount of freshwater consumed per year in human activities is lost through reservoirs alone [2]. These large, man-made lakes also displace between hundreds of thousands and millions of people, setting the situation up for a political and economic nightmare – in China, for instance, during original construction of the Three Gorges Dam over 1.2 million people were forcibly evicted and removed from their homes, and since then several hundred thousand more have been relocated again due to concerns of landslides and higher levels of water pollution from the reservoirs than anticipated [3]. In the initial relocation villages were paid, on average, between $1000 and $1500 per capita to distribute between building new community infrastructure and recompensing individuals [4]. Compensation for subsequent relocations is unclear as the Chinese government has refused to comment.

The construction of a hydroelectric dam also disrupts the natural river flow, affecting the lives of those living downstream. Because reservoirs slow down water flow and trap free-floating sediment at the bottom, many dam and reservoir systems face sediment build-up and the gradual, subsequent loss of carrying capacity in reservoirs. Downstream, the lack of natural water flow regularly depositing sediment also leads to river bank erosion [5]. The blockage of rivers and occasional water level fluctuations caused by dams can also greatly disturb local aquatic wildlife – since the dams along the lower Snake River in the US Pacific Northwest were put into operation, the natural chinook salmon population has plummeted by 90 percent [6]. Historically, the damming of and building hydroelectric dams in major rivers has also been a source of political conflict among regions sharing common water supplies. More recently, Ethiopia’s unfinished Grand Renaissance Dam has come under attack by neighboring downstream countries Egypt and Sudan for allegedly reducing the flow of the Nile into the Egyptian Aswan Dam by 25-30 percent. This allowed Ethiopia a monopoly over the water flowing from the Blue Nile basin – water that makes up approximately 85 percent of Egypt’s current incoming water supply [7].

Hydroelectric dams also contribute to global warming and climate change. Although the process of harnessing water flow for mechanical energy itself produces few to no CO₂ emissions, the rotting of vegetation and plant matter caused by submerging large regions of land under water tends to release copious amounts of both CO₂ and methane gas, a greenhouse gas more potent than CO₂. Depending on the circumstances under which the dam was built, the combined effect of these emissions sometimes surpass those of traditional oil-burning power plants – the greenhouse effect of emissions from Brazil’s Curuá-Una dam in 1990, for instance, was over 3.5 times what would have been produced had the same amount of electricity been generated from oil [8].

Run-of-the-river turbines

A possible alternative to conventional hydroelectric dams is the run-of-the-river turbine, which seeks to mitigate most, if not all, of the political, economic, and environmental issues associated with the hydroelectric dam and reservoir model. In a typical run-of-river structure, a portion of the river is diverted through a turbine system that turns with the river flow and powers a generator that then converts that mechanical energy into electricity for consumption (figure 3). Such installations also have a minimal effect on the rivers themselves – as the project scale is smaller and there is less infrastructure involved, run-of-river turbines inherently alter less of the natural environment than hydroelectric reservoirs. Water flow is also allowed to continue downstream as normal upon exiting the penstock pipes instead of being collected in reservoirs, further reducing the effects of run-of-river turbines on downstream aquatic life and ecosystems.

Figure 3: Typical run-of-river setup [41]

What run-of-the-river turbines lack, however, are both the flexibility and energy output potential of hydroelectric dams. More so than the dams, run-of-the-river turbines are, by design, dependent upon the actual flow rate of the rivers into which they are situated. As such, their energy output may be inconsistent depending on the water flow rate of any river at any given time. Therefore, they are only feasible in rivers which have both the high water volume and consistent flow rate necessary to push the turbines and generate sufficient energy to justify their installation. Such rivers include those found in lower Canada, which are consistently replenished every year by large volumes of melting ice, or China, where an elaborate system of rivers flowing at different altitudes ensures that flow rates are sufficient for operating turbines. As run-of-the-river turbines depend on river volume and flow their output energy is also much less than that of a hydroelectric dam. While most major hydroelectric dam-and-reservoir systems operate on the magnitude of approximately 1000 MW or greater and the largest hydroelectric dams operate on the magnitude of around 10 GW [9] – the lower bound for major run-of-the-river projects is around 100 kW, and the largest run-of-the-river systems output between 1000-3000 MW [10]. These outputs, though reasonable for smaller towns and villages of up to several tens of thousands of people, may not be as feasible on a national scale as a primary source of energy. The maximum output of these run-of-the-river projects is also geographically limited – unlike hydroelectric dams, which can, to an extent, boost their energy output by increasing reservoir size, run-of-the-river projects cannot simply expand the size and/or flow of the rivers in which they are situated.

Run-of-the-river structures also affect aquatic wildlife populations by diverting water flow and changing the natural environment. In particular, the small “headpond” dams required by most run-of-the-river projects in order to keep water-diverting pipes submerged disrupt natural wildlife migration cycles, occasionally sweeping fish downstream while still in their maturing stage or preventing fish from swimming upstream to mate and lay eggs. Downstream from the headpond, water flow is also greatly reduced due to water diversion into pipes headed for the turbines, and so both water temperature and movement are affected. These changes in turn affect the nutrient composition and habitability of the water for microorganisms such as algae and, as a whole, lead to a general decline in the entire ecosystem stemming through the food web – though still to a much lesser extent than hydroelectric reservoirs, which permanently cripple a river’s water flow and release cold, de-oxygenated water downstream, further inhibiting growth [11].

Unlike large-scale hydroelectric reservoirs and dams, run-of-river turbines also do not require large-scale relocations of communities and the flooding of surrounding ecosystems. Installed on a small enough scale many of the environmental effects of run-of-river turbines can also be largely mitigated, allowing small run-of-river turbines to be a feasible solution for energy in small, remote regions where fuel is scarce and energy usage does not exceed several hundred MW [12].

Pumped storage

Although not a form of independent hydroelectric power generation, pumped-storage hydroelectricity is important to mention as a potential method of storing and controlling the electrical output of other forms of power generation. It is especially useful in conjunction with renewable sources such as solar and wind, which are dependent on environmental factors and tend to be less reliable than traditional fossil fuel-powered plants and generators [13]. Pumped storage structures work by utilizing low-cost electricity during off-peak hours – hours when electrical power are in less demand such as at night – to pump water up from a lower container into an upper container. This consumes the electricity generated during periods of low demand, when the energy would otherwise be wasted as it isn’t being sold, in order to store energy in the form of the potential energy of water in the upper container (figure 4). This water is then released through turbines in times of high electrical demand in order to produce additional electricity for the plant.

Figure 4: TVA pumped storage facility at Raccoon Mountain Pumped Storage Plant [37]

As energy is consumed in the process of pumping the water up in the first place this method cannot be truly considered a form of power generation. Instead, pumped storage structures are helpful in that they shift rather than generate any electricity, allowing plants to raise their electrical output during hours of peak demand and lower electrical waste during hours when a portion of the electricity generated isn’t in demand. Because of this useful property experts have begun to consider using these set-ups alongside wind turbine farms in order to offset the latter’s known unreliability and stabilize energy generation. In Greece, for instance, as part of the country’s new initiative to switch to renewable energy researchers have determined that pumped storage is necessary for any large-scale, stable implementation of wind and photovoltaic electric generation [14][15].

Underground power stations are pumped storage setups installed underground, minimizing the effects of plant construction and daily operation on surface ecosystems. While underground power stations leave much of the above ground habitats untouched, for the sake of stability they must also be drilled through solid rock, both raising the cost of construction and lowering the number of currently undeveloped and developed sites at which they can be reasonably implemented.

Tidal plants

Tidal plants take advantage of the natural changing water levels of tides in order to generate electricity through potential energy. They capture water at high tide and release it through turbines either at low tide or during hours of peak energy consumption, generating energy to meet higher demand at variable times that an electrical generator with a fixed rate of generation may be unable to meet without wasting electricity during off-peak hours [Figure 5]. As tidal plants depend on the rising and falling tide of the ocean they also tend to be relatively more predictable than either solar or wind energy [16]. Because they require tidal changes of at least 7m [17] and a sizable coast for such generators and power plant facilities in order to be economically feasible there are only a few viable sites for tidal electrical generation, and so tidal plants have been harder to implement globally.

Of the major tidal power stations currently in operation, only two – South Korea’s Sihwa Lake Tidal Power Station and France’s Rance Tidal Power Station – exceed 20 MW in capacity, at 254 MW and 250 MW respectively. (For reference, the global average energy consumption is 3,500 kWh per household per year. A 20MW tidal power station can optimally produce around 50GWh of energy a year – powering approximately 14,000 homes [18]). The Sihwa Lake Tidal Power Station is especially interesting in that its secondary function is to flush out the Sihwa Lake reservoir, which at the time of implementation was polluted and unsuitable for agriculture [19]. There have been concerns, however, that opening the region to seawater will flood existing wetlands and marshlands in the region, and as of now the environmental effects of the tidal barrage on the Sihwa Lake region have been unclear.

Figure 5: Typical tidal barrage setup [42]

Hydroelectricity as a solution

Despite its shortcomings, hydroelectricity, when implemented with proper care taken to minimize environmental effects, continues to remain a viable source of energy in many regions of the world. According to the WEC Survey of Energy Resources 2007, for instance, of the top five countries with the highest hydroelectric energy potential in the world – China, United States, Russia, Brazil, and Canada – only two, Brazil and Canada, have developed either 25% or more of their full hydroelectric potential [1]. The International Energy Agency also predicts a doubling of hydroelectricity generation by 2050, with the largest growth of hydroelectric plants and dams in Asia and the Pacific, which is the region of the world with the largest capacity for hydroelectric generation and is currently using only 18% of its full hydropower potential [20].

The regions in which hydroelectric power is both economically and politically feasible tend to share the following characteristics:

Strong financial standing: Though the initial construction cost of any large-scale dam and reservoir system is dependent on specific factors such as location, materials, design, and peripheral costs such as compensation to individuals for loss of land, the World Commission on Dams found that, on average, the cost overrun of dam construction cost is around 56% – that is, for every $1 billion a country projects it will invest in construction costs, it tends to spend closer to $1.56 billion instead [21]. Such a discrepancy between projected and actual costs could be disastrous for smaller and/or less financially stable countries with little to no access to additional funds should such a problem arise during construction – Burma, for instance, has had to delay the construction of three dams so far due to a lack of funds, with the most recent delay, the Manipur Multipurpose Dam, only 13 percent complete so far [22].

Though the costs vary by location, the same could be said to a for run-of-the-river and any other smaller-scale hydropower projects, which, though much smaller in scale and therefore between a tenth and a hundredth of the cost of large-scale dam and reservoir systems, still require that any upfront costs be completely accounted for before the region funding such a project can begin to see any profit.

Proper geographical structures: Hydroelectric reservoir-and-dam systems and run-of-river dams both require sufficiently large running bodies of water in order to generate power on a large enough scale to be sensible 50 to 100-year investments. Tidal plants require differences of at least 7m between high and low tide for any practical use and underground power stations are only feasible where there are two bodies of water of different elevations with enough stable rock to be drilled into for the installation of turbines and pipes. It does not make sense, for instance, to install run-of-river turbines on the Nile River, which has a gentle drop of approximately 1m for every 13 km and therefore lacks the proper height drop to push a series of turbines unassisted by a reservoir. Alaska and other colder climates are also less optimal for run-of-river constructs as the rivers themselves have a tendency to freeze over in the winter, and the lower temperatures create icing problems for the turbines.

Relatively stable political atmosphere: Generally, hydroelectric projects require some substantial, continuous investment from the government – both in terms of funding and the usage of public water sources such as rivers. Unhindered, efficient construction of large-scale hydroelectric projects, especially those taking advantage of major rivers that run through multiple countries, may also require cooperation between multiple regional governments for an extended amount of time. For instance, the relatively efficient construction of the Itaipu Dam that annually supplies around 90 TWh of electricity to both Brazil and Paraguay [23] is the result of a treaty signed between the two countries in 1966 [24]. In contrast, construction on Brazil’s Belo Monte has been temporarily suspended due to protests and concerns of its impact on indigenous peoples living in the region [25], and Iraq’s Bekhme Dam has gone unfinished since construction began in 1979 due to various conflicts in the region, including the Iran-Iraq War in the 1980s and the US-Ira Operation Desert Storm conflict of 1990-1991 [26].

Proposed Solutions

Taking into account the above factors, the following are recommended actions to be taken by separate regions in terms of using hydroelectric power as a solution:

Renovate existing hydroelectric dams: Compared to the cost of building completely new dams, renovations to existing dams tend to be much cheaper and less environmentally harmful (table 2). Funding for more modern infrastructure, such as stainless steel pipes and other parts, extends the life of older dams and reduces the chances of catastrophic dam failure. Newer, more efficient turbines also increase both the overall energy production of existing dams at a fraction of the cost of new dam construction and allow for higher wildlife survival rates through the turbines – more eco-friendly turbines such as Voith Hydro’s Alden Turbines have purportedly raised the survival rate of small fish coming into contact with turbines up to 98% from the previous 80-85% [27].

Table 2: Major dams (>3000 MW) with potential for renovation based on time since last renovation [39]

In developed countries such as the United States, Canada, much of Europe, and China, renovating existing dams may be more useful than building new dams – though many of these countries do not lack the capital in order to fund new dams they also tend to have a multitude of dams already in operation, and building new dams would require more good rivers and surrounding land that may be better used as agriculture for food and/or biofuel production. Instead, these countries should fund government programs to renovate all existing dams and bring them back up to date – in the United States, for instance, a recent renovation of the Cheoah Dam in North Carolina yielded a 40 percent increase in electricity output, increasing the dam’s coverage capacity by approximately 8,200 homes [28]. Brazil’s Bento Munhoz power station also holds a major potential for renovation as it currently has space for an additional two generators which, if added, would increase the plant’s output from 1,676 MW to 2,511 MW – a difference of approximately 550,000 homes [29].

Due to environmental concerns many of these governments may also find themselves unable to fund new dams and reservoirs. In this case, renovations allow such governments to boost energy output from hydroelectricity without actually funding any new hydroelectric projects at all – and as many of these upgrades serve to make dams more efficient and eco-friendly, it is likely these renovations will be easier to implement than funding for entirely new dams, allowing countries to boost energy output without actually committing themselves to large-scale hydroelectric projects.

In smaller, less economically-sound countries such as India the renovation of existing dams becomes even more important, as many of these developing nations may lack the capital necessary to fully fund completely new hydroelectric projects, and regional political conflicts may prevent certain countries from implementing any plans for new dams. For these countries, then, renovating provides a means of increasing output at a much lower cost than building completely new dams, and the act of upgrading the parts of a dam both ensure that it lasts longer and is more structurally sound, allowing the dams to last longer and lower their initial investment cost more.

Build additional run-of-river dams and/or tidal plants: Unlike conventional reservoir-type dam systems, run-of-river dams and tidal plants are generally less environmentally impactful because they do not require flooding large regions of land. Advancements in turbine and damming technology have also attempted to lower their overall effect on local wildlife, making both more environmentally-conscious than the conventional reservoir-type dams.

Run-of-river dams are useful in smaller, more remote regions with energy usage not exceeding more than several hundred MW. Mini and micro hydro projects may be especially feasible in smaller villages in both Southeast Asia and regions of Africa where the people are isolated enough from nearby towns that importing fuel for electricity generators is costly and impractical. These regions would benefit from small hydroelectric run-of-river dams as they would provide these regions with cheap, local power funded by the local people themselves, and any potential surplus energy could be sold for additional profit.

Tidal plants are also useful for countries with large amounts of coastline, e.g. the United Kingdom and South Africa. In the former case, additional tidal plants placed both offshore and at the mouths of various estuaries could generate approximately 20 percent of the energy used by Great Britain in 2012 [30]. In the latter case, offshore tidal plants could potentially harness the power of the major ocean current system running along South Africa’s coast. Although the feasibility of this method is still undergoing testing off the coast of Durban, South Africa’s lengthy coastline does offer many other opportunities for tidal plants, allowing South Africans a more local source of energy that they could be convinced to invest in to help fund construction for.

Consider wind/solar power in conjunction with pumped storage: Wind and solar power are far more publicly-acceptable renewable sources of energy that, combined with the stabilizing effect of pumped storage hydroelectric generators, could easily become a reasonable source of less water-dependent energy within the near future [31][32]. Unlike biofuels, wind and solar power do not place as much strain on the existing water supply – even taking all of hydroelectric generation’s 260L/MWh into account the water usage pales in comparison to biofuel’s lower range estimate of 180,900L/MWh. They are also more accessible for regions incapable of sustaining enough agriculture for both fuels and food, and their dependence on wind and/or sunlight make them more flexible to implement in regions that lack very many other resources such as certain developing countries in Africa.

Fund development of hydroelectric power in developing countries: Hydroelectric power provides a cheaper, more local source of energy to poorer regions of the world lacking alternative energy resources – usually between one-fourth and one-half the cost of conventional electrical generation depending on the type of generators and fuel being used. The additional availability of electricity in these regions may also help improve the average citizen’s quality of life and instill an overall greater sense of national pride – both of which in turn help developing nations become developed nations by empowering the citizens of these nations and encouraging the nations themselves to grow.

It is in the best interest of nations such as China and the United States to ensure that their developing neighbors become relatively prosperous as well, as such development would allow for more trade and economic opportunities between the countries and foster overall economic growth in the region.

 

References

1. Renewable Energy Essentials: Hydropower. (2010). IEA. Retrieved October 2, 2013, from http://www.iea.org/publications/freepublications/publication/Hydropower_Essentials.pdf

2. Pottinger, L. (2010, January 22). How Dams Affect Water Supply. International Rivers. Retrieved November 7, 2013, from http://www.internationalrivers.org/resources/how-dams-affect-water-supply-1727

3. Watts, J. (2010, January 22). Three Gorges dam may force relocation of a further 300,000 people. The Guardian. Retrieved November 7, 2013, from http://www.theguardian.com/environment/2010/jan/22/wave-tidal-hydropower-water

4. Jing, J. (n.d.). Displacement, Resettlement, Rehabilitation, Reparation and Development – China Report . The World Bank. Retrieved November 7, 2013, from http://siteresources.worldbank.org/INTINVRES/Resources/DisplacementResettlementRehabilitationChinasoc203.pdf

5. McCully, P. (1996). Silenced rivers: the ecology and politics of large dams. London: Zed Books.

6. Following The Science in Snake River Salmon Declines. (n.d.). Save Our Wild Salmon. Retrieved October 15, 2013, from http://www.wildsalmon.org/facts-and-information/science/the-science.html

7. Eastwood, V. (2012, June 8). Ethiopia powers on with controversial dam project. CNN. Retrieved November 30, 2013, from http://www.cnn.com/2012/05/31/business/ethiopia-grand-renaissance-dam/index.html

8. Graham-Rowe, D. (2005, February 24). Hydroelectric power’s dirty secret revealed. New Scientist. Retrieved November 27, 2013, from http://www.newscientist.com/article/dn7046

9. List of conventional hydroelectric power stations. (2013, October 11). Wikipedia. Retrieved October 20, 2013, from http://en.wikipedia.org/wiki/List_of_conventional_hydroelectric_power_stations

10. List of run-of-the-river hydroelectric power stations. (2013, October 7). Wikipedia. Retrieved October 20, 2013, from http://en.wikipedia.org/wiki/List_of_run-of-the-river_hydroelectric_power_stations

11. Douglas, T. (2007, August). “Green” Hydro Power: Understanding Impacts, Approvals, and Sustainability of Run-of-River Independent Power Projects in British Columbia. Watershed Watch. Retrieved October 20, 2013, from http://www.watershed-watch.org/publications/files/Run-of-River-long.pdf

12. Run of River Power. (n.d.). EnergyBC. Retrieved November 13, 2013, from http://www.energybc.ca/profiles/runofriver.html

13. Bueno, C. (2006, August). Wind powered pumped hydro storage systems, a means of increasing the penetration of renewable energy in the Canary Islands. Science Direct. Retrieved November 13, 2013, from http://www.sciencedirect.com/science/article/pii/S1364032104001285

14. Anagnostopoulos, J. S. (2007, November). Pumping station design for a pumped-storage wind-hydro power plant. Science Direct. Retrieved November 18, 2013, from http://www.sciencedirect.com/science/article/pii/S0196890407002063

15. Caralis, G. (2012, June 12). The role of pumped storage systems towards the large scale wind integration in the Greek power supply system. Science Direct. Retrieved November 18, 2013, from http://www.sciencedirect.com/science/article/pii/S1364032112000809

16. Tide power. (2013, November 28). Wikipedia. Retrieved November 30, 2013, from http://en.wikipedia.org/wiki/Tide_power

17. Tidal Energy: Pros for Wave and Tidal Power. (n.d.). Ocean Energy Council. Retrieved November 24, 2013, from http://www.oceanenergycouncil.com/index.php/Tidal-Energy/Tidal-Energy.html

18. Wilson, L. (n.d.). Average household electricity use around the world. Shrink That Footprint. Retrieved November 30, 2013, from http://shrinkthatfootprint.com/average-household-electricity-consumption

19. Park, N. (2007, May). Sihwa Tidal Power Plant: A Success of Environment and Energy Policy in Korea. Environmental and Energy Research. Retrieved November 24, 2013, from http://www.eer.wustl.edu/McDonnellMayWorkshop/Presentation_files/Saturday/Saturday/Park.pdf

20. Technology Roadmap: Hydropower. (2012, October 29). IEA. Retrieved November 16, 2013, from http://www.iea.org/publications/freepublications/publication/name,32864,en.html

21. Economic Impacts of Dams. (n.d.). International Rivers. Retrieved October 22, 2013, from http://www.internationalrivers.org/economic-impacts-of-dams

22. Manipur multipurpose dam delayed because of financial problems. (2013, September 24). Burma Rivers Network. Retrieved November 30, 2013, from http://burmariversnetwork.org/index.php/news/685-manipur-multipurpose-dam-delayed-because-of-financial-problems

23. “Energy.” Itaipu Binacional. Itaipu Binacional, n.d. Web. 13 Nov. 2013. <http://www.itaipu.gov.br/en/energy/energy>.

24. Energy. (n.d.). Itaipu Binacional. Retrieved November 13, 2013, from http://www.itaipu.gov.br/en/energy/energy

25. The rights and wrongs of Belo Monte. (2013, May 4). The Economist. Retrieved November 30, 2013, from http://www.economist.com/news/americas/21577073-having-spent-heavily-make-worlds-third-biggest-hydroelectric-project-greener-brazil

26. Bekhme Dam. (2013, June 10). Wikipedia. Retrieved November 30, 2013, from http://en.wikipedia.org/wiki/Bekhme_Dam

27. Dham, R. (2011, October 21). Fish-Friendly Turbine Making a Splash in Water Power. Energy.gov. Retrieved October 24, 2013, from http://energy.gov/articles/fish-friendly-turbine-making-splash-water-power

28. Reed, M. (2013, August 14). Investments in Existing Hydropower Unlock More Clean Energy. Energy.gov. Retrieved November 27, 2013, from http://energy.gov/articles/investments-existing-hydropower-unlock-more-clean-energy

29. Foz do Areia Dam. (n.d.). Copel. Retrieved November 30, 2013, from http://www.chincold.org.cn/Files/20092817052803.pdf

30. Hydroelectricity. (2013, October 7). Wikipedia. Retrieved October 12, 2013, from http://en.wikipedia.org/wiki/Hydroelectricity

31. Budischak, C. (2013, March 1). Cost-minimized combinations of wind power, solar power and electrochemical storage, powering the grid up to 99.9% of the time. Science Direct. Retrieved November 28, 2013, from http://www.sciencedirect.com/science/article/pii/S0378775312014759

32. Pumped-storage hydropower projects attractive means of storing excess energy, Stanford study says. (2013, November 18). Hydro World. Retrieved November 18, 2013, from http://www.hydroworld.com/articles/2013/11/pumped-storage-hydropower-projects-attractive-means-of-storing-excess-energy-stanford-study-says.html

33. Federal Energy Regulatory Commission. (n.d.). Annual report of major electric utilities, licensees and others via ventyx global energy velocity suite. Retrieved from http://www.eia.gov/electricity/annual/html/epa_08_04.html

34. Tomia. (Artist). (2007, December 30). Hydroelectric Dam [Web Graphic]. Retrieved from http://en.wikipedia.org/wiki/File:Hydroelectric_dam.svg

37. (2012, March 8). Raccoon Mountain Pumped-Storage Plant [Web Graphic]. Retrieved from http://commons.wikimedia.org/wiki/File:Raccoon_Mountain_Pumped-Storage_Plant.svg

39. http://en.wikipedia.org/wiki/List_of_conventional_hydroelectric_power_stations

40. Frantzis, L., & Graham, S. (2011). Utility business models in solar: Opportunities and trends. Retrieved from http://www.navigant.com/~/media/WWW/Site/Insights/Utility_Business_Models.ashx

41. Small hydropower systems. (2001, July). Retrieved from http://www.nrel.gov/docs/fy01osti/29065.pdf

42. Selin, N. (n.d.). Tidal power (energy). Retrieved from http://www.britannica.com/EBchecked/topic/595132/tidal-power